The Homeowner`s Energy Handbook

The Homeowner`s Energy Handbook
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The mission of Storey Publishing is to serve our customers by
publishing practical information that encourages
personal independence in harmony with the environment.
Deborah Burns and Nancy D. Wood
A rt di r e c tion a nd book d e sig n by Carolyn Eckert
Te xt production by Gary Rosenberg and Theresa
E di t e d b y
Cov e r i l lustr ation by
© Michael Austin/Jing and
Mike Company
© James Provost, except
for © Michael Austin/Jing and Mike Company, 3,
14, and 104; and Ilona Sherratt, 127
I l l ust r ation ed iting by Ilona Sherratt
Phot ogr aph s a nd g r aph ics cour t e sy o f : Paul
Scheckel, 27; National Fenestration Research
Council, 85; PowerWise Systems, Inc., 99; www., 73 top left; Web Energy Logger,
103; U.S. Department of Energy, 127; Kestrel
Renewable Energy,, 141; UN
Development Program, 262
The information in this book is true and complete to the best
of our knowledge. All recommendations are made without
guarantee on the part of the author or Storey Publishing. The
author and publisher disclaim any liability in connection with
the use of this information.
Storey books are available for special premium and
promotional uses and for customized editions.
For further information, please call 1-800-793-9396.
I nt e ri or illustr ations by
Nancy D. Wood
Philip Schmidt, with contributions
from Hilton Dier III, Bret Hamilton, David House,
Chris Kaiser, and Ian Woofenden
I nd e xe d by
Te chni ca l ed it by
© 2013 by Paul Scheckel
All rights reserved. No part of this book may be reproduced
without written permission from the publisher, except by a reviewer
who may quote brief passages or reproduce illustrations in a
review with appropriate credits; nor may any part of this book be
reproduced, stored in a retrieval system, or transmitted in any
form or by any means — electronic, mechanical, photocopying,
recording, or other — without written permission from the
Storey Publishing
210 MASS MoCA Way
North Adams, MA 01247
Printed in the United States by Courier
10 9 8 7 6 5 4 3 2 1
Library of Congress Cataloging-in-Publication Data
Scheckel, Paul.
The homeowner’s energy handbook / by Paul Scheckel.
pages cm
Includes index.
ISBN 978-1-61212-016-4 (pbk. : alk. paper)
ISBN 978-1-60342-847-7 (e-book)
1. Renewable energy sources—Handbooks,
manuals, etc.
2. Dwellings—Insulation—Handbooks, manuals, etc.
3. Architecture and energy conservation—Handbooks, manuals, etc. I. Title.
TJ808.S328 2013
You alone are responsible for how you use the information in this book, and you must assume any and all liability for damage to people
or equipment. It is your responsibility to determine the suitability of any project, parts, assembly, and any and all results or outcomes, to
be used for any particular purpose whether presented in this book or not. It is up to you to use tools and equipment properly and to take
proper precautions with chemicals, mechanical equipment, electrical service, materials, and procedures. You alone are responsible for
injuries to yourself or others or for damage to equipment or property.
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Your Guide to Getting
handbook Off the Grid
Paul Scheckel
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Storey Publishing
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For Silas,
who reminds me every day
of the boundless renewable energy
inside us all.
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not, and could not be, anything
close to what I imagined at the conceptual
stage. It is much more and much better. For
this, I owe a debt of gratitude to all those who
offered their time, experience, expertise, en­­
couragement, and support for this project.
It has been nothing short of a pleasure to work
with the dedicated professionals at Storey Publishing. I specifically want to thank Deborah Burns
for her enthusiasm, followed by much patience
with my seemingly endless delays; Nancy Wood,
whose organizational and editing skills kept me
on track, and who continued to be patient (and
even encouraging) with even more delays; Phillip Schmidt for his incredibly thorough technical review and ability to draw clarity from foggy
bottom; and James Provost for his excellent
There are many more to thank for their various
contributions, including:
You, the reader, for taking the time to understand and explore renewable energy and energy
efficiency. Without individual motivation and
action, nothing will be as you imagine it could be.
My family, for their extended patience during the frenzy of endless deadlines and with my
obsession with getting the hands-on projects
This book is
just right. The porch, garage, yard, garden, and
even the closets are littered with the remnants of
The following professionals provided advice,
guidance, technical review, and personal contributions: Ian Woofenden, Home Power magazine;
William David House, Vahid Biogas; Bret Hamilton, Shelter Analytics; Hilton Dier, Solar Gain;
Gordon Grunder; John Dunham; Jim O’Riordan,
O’Riordan Plumbing and Heating; Tina Webber,
Swing Green; Paul Gipe, wind energy expert and
advocate; Home Power magazine, for all things
renewable; Tracy Vosloo, Kestrel Wind Turbines;
Chris Kaiser and Powell Smith, Mapawatt Blog;
Josh Van Houten for help with advanced chemistry; Paul Harris, the University of Adelaide;
Lori Barg, Community Hydro; Chris Pratt, Open
Sash; United Nations Development Programme;
Aprovecho Research Center; The Journey to Forever Project; Solar Energy International; Cornell
University, Waste Management Institute; Spenton LLC, wood-gas camp stoves; Powerhouse
Dynamics, home energy monitors; Blue Line
Innovations, home energy monitors; PowerWise
energy monitoring dashboards; Jock Gill, biomass expert and advocate; All Power Labs, wood
gasifiers; NASA’s Langley Research Center.
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Introduction 8
Part One:
H o m e E n e rgy E fficie ncy
1Getting Ready for
4Deep Energy Retrofits
Renewables 16
The Big and Little Energy Picture ● Basic
Considerations ● Systems and Planning ●
Renewable Habits ● The Value of
Electricity ● Energy Action in Cuba ● Build a
Bicycle-Powered Battery Charger
2Do Your Own Energy
5Home Energy
Monitoring 95
Audit 36
Getting Started ● Electricity ● Hot Water ●
Heating and Air Conditioning ● Thermal
Envelope ● Windows ● Prioritizing Your
3Insulating Your Home
Looking at the Big Picture ● A Team with a
Plan ● The Basement ● Above-Grade Walls ●
Windows ● The Roof ● Air Leakage ●
Ventilation ● Heating and Air Conditioning ●
Hot Water
Electric Energy Monitoring ● Gas
Monitoring ● Environmental Monitoring ●
My Hot Water Heating Story
How Heat Moves Measuring Insulation
Value ● Insulation Inspection ● How Much
Insulation Do You Need? ● Choosing and
Installing Insulation ● Stopping Air and
Moisture ● Roof Venting ● When “High
Performance” Doesn’t Perform
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Pa rt two:
R e n e wa b le E ne r gy
6Solar Hot Water
Types of Systems Solar Hot Water
Collectors ● Hot Water Storage ● Additional
System Com­ponents ● Sizing the System ●
Maintenance ● Homemade Hot Water ●
Build a Solar Hot Water Batch Heater
7Solar Electric
Generation 123
Solar Power Potential ● Planning for a PV
System ● PV System Wiring ● Orientation ●
Racks and Tracking ● Economics ● Safety ●
Living with Solar (and Wind) Power
8Wind Electric
Generation 137
Using Wind Energy at Home ● Estimating
Energy in the Wind ● Estimating Wind
Speed ● Efficiency and Power ● Wind
Machines and Controls ● Towers ●
Foundations and Anchoring ● Maintenance ●
Safety ● Wiring and Grounding ●
Wind Wisdom from an Expert
9Hydro Electric
Generation 159
Home Hydro ● Calculating Hydro Energy ●
Measuring Flow and Estimating Power ●
Intake Site Selection ● Penstock Pipe
Selection ● Turbines ● Power Generators ●
System Efficiency
10 Renewable Electricity
Management 174
Grid-Tie vs. Off-Grid ● Definition of
Terms ● Electrical Wiring ● Balance
of System Components ● Batteries ●
Mapping Motivations . . . and Watts
11 Biodiesel
12 Wood Gas
Venturing into Biodiesel ● What Is
Biodiesel? ● Benefits and Drawbacks ●
Essential Ingredients ● Equipment
Needs ● Safety ● Basic Steps for
Making Biodiesel ● Mixing Biodiesel
with Other Fuels ● Washing Biodiesel ●
Veggie Oil Conversion ● Create a
Biodiesel Kit
Wood Doesn’t Burn ● How Wood Gas
Generators Work ● Four Stages of
Gasification ● Gasifier Operation ●
Cleaning and Filtering Wood Gas ● Using
Wood Gas ● Storing Gas ● Types of
Gasifiers ● Working Safely around Wood
Gas ● Two Men and a Truck ● Build a
Simple Wood Gas Cook Stove
13 Biogas
The Basics Recipe for Making Gas ●
Solids, Liquids, and Volatile Solids ●
Temperature ● Retention Time and
Loading Rate ● Types of Methane
Generators ● Using Biogas ● Purifying
Biogas ● Biogas Is More than a Gas ●
Make a Biogas Generator
Resources 262
Metric Conversion Charts 273
Index 274
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s I w r i t e this, I have just lit the fire on my first batch of homemade
biogas. Food scraps and pig poop have been successfully transformed into
a gas, similar to propane or natural gas, that we can cook with. Biogas is
the combustible result of the decay that happens in nature just as easily as the sun
shines or the wind blows. The challenges in harnessing these energetic gifts from
nature lie in collecting, controlling, storing, and often transforming the primary energy
resource into a form that can be used to meet a particular need. Much of this book
is all about exploring the options for meeting your energy needs through natural
resources, along with the processes involved in focusing their potential toward some
particular need.
For years I’ve been fascinated with the idea of making biogas, but I was intimidated by what appeared to be complex and exacting science in the recipe requirements for optimum gas production. But experience is the best teacher and, after all,
this simple process of biomass decay happens all by itself in nature. So how hard
could it be to create the environment for gas to not only ­happen, but to actually be
produced? I found a 55-­gallon airtight barrel in the “inventory” (as I like to call it;
my wife calls it something else) behind the garage. I dumped in a 5-gallon bucket of
­compostable food scraps and a smaller bucket of poop from our two pigs, along with
a pile of grass clippings. Then I filled it halfway up with water and waited. One week
later, combustible gas was bubbling out of the barrel — no exact recipe or scientific
calculations required.
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The Road to SelfEmpowerment
energy is, in every sense
of the word, empowering. Watching the biogas
burn reminded me of the feeling I had when I
bought my first solar panel 25 years ago and set
up an off-grid room in the rental house I shared
— thrilling! This feeling of independence set me
down the path of exploring renewable energy and
energy efficiency as both a vocation and avocation.
I’ve spent lots of professional and hobby time
exploring the processes involved in meeting my
family’s energy needs through natural and locally
available resources. I do this mostly because it’s
fun but also because I want to wean myself off
the myopic, destructive, and often corrupt global
power structure of energy addiction. So, in addition to all the fun I’ve had, my family also enjoys
a certain level of autonomy from the energy supply machine, and that feels pretty good. But that’s
just me. You may have different reasons for making (and saving) energy.
M a k i n g yo u r ow n
What’s the Alternative?
Renewable energy sources have been dubbed
“alternative energy,” a phrase that marginalizes the true value of these traditional energy
sources. The fossil fuel era will be a tiny blip in
human history, and nuclear energy is not only
too expensive, it also continues to struggle with
its own, self-made image. These modern fuels
are really the “alternative” to traditional energy.
Humanity will need to use what nature offers,
without breaking the budget of the natural capital available to all of us and against which we
have borrowed heavily.
Nature has been providing earthly inhabitants
with abundance for millennia, and these natural
resources are available to all. The processes of
harnessing energy work best if you apply a little
knowledge and provide a catalyst to get things
started, then simply get out of the way and let
nature do its thing — and don’t ask for more
than you need. Making your own energy comes
with a new awareness of efficiency and facilitates a change of perception around comfort and
efficiency and renewable energy
consultant, I find it challenging to overcome some
of the rationale my industry uses to sell efficiency.
And I need to be honest: The industry is filled
with energy geeks who are passionate about what
they do, and this generally is a good thing.
However, most of us enjoy talking about de­tails
that put the average person to sleep. You want a
yes-or-no answer; we reply with building-science
theories and numbers.
When it comes to promoting the benefits of
energy efficiency improvements, many of us have
focused primarily on cost savings, simple payback,
and return on investment. Financial payback is not
why we buy most things, but it’s always the first
question when it comes to energy improvements
at home. Cars, couches, and music do not offer
financial returns and are not usually considered
investments, yet we buy them not just because we
need them but because they make us feel good.
Sitting on a couch listening to music is better than
sitting on the floor in silence. But if your couch is
next to a drafty window, it’s your comfort that’s at
stake, not your financial situation.
I’ve avoided lengthy discussion about economic
evaluations in this book because if you’re reading
As an energy
We are like tenant farmers chopping down the fence around our house for fuel when we should
be using Nature’s inexhaustible sources of energy — sun, wind, and tide. . . . I’d put my money
on the sun and solar energy. What a source of power! I hope we don’t have to wait until oil and
coal run out before we tackle that. — T h o ma s E d i s o n, inven to r (1847–1931)
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it, you probably have a number of motivations for
wanting to make and save energy. But if you’re
stuck on the idea of monetary cost-effectiveness,
the following are some simple ways to compare
costs and return on investment (just keep in mind
that simple analysis involves making guesses
about certain things and leaving some important
considerations out of the equation).
Simple Payback
To get a ballpark idea of the value of energy production from a renewable energy system, first add
up your installation costs for the system. Then,
multiply the annual maintenance costs by the
expected life of the system. Add the two sums
to find the lifetime operating cost of the system.
Next, figure the energy production of the system
over its lifetime. Divide the lifetime operating
costs (installation and maintenance) by the lifetime energy production value to find the cost per
unit of energy. Here’s an example using a solar
electric power generating system:
• A 3-kilowatt PV (solar electric) system costs
$15,000 to install after all incentives (if you’ve
taken out a loan for the system, don’t forget
to include the cost of financing). Assume it
will produce reliable power for 25 years. PV
systems do not require much maintenance
if you don’t have batteries, but assume that
you will need to replace the inverter every ten
years at a cost of $2,000 (this is a guess,
because who knows what inverter technology
and cost will be in 10 years). Your lifetime cost
to own and operate the system is $19,000.
• You expect power production to be about
3,600 kilowatt-hours (kWh) per year. Multiply
that by 25 years, and you’ll have produced
90,000 kWh of solar electricity over the
system’s life.
• $19,000 divided by 90,000 kWh = $0.21/kWh
• Compare this to current electricity prices,
and try to guess what the price might be in
25 years. Estimates of energy escalation (the
rate at which energy costs will rise over the
rate of general inflation) range from 1 to 10
percent, depending on whom you ask. Recent
history proves that the energy sector is highly
volatile in many ways, and economics react
quickly to volatility.
Up-Front Cost and
Lifetime Cost
When replacing older appliances in your home,
it pays to spend a little more up front for a more
efficient model. Buying the cheapest product
often results in the highest lifetime cost, with the
cost of energy to operate the equipment often
far exceeding the purchase price. The incremental cost of the high-efficiency choice often will
more than pay for itself over the lifetime of the
If you’re hoping to supply your home with a
renewable energy source, consider the cost of
increasing the size of your renewable system
to meet the additional needs of lower-efficiency
equipment. Buying energy is almost always more
expensive than saving it. As you’ll see in chapter
5, it’s probably worthwhile to evaluate how much
energy an appliance currently is using to see if
the energy savings alone are worth the cost of
upgrading. Don’t just assume that because it’s
old, it must be an energy hog.
More than Money
there are so many
more reasons to “get efficient” and to make
your own energy. Many of the non-energy-related
benefits of lowering your energy consumption
fall into more subjective or emotional categories
(which is how we humans tend to make decisions)
and may indeed outweigh the cost savings of
making efficiency improvements.
Nice to know, though, that energy efficiency up­­
grades and renewable energy systems are among
the few things you can buy that will actually pay
for themselves over time, promising to offset
the cost of that kitchen renovation you’ve been
wanting. If you want a more detailed analysis of
costs, savings, and carbon footprint, you can find
links to energy analysis tools on my website (see
Resources). The tools are fairly simple to use, but
Be y o n d s a v i n g m o n e y ,
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they require some knowledge of your existing and
proposed conditions.
Here’s a partial list of benefits or “value propositions” (in addition to saving money) to consider
when you’re thinking about making a change in
your energy situation. You may have your own
need or desire to add items to the list.
• Using less energy
• Increasing comfort
• Reducing carbon footprint
• Improving energy security
• Gaining energy independence and autonomy
• Stabilizing energy bills
• Diversifying your energy portfolio
• Increasing resilience to natural disasters and
interruptions in energy supply
• Reducing financial risk from exposure to
unstable energy markets
• Increasing home market value
• Reducing home maintenance
• Increasing convenience with modern, efficient,
and smarter appliances
• Minimizing mechanical systems size and cost
• Eliminating or reducing reliance on air
conditioning and humidity control
• Spending money locally to reduce the money
you send out of your state or country
• Using less water
• Improving indoor air quality, occupant health,
and safety
• Making your house more durable
• Reducing animal intrusion
• Minimizing noise between outdoors and in
• Adding storage space with a dry basement
• Reducing mold, dust, and other allergens
• Eating more fish (mercury emissions from coal
power plants poison fish and anything that
eats fish)
• Reducing combustion-related particulatematter emissions (helps reduce chronic
• Feeling good just by knowing you can do it
yourself, to be independent and meet your
family’s needs
Limitations and
this book could have
been a book in itself. My intention is to offer
the basics of specific technologies and present
enough information so that you can understand
the principles, without getting overly technical. If
you want to go deeper, there are references to
more information to help increase your expertise
in any given area.
Where practical, some chapters offer a do-ityourself project that can give you a feel for how
things work. This hands-on learning experience will
help you understand how to make and use your
own energy and, with a little trial and error, expand
beyond the experimental approach to help meet
your energy needs. As with any good hobby, you
can spend as much or as little time as you like
in the pursuit of homemade energy, with varying
degrees of success. Once you get started, you will
discover new ways of making things work better in
your specific situation.
Industrialized societies like to think big. When
building a commercial enterprise, there are economies of scale to consider, but when it’s just
you and the family to provide for, the economics change drastically. The key ingredient is your
own motivation for (at least partially) meeting
your resource needs. As for other ingredients, I
encourage you to use resources that are available locally, especially waste material. Anytime
you can use waste material to generate energy,
the “energy profit ratio” of that material greatly
increases (see Defining EPR on the following
Each chapter in
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iDefining EPRi
Energy profit ratio (EPR) is the ratio of energy output to the energy required to obtain the resource. If
it takes one barrel of oil to get 10 barrels out of the ground, then the EPR of oil is 10 to 1. This equation
stops or goes negative when you throw something away, but if a material is reused and recycled until
there’s nothing left, then you have maximized its EPR.
Efficiency of
world yet discovered will
deliver greater than 100-percent efficiency in
terms of energy used, produced, converted,
or transferred. While new heat and hot water
equipment might offer fuel efficiency percentages
in the high 90s, these values don’t account for
the energy required to extract and deliver the fuel
to your home.
In most cases, you’re doing great if you get 50
percent efficiency from a system. Consider that
most energy systems take the raw, or primary,
energy resource and convert it to the desired
form. Each conversion saps energy from the original source and effectively reduces overall process
For example, electric heating elements are
100 percent efficient at converting electricity
into heat. No amount of fancy gizmos or slick
marketing will ever change that fact. However,
Nothing in this
the process of generating the electricity and
getting it to your home might be only 30 percent efficient. If you want to get your electricity
from the wind, you need to convert the kinetic
energy in the wind to mechanical energy that
turns the generator, which converts it into the
electrical power that you want. That entire process might be 25 percent efficient. If the electrical energy produced from the wind generator
is stored in a lead-acid battery, itself having an
efficiency of about 70 percent, you will need
to put 30 percent more energy into the battery
than you take out in order to keep the battery
I can’t emphasize enough that the efficiency of
renewable energy systems is a distraction. Capturing free and abundant renewable resources
does cost something, but the power keeps on
coming. The measure most of us care about is
cost-effectiveness, which means: How much will
it cost to get a quantity of energy over a period
of time? How you value that energy is not always
about money.
S ystem eEfficiency
ffici en c y = =
The efficiency of a system is deter-
mined by multiplying the efficiencies
of each component of that system
together. A coal power plant might
be 33% efficient at converting coal
to electricity; the power distribution network (power lines, switches,
transformers between the plant and
the house) can lose up to 10% to
inefficiencies; and an incandescent
light bulb is only about 10% efficient
at converting electricity to light. The
overall efficiency of converting coal
into light in this case is only about 3%,
with the remaining 97% of the energy
being lost as heat.
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Have Fun and
Be Careful
renewable energy are
relatively simple, but the details and nuances
may take a lifetime to master. This book is
intended to engage you in understanding
the basics, but know that when you are
done you’ll have only scratched the surface.
While you can learn the basics in the comfort
of your reading chair, combining this knowledge
with even a small project will give you the handson experience you need to gain the skills and confidence for taking your energy goals further.
The concepts in
Finally, don’t be careless. There are no good
shortcuts. Shortcuts create problems, cause premature failure, impact components in unforeseen
ways, and increase the risk of personal injury. If
you’re unsure about how to do something, consider all the different and potentially catastrophic
ways something can fail, and consult a professional or your favorite curmudgeonly naysayer.
I applaud your willingness to take responsibility for your energy needs. I sincerely hope you
will experience the joy of invention in harnessing
the opportunities offered by our home planet to
meet those needs. I guarantee you will find many
rewards if you take it personally, and take action!
iOnly Humansi
Humans are the only inhabitants of the earth to use energy that does not come directly from the sun.
All life is in a constant struggle to gain more and more energy in different forms — it seems to be
the basis for a species’ success. Whether you’re on or off the grid or you use renewable energy or not,
energy prices and energy impacts will continue to grow. Any efforts to reduce your use will allow
you to meet your needs with fewer resources, expand your energy options, and help to put humans on
a sustainable energy path.
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Par t One
H ome E nergy
e f o r e i n v e st i n g i n renewables for your home,
it’s always best to reduce your energy consumption. A
big part of doing this is becoming aware of how and
when you use energy in your home. Do you really need your living spaces to remain at a constant temperature and humidity
level throughout the year, or can you learn (or relearn) to widen
your range of comfort? After you’ve completed your own home
energy audit, you can decide where best to focus your efforts for
comfort and cost control.
Most of us do not associate homes with performance, as you
might when comparing which car to buy. But with the proper understanding, along with a strategic approach and attention to detail,
your home can be transformed from an old clunker into an ultraefficient, high-performance place of comfort and energy autonomy.
Efficiency can become a challenge for you — and even a game
for the whole family — to see how low your energy use can go. Both
game and challenge can be enhanced through real-time monitoring and tracking with a home energy monitor, offering an immediate sense of reward and consequence. Make a plan, keep track of
your savings, and consider the future keepers of your home — and
the planet.
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Getting Ready
for Renew­ables
ac k i n t h e early 1990s, when I was converting gasoline-powered cars to
electric operation, my partners and I thought this was obviously the next step
in transportation. Technology was indeed ready, and we even found a few cus-
tomers, but we quickly discovered that it was much easier to convert cars than to convert driver behavior.
Batteries are the limiting factor in the viability of electric vehicles, and efficient
driving habits can increase the range of travel by up to 50 percent. Try as we did, it
seemed nearly impossible for many to unlearn wasteful driving habits. Stomping on the
accelerator from a dead stop does nothing to increase an electric car’s speed, but it puts
a huge drain on the batteries.
When it comes to energy use, most of us have some of the same bad habits with
our houses as with our cars. Getting your home — and yourself — ready for renewables
requires understanding what renewable resources you want to use, as well as the practicalities of how to harness that energy. This chapter will help to guide your decisionmaking, with a broad view of what’s required “behind the scenes.”
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The Big and Little
Energy Picture
that you can do to get ready for
renewables. You can do it all at once, if resources
allow, or you can take baby steps with incremental
improvements to make your home “renewableready,” ultimately resulting in substantial savings.
Shifting toward renewables requires that you
closely examine your relationship with energy and
your expectations around how it serves you —
and accept changes in both. Where is your energy
coming from now, and how will you get it, or make
it, in the future? On the fossil fuel main line, we
don’t just buy energy, but we also buy the convenience of throwing a switch or turning a dial to
meet our needs with very little planning, thinking,
or heavy lifting required. We have come to expect
energy to be an invisible and seamless part of
our lifestyle, keeping us in a very narrow bandwidth of comfort, without being anywhere near the
raw materials, processes, or awareness of this
huge global infrastructure.
Yet fuel prices are rising fast, as are concerns about all the resources required to sustain
increasing levels of imported energy — resources
ranging from money to land to human lives. When
you think about it, it seems crazy to take fuels like
natural gas and oil (which are highly processed,
costly, complex, and difficult to obtain), transport
them around the world, and burn them for heat.
It's crazier still when you realize that the industry
There is much
Renewable energy
resources are all around us.
Sun, wind, water,
trees, and even
food waste can be
converted to heat, hot water, or electricity.
of refining petroleum products is the single biggest energy consumer in the United States.
All of these factors make homegrown options
attractive on many levels. Equivalent heat is available from the sun or from “low-grade” (minimally
processed, easily obtainable) biomass fuels
found much closer to home. Drawing from local
sources to heat your home can be as simple as
planning at the design stage to take advantage of
solar heat gain, or as complex as using a groundsource heat pump to scavenge heat from the
earth and redirect it into your home. Somewhere
in the middle of the cost and complexity scale
might be installing a wood stove in your home,
R e c og n i z i n g O u r E n e rgy B a gg a g e
For perspective: If we each took
responsibility for societal energy
impacts, every American would
take receipt of one-third of a
pound of high-level radioactive
waste (currently stored at nuclear reactor sites), plus another
quarter-ounce produced on our
behalf each year. We would also
receive a few ounces of airborne
mercury that is produced by
burning coal and eventually rains
down onto our soils and water.
The fish we can’t eat due
to the high mercury content
in their flesh cannot be decontaminated. Much land has been
rendered uninhabitable due to
oil spills, nuclear accidents, and
hydropower reservoir construction. Energy security is a huge
We are all complicit in filling
the bags of energy liability
because we continue to demand
the lifestyle that cheap energy
brings us. We have reached
the point where we can’t force
that bag closed even by sitting
on it! The zipper has popped
and the baggage is spewing
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or adding an active solar thermal or solar electric
system with substantial collection area and sufficient storage capability, coupled with effective
and efficient delivery of that energy.
Your Energy View-Shed
Society has energy choices to make, and so do
you. These are not easy decisions because there
are economic, environmental, social, political,
and personal values associated with any energy
source. These values can be viewed from both
micro and macro vantage points, and you can bring
your own value propositions into the discussion.
The question is: What do you want in your
backyard — or in policy-speak, your energy “viewshed”? In terms of energy impact, the view from
your house might have both visible and invisible
components. You might see electric transmission
lines, coal-burning power plants with their smokestacks, or wind turbines. Less visually dramatic
but equally tangible impacts of energy production
include the effects of smog when you breathe.
You might not see an entire mountaintop removed
to get at the coal or uranium underneath, but you
know that the natural world has been affected.
You’ll experience fewer impacts, a better
view, and easier rest if you and your neighbors
are using energy efficiently. If you opt for energy
status quo, then you also choose to accept your
iTake a Deep Breathi
Our nation spends $15 billion each
year on asthma medication. The
increase in people suffering from
asthma is partly due to increases in
air pollution from dirty coal-burning
power plants around the world. And
we all share the same air. In America,
many eastern states are downwind
of coal power plants in the Midwest.
When it’s hot in Ohio, for example,
locals crank up their air conditioners,
share of the pollution and other impacts of various generation sources.
The Effects of Our
Carbon Footprint
The term “carbon footprint” refers to the annual
amount of greenhouse gases (GHG), or the gaseous emissions of substances that have been
shown to contribute to the effects of climate
change, for which every human is directly or indirectly accountable. There are many such gases,
and they are often expressed in terms of carbon
dioxide equivalency (CO2e) because CO2 is the
primary GHG.
The average American has a carbon footprint
of about 23 tons per year, nearly 80 percent of
which comes from burning fossil fuels. That’s
enough carbon dioxide (CO2) to fill over 18 average homes full of this potent greenhouse gas. If
you took all the oxygen (O2) out of the 23 tons
of CO2, you would have a pile of carbon weighing almost 61/2 tons. This is often called carbon
equivalency or Ce.
Where do we store these gases other than the
closet of our atmosphere? And the fallout, literally and figuratively, is that we must put up with
days where ozone, smog, and unexpectedly high
particulate matter limit our ability to breathe while
increasing societal health care costs.
and that ultimately raises the level of
asthma-triggering particulate matter
in the air of New England states.
To continue down the road of
energy status quo means accepting
continuous environmental degradation
from acid rain and adjusting to a
shifting global climate. We’ll have
to accept mining disasters, wars,
increasing military budgets, and
political destabilization as we wrangle
for resources, as well as displaced
people, extinguished wildlife, rising
costs, and continued warnings to
avoid certain foods that absorb
various pollutants. And, every once
in a while, we’ll need to accept
radioactive rain and witness
productive farmland being reduced
to wasteland. The environment in
which we live is a closed system
in motion. In terms of energy impacts,
our backyards have expanded to
include the entire planet.
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On and Off the Grid
Animals are completely dependent on natural resources
for survival. Humans have the capability to capture, harness, and manipulate these resources to serve specific
needs. Our only limitations are imagination and desire.
Comparing Energy
All energy systems have a downside, and renewable energy sources are not to be excused for
their contribution to environmental and social
impacts. Land is submerged for huge hydropower
operations, and people are displaced from their
homes. Substantial wind resources are often
found within sensitive ecosystems where roads
and construction projects will take their toll.
These installations may have a permanent impact
on the landscape and local environment, but they
do not have the continuous impacts of resource
exploitation and pollution production that fossil
energy sources do.
ready for renewables
means taking incremental steps toward meeting
your own energy needs with minimal impacts.
This can be done in a relatively pain-free way
while you’re doing other renovation work, as long
as you plan for the eventuality of integrating
renewables into your home and lifestyle.
M a k i n g y o u r h o me
The “grid” is the network of electrical
generation (power plants), transmission
(power lines), and distribution (transformers, controls, and switching stations)
required to generate and move electrons
to your home. This varied network ties
communities, states, and regions together
much in the same way superhighways are
connected to rural roads. (Imagine cars
as the electrons, having been generated at
an auto manufacturing plant and pushed
out onto the highways.)
Nearly every home in the developed
world is connected to the power grid, and
eventually this grid will be “smart” enough
to move electrons around the country
seamlessly, taking them from wherever
they’re generated (such as the solar panels
on the roof of your house) to wherever
they’re needed (such as a neighboring
state where a power plant has just been
closed for maintenance).
Remote rural places may be so far
from power lines that — if you want
electricity — there is no power grid to
connect to. Your choices are either to bring
power lines to your site and connect to the
grid, or build your own off-the-grid power
generation system where you keep all the
electrons you make. Typically, the term
“grid” is applied specifically to the electrical power network, but it can be used
metaphorically (as I often do) to refer to
the similar network of fossil fuel production and delivery systems. How far “off
the grid” can you get?
As you make your plans, consider your needs:
• What do you want to use renewables for?
• How much energy will you need after
efficiency improvements?
• What equipment is needed and where will it
At the same time, consider available
resources that can help you meet those needs:
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• Do you live in a sunny place?
• Do you have at least an acre of land and
plenty of wind?
• Do you own wooded property?
• Are you near falling and/or flowing water?
• Are you a farmer with excess crop waste and
manure to manage?
• Are you (or do you know) a restaurant owner
with waste vegetable oil and/or food scraps
to dispose of?
• How much energy can the available resources
Of course, everything starts with efficiency. You
don’t want to buy or produce energy only to lose
or waste it to inefficiencies. Reduce the energy
use of your dwelling and maximize efficiency
through weatherization and upgrades to heating and cooling systems and appliances. A small
energy footprint allows you to meet a greater
portion of your energy needs through a diversity
of options.
Reducing your use means that a smaller, less
costly renewable energy system can meet a
greater portion of your needs. If you’re off-grid, it
also means less reliance on a fossil fuel generator to keep your system’s batteries charged.
While it’s certainly possible for renewables to
meet all of a home’s energy requirements, it’s
typically most cost-effective to supply up to 80
percent of your annual energy needs with renewables. This is because adding sufficient capacity
for that last 20 percent, which you may need only
for a short-lived, worst-case scenario, can double the system capacity and cost. In most cases,
the technology is relatively manageable. The
more challenging aspect to consider is your lifestyle and how much you are willing to personally
engage in the process of assembling and managing your own energy systems.
5An efficient home, inhabited by a conscientious family,
can harness a diversity of natural resources to meet the
majority of its energy requirements.
Management and
If you’re a hands-on person and are able, willing,
and available to address maintenance issues as
they arise, you might have the flexibility to experiment with various approaches and systems to
see what works best for you. On the other hand,
if this level of oversight isn’t realistic or desirable, you’ll probably need to hire a professional to
install and maintain a more conventional system,
and you will need to budget for maintenance.
Set realistic goals around how much purchased
energy can be offset with renewables.
Don’t forget to look into state and local zoning restrictions that may affect structure height
or the visual appearance of your home. Be ready
to work with neighbors and officials to change
laws that may prohibit the use of solar collectors,
wind towers, micro-hydroelectric turbines, or even
Living with renewable energy will change your
awareness of that resource. To make the most use
of it, you’ll need to be open to changing your habits
to live within the requirements of renewables and
possible constraints on their availability.
iDefining Btusi
A British thermal unit (Btu) is the amount of energy it takes to raise the temperature of one pound
(one pint) of water by 1°F, or about the same energy released when a wooden match is completely
burned. The energy output of many heating, cooling, and cooking appliances is measured in Btus.
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Renewable Energy
There’s a good chance that your home is more
ready for renewables than you might think.
Sunlight falls everywhere, and proper design
(or redesign) of your home can allow you to
take advantage of solar heat gain to offset your
heating needs while also reducing your cooling
Even if your home isn’t ideally oriented, a rooftop or yard with good access to the southern sky
offers the potential to harness solar energy for
use in water heating and electrical power for the
home. A reasonable flow of wind or water offers
additional opportunities for home power generation. Wood is widely available in split logs (cordwood) or pellets, and either option can be a good
choice for home and water heating (see below).
H e a t i n g a n d Coo k i n g w i t h Woo d
If cordwood or pellet heat is in your future, you’ll
need to consider the best equipment and setup
for your needs. Decide if you prefer cordwood
or pellets, then if you want to burn the fuel in a
stove or in a furnace or boiler. Some wood heating systems can be located outdoors. Outdoor
systems have the advantage of putting the
equipment and mess outside but come with the
added expense of moving the heat to the indoors.
The chimney is another factor. Inside chimneys
perform better and last longer than chimneys on
the outside of your house, simply because they
are warmer (yielding a better draft) and aren’t
exposed to the elements.
Outdoor wood boilers are becoming a popular choice
for home and water heating. Be sure to select a model that
meets US EPA guidelines for low particulate emissions.
Less smoke is not only an indicator of efficiency, but will
surely lead to better relations with your neighbors.
Next comes the question of where to store a
ton or two of pellets or a few cords of wood to
keep them dry and to minimize handling. Wood
pellets are often sold in 40-pound bags, so they
can go anywhere. Bulk pellets require a large
storage bin, or hopper, near the heat system.
Cordwood, on the other hand, has a high moisture
content. If you store it indoors, much of that moisture ends up in the air as the wood dries, and this
can lead to problems with mold or mildew. Better
to keep it outside under a well-ventilated shelter.
Wood can also be used for cooking, and not
just in a campfire. The top of a wood stove is a
convenient place to keep a kettle of water for hot
drinks, or to simmer or fry a meal. A hot bed of
coals is a great place to bury and cook potatoes
or assorted veggies wrapped in foil. A homemade
metal box (with air vents to control the temperature) sitting a couple of inches above the top of a
wood stove can be an effective way to bake.
A pound of wood packs a heating value of
around 8,000 Btus, roughly equivalent to cooking
on a gas range set to a high flame for about 30
minutes. If you’re looking for a fuel-free cooking
solution, the sun is the obvious option. But solar
cooking is a slow process and limited to locations
with plenty of sunlight. Even in an ideal location,
the sun delivers between 200 and 300 Btus per
hour for each square foot of solar collector area.
Solar cooking is certainly cleaner than wood
cooking, but with good stove design, wood can
become much more clean-burning and efficient.
See chapter 12 to explore this option.
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Systems and
W h e t h e r y o u r h o m e is new or old, you
can affordably make renewable energy part of
your future by phasing it in to help control costs.
For example, a little advance planning goes a
long way toward minimizing labor costs of future
installations of renewable energy systems. It’s
a good idea to work with a professional energy
consultant or installation contractor to understand
all the major components of the technology you’re
considering and to plan for things that will be
hidden in the walls, such as wiring and plumbing.
We collect the
sun’s heat through
the windows in our
home and control
it by opening and
closing shades.
The heat is stored
in high-mass
material and
released when
the sun no longer
provides heat. 
side of the house, converting the energy in the sunlight into fluid heat. A solar hot water storage tank
may live in the basement alongside a backup water
heater, with controls (sensors, an electronic brain,
and wires) between the collectors and storage tank
to control fluid flow and heat exchange between the
sun and the storage tank. Another important element, of course, is the plumbing that connects the
collectors to the storage tank.
For solar electric systems, there are collectors (solar panels), possibly storage batteries,
power management controls, and wiring between
them all. If you’re considering wind energy, you’ll
need to know where the tower will go and how the
power cables will get to your batteries or interconnect with utility power lines.
With utility-connected (grid-tied) electrical
systems, the grid serves as the storage facility to which electricity is delivered as it’s produced, and from which electricity is drawn when
needed. Renewable energy sources are seldom
consistent, so matching the supply rate to storage capacity is an important consideration. Most
energy systems will also have some sort of monitoring facility so that you can see what is happening within each subsystem.
A Building Plan
Collection, Storage,
and Control
Renewable energy technologies have three basic
interacting systems: collection, storage, and control. You must provide a place for each of these
systems to reside in (or outside) your home, as
well as means for them to interact with and connect to one another.
Integrated within these systems is the process
of energy conversion. With solar hot water, for
example, the solar thermal collectors may live on
the roof (or on a ground-mounted rack) on the south
As you make home improvements or renovations,
think about the master plan you have for all of
the systems you’re considering, and provide for
their future inclusion as you work. One of the best
things you can make available to your renewable
energy installer is a chase (groove) between the
roof and the basement that allows easy access
and plenty of space for running wires, plumbing,
or even a chimney without having to cut into walls.
If you’re doing roof work, installing supports for
future solar collectors will save time and money
down the road when you’re ready to put up your
panels. This requires knowing the dimensions
and mounting requirements of the equipment, so
be sure to do your research. As mentioned, it’s a
good idea to bring in a system designer or experienced installer early in the process, and make
sure the roof can handle the additional load of
solar panels.
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Plumbing or electrical lines
between collection and storage
Through an interior wall
Alongside a chimney
Through a box built
into a corner
A chase can be found
within or built into
walls to provide a
hidden path for wires
or plumbing to run
between floors.
Control center
Renewable Habits
work for you, but
don’t expect technology to do it all. Living with
renewable energy is about living within the means
that nature provides. Adopt renewable habits,
such as “one person, one light,” and simply be
aware of all energy being used in your home.
There are times when the sun doesn’t shine
or the wind doesn’t blow, and those are times for
conservation. But when nature gives, take advantage of the opportunity for abundance. For example, save your hot-water clothes washes for when
the sun can heat the water.
Put technology to
Becoming aware of your energy habits and
applying energy-smart strategies can make a big
difference in the size and success of your renewable energy system. You can live in the greenest, most efficient dwelling and still use a ton of
energy if you have not adopted efficient habits.
Here are some tips to help enhance your renewable acumen.
Readiness tip #1: Increase your energy awareness by understanding what’s happening in your
house and why.
• Are there lights on that don’t need to be?
iPiggyback Projectsi
Knowing your long-term needs allows you to piggyback projects with little or no extra cost. When
we did some work on our driveway, I took advantage of having a backhoe and crew already on-site.
They dug out trenches for running conduit between my house and a future wind tower site, as well
as for piping between rain collection barrels. It took less than an hour of additional backhoe time, and
I ended up a step ahead on two projects.
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• Do appliances have standby loads that always
consume power?
• If you have a private water system, do you
know when your well pump is on?
• Is the furnace pilot light on in the summer?
• Are the computer’s energy-saving features
turned on?
Readiness tip #2: Assess your energy use on
every level by doing your own energy audit (see
chapter 2). For example:
Readiness tip #3: Research products when
replacing lights and appliances, and use only the
most efficient models you can find. The ENERGY
STAR website (see Resources) is a good resource
that lists thousands of products and their energy
consumption. Plan ahead by researching for
future appliance purchases so you know what you
want. That way, if an appliance breaks down and
you need to replace it right away, you’ll know what
to buy and not end up with an energy hog simply
because it’s on sale.
Readiness tip #4: Adopt the most efficient
• Look at every outlet; know what’s plugged in
and why.
practices, preferably those that don’t use any
energy at all. These include:
• Learn to read your electric and gas meters
and understand where every last Btu or
kilowatt-hour is going. Examine a year’s worth
of energy bills, look at monthly and seasonal
trends, and think about what happens in your
home during those periods.
• Hanging clothes to dry on a passive solar
clothes dryer (a clothesline)
• Try to determine how many fuel units are
used for heating, hot water, air conditioning,
and other electrical uses.
• Watching the cat or the kids (or the
neighbors) instead of TV
• Know something about everything in your
home that uses energy — when it’s needed
and why, how much it uses while operating,
and how best to control its operation.
• Employing passive heating and cooling
• Using solar-heated water
• Taking advantage of nighttime air to cool your
house with open windows and fans, then
closing the windows and shades before the
air warms in the morning
Readiness tip #5: Control what you can. This
might include:
Yes, money (and energy) do fall from the sky! 
• Keeping the thermostat as low as you can
in winter and as high as you can stand it in
• Making sure your water heater is set no
higher than 120°F
• Installing low-flow showerheads and low-flow
aerators on faucets
• Putting appliances with phantom loads
(see page 41) on switched or automatically
controlled power strips
• Turning off the water heater if you’re away
from home for more than a few days
• Keeping humidity levels under control by
removing moisture at its source; if you must
use a dehumidifier, pay attention to the
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relative humidity and do not over-dry the
space or dry more space than necessary
on all aspects of creating and maintaining
home energy systems.
• Using timer controls and occupancy sensors
for lighting that tends to get left on
• Home Energy magazine Another good
periodical and website devoted to all matters
of efficiency. Though it’s geared primarily
to the energy professional, interested
homeowners will find lots here to chew on.
• Using switched power strips that allow
you to turn things off (such as an entire
entertainment system or office peripherals)
with ease
Readiness tip #6: Minimize optional or discretionary uses of energy, such as clothes-drying,
outdoor lighting, and use of air conditioning when
outdoor temperatures are not life-threatening.
Doing Your Homework
As you explore practical renewable energy options
that fit your needs, location, climate, and lifestyle,
be sure to research state, local, utility, and federal incentives that may be available for renewable energy and energy efficiency projects. Contact your state energy office and local electric
and gas companies about services and incentives, and ask a tax professional about applicable federal tax credits for efficiency upgrades and
In addition, here are some of my favorite
resources that can help you identify incentives
and keep you abreast of developments in renewable energy and energy efficiency (see Resources
for websites):
• Database of State Incentives for Renewable
Energy An online resource for incentives and
policy information for renewables and energy
efficiency improvements, including initiatives
sponsored by states, local governments,
utilities, and some federal programs.
• Tax Incentives Assistance Project (TIAP)
Developed as part of the Energy Policy Act of
2005, this online resource helps homeowners
and businesses make the most of federal
income tax incentives for renewable energy and
energy-efficient products and technologies.
• Home Power magazine An excellent resource
for all things renewable. Content ranges from
homeowner profiles to highly technical details
The Value of
that a human in decent
physical condition can generate only about 1/4
horsepower (hp) — or around 200 watts — of
energy for any length of time. I got a chance to prove
this when the Vermont Energy Education Program
asked me to build a bicycle-powered generator
for a school energy demonstration project.
Mounted on a modified bicycle trainer, the
rear wheel of the bike drives an electrical generator that powers four light bulbs. First, I screwed
in four 100-watt bulbs and jumped on the bike.
I could barely move the pedals. It was like trying to bike up a vertical incline. I switched off
three of the four bulbs and pedaled happily for
a couple of minutes before breaking a sweat.
Then a second bulb was switched on, and after a
minute or two of producing 200 watts, the lights
dimmed as my energy was drained and I pedaled
more slowly.
To generate one kilowatt-hour (kWh) would
require pedaling for five hours with two 100-watt
light bulbs switched on (2 x 100 watts x 5 hours
= 1 kWh). At a cost of only 10 or 20 cents from
the power company, a kWh is a pretty good deal!
The instructors using the bicycle generator
sometimes offer a $10 bill to any student who
can produce 10 cents worth of electricity. When
the 100-watt incandescent bulbs are replaced
with high-efficiency, 25-watt fluorescent bulbs, all
four light up with the equivalent light output of
the four incandescents — and minimal complaint
from the rider. Still, no rider has yet been willing
to ride for long enough to take home the $10.
I r ea d s o me w h e r e
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c l os e - u p
Power Equivalents
Here are a few comparisons to help you get
a feel for what a kilowatt-hour is:
• A gallon of gasoline contains the energy
equivalent of over 36 kWh.
• A car battery stores less than 1 kWh of
• It takes 861 food calories (more than
1/4 pound of butter) to supply the energy
equivalent of 1-kWh — about the amount
of energy you’d burn up during two solid
hours of high-impact aerobics.
If you like math, you’ll like what James
Watt did back in the 1700s. He determined
that an average horse could lift a 550-pound
weight one vertical foot in one second. This
rate of work is now known as horsepower
(hp), and can also be expressed as 550 footpounds per second. A horse can perform
work, and so can electricity. Horsepower can
therefore be expressed in terms of electrical power. Electric motors are often rated in
In an ideal world, one horsepower is equal
to 746 watts or 0.746 kilowatts. However, in
reality no activity or process is 100 percent
efficient, so a 1 hp motor will demand about
1,000 watts, more or less, depending on the
motor’s efficiency and how hard it is working. It’s helpful to understand this relationship when determining the power consumption of the various motors around your home
or when estimating the size of a motor you
might need to do some work for you.
Energy Action
in Cuba
robust trade with the former
Soviet Union. Major components
of the trade relationship were Cuban sugar
and Russian oil. That partnership came to
an abrupt end with the fall of the Soviet
economy, which subsequently led to the
crash of the Cuban economy. This started
what the Cubans euphemistically call the
“Special Period,” when dramatic reforms and
austerity measures became necessary for
the nation’s survival.
Due to the demise of their major
trade ally, the Cuban people suddenly
found themselves without jobs, money, or
resources, and they suffered lengthy daily
power outages. Cuban leaders understood
that people needed basic services, but that
sacrifices would have to be made.
The government immediately invested
in public transportation, purchased one
million bicycles, mandated energy-efficient
lighting and refrigeration, upgraded its power
grid, expanded the use of renewable energy,
and developed electric rate structures that
provided affordable electricity to meet basic
needs while discouraging overuse.
Out of economic and practical necessity
Cuba reduced its energy consumption by
half over a period of four years. It has now
become a global leader in practical, innovative
approaches to energy efficiency, renewable
energy, and community energy solutions —
all on a very tight budget. Cuba also looked
to increase international cooperation. It now
exports technical expertise in health care
and has its own solar electric panel assembly
efore 1990, Cuba
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Hydroelectric station 
facility, which meets its growing needs with
some left over for export.
I was impressed by the small hydro­
electric power station (above) that used
30-year-old Russian technology to provide
power for 57 households. The same size
system might provide enough power for four
average American homes. Each family takes
pride in some level of “ownership” of the
station and understands the limitations of
a finite resource. If one family is being an
energy hog, the whole neighborhood feels
it. The local school takes power priority and
has a solar electric system as a backup.
You might think that all this frugality
makes Cubans grumpy, but the society has
worked such circumstances to its advantage.
For example, the high price of chemical
fertilizers (manufactured from fossil fuels)
has facilitated advances in organic farming
using locally produced compost as fertilizer.
This saves money while growing healthy, local
food in a closed-loop system.
Coffee was once an import, but the
connection between agriculture and economy
is very strong: Why pay someone else for
something you have the resources to do
yourself? The result, I’m happy to report,
is quite delicious. Farming in that industry
has become a well-paid and highly soughtafter vocation. One local grower offers
benefits that exceed the standards of even
progressive U.S. employers.
Throughout these struggles, every
citizen has been provided with health care,
a home, and education. But I’m not trying
to put a happy face on all of this. Change is
always a struggle, and there was substantial
change on many levels. Not everything tried
has worked. Many of those bicycles are now
rusting away; despite good intentions, there
was no infrastructure for repairing or even
riding bicycles in many places. Also, the
bicycles chosen were frumpy, single-speed,
utilitarian clunkers rather than something
one would actually look forward to riding.
Energy advances in Cuba were the
result of dire circumstances that led to a
quantum shift in awareness, policy, behavior,
and community-level action. Island people
generally have an innate sense of finite
re­sources, and we can learn a lot from
the Cuban response to hardship. For more
information on Cuba’s energy situation,
I recommend a video called The Power of
Community — How Cuba Survived Peak Oil,
produced by Community Solutions (see
My Ex p erience
Every once in a while,
an experience can completely crumble some
long-standing preconceived notion. Such was
the case when I returned
from a weeklong trip
to Cuba with a group of
20 other energy professionals, sponsored by
Solar Energy International
and Global Exchange
(see Resources for websites). The purpose of
the trip was to explore
Cuban solutions for
curbing energy consumption and increasing the
use of renewable energy
in the face of dire circumstances.
Out of economic and practical necessity Cuba reduced its energy consumption
by half over a period of four years. It has now become a global leader in practical,
innovative approaches to energy efficiency — and on a very tight budget.
energy action in cuba 27
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Bicycle Power
A bicycle is an extremely efficient mode of transportation. With a multi-gear drive mechanism, it can be modified to efficiently deliver mechanical power that can be used for anything from grinding grain to spinning an electrical generator.
There are several approaches to using a bicycle to provide electrical or nonmotive
mechanical power. Options range from chain or gear drive to direct mechanical drive. The
design featured in the project on page 29 uses a bicycle trainer that lifts the rear wheel off
the ground, and replaces the trainer’s resistance unit with an electrical generator. Mechanical power generated at the roller shaft is coupled directly to the generator shaft, and output
voltage depends upon how fast you pedal.
To produce electrical power with a bicycle, you need to generate low-voltage direct current
(DC), not alternating current (AC). This is because AC appliances require a steady voltage
(120 or 240 volts) and frequency (60 or 50 hertz) for proper operation. That would require
careful control of the generator’s speed, expressed in rotations per minute (rpm).
When mechanical energy input, such as the spinning of a bicycle wheel or wind turbine,
is used to create electricity, the speed (and therefore the frequency in the case of AC) will
vary according to the force applied. In order to achieve greater versatility with power management, using DC power provides the necessary flexibility. Generating 12-volt DC power
allows you to charge batteries, and battery power can be converted to AC power using an
electronic inverter, or it can directly supply DC appliances, such as those made for camping
and recreational vehicles.
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his project shows you how
to build a 12-volt DC battery charger with a DC-to-AC
inverter, so you can use the power
generated to supply conventional (AC)
electrical devices. I’ve built seven
generators with this basic design, but
no two are identical. Bicycle trainer
designs are constantly changing, and
this necessitates modification of the
design. Since the trainer you use is
very likely to differ from mine, there’s
no point in offering detailed templates, and the parts may vary. My
goal is to provide enough guidance
to get you on the right track using
your own parts and materials.
The Parts
The most costly part required for
this project is the DC generator, if
you buy it new. However, you may
be able to find a suitable used unit
for a fraction of the cost of a new
one. Check online for used and surplus electronic equipment suppliers.
The type of trainer I use has
a friction roller that’s driven by the
bike’s rear wheel. Prices for trainers
vary widely, but magnetic and airresistance types typically are the
least expensive. You will remove
the resistance unit and connect the
generator to the shaft of the roller.
Therefore, look for a simple trainer
with a flat-bottomed roller mount
and a roller assembly that can be
The Wiring
The electrical wiring must provide
safe and efficient means to transfer
power from the generator to the battery. This requires the proper gauge
of wire, solid electrical connections,
a sturdy connector between the
generator and battery and between
the battery and inverter, and fuses
to protect against over-current. You
will also need a diode, which is an
electronic “check valve” that allows
current to flow in only one direction.
Without the diode, electricity would
flow from the battery and spin the
generator as a motor, and you would
have an electric bike.
This charger design uses clips
on the wires that connect to the
battery, allowing for easy disassembly and transportation. If you have a
more permanent location for the
bike and charger, consider using wire
friction roller
Build a Bicycle-Powered Battery Charger
terminals that offer a more solid
connection to the battery. Most of
these parts can be found at auto
or electrical supply stores.
The Generator
The generator essentially is a motor
that can be operated in reverse to
produce electricity rather than consume it: You supply the mechanical
energy to spin the shaft, and the generator turns it into electricity. Choose
a DC permanent-magnet motor (brush
or brushless) rated between one-sixth
and one-third horsepower (125 to
250 watts), capable of generating up
to 20 amps of current and about
14 volts when spinning somewhere in
the vicinity of 2,000 rpm (see Figuring
RPM on the next page). The output
voltage will vary with the generator
speed, which depends on how fast
the bike wheel is spinning.
Bike trainer
with friction
roller assembly
resistance unit
flat-bottomed roller mount
(with adjustment screw)
The electricity produced by this generator can be potentially lethal. Also, batteries contain harmful acid and can deliver
incredible amounts of energy if the terminals are shorted (connected together). If you are uncertain about any electrical
or mechanical aspects of this project, consult an expert or qualified professional who can help.
B u ild a B icycle- p ow ered Battery Char ger 29
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Build a Bicycle-Powered Battery Charger
Figuring RPM
The power specifications for this
battery charger are based on
using a 26" O.D. bicycle tire. I
recommend using a smooth tire
with little or no tread (to reduce
noise) that is about 1" smaller in
diameter and won’t appreciably
affect performance. Likewise,
using a 27" or 700 mm tire will
provide similar output.
The friction roller (on the
trainer) has a diameter of 1.2".
This gives you a drive ratio of
about 22 to 1, meaning that for
every one revolution of the bicycle wheel, the roller (and therefore the generator shaft) spins
22 times. If you ride the bike at
a speed of 7.5 mph, the wheel
spins at about 100 rpm, and the
roller spins at around 2,200 rpm.
Experience suggests that this is
a reasonable compromise for
effective power production by a
wide range of riders.
M at e r i a l s
Trainer Assembly
Bicycle trainer
One 6" x 14" piece ¼" aluminum plate
12-volt DC motor/generator (Dayton
Two ¼" x 1½" #20 bolts
Two ¼" #20 nylon locking nuts
Four ¼" x 2" #20 bolts with eight nuts
One jaw coupling with I.D. (inner
diameter) to match generator
shaft O.D. (outer diameter)
One jaw coupling with I.D. to match
friction roller shaft O.D. (the body
size of both jaw couplings must
be the same)
One jaw coupling insert sized to match
both jaw couplings
Generator to Battery
One ¼" spade-type crimp connector for
12 AWG wire (for diode anode lug)
Two 2" lengths of ¼"-diameter
heat-shrink insulation tubing
One ring-type crimp connector for 12
AWG wire with ¼" hole (for
diode cathode stud)
One 1N1190A diode
One 16" length 12 AWG wire
One wire nut (sized for two 12
AWG wires)
One automotive-type fuse holder
20-amp automotive fuse
Two battery clips to attach 12 AWG
wire to battery (one clip should
be red, the other black)
One 8" length of 1"-diameter
protective wire loom
Two wire ties
Battery to Inverter
(see Facts below)
Two 12" lengths and one 24" length of
4 AWG wire
Six ring-type crimp connectors with
¼" hole (for 4 AWG wire )
Eight 2" lengths of ½" heat-shrink
insulation tubing
DC-rated fuse or circuit breaker (sized
per inverter manufacturer specs)
Two battery clips (for 4 AWG wire; one
clip should be red, the other black)
One 12-volt to 120-volt inverter
DC voltmeter
A F e w E s s e n t i a l Fac t s
Notes on the electrical parts used to connect the battery to the inverter:
• Connectors: The type and size of
connectors and cables you use, as
well as the kinds of connections you
make, will be determined by your
specific setup and size of fuses,
cables, battery clips, and inverter
connection. The wiring harness
described here is sized for a 600watt inverter and incorporates
a resettable circuit breaker. Use
smaller wire and connectors for a
smaller inverter. See the table on
page 179.
• Heavy-gauge wire: For greater
flexibility, use fine-strand welding cable
instead of standard battery cable.
• Inverter: Size the inverter according
to the needs of the appliance you
hope to operate. Anywhere from
200 to 600 watts would be an
appropriate size for this project.
True sine wave inverters will offer
better performance than “modified”
sine wave models, but the former
are more expensive.
• DC-rated fuse or circuit breaker:
Size this according to the inverter
manufacturer’s specifications.
I used an 80-amp resettable
DC-rated circuit breaker for a
600-watt inverter. The DC rating
is critical, since DC-rated devices
are electrically different from
AC devices.
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Remove the
roller assembly
from the frame,
then remove the
resistance unit
and counterweight from the
roller assembly.
resistance unit
friction roller
1. Disassemble the trainer roller
The friction roller shaft will likely have a housing
for the resistance mechanism on one end and
a counterweight on the other end. Remove any
screws as needed to get inside the housing, then
disconnect the resistance mechanism from the
end of the shaft. Remove the counterweight from
the other end of the shaft; the weight is likely to
be threaded onto the shaft. Remove any bolts or
screws as needed to separate the roller assembly from the mount on the trainer frame.
2. Modify the friction roller.
You will connect the generator to the end of the
roller shaft that had the counterbalance (which
may have a screw thread) using a jaw-type coupling. The coupling won’t hold well on threads,
so you have to cut off the threaded portion, using
a grinder with a metal cut-off disc or a hacksaw
or reciprocating saw. Secure the roller shaft in a
bench vise to hold it while you make the cut.
Using a 6" x 14" piece of 1/4" aluminum, cut a
notch to create a tab that slides underneath the
roller mount. For my trainer, the notch measured
31/2" x 23/4". Cut the plate with a jigsaw and fine
metal blade.
Drill two 1/4" holes in the roller mount for
attaching the generator plate. Slide the aluminum
plate underneath the mount, and align the plate
so it’s square with the roller mount, then clamp it
in place. Poke a center punch through the holes
in the mount to transfer their locations to the aluminum plate. Remove the plate and drill two 1/4"
holes through the plate. Clean up the holes and
metal shavings, then attach the generator plate
to the roller mount with two 1/4" x 11/2" #20 bolts
and locking nuts. Note: You may need to cut a
notch in the plate to provide clearance for the
trainer’s adjusting screw.
Cutting off the
threaded section
of the roller shaft
3. Cut and install the generator
mounting plate.
The generator mounting plate supports the weight
of the generator and connects it to the roller
mount on the trainer, while the entire assembly
remains adjustable to fit various sizes of bike
B u ild a B icycle- p ow ered Battery C har ger 31
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Build a Bicycle-Powered Battery Charger
notch for screw
<Top view: ¼” holes drilled through roller bearing mount
<Bottom view: Generator mounting plate installed with bolts
½" gap between shaft ends
<Transferring the centerline of the roller shaft to the
<Aligning roller and generator shafts
4. Fit the generator to its mounting
roller shaft, keeping their ends precisely 1/2" apart
(this space is required for the shaft couplings).
Using the centerline on the mounting plate as a
reference, carefully measure and mark the locations for the generator mounting holes. Note:
It may be easier to complete the assembly by
removing the mounting plate.
Drill four 1/4" holes through the plate for the
1/4" x 2" #20 generator mounting bolts. The bolts
will thread directly into the generator housing. To
adjust the height between the generator and its
generator mounting plate Reinstall the friction roller onto its mount. Carefully measure where the centerline of the roller
shaft extends over the generator mounting plate.
Use a straightedge or small square to mark the
centerline across the mounting plate; this line will
serve as a guide for locating the holes for the
generator mounting bolts.
Place the generator on the mounting plate and
align the center of the generator shaft with the
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<Fitting the generator and plate into position, with the
<Completed generator and roller assembly
mounting plate (for aligning with the roller shaft),
add a nut on each side of the mounting plate,
and thread the bolts into the generator housing.
Later, you can adjust the nuts as needed to move
the generator up or down, then tighten them to
secure the generator in the correct position.
Leave the nuts loose for now so you’ll be able to
move the generator for fitting the couplings.
6. Prepare the generator wiring.
couplings loosely fitted onto the generator and roller shafts
5. Complete the mechanical
Slip a jaw coupling onto the end of the generator
shaft, using the appropriate size coupling; do the
same with the roller shaft. Install the rubber jaw
coupling insert. Reinstall the mounting plate with
the generator onto the roller mount while aligning
the shaft couplings.
Use the double-nut system to adjust the generator height to align the two couplings.
Once the shafts are perfectly aligned, slide the
jaw couplings together and tighten all hardware,
including the setscrews, to secure the couplings
to the shafts. Test-fit the bike on the trainer.
N ote : The mounting plate may need additional
support so the generator’s weight does not bend
the plate and cause misalignment; a simple wood
block custom-cut to size and tucked under the
free end of the mounting plate will suffice.
Strip 2" of sheathing from the loose end of the
generator output cable to expose the three
insulated conductors inside. The green wire is
intended for equipment grounding, but it is not
required in this case; you will be working with only
the black and white wires, both of which will carry
electrical current.
Operate the generator with the bicycle
mounted on the trainer by pushing a pedal down
with one hand, causing the back tire to spin. Use
a voltmeter to identify which of the conductors is
positive and which is negative. Polarity depends
upon the direction of rotation. Mark the positive
conductor with a piece of red tape. Strip 1/4" of
insulation from the positive wire, and strip about
1/2" from the negative wire.
Attach a spade terminal to the positive wire of
the generator and crimp it using a crimping tool.
Slide a piece of heat-shrink insulation tubing over
the terminal and apply heat with a hair dryer so
that the insulating tube shrinks tightly over the
wire and connector.
7. Attach the diode.
The diode has two ends: the anode and the cathode. The anode is the end marked + (plus) and
connects to the positive conductor of the generator. The cathode is the end marked – (minus)
B u ild a B icycle- p ow ered Battery Char ger 33
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Build a Bicycle-Powered Battery Charger
Cathode side
Anode side
Diode with schematic
diagram 
and connects to the battery’s positive terminal.
Look for this represented by a schematic diagram
printed on the body of the diode.
Attach the spade terminal of the positive
generator wire to the anode of the diode. Slide
a piece of heat-shrink tubing over one end of
the fuse holder wire, attach the ring terminal
to the fuse holder wire and crimp it. Apply heat
to the heat-shrink tubing. Bend the terminal at
a 90-degree angle and attach it to the threaded
stud on the cathode side of the diode, using the
nut supplied with the diode.
8. Complete the generator output
Strip about 1/2" from each end of the 12 AWG
wire. Use a wire nut to connect the negative side
of the generator to one end of the 12 AWG wire.
Prepare the other end of the fuse holder wire
by stripping back about 1/2"of insulation. Attach
each of these two wires to its corresponding battery connector (the fuse holder wire is the positive wire, and so is connected to the red battery
clip) by crimping and soldering the connections,
or use a terminal connector and screw. The type
of connection you make depends on the type of
battery connector you have, but avoid wrapping
bare wire around a screw, as this is not a secure
Make sure all exposed electrical connections
are covered and protected to prevent exposure
and physical stress.
Slide the wire loom over the diode and its connectors, and secure it in place with wire ties. This
will help to protect the connections and parts
both physically and electrically. You can dress
+ positive side
<Completed wiring between generator and battery. Cover the connections with wire loom for protection.
<Parts for battery-to-inverter wiring
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Completed battery-
up the entire wiring harness by covering all of it
with wire loom. If the bike generator is likely to be
moved around a lot or otherwise abused, you can
increase the durability of the wiring harness by
using a piece of PVC tubing in place of the loom.
In any case, be sure to leave access to replace
the fuse if needed.
DC-to-AC inverter
to-inverter wiring
9. Connect the battery to the inverter.
Be sure to read A Few Essential Facts on page
30. To complete the wiring connections, strip
about 1/2" from each end of all three 4 AWG
wires. Slide a crimp connector onto each end
and crimp the lug securely onto the wire. Slide
a piece of 1/2" heat-shrink tubing over each lug,
leaving the hole exposed, and apply heat.
Connect one end of each of the two short
wires to the fuse or circuit breaker. This is the
“positive” side cable. Attach a red battery clip to
the cable coming from the fuse or circuit breaker
connection point marked “line.” Attach the free
end of the positive cable connected to the other
side of the fuse or circuit breaker marked “load”
to the inverter’s positive terminal.
circuit breaker
Connect one end of the long wire to the negative battery clip, and connect the other end to the
negative side of the inverter.
Follow the manufacturer’s instructions to connect the inverter to the battery. Typically, you
would attach the negative side to the battery
first, then make the positive connection. Observe
polarity carefully, as electronic equipment can be
destroyed if hooked up backward.
U s i n g Yo u r B at t e ry C h a r g e r
Once you’re all hooked up, you
can start pedaling to charge
the battery. But you won’t know
when the battery is full, when
to stop pedaling, or how hard
you need to pedal to keep the
battery full of juice. The only
way to know is to hook up a
volt­meter to the battery and
watch the numbers. You can
find inexpensive voltmeters
at electronic supply stores, or
devise a scheme to hook up
a panel-mounted automotivetype meter to the battery.
Try not to let the battery
charge level drop below 11.5
volts or rise above about 14.5
volts. Pedal faster or slower
to vary the charging rate.
Higher and lower voltages
can damage batteries. Higher
voltages may damage the
inverter. There’s no need to
have everything connected all
the time; the inverter needs to
be connected only when power
is being used, and the charger
must be connected only when
you’re pedaling to charge.
Please be aware that incredible amounts of energy are
stored in a battery, and its acid
electrolyte will burn through
skin, clothing, and lots of other
things. If a tool or other piece
of metal creates a short circuit
across the battery terminals,
the result could be a melted
tool and an exploded battery
with splattered acid. Insulate
the battery terminals and
consider enclosing the battery
in a protective box to keep the
young and uninitiated away.
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Do Your Own
Energy Audit
er f o rm i n g a n e n ergy audit in your home is a great way to learn
about your house, assess your habits, reduce your energy use, save money,
fix problems, and find lots of things you thought you’d never see again. An
audit implies investigation, and not necessarily action. But why bother with the investigation if you don’t intend to do anything with the information you gather?
Therefore, this chapter covers a number of improvements you can make to reduce
your energy use, along with some discussion to give you a basic understanding of the
issues. Your goal is to identify the amount of energy used by the myriad products and
appliances in your home, so you know where to begin to look for savings.
While some auditing tasks are best left to a professional, there are plenty of things
you can learn to do on your own. You may not find one silver bullet that saves you
barrels of energy and money, but if you tackle the manageable items — taking care
of the biggest things first, then working on the smaller changes over time — your
savings can really add up.
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Getting Started
entering your house
for the first time. When visiting any new place, we
look at all the things the locals take for granted:
architectural details, sounds, smells, cracks in
the sidewalk, the unique view — even the main
attraction that you may have traveled thousands
of miles to see. Approach your energy audit as if
you were going on vacation to some exotic place.
As a professional energy auditor, I use my skills,
experience, and tools to find obvious and hidden
energy users and wasters throughout a home. It
might take two to four hours to test and investigate, and I won’t catch everything, due to time
and other constraints. As a homeowner, you’re not
subject to these constraints, so you’re in the best
position to spend the time it takes to investigate
the energy use and savings potential in your home.
Your energy audit starts with an inventory of
everything in your home that uses energy, followed
by a review of your energy consumption. Gather a
year’s worth of utility bills from all of your energy
suppliers. How much of each fuel do you use in a
year? What are the seasonal variations? Find the
daily energy consumption of each fuel during each
month of the year by dividing the total monthly
usage by the number of days in that month.
You may use more electricity in the summertime when the air conditioner is running, then
less in the fall, and more again in the winter when
the furnace is operating. While you may find that
Ima g i n e t h a t y o u ’ r e
your energy use varies seasonally, you probably
have a consistent base load. This is energy-geek
lingo for the lights and appliances that are used
consistently year-round. Gas base load might
include things like water heating and cooking,
while your electric base load might be made up
of refrigeration, lighting, and clothes washing.
Base load may be reflected in the entirety of
your electric bill during the few months out of the
year that do not include use of heating or cooling
energy systems, or other season-specific energy
users. Energy use that changes with the seasons,
such as heating and air conditioning, is not base
load. Like a good detective, don’t take anything
for granted, but gather the information and the
evidence, then look objectively at those findings.
“AAA” Approach to
Energy Savings
My professional audit of any home starts as I pull
into the driveway, taking in a broad view of the
house. On one job I saw a garage with two 300watt halogen floodlights burning brightly in the
middle of the day. When I asked why, the answer
was “the switch broke.” Those lights were costing
the homeowner $48 per month and the fix was a
simple $2 switch. Even if the homeowner paid an
electrician $75 for the repair, the simple payback
(see page 42) would be less than two months.
With the above example in mind, let me introduce my “AAA” approach to energy efficiency:
No special tools are required to understand and accomplish many of the basics — your primary
inspection tools are your eyes and ears — but a few basic tools will make your job easier:
• Flashlight
• Screwdrivers
• Tongue-and-groove pliers
• Tape measure
• Wooden BBQ skewer
• Dust mask or (better) respirator
• Notepad and pen
• Camera
• Fearless curiosity
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• Awareness of the equipment and conditions
you have in your house, along with your habits
(notice that you have lights, that the lights are
on, and ask yourself, “Why?”)
• Assessment of the energy use of the
equipment in your home and how your
habits affect energy consumption and costs
(calculate the energy used and cost of the
lights being on)
• Action to reduce your use (replace the switch)
Le t ’ s s t a r t b y taking a look at the usage of
electricity in your home, using the AAA approach.
I’ve been in many homes where so much work
has been done to them over the years that it’s
hard to figure out what’s going where and why.
One home had mysteriously high electric bills that
we tracked to an electrically heated radiant floor
in the kitchen that was unknown to the current
owners. It was found only with the aid of an
infrared camera.
Take an inventory of electrical appliances and anything that’s plugged into an outlet. Crawl around,
look under and behind things to find those dusty
power strips hidden by the entertainment center,
then find and list everything that’s plugged in.
Remember that some electrical users, such as
water heaters and furnaces, are wired directly to
a house circuit (which leads to the circuit breaker
box) rather than having a cord and plug that connects to an outlet. Go to the circuit breaker box
and identify what every breaker is for. If there are
mysteries, get to the bottom of them by turning
breakers on and off and identifying what’s connected to each circuit.
The Sample of Household Electricity Usage
chart on the next page shows a billing history
of consumption both numerically and graphically.
Remember that electrical energy is expressed in
kilowatt-hours (kWh), which is the electrical quantity unit for which the power company bills you.
The electric company may not read your meter
on the same day of every month, and this may
cause confusion when one read period is longer
or shorter than another. For this reason, knowing
how many kWh are used in a day is a more useful
way to understand electrical consumption.
To assess your electrical use means to understand how much electrical energy each appliance
uses. Power consumption of appliances can be
discovered in several ways, although some are
more accurate than others.
<Breaker boxes should contain
electrician’s notes indicating
what’s on each circuit (but these
are often incomplete). Switch the breaker to the OFF position to
cut power to the circuit.
<Older electrical service panels
have fuses. Unscrew the fuse
completely (and set it aside) to
shut down the individual circuit.
Looking down the table of numbers in the billing
history, we see a base load of around 28 kWh
per day or 840 kWh per month in May and October. This monthly consumption is higher than that
shown in the table because the read periods for
those 2 months are less than the number of days
in the month. Multiplying kWh per day used by the
number of days in the month serves to “true-up”
the monthly consumption.
If summer vacation in July lasted for the whole
month, we could see what the house itself uses
in a month (all the appliances left on but no occupancy use, such as lights, TV, electronic games,
and so forth). But the actual 2-week break does
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Sam p l e o f H o u s e h o l d E l e c t r i c i t y U s a g e
Read date
# days between
meter readings
read period
January 15
furnace blower, electric heat, lots of lights
February 12
more furnace use, less electric heat
March 9
same as February
April 15
close to base load, still a little heat
May 14
base load use; no heat, no air conditioning
June 15
opened the pool June 1st, air conditioning
July 19
two-week vacation, left pool pump on
August 15
pool, air conditioning, dehumidifier
September 16
less of all the above
October 14
base load
November 14
start of heating season
December 15
same as January, less electric heat
k w h p e r d ay
offer a clue to consumption habits. The 1-horsepower (HP) pool pump runs continuously and
uses about 24 kWh per day (one HP is roughly
equivalent to 1 kilowatt). Subtracting 24 kWh
from the actual July usage of 36 kWh per day, the
resulting 12 kWh per day is the lowest monthly
reading — even lower than the base load months.
This tells us that occupant behavior contributes
quite a lot to the home’s power consumption.
Knowing the base load and the pool pump use
can help tease out the usage of the air conditioner.
For example, the base load is 840 kWh per month,
the pool pump uses 730 kWh per month (1 kilowatt x 730 hours in a month), and we’ll estimate
the dehumidifier at 50 kWh per month, for a total
of 1620 kWh. This family used 1810 kWh in
August, so the remaining 190 kWh is air conditioning, plus any additional occupancy-related items
that occurred during that month. This kind of disaggregation is not precise, but it works well to gain
perspective on the bigger energy-use picture.
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Appliance Power Rating
An easy but not always accurate way to assess
electrical use is to look at the tag on the appliance indicating the operating voltage and the
power consumption in watts. If it shows amps,
multiply amps by volts to get watts. Most appliances and anything that plugs into a standard
outlet require 120 volts; electric dryers, ranges,
and many heaters require 240 volts.
1. Add
up how many hours each appliance is
turned on during an average month.
2. Multiply watts by hours of on-time and your
answer is in watt-hours.
3. Next, divide by 1,000 to arrive at kilowatthours (kWh), then multiply kWh consumed by
your cost per kWh and you know how much the
appliance is costing you each month.
Here’s an example of a television that draws
5 amps and is on for three hours every day:
5 amps x 120 volts = 600 watts x 3 hours
= 1,800 watt-hours
1,800 watt-hours ÷ 1,000 = 1.8 kWh
How much is that TV usage costing you? Look
at your electric bill to find how much you pay for
each kWh and multiply that by the number of kWh
the appliance uses. For this example let’s say
your electricity rate is $0.12/kWh:
1.8kWh x 0.12 = $0.216 per day x 365 days
= $78.84 per year
A simple wattmeter plugs in
between the wall outlet and
appliance and tells you exactly
how much electricity the appliance uses. 
To get the most accurate understanding of the
energy use and cost of individual appliances, use
a wattmeter (such as Watts Up? or Kill A Watt;
see Resources) to measure the actual power
used by the appliance. This is the only option
for determining the actual consumption of appliances that frequently cycle on and off, like refrigerators and freezers.
After assessing your electrical use, it’s time to
start exploring some options and make a plan for
action. Let’s say you’ve added up all your lighting use over a month, and it totals 100 kWh. If
you pay 12 cents a kWh, that’s $12 per month,
or $144 per year. If you replaced all your incandescent light bulbs with LEDs or compact fluorescent bulbs, and maybe installed occupancy sensor switches where needed, you would use about
one-quarter to one-third of the power to provide
the same amount of light.
As you replace those bulbs, take a close look
at where the light falls. Does it light up the countertops or the top of the cabinet? Put light where
you need it by changing the lighting layout to
make best use of those lumens.
Refrigerators, air conditioners, ceiling fans,
computers, televisions and set-top boxes, clothes
washers, and dishwashers are all candidates
for efficiency improvements. Explore the many
options and compare the energy consumption of
many different appliances at the ENERGY STAR
website (see Resources).
Planning Your Energy Investments
Knowing the existing appliances’ power use before
researching new ones gives you the knowledge you
need to calculate savings potential and make an
informed replacement decision. Don’t replace appliances just because they’re old. Assess their energy
use first and compare their energy consumption
with new equipment. See chapter 5 for more information about energy use monitoring.
Once you have an understanding of what’s
happening in terms of base and seasonal loads,
and exactly where that energy is going, you
can begin to explore improvement options and
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savings scenarios. When you consider making an
investment, you want to know what rewards that
investment might offer you over time. Often, that
reward is quantified in terms of how many dollars
you may save over a period of time. Investments
in energy efficiency have value beyond financial returns, such as the immediate payback of
increased comfort. Efficiency is a good excuse to
upgrade, since there is almost always a financial
gain in terms of energy cost savings.
Most home
equipment is
never really “off”
unless unplugged,
and it can eat up a
surprising amount
of electricity.
Changing Habits
Awareness and habits go hand in hand. Changing
habits starts with identifying what you currently
do and how you do it. This means washing full
loads of dishes and laundry, turning off lights that
are not needed, and simply being aware of what
is in use in your home. For example, if you have
a private water system, do you know when the
well pump is on? A leaky toilet valve can lead to
a mysterious increase in electrical use due to the
increased run-time of the well pump.
Don’t forget about gas standby loads (see box
below), such as pilot lights. A water heater or
furnace pilot light might use 1,000 Btus each
hour, while gas range pilot lights can use 250
Btus. If your heating season is six months long
and you leave the furnace pilot light on during the
summer months, you’ll have paid for nearly 4,400
cubic feet (or 44 therms; one therm is equal to
100,000 Btus or 100 cubic feet of natural gas
that was ultimately wasted. Many modern gas
appliances have electronic ignition so no pilot is
W h a t Ar e S t a n d by Lo a d s ?
Many appliances appear to be
off but are really using a small
amount of power. Eliminating
these standby or “phantom”
loads represents savings that
really add up. When it comes to
controlling standby power, a few
inexpensive, well placed, and
intentionally used switchable or
automatically controlled power
strips are well worth the investment. A switched power strip
turns everything plugged into it
on or off with a single switch.
A controlled power strip (see
the Smart Strip in Resources)
uses the on/off action of one
component plugged into it
to switch other components
plugged into it on or off. For
example, when you turn on your
computer monitor, the power
strip automatically turns on the
printer, modem, and anything
else plugged into it. When the
monitor is powered off, the power to all peripherals is automatically switched off. Some power
strips also have built-in power
meters so you can monitor how
much electricity the plugged-in
devices are using.
Although a few watts of
standby energy use per
appliance may sound like small
potatoes, the combined energy
use of these loads adds up fast.
Phantom loads in a typical
American household amount to
over a kilowatt-hour per day. You
might find some surprises as
you meter the many gadgets
plugged into our modern homes.
My microwave oven uses
5 watts of power when it is
“off.” That is, it presents a constant power drain of 5 watts.
That works out to 120 watthours per day, or 44 kWh per
year. Since our total household
usage is only 7 kWh per day,
that’s equivalent to about
six days of power consumption
over the course of a year.
The nuker is now plugged into
a $7 switchable power strip
that’s easily accessible.
This power strip has a simple
payback of a little over a
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ISimple PaybackI
Simple payback, often expressed in years, is the cost of the improvement divided by the annual energy
cost savings. For example, if you spend $1,000 today to save $100 per year, the simple payback is
10 years. After 10 years, you start making money from the improvement. As energy costs rise, the
payback period shortens.
Hot Water
take a look at your hot water usage. Hot water
is probably the second largest energy user in
your home, after space heating (if you live in a
heating-dominated climate).
Continuing the AAA approach,
Clear a path to your water heater and take a good
look at it. Answering a few questions will get you
started down the AAA path, offering clues about
the condition of your water heater, how much
energy it might be using, and whether or not it’s
time to repair or replace.
• What is its energy source? Gas, electric, or
something else?
• Is the water heater rusty or leaky? How old is it?
• If it’s a gas-powered unit, examine the flue. Is
it connected to the chimney and does it slope
upward? Is there any rust flaking from the flue
• Have you ever performed any maintenance
such as draining, flushing, or changing the
anode rod?
• Do you run out of hot water frequently?
Open a hot water faucet and listen carefully
while standing quietly next to the water heater. Do
you hear anything? If you hear hissing or popping,
it could indicate a leak or perhaps the sound of
the heat being applied to sediment buildup inside
the tank. Be sure that electrical connections and
thermostats are safely covered.
Check your water faucets. Do they have aerators installed to restrict the flow? Aerators are
available that deliver various flows, but the maximum flow rate of 2.5 gallons per minute (gpm) is
a federal regulation initiated to save both water
and energy. Showerheads and faucet aerators
that deliver less than 1.5 gpm are considered
“low flow.” Look for flow rate printed on the side
of the aerator or showerhead.
Hot water habits are hard to break. One study
performed by Lawrence Berkeley National Laboratory concluded that as much as 20 percent of
water-heating energy is wasted by waiting for hot
water to arrive at the faucet. If you run hot water
and it barely gets hot by the time you turn off the
water, all that heat is lost in the pipes, and you’ll
save by using cold water instead.
The average American uses about 17 gallons of
hot water each day. To assess your hot water consumption you’ll need a few additional tools for
measuring temperature and flow rates:
• Thermometer
• 1-quart measuring jar
• Stopwatch or watch with second hand
A low-flow showerhead
with on-off control lets
you stop the water flow
while you shampoo and
soap up. The water stays
at your set temperature
for when it’s time to
To measure the hot water temperature, put the
thermometer into the jar and run hot water into it
until it’s good and hot. Check the temperature —
it should be 120°F or less. You may have a mixing valve on the outlet of the water heater, which
helps prevent scalding temperatures at faucets
by mixing cold water with the hot. The presence of
a mixing valve can give you a false reading about
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control dial
In-line mixing valves
blend hot and cold
water before it goes
to faucets and other
fixtures. A valve on top
controls the water temperature setting.
60 (seconds per minute) ÷ 4 (quarts in a
gallon) ÷ number of seconds required
to fill the jar = gpm
Cold in
the actual tank temperature. If you can adjust the
mixing valve, turn it to the highest setting before
taking your temperature reading at the faucet, but
this still may not give you an accurate reading of
the tank temperature.
Look at the temperature and pressure relief
valve (TPRV or TPR valve) located on the top or
side of the water heater. It should not be dripping
or have any evidence of rust or corrosion. The purpose of this safety valve is to blow off steam in
the event of high temperature or pressure inside
the water heater. Sometimes these valves can
stick and need to be replaced, but you can do
a simple check. With a bucket under the outlet
of the TPRV, operate the lever to allow water to
escape. Be careful: It will be very hot and come
out forcefully. Measuring the temperature of this
water is an accurate way to find the tank temperature setting.
relief valve
To check the flow rates of your showerhead,
turn on the water and adjust the flow to where
you normally set it when you shower. Hold the jar
under the showerhead and time how many seconds it takes to fill. Flow rate is measured in gallons per minute (gpm), so you’ll need to make the
conversion from a 1-quart jar, using the Flow Rate
chart below or the following calculation:
Testing the TPR valve of a
tank-style hot
water heater
As an example, if it takes five seconds to fill
your 1-quart jar, then:
60 ÷ 4 ÷ 5 = 3 gpm
If your showerhead flow rate is more than 2.5
gpm, it’s probably worthwhile to get a new one
with a lower flow.
F l o w Rat e
( i n Ga l l o n s p e r M i n u t e )
# of seconds to fill
Quart Jar
Gallon Jug
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Multiply the showerhead’s gpm by the number
and length of showers each week, and by the percentage of hot water in the mix. See Hot Water
Used in a Shower (below) for a way to determine
this. Then add in the hot water used for laundry,
dishes, and washing. These can be tricky values
to uncover since older clothes washers can use
up to 40 gallons a load, while modern front-loading machines use 10 to 20 gallons. You probably do laundry loads at various temperatures, so
you’ll need to do some estimating.
Water Heater Efficiency
The efficiency of a water heater is reflected in its
Energy Factor (EF) rating. Electric water heaters
have an EF of around 0.90, meaning that given
a certain hot water usage (based on a standardized test), the heaters convert 90 percent of the
electrical energy supplied to them into hot water.
The remaining 10 percent is heat lost through the
walls of the storage tank.
Ho t W a t e r U s e d i n a S h o w e r
The water coming out of the showerhead is a mix
of hot and cold. You can easily measure the temperature of the shower water when you measure the
flow rate by putting a thermometer into the measuring container. To determine how many gpm of your
shower flow is hot water requires a bit of math, or
you can just use the table below.
Pe r c e n t o f h o t wat e r m i x
for 104°F (40°C) shower
Gas water heaters generally have a lower EF,
due in part to the additional heat lost out the
flue. On-demand water heaters have a higher
EF be­cause there is no hot water storage tank
through which to lose heat. The EF for on-demand
gas water heaters can be as high as the upper
90s for high performance models.
When I need to estimate hot water usage for a
household, I use a shortcut that will get me in the
ballpark of expected annual hot water energy use.
It’s based on an average daily hot water use of 17
gallons per person per day. Here’s the formula, followed by an example using a four-person household and a gas water heater with an EF of 0.65:
3.8 million Btus x number of people
in the household ÷ EF
3.8 x 4 ÷ 0.65 = 23.4 million Btus (MMBtu)
The answer doesn’t mean much unless you
know the energy content (in Btus) of the fuel you
You can use the following formula to calculate the
percentage of hot and cold water in your warm water
mix if you know three things:
1 Hot water temperature
2Cold water temperature
3Warm water shower temperature
The formula compares the difference between the
hot- and warm-water temperatures to the difference
between the hot- and cold-water temperatures.
H = Hot water temperature
Hot water temp*
% mix of hot water
104° (40°C)
110° (43°C)
W = Warm water temperature
115° (46°C)
120° (49°C)
125° (52°C)
130° (54°C)
The percentage of cold water in the warm water
stream is equal to:
(H – W) ÷ (H – C) x 100 = percent of C
(130 – 104) ÷ (130 – 55) x 100 = 35% Cold, or 65%
135° (57°C)
140° (60°C)
145° (63°C)
C = Cold water temperature
If your shower flow rate is 3 gpm, and 35 percent
is cold, then 65 percent is hot. That works out to
about 2 gpm of hot water flow in the shower.
*Assumes cold water temperature of 55°F (13°C)
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use to heat water. The Fuel Energy Content chart
on page 57 supplies this information. If you have
a natural gas water heater, 23.4 MMBtu translates
to 234 CCF (or therms) of gas each year. For an
electric water heater, divide MMBtus by 3413 to
express the value in kilowatt-hours (23,400,000 ÷
3413 = 6,856 kWh).
Reducing water use and the energy used to heat
water takes both technology fixes and behavior
• Repair dripping faucets.
• Use cold water whenever possible.
• If you find yourself running the hot water for
less time than it takes to get hot, use cold
water instead.
• Insulate the tank and pipes (materials are
commonly available at hardware stores).
• Install low-flow showerheads and faucet
• Turn the water heater temperature down to
just over your favorite shower temperature.
If you’re concerned about Legionella or
other bacteria, one effective solution is
to shock the tank each month by turning
the temperature up to 140°F for a day and
flushing the hot water pipes at this high
• Wash laundry in cold water. If you feel
you need to wash in hot water to control
allergens, try Allersearch or De-Mite coldwater detergents (see Resources).
• Upgrade hot-water appliances, such as
dishwashers and clothes washers, to more
efficient models that use less water.
• Turn off the water heater when you’re away
from home for more than a few days.
• Plan ahead. If the water heater is more than
12 years old and hasn’t been maintained,
shop now and pick out the water heater
you want so that when the time comes, you
don’t have to shop while you mop. Decisions
made in such an emergency tend to ignore
• When it’s time to replace the water heater,
consider a high-efficiency on-demand unit. Be
aware that with on-demand water heaters, the
best thing about them is that you can get hot
water all day long. The worst thing about them
is that you can get hot water all day long —
meaning that you will not realize any savings if
you’re taking longer showers, because the hot
water never runs out. You will also find yourself
waiting longer for hot water at the tap because
the water needs to heat up first. As with all
energy-using appliances, the incremental cost
of a more efficient model will be recouped over
its lifetime when it is properly used to take
advantage of its efficiency.
Adjusting the Thermostat
To adjust the thermostat on an electric water
heater, first disconnect the power at the circuit
breaker. Failure to disconnect the power before
working on an electric water heater can result in
death! It is very easy to slip with a tool or finger
and hit a live wire.
1. Remove the heating element access cover(s)
located on the side of the water heater; there are
usually two screws holding each cover on.
2. Pull back the insulation that may be behind
the access panel, filling the space around the
Behind an electric
water heater element access
cover. Assume that all wires are
electrically live
unless the circuit
breaker is off.
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gas shutoff valve
Thermostat on a gas water
heater 
adjustment knob
thermostat. You may also find a plastic shield covering the wiring with an access opening to adjust
the thermostat.
3. You
should now be able to see the thermostat. It should look like the illustration on page 45.
The thermostat is the rectangular piece toward the
top; the heating element is below the thermostat
and is screwed into the tank. While you’re there,
look for leaks or rust around where the element
disappears into the tank.
Finding and Adjusting
an Aquastat
Oil and indirect-fired water heaters (those that
use a hot water boiler to heat domestic hot water)
use a not-so-obvious aquastat. An aquastat is a
temperature-sensitive switch designed for use in
water systems. It senses water temperature by
means of a probe that’s in contact with the water
to be monitored and connected to a switch that
activates a hot water circulator. When the water
cools off, the switch closes, and the heat source
is activated, sending hot water to the storage
tank. The aquastat is often inside a small gray
box attached to the water heater. The temperature adjustment is inside its housing. Sometimes
it is accessible, sometimes not.
To adjust the temperature, turn off the power
to the boiler or water heater at the circuit breaker
(the wiring you’ll be working near is typically lowvoltage, but turn off the power to be safe). If you
don’t see the temperature adjustment, remove
the control box cover (there are usually one or
two screws holding the cover on), and you will
see a well-camouflaged temperature dial inside.
Look closely at the dial for temperature markings, and turn it with your finger to make the
4. Use a screwdriver to turn the dial to a lower
Some thermostats have no temperatures
printed on the thermostat, just the vague words
“warm” and “hot.” Or maybe it is not even adjustable at all, as some thermostats are preset to
a specific temperature. If there are two heating
elements, set both the top and bottom thermostats to the same temperature. If you have a new
thermostat installed, be sure the plumber sets
the temperature where you want it— not at the
factory preset.
The thermostat on a gas water heater is usually mounted outside on the bottom half of the
unit and is fairly obvious. You don’t need to
turn off the gas to make the adjustment. Simply turn the thermostat knob to the desired water
Inside an aquastat. The notched dial on the left adjusts the temperature. 4
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Flushing the Water Heater
The average lifetime of a water heater is 10
to 15 years, but simply flushing once a year to
remove sediments and mineral scale buildup
can increase efficiency, reduce maintenance, and
extend its lifetime.
Look for a descaling or de-liming product (such
as Mag-Erad or Un-Lime) at hardware stores.
Alternatively, you can use white vinegar or muriatic acid (mixed with 10 parts water to 1 part
acid). Be careful: Too strong an acid solution can
eat through the walls of the tank, especially if it
is old or damaged. I’ve had success with pouring
a quart or two of vinegar into the tank through a
plumbing union at the tank inlet, then adding a
gallon or two of water and letting it sit for a few
A union is a threaded plumbing connection
that allows you to easily disconnect the water
supply pipes. Adding a union will only cost a few
extra dollars when installing the water heater and
is well worth the convenience. If your tank is more
than 15 years old and you’ve never flushed it, or
if there is evidence of rust or leaks anywhere on
the tank, you can flush the tank, but do not use
the acid solution.
Here’s how to flush your water heater:
turning the cold water inlet valve on and off. This
will help loosen scale.
7. Close
the water supply valve and the drain
8. Loosen the plumbing union on the hot or cold
pipe. If no union exists, you will need to have a
plumber install one. If you have an electric water
heater, you can access the tank via the hole that
exists after you remove the heating element (you
do this with a socket wrench after taking off the
electrical wires).
9. Mix the flushing solution.
10. Using
a funnel, pour the mixture into the
water heater and let it sit for as long as the instructions indicate.
11. Pulse
the cold water, and drain the tank
12. Repeat
steps 10 and 11 until the water
runs clear.
13. Close
1. Turn off the power or fuel supply to the water
the drain, remove the hose, attach
the union, and open the cold water inlet valve
to fill the water heater. Leave the hot water tap
open until the air is cleared from the line and
water flows.
heater, and make sure you know how and where
to relight the gas pilot when you’re finished.
14. While you’re at it, check the TPRV for prop-
2. Turn
off the cold water supply to the water
3. Open a hot water faucet to allow air into the
water heater or the water won’t drain completely.
4. Attach a hose to the drain valve of the tank,
run the other end into a utility sink, bucket, or
outdoors, and open the valve to drain the tank.
5. Drain
the first few gallons of water into a
bucket and take note of the water condition as
it comes out of the tank. Look for discoloration,
rust, sand, or flaky mineral deposits.
6. Once
the tank is empty, and with the drain
valve still open, pulse the cold water by quickly
er operation by manually activating its lever (see
page 43). Sometimes this valve can stick due to
rust, debris, mineral deposits, or age. Replace
the valve if the operation is not smooth or water
trickles out instead of gushing.
15. Turn on the circuit breaker or the gas valve,
and relight the pilot.
Anode Rod Inspection
To get even more life out of your water heater,
remove and inspect the anode rod for excessive deterioration every few years, and replace
it if necessary. The mysterious anode rod lives
and dies silently inside your water heater, sacrificing itself so that your water heater may live. It
works to prevent rust inside the water heater by
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attracting the electrochemical activity that would
otherwise corrode the steel tank.
Anode rods are about 1/2" in diameter, 3 or 4
feet long, and are usually made of aluminum, magnesium, or zinc. The rod is sometimes attached
to the hot water outlet side of the water heater
but is often separate. It should be removed and
inspected every few years — more often if you
have hard water. If you have a water softener, you
may want to check the anode rod every year. With
a water softener, hard minerals in the water are
exchanged for salt, and this salt can consume an
anode rod up to three times faster than calcium
carbonate (the typical anode-consuming mineral
in hard water). Once the anode rod is depleted,
your water heater’s days are numbered.
Heating and Air
conditioning are collectively
called space conditioning. Together they repre­
sent the largest piece of the energy-use pie in
most homes. High-efficiency heating and cooling
appliances are available that will help reduce
energy consumption. But as important as efficient
equipment is, improvements in insulation, reduc­
tions in air leakage, and an increase in your
tolerance for variation in temperature and humidity
will all work together to exponentially reduce space
conditioning energy use.
Hea t i n g a n d a i r
Get to know your heating and air conditioning
systems by taking a close look and asking some
basic questions.
New anode rod
(top) and
spent, used rod
• How old are they? Average lifetime is 15 to 20
• Do you have a furnace (blows hot air), a boiler
(circulates hot water or steam), or a space
heater, such as a wall-mounted gas heater or
wood stove?
• What is the heating fuel?
• Do you have the heating system
professionally serviced at least once every
two years?
Install a new water
heater to allow
enough room for
• For central air conditioners, is the cooling
coil kept clean? This is accessed inside
the ductwork and may require professional
• For room air conditioners, is there a gap
around where the unit goes through the
window, providing a direct path for losing
cooled air to the outdoors?
• Listen to your heating and cooling equipment
while they operate. Pay attention to any odd
noises and whether they turn on and off fairly
frequently (called short-cycling), which could
indicate a functional problem but also may
indicate that the system is oversized for the
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Maximum efficiency with heating and AC systems requires periodic, professional cleaning,
tune-ups, and efficiency testing. Heating system
inspections include, among other tasks, combustion analysis and a flue draft check. Inspect the
flue for solid connections and an upward slope
toward the chimney. Examine the chimney for
loose mortar (if it’s a traditional masonry structure), and have a chimney sweep inspect the
inside of the chimney. Any rust or disconnected
flue pipes need immediate attention.
Next, check that the space conditioning distribution system is in good shape. Air ducts for a
forced-air (furnace and/or central air conditioning)
system is should be solidly connected, sealed at
the seams and connections, and insulated. On
hot water (boiler) systems, the water pipes should
be insulated. Make sure to have working carbon
monoxide alarms on each floor (see Resources).
For central air conditioning, a professional will
need to check that the refrigerant charge level is
correct, along with other routine inspection items
such as checking for proper temperature delivery
and dehumidification control.
Efficiency and Expense
The energy required to condition your home
for comfort is based primarily on the ability of
the home’s thermal envelope (the boundary
between indoors and out) to retain the energy
delivered to that space. It also depends on
the efficiency of the heating and cooling system, as well as the habits of the occupants. A
more efficient thermal envelope allows you to
use smaller, less expensive space conditioning
systems. Many heating and cooling systems are
oversized, meaning they can supply more heating or cooling energy than what’s required by the
home. This may not sound like such a bad thing,
but it’s a situation that can lead to inefficient
operation and discomfort.
Once you’ve made efficiency improvements to
the thermal envelope, an oversized heating and/
or cooling system may effectively become even
more oversized than before, exacerbating the
problems. You should still complete any necessary insulation and air leakage improvements
(see chapter 3), but follow these by having a professional heating contractor or energy auditor perform a heat load analysis. This will give you accurate data for sizing new heating or air conditioning
equipment for your more efficient home.
How much fuel do you use to heat your home in
an average heating season? How much electricity
do you use to keep cool? If your heat, hot water,
and/or cooking appliances share the same fuel
source, you will need to review a year’s worth of
energy bills so that you can tease out the base
load from the seasonal loads, much as you did for
electrical use (see page 37).
Assessing the condition of a “heating plant”
(the furnace or boiler) and its associated fuel
usage is a matter of the heating plant’s combustion efficiency and heat distribution system’s (air
ducts’ or water pipes’) efficiency. There are two
measures of efficiency for heating equipment.
The first, called instantaneous or steady state
efficiency (SSE), is analogous to the highway fuel
efficiency of a car. The SSE can be measured and
adjusted by a technician using a combustion analyzer and the unit’s efficiency at converting the
fuel energy into heat energy is reported in terms
of a percentage.
The second measure of efficiency is a seasonal
value called the annual fuel utilization efficiency
(AFUE). It is based on a standardized factory test,
and can be compared to the combined city and
IHot and ColdI
A furnace that is too big may short-cycle (operate with rapid on-off cycles), causing wide
temperature swings. An oversized air conditioner may cool off the home quickly but will not be
effective at controlling humidity, a significant factor in summertime comfort.
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highway fuel efficiency of your car. AFUE will be
lower than the SSE because it accounts for warmup and cool-down losses, along with the heat lost
up the chimney.
Every new heating plant will have the AFUE
listed on the energy use guide that is fixed to its
cabinet. Older heating equipment may have an
AFUE of anywhere between 75 and 85 percent,
while modern high-efficiency gas equipment can
range from 90 to 98 percent.
To evaluate a central air conditioning system,
special equipment and skills are required to test
for the proper refrigerant charge. The steady
state efficiency rating of an air conditioner is the
energy efficiency ratio (EER), and the seasonal
efficiency rating is the seasonal energy efficiency
ratio (SEER). Older central air conditioners (when
properly installed and adjusted) have a SEER of
10 or less, while newer models can achieve SEER
16 or higher. SEER and EER are measures of how
many Btus can be delivered for each unit of electricity consumed. Higher EER and SEER values
mean greater efficiency, though requirements
should be tailored to your climate.
Duct joint sealed
with mastic
applied “thick as
a nickel” to all
seams on supply
and return ducts
UL-approved foilfaced duct tape
After the duct
joints are sealed,
wrap all ducts
completely with
insulation. Air
supply ducts are
a higher priority for insulation
than return
Once you’ve evaluated your heating and cooling system components, you can take the steps
needed to increase their effectiveness at doing
their respective jobs.
• Check the furnace filter monthly and replace
as needed.
• Clean the furnace fan blades if they’re acces­
sible (usually behind the filter), making sure
that the power is off first. If you have a furnace
and central air conditioning, the same fan is
used to move both heated and cooled air.
• Seal ductwork joints with mastic or foil tape
(not standard plastic/cloth “duct” tape), and
wrap ducts with insulation.
• Clean dust off the air conditioner evaporator
coil located inside the ductwork, if accessible.
This task may require a professional.
• Keep forced-air registers free and clear.
• Insulate hot water or steam boiler pipes.
• Save up to three percent of your heating
energy for each degree you turn your thermo­
stat down throughout the heating season.
Use a programmable thermostat so you don’t
have to remember to turn it up or down.
• Control sources of interior heat and moisture;
keep them in or let them out based on
seasonal needs.
• Have a professional perform an efficiency test
on the heating system and perform a “clean
and tune” service. Have the technician check
the heating plant’s steady state efficiency
and, if it’s below 80 percent, consider an
upgrade or replacement to the highest
efficiency equipment available.
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• Have a technician check for proper air flow
through the ductwork and evaluate the
duct system for proper sizing and layout of
supplies and returns.
• Ask your heating contractor about upgrading
to a modern, efficient, electronically controlled
furnace fan motor.
• Have a professional check the refrigerant
charge of your central air conditioner.
• Add more heating zones to improve the
temperature control of different areas in the
• If you need a new furnace or boiler, gas
heating systems are available with efficiency
ratings over 95 percent, while better oil
systems are around 85 percent efficient.
Thermal Envelope
of your home
includes everything between (and including) the
paint on the inside to the paint on the outside of
the walls. Framing materials, wallboard, insulation,
siding, windows, doors, roof, and foundation walls
— anything that separates the inside from the
outside — make up a building’s envelope.
The envelope of a home needs to keep you
com­fortable, protect you from the elements, and
be durable and aesthetically appealing. All of the
envelope components, including the materials
they are made of and how they are put together,
affect the energy consumption and durability of
the building.
T h e t h e r ma l e n v e l o p e
Begin by taking a broad view of your home.
Stand on the sidewalk across from your house
and just look at it.
Start at the roof:
• Do you see any broken or flaking shingles?
• Is there moss growing on the shingles?
• Are the gutters and downspouts clean and in
good repair?
• Are there any rotten or missing boards on the
soffits or evidence of animal damage such as
holes or bits of insulation poking out?
• If it’s cold and snowy, do you see icicles or ice
dams indicating excessive heat loss?
• Does the snow melt off certain parts of
the roof faster than other parts, indicating
insulation defects?
Move down to the walls:
• What is the condition of the siding? Do you
see peeling paint or warped clapboards that
may indicate moisture damage?
• Are there unsealed holes for utility cables
where air, water, and bugs can get in?
• Check the condition of the windows. Are they
double- or single-pane? Are they all straight
and tight or are there broken panes and
rotten sashes and sills?
• Inspect behind the siding by first looking
carefully for hazards like nails and wasp
nests, then putting your fingers behind the
first course of clapboards just above the
foundation; does the wood feel wet, soft, or
rotten, indicating water intrusion?
Look at the foundation:
• Sight down the side of the foundation along
ground level: Is it straight? Any variations
could indicate areas of unwanted exchange
between indoor and outdoor environments.
• Are there cracks or holes that might allow
water in or indicate structural problems?
• How does the foundation connect to the
wooden framing of the house? Are there any
gaps in that junction causing air and/or water
leaks? This detail may be best seen from
inside the basement, looking at the juncture
between the top of the foundation wall and
wood framing.
• Is the ground wet around your foundation?
Gutters and leaders, along with ground
that slopes away from the house, will allow
rainwater to drain away from the house rather
than into the basement.
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T e mp e r a t u r e M y t h B u s t e r
Myth: It takes more energy to heat (or cool) a
cold (or warm) house than it does to keep it warm
(or cool) all day, so don’t bother turning the temperature down (or up) when you leave for the day.
Fact: The warmer your house is during the heating
season, the faster it will lose heat, and the harder
the heating system will work to keep up with
that heat loss. Keeping the house warmer than
• Where are the electric, water, and gas
meters? Do you know how to read them, so
you can gauge your own daily consumption?
• How does electrical service get to your
house — overhead or underground? Are there
trees growing into the power lines, and do
you know where underground electric, gas,
and water lines are?
Once you’ve had a good look around and
poked and probed for signs of weakness, you can
move indoors and pick apart all the various thermal envelope systems and components in your
home. It’s important to recognize that all of these
systems work together; if you change one thing,
it will affect something else. For instance, back in
the early days of weatherization efforts during the
1970s, builders and weatherization professionals found that sealing up air leaks in old homes
created moisture problems that led to mold and
decay in wood framing.
The building needs to be put together so that
moisture stays out of walls and insulation, but the
design needs to be resilient enough so that when
water does get into the walls (and it will), there
is a way for it to drain and dry. Building science
has come a long way in understanding how systems interact with one another and in developing
you need it during the day is like keeping a pot of
water hot on the stove all day just because you
want a cup of tea when you get home. It might
take a bit longer to boil, but you’ll have saved
energy by waiting. The same is true for keeping the
house cool during warm weather. Heat moves in
the direction of hot to cold, and the rate at which
it moves increases with the temperature difference
between the two zones.
successful strategies for durable, efficient building upgrades.
Assessing the envelope involves evaluating insulation levels and airtightness of all the various
assemblies in the house, and this is discussed
in greater detail in chapter 3. One critical aspect
of the envelope, in terms of energy use and comfort, is how much air leaks between indoors and
Air leakage is driven primarily by wind but also
by temperature and pressure differences within
the house, and between the house and the outside. For every cubic foot of air that enters a building, a cubic foot of conditioned air escapes. You
can use an incense stick on a windy day to locate
air leaks by observing when and where the smoke
moves erratically. Professional energy auditors
measure air leakage and identify leakage paths
with a “blower door,” and they reveal insulation
defects with an infrared camera that “sees” heat.
Using a blower door in conjunction with an
infrared camera can be invaluable in identifying
air leakage and insulation problems. With specific
knowledge about the shortcomings of the building
envelope, homeowners can focus their air leakage reduction efforts for maximum benefit.
ILeaky House SyndromeI
Even if your house doesn’t feel drafty, air leakage can account for 20 to 50 percent of your home’s
heating and cooling energy loss. Reducing air leakage is generally a low-cost improvement that can
yield substantial energy savings.
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A blower door (far left)
seals over an exterior
door opening and has a
large fan that exhausts
air from the house.
Gauges used with the blower door (left) measure air pressure
and flow to quantify
the air leakage of the
An infrared camera measures surface temperatures to
identify air leakage and insulation problems. This is what the camera “sees” when focused on the finished
room. The darker areas in the infrared image represent
cooler temperatures, revealing thermal bridging (a path of relatively rapid heat conduction; see page 63)
created by the roof rafters above the sloped ceiling. The camera also shows evidence of a poorly insulated
section of the end wall.
Air-sealing a house requires great attention to
detail. Air carries moisture, and because heat and
moisture naturally move from areas with more heat
and moisture to areas with less of the same, the
building envelope is the front-line defense in this
battle between conditioned indoor air and the outdoor environment.
Ventilation and Humidity
You always want to stop air leakage before adding
insulation, as leakiness reduces the effectiveness
of insulation. At the same time, too little fresh air
can lead to poor indoor air quality and moisturerelated problems within the building envelope.
The solution to this balancing act is summed up
by this phrase from the building science industry: “Build tight, ventilate right.” This means that
there is no such thing as a house that’s too tight,
but rather that it may be underventilated.
It is important to regulate the amount of
fresh, outside air allowed into the house by using
a mechanical ventilation system, such as an
exhaust fan or air-to-air heat exchange ventilation system (see chapter 4). Having and using
a mechanical ventilation system does not mean
you can’t open windows when it’s nice outside,
but it does ensure a supply of fresh air even when
the windows are closed.
Keeping relative humidity (RH) levels under
control can keep you comfortable and keep your
house dry. Humans have a wide comfort range
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in terms of humidity. If your windows regularly
develop condensation on the inside during cold
weather, it may be an indication of high indoor
humidity levels, which in turn may indicate a moisture source problem or insufficient air exchange.
Keep track of RH using a hygrometer and operate
exhaust fans as needed to remove moisture from
the home.
your old windows often is not the most costeffective solution to high heating bills. There
are several simple, inexpensive repairs and
improvements you can make to increase the
thermal performance of your existing windows.
When assessing your windows, look at the
number of layers of glass (also called glazing) and
how tightly the windows close. If the sashes rattle
against each other when closed and locked, they
are good candidates for air-sealing improvement
measures such as weatherstripping and sidemounted sash locks. If the sashes and frames
are rotten (wood) or cracking (vinyl), it may be
time to think about replacement.
Upgrading old single-pane windows to new double- or triple-glazed units can save energy when
they are properly installed to include air-leakage
control around the frame. However, air-sealing,
insulating, and adding storms are more costeffective options, especially when these improvements are combined. Replacing windows is worthwhile if they are damaged or if they are causing
damage to another part of the building (for example, leaking window sills can cause wooden framing to rot).
If you do replace your windows, it’s best to
pay the extra cost for highly efficient units. Over
the long run, the incremental cost of upgrading to a triple-pane window will pay for itself in
efficiency gains and reduced energy use. Since
you will probably replace the windows in your
home only once, this is a decision with long-term
C o n t r a r y t o p o p u l aR b e l i e f,
Air Infiltration
In most cases, any discomfort you feel when
standing next to the window is due to air infiltration around the perimeter of the window frame.
If you were to pull off the trim from around the
inside of a window, you might be able to see
from inside the exterior sheathing or even daylight. Sometimes this gap, or shim space, is
filled with fiberglass insulation; however, like a
sweater, fiberglass does not eliminate air movement. The fiberglass should be removed and
replaced with non-expanding foam or caulk as
an air barrier.
Windows occupy 12 to 25 percent of the average home’s wall area. Because of their lower insulating value (relative to the framed, insulated wall),
windows lose heat much more rapidly than do
walls, so it pays to install good, energy-efficient
windows to reduce that loss. More windows in your
walls increase the potential for both heat loss to
the outdoors and heat gain from the sun.
Choosing windows based on their location,
their insulating value (U-factor), and their ability to
accept or reject the sun’s heat (solar heat gain
coefficient, or SHGC) will result in greater energy
savings and increased comfort (see chapter 4 for
meeting rails:
close gap with weatherstripping
sash perimeter:
close gaps with
shim space gap:
fill with foam
or caulk
5Where windows leak air
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more information on choosing and locating windows). Whether you live in a hot or cold climate,
the right window in the right place offers a good
balance of efficiency, light, and solar heat gain.
Here are some important steps for improving the
performance of your home’s thermal envelope:
• Let the sun in when it shines during the winter.
• Hire an energy auditor to measure air leakage
with a blower door and perform an infrared
scan to direct comprehensive air-sealing
efforts and identify thermal defects.
• Add window treatments, such as awnings
and insulating curtains or cellular shades, to
provide window insulation and solar heat gain
• Add insulation to the foundation, walls, and
ceilings where appropriate.
• Reduce space-conditioning loads before
replacing any heating or air-conditioning
equipment, so you can properly size the
systems to match the new loads.
Prioritizing Your
broken down into things you can do now and
things you may need to plan (and budget) for
doing later. Some are cheap and easy, some are
expensive and difficult, but all should ideally be
part of a comprehensive plan that considers the
entire house and how the various systems will
interact with one another.
These considerations will help you prioritize
i m p r o v eme n t s
• Low- or no-cost improvements often involve
awareness of (and perhaps changing) habits.
These can be more difficult than technology
fixes but can offer substantial savings.
• Fast and easy improvements that offer
instant savings include: shorter showers,
low-flow showerheads, hot-water pipe
insulation, efficient lighting, eliminating
standby loads, turning down the heat and
hot water temperature, washing full loads,
weatherstripping windows and doors,
repairing leaky faucets and other fixtures, and
using a clothesline instead of a clothes dryer.
• Envelope improvements, such as air-sealing
and insulation, are very cost-effective and
allow you to reduce the size of your heating
system when it comes time for replacement.
Start by air-sealing the top floor between the
ceiling and the attic, then add insulation.
Repeat in the basement, then the side walls.
• Heating system distribution improvements
can increase your comfort. Add supply and
return ducts where heat distribution is poor,
and balance, seal, and insulate ductwork. If
you have hydronic (hot-water) space heating,
make sure the system is zoned for optimal
comfort and efficiency, and insulate all the
• New electrical appliances can offer quick
returns on your investment if the old
appliance was an energy hog and the new
one is exceptionally efficient. Meter the
energy use of the old appliance first, so you
can assess savings potential.
• Change your lighting plan to put light where
you need it.
• Heating plant and water heater replacement
may not be cost-effective if the system is
moderately efficient and still has some
life left in it. When it’s time to buy new
equipment, have it sized by a professional to
match the heating requirements of the home.
Pay a bit more up front for comprehensive
sizing analysis and the most efficient
equipment to save energy and money over
the lifetime of the equipment.
• Add storm windows to single- or even doublepane windows. These can be permanent,
operable units or removable.
• Improving existing windows and adding
window treatments and storm windows are
often more cost-effective than replacing
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• New windows should be considered only if
you’re renovating or if existing windows are
damaged and need replacing anyway. Choose
new windows with energy performance and
orientation in mind.
• Add south-facing windows to increase solar
heat gain into your home.
• Add thermal mass (tile, masonry, dense
materials) to floors and walls to absorb and
store solar heat.
• Install renewable energy systems only after
making all of your efficiency improvements.
How Can an Energy
Auditor Help?
You don’t need to call a doctor to put on a bandage, but if you break a bone or need serious
attention, self-medication is not the best solution.
Don’t be afraid to call in an expert energy auditor
to help you identify and prioritize where to spend
your energy improvement dollars. Often, after I
perform a whole-house audit, the homeowner will
say to me, “I never knew you could find out so
much about a house.” Imagine touring a hospital for the first time and being awed by all the
diagnostic gizmos used to peek into and probe a
human body. Building energy specialists have the
tools and skills to diagnose and fix almost any
problem your home might have.
An energy auditor will walk through your home
from the attic to the basement, examining every
room as if on an exotic vacation, taking in all the
details. Common diagnostic functions in an audit
include a blower door test to measure and pinpoint air leakage within the home, an infrared
camera scan to check for insulation voids inside
a wall or ceiling, and a duct leakage test to determine the efficiency of the heating/cooling distribution system. An auditor might also perform
U n d e r s ta n d i n g t h e S tac k E f f e c t
When air leaves a building by way of exhaust fans
or air leaks, replacement air must come from
somewhere else to take its place; this is called
make-up air. All buildings leak air. Warm air in
your home rises and finds its way out through
airflow paths in the ceiling as cool make-up air
enters through the lower part of the house.
This air movement sets up a convective heat
flow within the house, called the “stack effect” (as
in a chimney), which also creates a pressure differential within the house. The upper levels are under
higher pressure than the lower levels, creating a
natural draft within the house. This is not to say
that all air and moisture moving within the house
will follow only this path, but the stack effect is an
important consideration when addressing air leakage issues.
To reduce the stack effect in your home and its
energy-robbing heat loss, seal all uncontrolled air
leakage paths in the envelope. Start at the ceiling
where the warm, moist air is escaping (causing
potential moisture-related damage in the attic),
then break the entire air leakage “circuit” by sealing up air entry paths in the basement. Walls and
windows can come later (unless they’re extremely
drafty and your comfort dictates more immediate
5Air leakage and stack effect
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A typical home
a combustion test of your heating system and
check the refrigerant charge on your air conditioner, as well as make a metered test of your
refrigerator to determine its energy consumption.
Additionally, many auditors now incorporate
health and safety checks into their work scope,
including carbon monoxide tests on all combustion equipment and keeping an eye out for any
moisture or mold problems that may exist. Bear
in mind that an auditor may not be a building
inspector and therefore may not be looking into
detailed structural or code-related deficiencies of
the home. For a list of contractors with an eye
toward comprehensive home improvements, visit
the Building Performance Institute website (see
checkup can take
from 2 to 4 hours,
depending upon the
tests performed,
and auditors may
charge a flat rate or
by the hour. Some
may refund the
entire audit cost if
you choose them to
make the improvements. Always ask
what specific tests
they will perform,
how they charge
for services, what
the cost will be,
and how the results
will be presented
to you.
Hiring an Energy Auditor
Auditors can be trained and certified by energy
auditing organizations, and while there are plenty
of talented and certified auditors out there, nothing is as important as experience. Before hiring
an auditor, ask for references and actually follow
Fuel Energy Content
Home Heating Oil
Natural Gas
therm or CCF
Liquid Petroleum
Gas (LPG)
21 million
20 million
cubic foot
Enriched Uranium
33 billion
Solar Home
Storage Battery
up by contacting some of the references. Two
relevant certifications require auditors to have a
minimum level of knowledge and experience (see
Resources for websites):
• Residential Energy Services Network certifies
contractors through the national ENERGY
STAR for New Homes program.
• Building Performance Institute certifies
contractors through the national Home
Performance with ENERGY STAR program.
You can find certified energy auditors in your
area through both of the programs above or
through your state’s energy office.
*Note: Energy content per unit of fuel may vary due to additives,
impurities, and source.
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H ow B i g I s M y C a r bo n F o ot p r i n t ?
Carbon (C) is present in fossil fuels. When we
burn these fuels, carbon is oxidized (forms a
chemical bond with oxygen, O2) to form the potent greenhouse gas carbon dioxide (CO2). You
can calculate your household’s CO2 production,
or carbon footprint, by quantifying how much of
various fuels you use over the course of a year,
then determining how much CO2 is released
when each unit of that fuel is burned.
When discussing carbon footprints, carbon
dioxide is the most common way to quantify
greenhouse gas emissions. Greenhouse gases
(methane, chlorofluorocarbons, and the like)
are often expressed in terms of their “CO2
equivalent,” where their global warming potential (GWP) is compared to that of CO2, which is
assumed to have a GWP of 1. This is often represented as CO2e, where e means “equivalent”.
Sometimes you will see a reference to carbon
equivalent, or Ce. Carbon makes up 27 percent
of the weight of carbon dioxide (the rest is oxygen). To convert a quantity of carbon dioxide to
carbon, multiply by 0.27.
It’s easy to confuse carbon, carbon dioxide, and their equivalencies, and any one of
these metrics can be used to represent carbon
footprint. Look closely at the fine print when
you’re making assessments, comparisons, or
You can easily determine your direct carbon
footprint, the carbon or carbon dioxide resulting from the energy you actually buy. It is more
difficult to quantify the indirect components
of energy use, such as the amount of energy
required to produce, transport, and dispose of
the food and goods we buy. To determine your
direct carbon footprint, simply add up all the
energy you buy for your home and travel, and
use the chart at right to calculate the pounds of
carbon dioxide produced.
For example, if you drive 12,000 miles
per year and your car gets 20 miles per gallon (mpg), you’ll burn through 600 gallons of
gasoline and produce 11,760 pounds of CO2, or
3,175 pounds of carbon (11,760 x 0.27).
The concentration of carbon dioxide in the
atmosphere has been rising since the beginning of the industrial revolution and, according to many climate scientists, is nearing the
point of climate crisis. The U. S. Environmental
Protection Agency estimates that the average
carbon footprint for an American household of
two people is about 41,500 pounds (almost 21
tons) of CO2 per year.
Climate science suggests that in order to
achieve climate stability, each individual on
the planet has an annual carbon (not carbon
dioxide) “budget” of around one ton — that’s
about 3.7 tons of CO2. For perspective, that’s
the amount of CO2 released by burning 370
gallons of gasoline. How would you spend
your ton of carbon? If carbon becomes taxed
or otherwise valued in the marketplace, it will
be important to understand these details. For
more on climate change and greenhouse gas
emissions, visit the Environmental Protection
Agency’s (EPA) web page on climate change
(see Resources).
CO 2 E m i s s i o n s o f Va r i o u s
Energy Sources
Type of Fuel
Pounds CO2
per unit
Heating oil, diesel fuel
Natural gas
Liquid propane gas
*National average shown, value varies by state.
Note: Wood is generally considered to be carbon neutral,
given its relatively short regrowth period and the CO2absorbing properties of trees.
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Insulating Your
Your Home
n a n e ff o r t to maintain universal law, order, and equilibrium, heat moves
from areas of more energy (hotter) to areas with less energy (cooler). And the
greater the temperature difference, the more rapid the energy transfer. Unfor-
tunately, this physical law is tied directly to our bank accounts and the comfort level
in our homes, giving you a vested interest in not squandering the labor and cost
associated with meeting your energy needs.
Whether it’s wrapped around our bodies or stuffed inside our buildings, we use
insulation to slow the flow of heat energy transfer. This chapter is not an exhaustive
guide on how to insulate your home, nor does it cover all the pros and cons of various insulation choices. Rather, it provides some general guidance and references
to available resources so that you can get the understanding and information you
need before starting on your insulation project.
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How Heat Moves
three distinct ways, and
a good insulation product (or combination of
products), along with careful installation, will
help slow all three avenues of movement to
keep heat loss and energy costs under control.
Hea t m o v e s i n
Heat conducts through materials in contact with
each other. Your warm hand wrapped around a
glass of cold water conducts body heat to the
glass. Your hand feels cool as it loses heat and
warms the glass along with its contents. More
dense materials (such as metal) conduct heat
better than less dense materials (such as air).
Insulation works by trapping air in tiny pockets,
reducing conductive heat loss.
the air at the top of your house (and the water at
the top of your water heater) being warmer than
at the bottom. This is due to density differences
in the air or water. Hot air is less dense than cool
air, so it rests on top of the cooler, denser material — thus, the conventional understanding that
“hot air rises.”
Convective heat loss in a building occurs in
several ways. It is primarily the result of wind acting on the outside of the home, carrying away
heat radiated and conducted from the house and
leading to greater air leakage within the home.
Temperature differences between materials, such
as a cold window and warm air, create air movement called convection currents. Cold air migrating into a warm, insulated wall cavity creates convection currents within the cavity, reducing the
effectiveness of the insulation.
Heat transfer due to movement within or between
liquids and gases is called convection. When
you blow on a hot drink, convective heat transfer occurs between the drink and the air as the
passing air extracts heat from the liquid. Another
example is wind causing convective heat loss
from your skin. Convection is also responsible for
Heat passing through space (across the room or
across the universe) from one object to another
is said to radiate. A hot wood stove and the sun
both radiate heat that you can feel on your skin.
When you stand next to a cold window, your body
radiates heat toward the relatively cooler window,
causing you to lose heat and feel cold. Dropping
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an insulated shade over the window makes you
feel warmer because it reduces the flow of radiant heat transfer from your warm body to the
cold window surface. Reducing radiant heat flow
away from your body makes you feel warmer
and is often more effective than turning up the
In a similar way, low-E (E means emissivity)
coatings on windows also help to reduce radiation heat loss. Emissivity describes a material’s ability to emit, or radiate, energy, and is the
key to understanding heat radiation. In general,
more reflective materials have a lower emissivity, while materials that absorb heat have a
higher emissivity. Radiational heat transfer will
occur as long as there is a temperature difference between two objects, and the objects are
separated by space (a fraction of an inch or 100
million miles).
Aluminum foil is a good example of a radiant
barrier. Hold a piece of aluminum foil between you
and a heat source (or between you and the cold
window), and almost all of the radiant heat energy
transfer is eliminated, having been reflected away.
But radiant barriers may also be good conductors of energy. If your piece of aluminum foil is in
direct contact with a hot surface, it gets hot as
heat is readily conducted through it.
A foil-faced radiant barrier under the roof will
reflect heat away from the home in hot weather,
provided there is an air space between the radiant barrier and roofing material. In combination
with good attic insulation, proper air leakage control, and reflective roof colors, a radiant barrier
is a valuable component in a system that will
help increase comfort and reduce cooling loads
by keeping the attic cool and slowing heat movement to the living area. Some insulation products
have integrated foil-faced radiant barriers, and
other products are available with a radiant barrier
fixed to sheet material that can be used for a roof
deck (see Resources).
A radiant barrier is not, in and of itself, insulation. For a radiant barrier to be effective, there
must be a calm air space between it and any adjacent materials; otherwise, the radiant benefit
can be short-circuited through conduction or convection. Some roofing materials are designed to
decrease cooling loads in hot climates. You can
learn more about these from the Cool Roof Rating
Council (see Resources).
Heat transmitted through the building envelope
is driven by the temperature difference between
indoors and out, along with wind loads acting on
the outside of the house. Conduction, convection,
and radiation, along with air leakage, all contribute to heat loss in your home. In addition to insulation, addressing air leakage between indoors
and out and eliminating air movement within the
insulation reduce heat loss by all three transmission paths.
heat is reflected away from house
How radiant barriers
work to effectively
reduce both heating
and cooling demands
radiant barrier
heat is reflected
back into house
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Insulation Value
t h e U n i t e d States, all insulation
products must comply with Federal Trade
Commission testing and labeling requirements.
This makes it easy to compare insulation
ratings and know that, for example, R-19 is
R-19 regardless of product or manufacturer.
However, the product must be installed properly
to perform at or close to its rated R-value.
U-factor and R-value
The performance of insulation products is stated
as R-value, or resistance to heat flow. R-value
has no dimension, meaning that there is no engineering value associated with it, but higher R-values indicate higher levels of insulation, and thus
slower heat movement through the insulation.
Some products, notably windows, are
described by a different heat transfer value,
called U-factor. U-factor is a measure of the
thermal conductance of a material. The U-factor
expresses how much heat, in Btus (see page
20), is transmitted through one square foot of
material in one hour when the temperature difference between opposite surfaces is 1ºF (.56ºC).
A higher U-factor indicates greater conductivity of
heat and corresponds to a lower R-value.
U-factor and R-value are the inverse of each
other. Mathematically, that means:
1 ÷ R-value = U-factor or
1 ÷ U-factor = R-value
Therefore, a wall with an insulating value of
R-19 has a U-factor of 0.0526, while a window
with a U-factor of 0.40 has an insulating value of
W h e r e Yo u N e e d I n s u l at i o n
The question of where to install insulation may appear to
have an obvious answer: walls, ceilings, floors, and foundation. Yet one basic concept is consistently overlooked:
The building’s “thermal boundary” must be well defined
in order to develop an effective insulation plan. The thermal boundary is comprised of the building assemblies
that delineate indoors from out.
To identify your home’s thermal boundary, draw a
cross section of the building onto paper. You may need
several cross-sectional diagrams depending upon how
complex the building is. Now, with a different color pen,
add a line that indicates where there’s insulation. You
should be able to trace the insulation line of the cross
section with your finger all the way around the house —
from the roof, down the walls, across the foundation, and
back up to the roof on the other side — without lifting
your finger off the paper.
If you need to lift your finger to jump to the next
place that is insulated, you have a break in the thermal
boundary. This means you have uncontrolled heat loss to
(or gain from) the outdoors. You may find that you have
two parallel but unconnected thermal boundaries, such
as an attic floor and ceiling that are both insulated, or
insulation in both the back side of kneewalls and the roof
above. This “doubling up” is simply a waste of material.
Understanding where insulation is, where it isn’t, and
whether it’s effectively installed is the first step in developing an insulation plan.
Thermal boundary. Create a simple cross section of your
house to note where insulation exists — or not. The entire
thermal boundary should have a continuous line of insulation around the living space. 6 2 I NS U L ATI NG YO UR H O M E
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Thermal Bridge
Insulation is not, however, the only material in the
building envelope. Wood or metal framing also
affects the overall R-value of a building assembly. Each stud, rafter, or joist presents a “thermal
bridge” — in effect, a short circuit — within the
insulated assembly. Wood has an insulating value
of about R-1 per inch of thickness. For example, a
2x4, which actually measures about 11/2" x 31/2",
has an R-value of about 1.5 when laid flat or 3.5
when on edge.
In terms of U-factor, a 1"-thick piece of wood
conducts heat at the rate of 1 Btu per square
foot per hour per degree of temperature difference. A wooden 2x6 stud will conduct heat faster
than the insulation-filled wall cavity between the
studs but a little slower than an empty cavity with
no insulation. What this means is that when it’s
warmer indoors compared to outside, the studs
in a wall will be cooler (on the inside of the wall)
than the insulated wall cavity. On the outside, the
studs will be warmer than the insulated part of
the wall because the studs conduct heat away
from the warm indoors faster than insulation
A thermal bridge can be fixed by using a “thermal break,” which is simply a less conductive
material (such as a piece of insulation) between
two thermally conductive materials. For example,
in addition to insulating the stud cavities in a wall,
a well-insulated building will have a continuous
insulation layer, such as rigid foam board, over
the studs so that the thermal connection, or conductive channel, presented by the stud frame is
minimized. Many energy auditors use an infrared
camera to locate thermal bridges within building
In theory, we can calculate the overall R-value
of each component in a building and arrive at
an average R-value for each assembly or for the
building as a whole. In practice, however, the
actual thermal performance of a building depends
a great deal upon how well the insulation was
insulation plan, first identify
where it currently exists, then determine where
it needs to be and how much of it is needed.
I like to start at the top and work down.
To develop an
Attacking the Attic
Some attics have floors, some are open and insulated in between rafters, sometimes instead of
an attic there will be a cathedralized ceiling covered with finish material, and many homes have
some combination of these. If you have an attic
with access, it’s relatively easy to see what’s up
there. A cathedralized ceiling, however, requires
a removal of the finish material or an infrared
inspection. Put on some old work clothes, gloves,
and a respirator, get a tape measure and a flashlight, and go look! Be careful to step only on
wooden framing members. Once you’re in the
attic, ask yourself:
• What is the condition of the insulation?
• Is the insulation a consistent depth?
• Is there evidence of damage from animals?
• Are there places that are matted down or
• Any evidence of water damage?
• Can you see the top of the ceiling surface
below (the back side of the drywall or plaster)?
• Are there any visible framing materials? (This
would present a thermal bridge between the
house and the unconditioned attic.)
While you’re up there, look for vents from bathroom exhaust fans, dryers, or other appliances
that may be terminated in the attic. This situation can ultimately lead to moisture, durability,
and health issues such as mold and wood rot. All
exhaust ventilation systems should terminate outside the building. Terminating an exhaust in front
of an attic vent or louver is not reliable because
airflows could bring the exhaust right back into
the attic.
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Properly installed fiberglass insulation in an attic. There
How not to install insulation. Insulation must be in con-
Fan boxes or lighting fixtures mounted in the ceiling below may be visible and often are sources
of significant air leakage between indoors and
out, if we consider the attic to be essentially outdoors. Recessed lighting fixtures should be properly specified for insulation contact, a designation known as “IC-rated.” This means it’s safe for
them to contact insulation without concern about
overheating. When installing IC-rated fixtures,
caulk between the fixture housing and ceiling to
air-seal it, then cover the top of the fixture in the
attic with insulation. Do this only with IC-rated fixtures; covering standard recessed fixtures with
insulation may create a fire hazard.
near a chimney or other combustion appliance
vent must be approved for use on hot surfaces.
If you are in doubt, check with your local code
inspector or the product manufacturer before
are two layers of insulation: the first lies between the
framing members on the attic floor; the layer on top is
perpendicular to the one on the bottom, eliminating the
thermal bridge of wood framing.
If chimneys or plumbing pipes are poking
through the attic floor, there is a good chance
that a “bypass” condition exists. A bypass is
a place where heat and air are permitted to
move around an insulated assembly, breaking
the thermal boundary and reducing the effectiveness of the insulation. All bypasses must
be sealed against air leakage with appropriate
materials, such as rigid foam, caulk, wood, or
sheet metal. Fibrous insulation will not prevent
air movement, so simply stuffing fiberglass into
a hole is not effective. Any materials used on or
tact with the surface it is intended to insulate, or it will
be less effective. There is also the potential to crush the
flexible vent duct under the insulation.
Wall Insulation
Checking wall insulation is a bit more challenging, but it’s easy to find enough clues to draw
some conclusions. First, find out how thick your
walls are. Measure the depth of a window or door
frame, and subtract the thickness of the sheathing, siding, wallboard, and the amount the trim
stands out on each side; what’s left is the wall
cavity depth. Most standard wall framing is either
2x4 or 2x6, yielding a 31/2" or 51/2" cavity depth,
Another way to determine the depth of the
wall cavity and, if you’re lucky, also see what kind
of insulation exists (if any), is to find or make a
small hole in a hidden area, such as a closet.
Poke a wooden (not metal, in case there are
exposed electrical wires) barbecue skewer into
the hole, mark where it stops with your finger, and
measure how far it went in. There should be a bit
of resistance caused by the insulation, and you
might find some material caught on the skewer or
twisted around the drill bit you used to make the
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exterior siding
wall sheathing
interior wall board
wall cavity
probably rigid foam-board insulation under the
In some cases, the basement ceiling may be
insulated instead of the walls, but there is no
need to insulate both. Decide where you want
your thermal boundary to be and install your insulation there. Note that it is quite difficult to separate the basement from the rest of the house in
terms of air leakage, so best practice often leans
toward insulating and air-sealing the perimeter
of the foundation rather than the basement ceiling. This has the added advantage of bringing the
basement into the conditioned area of the house,
which can begin to make it a more useful space.
Also, if there are ducts or hot water pipes running
through the basement, it’s best to insulate the
walls, not the ceiling.
Cutaway of a framed, insulated wall
hole. Be sure to spackle over the hole you made
or otherwise seal up that air leak.
Alternatively, you can usually find a gap in
the wallboard around electrical boxes for light
switches and outlets. Turn off the power at the
circuit breaker, remove the cover plate from the
switch or outlet, and poke your wooden skewer
into the gap between the electrical box and the
wallboard. Wiggle it around and try to pull out a
bit of insulation to see what type it is. A professional energy auditor may use a borescope, a
flexible fiber-optic viewing tool, to look into wall
What Lies Beneath
Basements and foundations may be insulated
on either the inside or the outside, and covered
with finish material. Rigid foam board is commonly used for insulating the exterior of concrete
foundations. This may be covered with stucco or
other durable material on the exposed portion of
the wall. If you don’t see exposed cinder blocks
or concrete on the outside of the foundation,
knock on the surface. If it sounds hollow, there’s
3Rigid foam board
insulation around
the perimeter of a
concrete foundation. This insulation
should be covered
to protect it from
sunlight and physical damage.
Most basements are partially above, and
mostly below, grade (the ground level around the
building). The most important place to insulate
is above grade, the area of greatest heat loss.
Since the average ground temperature for any
given location is approximately the same as the
annual average outdoor air temperature, the temperature difference between the basement and
the ground is usually much less than the difference between indoor and outdoor air temperatures. However, if you plan on heating your basement, it is important to insulate the full height
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T h e E f f e c t s o f Co n d e n s a t i o n
Basements are often cool and damp — a potentially nasty combination. Condensation occurs
when warm, moist air comes into contact with a
cool surface. This means that opening windows
in a cool basement during a warm, humid summer
will only increase the dampness of the basement,
as moisture from the air condenses on the relatively cool foundation walls.
Condensation can also occur inside abovegrade walls, but it’s usually the result of warm,
humid air migrating out into the cooler wall
cavity. If the dew point (the temperature at which
moisture condenses out of the air) is reached
within or behind the wallboard or insulation,
moisture-related damage can occur, and there
is potential for mold to grow on these hidden
Therefore, it’s important to keep moistureladen air out of places where dew points are
reached, especially where the materials cannot
readily dry out. The best approach to solving this
issue is to eliminate the movement of humid air
into these spaces by paying close attention to
air-sealing details (see page 72). Sometimes this
can be difficult or impossible to achieve, in which
case the materials must be resistant to moisture
damage, and there must be a means for draining
and drying the space where condensation occurs.
How Much
Do You Need?
Insulated concrete
form. The insulation provides the
form into which the
concrete foundation
is poured. 4
in a climate that requires
no heating or cooling, the more insulation you
have, the less space-conditioning energy you’ll
need to stay comfortable. There may be a point
of maximum cost-effectiveness and return on
investment, but with today’s volatile energy market,
that is a moving — and often subjective — target.
With our current awareness of global energy
issues, it’s increasingly evident that we need to
build durable, long-lasting homes, using minimal
materials with low embodied energy (the energy
required to produce the material), creating little
waste, and requiring a minimum amount of energy
to condition for comfort. Minimal home energy
use makes it possible to achieve a fair amount
U n l e s s yo u l i v e
of the entire foundation perimeter for maximum
efficiency and effectiveness of the insulation.
Insulated concrete forms (ICF) can be used
when pouring new basement walls. They serve
as a pouring form and also provide insulation on
both the inside and outside of the wall.
iNeed New Siding or Roofing?i
When it’s time to replace the siding or roofing on your house, look into the value of increasing the
wall-cavity insulation and adding a few inches of sheet insulation, such as rigid foam board, to the
outside of the wall sheathing or roof decking before putting the new siding or roof on. (Note: Do this
on the roof only if the rafters are insulated; don’t do it if only the attic floor is insulated.) See chapter
4 for more information.
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of autonomy and offers some protection from the
risks of a volatile energy market, while making it
more practical to meet your energy needs with
renewable energy.
Understanding Heat Loss
Heat loss math shows that 90 percent of conductive heat loss is eliminated with an insulation level of only R-11 as compared to R-1. This
doesn’t mean that it’s not cost-effective to install
much more insulation; there are huge savings to
be earned with higher R-values. Increasing the
level from R-11 to R-100 reduces energy use by
an additional 90 percent.
Over time, the extra investment you make to
achieve more substantial energy reductions will
pay for itself in many ways, including lower energy
costs, increased comfort, smaller carbon footprint, and increased energy security. Many small
improvements made on an individual level add up
to huge global impacts.
Upgrade When You Can
Given that the majority of the cost of insulation
is usually the labor of having it installed, it is
often prudent to take advantage of the work
crew’s being on site to install as much insulation
as possible. The incremental cost of upgrading
from some minimal level to the highest practical
level typically is not unreasonable. If you have 3
feet of height in an unused attic, why not fill it
entirely with insulation? Take advantage of other
work being done on your home to add insulation
and fix air leaks; the savings can help to pay for
the remodeling work.
Building science researchers recommend target levels of insulation for both new construction
and existing home retrofits in heating climates
(see Recommended Insulation R-Values, above).
These are based on cost, practicality, and durability. Additional analysis can take into account
the tradeoff of the global-warming potential of
manufacturing and installing these products vs.
the amount of energy they might save over their
iInsulation R-Valuesi
• Under concrete floor slab/basement slab: R-10
• Foundation walls: R-20
• Above-ground walls: R-40
• Ceilings: R-60
• Windows: R-5 (triple pane)
Choosing and
Installing Insulation
different insulation products
on the market today that can greatly enhance the
thermal performance of your home. It can be
difficult to choose which product, or combination
of products, will work best without some clear
guidance from an expert who lives in your climate.
The expert you need might be an energy auditor or a builder who specializes in high-performance home design or energy retrofits. He or she
should understand what your house needs, your
long-term goals, and how your house will behave
when improvements are completed. Choosing the
right product and how much of it to use depends
on many factors:
There are many
• Climate
• Availability
• Practicality
• Cost
• Suitability for the specific assembly that
needs insulating
• Building science issues, such as air and
moisture permeability properties
• Durability
• Fire resistance
• Need for sound control
• Embodied energy
• Recycled content
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• Recyclable value at end of life
panels with an insulating value of R-30 or more
per inch (see Resources).
• Global-warming potential
• Ozone-depletion potential
• Health risks due to off-gassing of blowing
• Local code requirements
To further explore these issues, two unbiased
references to begin with are BuildingGreen Inc.,
(publishers of Environmental Building News)
and Green Building Advisor (see Resources for
Insulation Options
If you understand the basic principles of how
insulation works and what it needs to do in a
specific situation, you’ll have a good start toward
understanding which product(s) to use. Some cutting-edge products hold great promise but are too
costly to use at this point except in high-end or
critical situations. These include products made
from translucent silica, and vacuum-insulated
I n s u l at i o n R - va l u e c o m pa r i s o n
Average R-value
per inch
Fiberglass batts, standard
Fiberglass batts, high-density
Fiberglass, spray-applied
Cotton batts
Cellulose; loose fill, dense
pack, damp spray
Extruded polystyrene
(blue/pink/grey board)
Expanded polystyrene
(bead board)
Spray foam, open-cell
Spray foam, closed-cell
Mineral wool
Foamglass, cellular glass
Installing Insulation
by Type
Many insulation products can be installed by
the average homeowner with little experience
— but always remember that proper installation is just as important as using the right product in the right place. Consider your health and
safety first when removing or installing insulation products (also see Vermiculite Warning on
page 74). Read all manufacturers’ precautions
and always use a respirator when working with
foams and fibers, in addition to providing adequate ventilation.
Batts and Blankets
Batt or blanket insulation, made from fiberglass
or cotton, can be rolled out and cut to fit into
place. The R-value will be stamped on the package and/or on the batts. Look for high-density
batts offering greater R-value per inch. Installation is fairly simple with the right tools and
attention to detail. Long-bladed scissors or a
long, sharp knife and a straightedge make cutting easier. The insulation should be fully lofted
and cut to fit snugly inside and around anything
inside the cavity. Don’t forget to seal up air leaks
between indoors and out, or between the house
and attic (where plumbing and wiring is often run
through drilled holes), with caulk or spray foam
before adding insulation.
Loose-Fill Insulation
Three common types of loose-fill insulation are cellulose, fiberglass, and mineral wool. All of these
materials are available in bags of manageable
size and are made from some percentage of recycled raw material. The R-value of each depends
in part upon the density with which it is installed.
Overly dense materials conduct heat more readily,
while too little density allows excessive air movement within the material, increasing convection.
Look at the label on the bag to determine
the depth required to reach the desired R-value,
as well as the coverage per bag at the desired
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Poorly installed wall insulation with compression, gaps,
and voids
Insulation properly cut to fit around wires and fit snugly
into wall framing
depth. Keep in mind that loose-fill insulation
will settle (up to 20 percent), and it’s the settled depth and R-value that’s important. The
material can be poured out onto an attic floor
and pushed into place, but some home supply
stores rent or loan a blowing machine with the
purchase of the insulation.
Loose-fill fiberglass is essentially the same
material found in fiberglass blankets or batts but
in a different form. It has an insulating value of
about 2.7 per inch when installed at a density of
about 1 pound per cubic foot.
Prior to installing
loose-fill insulation, install paper
measuring tapes at
various locations
around the attic to
help gauge the insulation depth (and
thus the expected
U s i n g V a por B a rr i e r s
Some insulation products include a vapor
retarder, or vapor barrier (such as kraft paper
or foil), which may or may not be appropriate to
use in your climate or for the specific construction type or assembly you’re working with. If
you’re in doubt about whether or where to use
a vapor retarder, consult with a local building
expert; it may mean the difference between
a lifetime of maintenance-free durability and
comfort and a future expensive repair due to
moisture damage within the wall. As mentioned
earlier, the more important part of moisture
control is to prevent moisture-laden air from
entering a cold building cavity through air infiltration. It has been found that far more moisture is transported into a building cavity via air
movement than through water vapor migration
through building materials. Only vapor movement through materials is controlled with a
vapor-retarding barrier.
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Loose-fill cellulose or fiberglass blown into an attic is an
Closed-cell spray foam insulating a basement band joist.
Mineral wool (sometimes called rock wool)
can be made from minerals, ceramic, or the stone
slag left over from processing iron ore. It is naturally fire resistant and has an insulating value of
about 3.3 per inch when installed at a density of
about 1.7 pounds per cubic foot.
Cellulose is often made from recycled paper
products that are treated for fire and insect resistance. It has an insulating value of about 3.7
per inch when installed at a density of about 2
pounds per cubic foot.
Damp-Sprayed Insulation
excellent choice for insulating attics with complex framing, conforming easily around lumber, vents, and other
Dense-Pack Insulation
Dense-packing insulation is a way to optimize the
insulating value of insulation within an enclosed
cavity. Any of the loose-fill insulation materials
may also be dense-packed, but the technique
requires a knowledgeable, experienced contractor with the right equipment. The density of the
material must be correct to achieve the rated
performance: 3.5 pounds per cubic foot for cellulose; 1.5 pounds per cubic foot for fiberglass and
mineral wool. If the blowing machine pressure is
too high or the walls are not properly braced, it’s
possible to blow out the drywall on the interior.
Pressure that’s too low can lead to voids in the
material and lower R-values.
Note how the foam seals around penetrations through
the joist to prevent air leakage to the outdoors.
Cellulose and fiberglass can be sprayed into an
open wall cavity or other building assembly. When
mixed with the right amount of water, the material
clumps together and adheres to the wall cavity. It
is ready for wall covering after a day or so of drying. Damp-spraying insulation requires the right
equipment used with careful control and attention to detail to prevent both material and building failure. For this reason, it should be considered a professional job. It may be preferred when
there are open walls to be insulated because it is
faster to apply than dense-pack, and the insulating value is about the same.
Spray Foam
Spray foam insulation is usually synthetic polyurethane or polyicynene, though there are some soybased products on the market. Material is fed in
two parts, combining at a nozzle from which the
mixture sprays, and adheres to wood, stone, concrete, or other building material. The foam cures
and expands, releasing heat as it does so.
It is available in both closed-cell and open-cell
forms; the best type to use depends on the insulating and moisture permeability requirements of
the specific job (consult with a building energy
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Insulating walls with cellulose installed from
the outside requires using a blowing machine
that packs the cellulose into the wall cavity to
a predetermined density.
Shooting spray-applied cellulose into an
open wall. Binders in the material keep
it in place.
professional for on-site guidance on this subject).
At about R-6 per inch for closed-cell and R-3.6 per
inch for open-cell, spray foam is a good choice for
irregular surfaces or where air leakage control is
required in addition to insulation.
Expanding spray foam is available from hardware stores in small cans for small jobs. For
After the excess material is screeded off, the
insulation is allowed to air-dry, then the wall
is ready for finishing.
mid-size jobs, such as insulating the perimeter of
a basement band joist, two-part closed-cell foam
can be purchased in a kit that will cover up to
600 board feet. Board footage is a measure of
coverage area and thickness of the insulation.
With spray foam, you can apply a 1" to 4" layer,
depending upon whether you want to air-seal only
or to also add lots of insulating value. With a little
practice, you can achieve good results.
Kits are available at efficiency specialty stores
or on the Internet from The Energy Federation,
Tiger Foam, and Foam It Green, to name a few (see
Resources). For larger jobs or for working in colder
conditions, it’s best to consult a professional.
Rigid Foam
3Spray foam
kits for DIY
include the
foam, hoses,
spray gun,
and spray
tips. Rigid foam boards made of polyisocyanurate or
expanded or extruded polystyrene can be fastened to wood or metal framing, typically on the
exterior, using construction adhesive or screws.
Basements and crawl spaces also can be insulated with rigid foam on the inside or outside.
Extruded polystyrene foam boards are resistant to moisture and can be in contact with the
ground, but they must be protected from physical damage, sunlight, rodents, and bugs, such as
ants and termites.
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Stopping Air
and Moisture
useless if air is
allowed to move through it, and fibrous insulation
(such as all loose-fill materials) itself will not
stop air movement. Therefore, it is extremely
important to eliminate any air leakage paths
within and through the assembly before insulating.
Leakage paths commonly exist around the
boundaries between spaces, such as:
Rigid foam boards are
commonly used on
the exterior of wall
and roof structures to
prevent thermal bridging. Different types are
effective for various
applications, including
insulating basement
walls, band joist
cavities, and other new
construction or retrofit
applications. 4
I n s u l a t i o n i s n ea r l y
• the top-floor ceiling into the attic
• interior or exterior walls where the top of the
wall extends into the attic
3 Pulling back the
insulation around
the chimney, you
will often see a gap
between the chimney and the attic
floor framing. This
provides an unwanted path for air
movement between
the basement, the
attic, and all floors
in between.
Important Installation
Regardless of the type of insulation you choose,
proper installation is key to realizing maximum
thermal performance. This means full and even
coverage within the entire cavity, without voids or
compression. Compression reduces the insulating value, so don’t be tempted to stuff an R-19
batt (usually 6" thick) into a 2x4 wall cavity.
Be sure to cut the insulation so that it fits
snugly around and behind anything inside the
framing cavity, such as plumbing, wiring, and
structural bridging or blocking. The insulation
must be in full and direct contact with all six
sides (including the interior wall finish) of the cavity it is intended to insulate. When installing fiberglass batts with foil or kraft paper backing, always
staple the tabs onto the front, not the inside, of
the stud.
Avoid gaps in the insulation. Leaving just 5 percent of an assembly uninsulated (50 square feet
in a 1,000-square-foot attic) can increase heat
loss through that assembly by up to 40 percent!
Keep in mind that insulation gaps usually aren’t
in the form of one big void but rather many small
gaps throughout the area, all of which contribute
to the reduction of insulating performance.
interior wall
high temperature caulk
3 Close this gap
around the entire
chimney with strips
of sheet metal
screwed to the
wood framing and
sealed along the
chimney masonry
with high-temperature caulk.
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insulation covering
hatch panel
applied to seal
the perimeter of the
hatch panel
5Stop heat loss
through an attic
access hatch by
sealing around
the opening with
and covering the
panel with insulation (fiberglass and
rigid foam board
insulation are two
practical options).
5 Common paths for air leakage
• plumbing, electrical, and duct runs or chases
• plumbing vents and chimneys
• attic access hatches
• any place where two different materials meet,
such as where the wooden sill plate meets
the top of the concrete foundation wall, or
where the bottom plate of a stud wall meets
the plywood floor decking.
These areas should be caulked, foamed, or — if
it’s a large hole — sealed with an appropriate
sheet material such as rigid foam board insulation, drywall, or sheet metal.
In order to perform at its rated R-value, insulation must be used in conjunction with an air
barrier to prevent wind washing, the effect of
air forcing its way into the wall and through the
insulation, removing heat and reducing the insulation’s effectiveness. Imagine wearing a sweater
on a cool day: You’ll be warm until the wind
blows, but then you have to put on a windbreaker.
The entire thermal boundary of your home
should be in contact with an air barrier. Ideally
this includes an airtight interior wall surface as
well as an exterior air barrier (such as plywood
sheathing and building wrap) with airtight surfaces around all the edges to prevent air movement into the insulation from either direction.
3Insulation with
interior air barrier. Note that all seams
and connections to
framing are taped.
Common places where an air barrier might be
missing are spaces behind kneewalls, built-in
shelves, fireplace surrounds, bathtubs, shower
enclosures, dropped interior soffits, and walls
adjoining porch roofs.
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Dealing with Moisture
Wet insulation has almost no insulating value.
That’s why it’s extremely important to keep water
and water vapor out of insulation products. This
is best accomplished with a durable, weatherresistant exterior finish, along with an airtight
interior finish to slow or eliminate moisture-laden
air moving from the living spaces outward to the
Note the lack of the term waterproof, which is,
in a practical sense, not possible with traditional
building materials. The best approach is to allow
moisture to drain away from, and dry out of, the
wall or other assembly. Because water vapor molecules are smaller than air molecules, it is possible for materials to allow water vapor through
while blocking air movement. This is the basis
for products such as Gore-Tex and some building
wraps. A vapor retarder on the inside of the wall
frame is different from an air barrier (see Using
Vapor Barriers on page 69).
It’s also important to note that there is no
requirement for a house to “breathe.” This is
an outdated concept based on early attempts
to weatherize older homes without our current
understanding of building science, particularly in
regard to the dynamics of air and moisture movement. As with those older homes, your house
behaves in certain ways that involve all of its
systems interacting in a balance. This balance
may or may not produce the results you want,
but the systems are at least familiar to you. As
you make additional improvements, expect to
rethink how your home behaves.
You face many choices when it comes to
building or remodeling your home. For longlasting energy savings, lower maintenance, and
increased durability, proper insulation and airsealing techniques are at least as important as
the finish materials you choose. What good is a
shiny new paint job on a car that doesn’t run well
or uses so much fuel you can’t afford to drive it?
taped and
sealed at all
house wrap
taped at all
seams and
foam or
caulk at all
and junctions
This cutaway shows a simple wall assembly with ele-
ments to stop airflow while allowing for the movement
of water vapor. A well-sealed drywall finish on the inside
stops airflow and slows water vapor. On the exterior,
sheathing and building wrap keep air out of the wall cavity and let water vapor drain away to keep the cavity dry.
V e rm i c u l i t e W a r n i n g
If you are renovating your home and you
find vermiculite insulation (commonly used
between the 1950s and 1970s), be aware
that many samples of vermiculite have been
found to contain the carcinogen asbestos.
Vermiculite looks a bit like a small, broken
wood chip — a fibrous-looking chunk of compressed material about ½” across. The best
thing to do is to leave this insulation alone
and not stir up any dust. If you are concerned
about its presence, you can have it professionally removed, but it will likely be costly and
disruptive. In some cases it’s possible to blow
in new insulation on top of the old while
causing minimal disturbance, but this should
be done only by licensed contractors and
in conformance with local code requirements.
Many contractors are not taking on this
liability as health and safety codes specifically
address the issue of asbestos.
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Roof Venting
heat and
moisture from within the roof framing and attic,
while keeping the roof itself “cold” (meaning
closer to the outside temperature than the indoor
temperature). This helps to prevent snowmelt
and ice damming (see Anatomy of an Ice Dam
on page 76).
A properly vented roof will move outdoor air
into a vented soffit at the eaves, up along the
roof slope through a vent channel between the
roof deck and the insulation, and out through a
ridge vent or gable-end vent. The vent channel is
commonly created with a rigid, corrugated foam
sheet designed for the purpose, but you can also
use rigid foam insulation installed 2" away from
the roof sheathing if you want to add R-value.
In addition to a vent channel that creates air
space underneath the roof deck, the air coming
into that air space by way of the soffit vent needs
to be shunted away from the insulation. Install a
baffle at the eave-end of the insulation, inside the
rafter or joist bay, to prevent air movement into
and within the insulation. The baffle also prevents
insulation from blocking the soffit vent.
The illustration at right shows properly insulated, vented, and baffled roof insulation. Note
also that the ceiling insulation extends over the
top plate of the wall, eliminating a potential path
for losing heat. It is widely believed that increased
attic venting will prolong the life of asphalt roofing shingles by keeping them cool. But research
shows that venting has very little, if any, effect on
shingle temperature. The most important issue
in shingle temperature appears to be the color of
the shingles. Light-colored shingles reflect sunlight and don’t get as hot as dark shingles. The
same insulation, venting, and baffling schemes
apply to other roofing materials, such as metal
and slate.
R o o f v e n t i l a t i o n r em o v e s
Airflow Path
Like all air movement, the airflow path from soffit vent to ridge vent requires an imbalance in
pressure. Typically, heat loss from the house (or
from solar heat gain into the attic) drives this
air movement. As heat passes through the attic
insulation, the air in the attic is warmed, causing
it to rise and exit via the ridge vent, drawing in
make-up air through the soffit vents. This airflow
also removes any moisture that may be in the
attic area, reducing the potential for condensation buildup within the attic.
Given this information, you may be tempted
to increase the ventilation in your attic by adding an attic exhaust fan. Be very careful with this
approach and don’t exceed the venting area’s
ability to move air. The fan may create a negative
pressure condition in the attic, with respect to
the inside of the house. If this happens, air can
be pulled from inside the house into the attic.
Moving conditioned air into the attic wastes
energy and increases the potential for mold
growth in the attic.
Roof venting was born long ago as a moisture control strategy for cold climates. Builders
knew that heat and moisture would escape from
the house into the attic and cause the problems
we’ve just discussed. The old-time fix was to
increase air movement through the attic space
to quickly remove that heat and moisture. With
today’s building techniques, it is not much of a
stretch to build a ceiling assembly that is well
air-sealed and contains enough insulation to
prevent problematic levels of moisture and
heat flows. While ventilated roofs are not
necessarily a bad thing, they can be
avoided with proper design and
soffit vent
wind wash baffle
3Insulation extends
airflow path for
roof ventilation
all the way over
the top plate of the
wall, with the end
of the insulation
shielded from wind
wash by a baffle.
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A n a t omy o f a n I c e D a m
If you live in a cold region, take a look at the roofs in
your neighborhood the next time it snows. If you can
see vertical stripes, you are looking at the thermal
bridging effect of the rafters, warm areas that melt
snow faster than the insulated cavities between the
rafters. If you see ice dams and icicles, or places on
the roof where all the snow has melted, you know that
a serious insulation or air-leakage problem ­exists.
Icicles and ice dams are the result of poor
insulation and/or air leakage paths between heated
warm roof deck
snow pack
melting snow
cold roof
pulls heat out of
spaces and the roof. This may be due to poor roof
drainage and sun melting the snow, but more often
the problem is due to heat moving rapidly away from
inside the house — an indication of wasted energy
and ineffectual thermal and/or air boundary control.
Trouble Spots
Icicles often lead to ice dams, especially around
dormers, roof valleys, or other hard-to-drain areas.
When snow melts on a roof, runs down in the form
of water, then refreezes near the eave in an ongoing
process, the result is an ice dam. Ice can push its
way under roofing material, causing water leaks and
damage to the home. Understanding how ice forms
on a roof is to understand much about the nature of
insulation and air leakage.
To state the obvious, snow melts when it’s warm.
Your roof deck should not be warm enough to melt
snow. If it is, you’re losing heat from indoors. The
source of that heat may be poorly insulated ductwork in the attic, poor ceiling or wall insulation, or
air leakage from indoors into the attic or cathedral
ceiling space. The failures listed below result in thermally connecting the indoor heated space with the
roof, which, as you now know, warms the roof and
melts the snow:
• Poorly insulated or air-sealed spaces behind
• Interior walls that connect to the roof or attic
space without proper insulation or air barrier
• Insulation that does not cover the entire ceiling
due to voids, gaps, or the failure to extend it all
the way over the top plate of the wall below
• Outdoor air moving through the soffit vent and
into the insulation where it rapidly removes heat
(wind washing)
5How an ice dam forms. Heat escapes from the house,
warms the roof, and melts the snow. Melted snow turns
to water, and when the water runs down the roof and hits the cold eaves (where there is no source of heat to
warm this area), it freezes and turns to ice. When water
turns to ice, it expands; this expansion is more powerful than most roofing materials can withstand. The ice
can literally migrate into the soffit or attic, damaging
anything in its way.
• Thermal bridging caused by rafters and complex
roof framing details
Good planning while framing the roof, and attention
to insulation and air-sealing details, will help reduce
heat-loss into the attic, keeping the roof cool and
preventing snowmelt.
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clo s e - up
When “High Performance”
Doesn’t Perform
to take a look at his 6-year-old home in northern Vermont. Frost was
forming in the attic on the inside of the roof sheathing, and he was concerned that the moisture would
eventually rot the roof. I agreed to visit the home, although it was now June and the frost was long gone.
Walking up to the two-story house, I noticed that the windowsills were unusually deep for typical new construction.
h o me o w n e r a s k e d me
B r e t Ham i lto n
is an energy efficiency
and building science
consultant. He is also my
business partner in
Shelter Analytics, LLC,
based in central Vermont
(see Resources). Here
he tells how a missed
insulation detail in a
high-performance home
caused significant
energy loss and created
a building durability concern. We have come to
expect modern, efficient
homes to perform in an
effective way to deliver
maximum efficiency
and long-term durability. In order to meet this
expectation, apparently
small details become
extremely important.
I inquired about this, and the homeowner
told me that he had had the builder create a
double-studded wall to accommodate 12" of
insulation, a little more than double the usual
amount. He went on to say that he wanted
the house to be affordable for the long term
and didn’t want high energy prices to dictate
his lifestyle when he eventually retired.
The attic was similarly well insulated,
with 12" fiberglass batts carefully laid out
over, and perpendicular to, 6" batts in the
attic joist cavities, making a fairly impressive nominal R-60 attic. Looking closely
at the underside of the roof sheathing
from inside the attic, I did see the telltale
signs of staining from previous “moisture
events.” These moisture stains usually
appear fairly random in their positioning, a
function of hidden holes under the insulation, eddies in the air currents, location of
attic vents, and so on.
In this attic, the stains were right around
the outside edges of the attic, just above
the exterior walls. Peeling back the layers of
insulation on the attic floor, I saw that the
exterior walls were nicely filled with big, fluffy
batts of fiberglass insulation, but they were
completely open at the tops. If I could have
removed the insulation, I would have been
able to drop a quarter two stories down the
wall into the first floor. This type of framing
is called “balloon framing” and dates from
the late nineteenth to early twentieth centuries, when wood timbers were both long and
plentiful. But I had never seen a new home
framed in this style.
The good news was the problem was both
apparent and easy to fix. All winter long, the
warm, humid air from the home seeped into
the wall cavity and rose straight up as if the
wall were a chimney (fluffy insulation does
not stop air movement), and exited the wall
at the attic floor. It then flowed up to the cold
roof, where the moisture condensed out of
the air and created the frost the homeowner
saw on the underside of the roof.
We asked a local insulation contractor to
spray foam insulation over the openings at
the tops of the walls to seal them off and
stop the flow of air. Then we installed a timer
on the bathroom exhaust fan to run 30 minutes every hour, around the clock, to reduce
humidity levels in the house. The fix worked.
Frost no longer forms on the roof deck, and
the homeowner reports that the home is
more comfortable than ever.
If I could have removed the insulation, I would have been able to drop a quarter
two stories down the wall into the first floor. This type of framing is called “balloon
framing” and dates from the late nineteenth to early twentieth centuries.
W hen " high performance " doesn ' t perform 77
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Deep Energy
o m e e n e r gy i m pr ov e m e n t s generally consist of a wide variety of
measures that encompass electrical and thermal upgrades. Small improvements make small impacts. But if you go “wide” enough in your approach,
lots of small changes will add up to larger savings: efficient lighting and appliances,
low-flow showerheads, weatherstripping around windows and doors . . . you get the
idea. Energy savings can range from minimal to 20 or even 30 percent if you’re diligent and work with a good contractor.
You can also choose to go “deep” with your improvements; rather than just adding insulation to your attic, for example, you first prepare the attic thoroughly by sealing up air leaks between the house and the attic, repair any damage, address the
attic and roof from a “renewable ready” standpoint, and then (finally) install as much
insulation as possible. While working on the attic and roof, you might also make
preparations for a future, similar treatment to the walls. With all of this done, neither
you nor a future owner will ever need to address efficiency or durability issues in the
attic space again.
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Looking at the
Big Picture
P i e c emea l e f f i c i e n c y i m p r o v eme n t s
do reduce energy use, but consider the
synergies of a holistic approach to go both
wide and deep. Taking a systems view of your
home’s energy-consuming appliances — and
how they interact with the envelope assemblies
and occupants — allows you to multiply your
savings along with improving comfort. As you can
imagine, this whole-house deep energy retrofit
(DER) can be a costly and intrusive process, but
short-term pain will yield long-term gain.
One study by the New York State Energy
Research and Development Authority (NYSERDA;
see Resources) suggests that a comprehensive
DER in a cold climate costs about $18 per square
foot of shell area (surface area of all six sides
of a house), adding up to over $75,000 for the
average modern home. This includes many nonenergy–related improvements that will likely be
encountered along the way.
With a deep energy
retrofit, every aspect
of a home’s energy,
comfort, durability,
health, and safety are
addressed. 
Admittedly, we are in the “barnstorming”
years of product development and installation
procedures for such comprehensive energy savings projects. Forward-thinking entities such as
NYSERDA, among others, are helping to drive
down costs by investing in research projects
and utility program developments that will offer
national guidance and promote market transformation in this area. For the homeowner, costs and
scheduling are made more manageable by developing a plan that allows you to stage, or phase,
improvements over time. Addressing immediate
needs first allows you to fix the biggest holes in
your home’s energy bucket while incorporating
those improvements into the building’s long-term
plan without a huge up-front cost.
What a der Involves
Most homes are designed for appearance and
functionality. Unfortunately, they are not always
designed around the fundamental idea of matching the mechanical systems (heating, cooling, and
ventilation) with the envelope assemblies, and
Air leaks elim­
inated between
conditioned and
High level of
insulation in all
building assemblies
Continuous layer of
insulation added to
eliminate thermal
Triple-glazed windows
thermal and air
barriers around
entire building
Water drained
away from house
with gutters
and landscaping
High-efficiency lights
and appliances
joist space in
basement and
air-seal between
foundation wall
and floor above
Dry basement
with insulated
water heater
and cooling
ventilation system
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iPerformance Levelsi
Depending upon your climate and the current condition of your home, the requirements of a DER can
vary. A typical deep energy retrofit in cold climates, such as those in the northern half of the United
States, involves upgrading to the following minimum performance levels:
• R-10 basement or ground-floor slab
• Air leakage reduced to an absolute minimum
• R-20 basement walls with continuous insulation,
• Ventilation system to provide healthy indoor air
water drainage, and air and moisture control
• R-30 to R-40 walls with air, vapor, and water
control layers
• Upgraded windows — by adding storm windows
or replacing old windows with highly insulating
(triple-pane) units with orientation-tuned glazing
• R-60 roof with air, vapor, and water control layers
• Renewable energy systems where practical
how these relate to the home’s performance in
terms of energy use, occupant health and safety,
indoor air quality, and structural durability. The
goal of a deep energy retrofit is to overhaul the
way an existing home works with the above points
as guiding principles. It often includes many of
the following improvements:
Great attention to all detail is required, as are
skills, experience, creativity, and a commitment
to doing things right, not to mention the tenacity
to redo things if necessary until they are right.
If the costs of improvements are financed at
market rates, there can be a fairly long financial
payback period. Also (and this is important), the
homeowner must be able and willing to accept
several months of substantial disruption in the
home if all the work is done at once. In short, a
DER demands a rare combination of contractor
skills and homeowner motivations.
• Insulating and air-sealing to substantially
improve the thermal envelope
• Upgrading lights and appliances to meet the
highest performance specifications
• Adding a whole-house ventilation system,
such as heat recovery ventilation
• Upgrading to high-efficiency and properly
sized heating, cooling, and hot water systems
• Improving distribution of conditioned air
• Increasing window area on south-facing walls
to capture heat from the sun
• Adding thermal mass to floors to capture and
store solar heat
• Incorporating renewable energy systems
• Reusing, repurposing, or recycling all building
materials removed from the home
A Team with a Plan
retrofit plan spells out the
methods and approaches for upgrading all the
various and interconnected energy-related pieces
of the building. The plan is an important piece that
should not be ignored; without it, you may later
find yourself redoing things that did not go deep
enough. Or worse, you may make mistakes that
can’t be undone without great cost and effort.
The plan starts with a full energy audit and building inspection by a qualified efficiency consultant
A d ee p e n e r g y
iThe Best Performer on the Blocki
Together with the homeowner, a DER team can transform an energy-hog building into a high-performance
twenty-first-century home that is comfortable and durable — and uses 80 percent less energy than the
average home. Your house has the potential to be far more than a container for all your stuff. Substantial
investment in well-planned improvements will lead to meaningful savings over the life of the home.
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iEndgame: Renewablesi
Efficiency makes renewables more affordable, as less demand from the home means smaller, less
expensive energy generation systems. The DER level of energy reduction allows you to meet most or
all of your home energy needs with renewables. Think of a DER as endgame planning for the energy
use, cost, comfort, and durability of your home.
who can develop and lead an integrated design
team. This team is critical to achieving comprehensive and technical excellence with the project.
The consultant must be able to communicate well
and coordinate the work of an architect, a general
contractor, all representatives of trade subcontractors, and the homeowner.
The purpose of the team model is to bring
together the decision makers and contractors to
engage in goal-setting, planning, road-mapping,
accountability, and team-building. Everyone must
know what they’re getting themselves into and
what is expected of them. It’s important to find
experienced team members who communicate
openly and honestly and are willing to take risks
in an intelligent and informed manner.
A good plan makes it possible to stage improvements so that you can make upgrades separately
and incrementally, if desired, while making sure to
accommodate the next improvement phase. The
plan can also help you take advantage of natural replacement cycles. For example, roofs need
to connect with walls, and walls, of course, have
windows in them. When it’s time for a new roof or
new siding, use this as an opportunity for deep
efficiency improvements. Once your thermal envelope is improved, you can optimize the heating
and cooling systems to meet the reduced needs
afforded by the better envelope. Now it’s time to
consider on-site renewable energy systems.
Unpleasant Surprises
In the process of making thermal performance
improvements and other efficiency upgrades,
you may encounter health, safety, durability, and
deferred-maintenance issues that need to be
addressed. For example:
• Lead paint
• Asbestos insulation or siding materials
• Failing roof
• Wet basement
• Substandard wiring
• Radon
• Structural issues
These and other problems can present practical challenges to builders and budget challenges
for the homeowner. In any case, performing such
work on your home will be very specific to its particularities and your climate.
Every Job is Custom
There are many products on the market today, and
many different approaches to the various situations that can arise. When it comes to a deep
energy retrofit, it’s important to apply building science to your specific project and climate. There
are no plug-and-play, off-the-shelf, one-size-fits-all
widgets available.
With that in mind, the remainder of this chapter describes some very general approaches to
deep energy savings without going into specific
products or details, any of which may or may not
be appropriate for your situation. A comprehensive DER is not a suitable DIY project for the average homeowner, but there are plenty of opportunities for you to step in during the work phases you
are comfortable with.
The methods described here are not intended
to represent the “best” approach. There is no
such thing (yet) as a generic deep energy retrofit, and a comprehensive whole-house treatment
involves almost excruciating detail. Therefore,
while the following information covers the basic
approaches and rationale behind DER improvements, it is by no means a compendium of all the
various details involved.
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The Basement
most homes are
either concrete slabs, dirt, or gravel. Regardless,
controlling water and dampness in the basement
is an important part of a DER project. This is
because moisture from a wet basement will
increase the humidity in the house and can
quickly and easily compromise your health (and
building materials) as you tighten up and insulate
the floors over the basement.
Addressing moisture may mean installing gutters, downspouts, and downspout extensions on
the outside of the house, and possibly making landscaping changes, so that water drains away from
the building. It may also mean installing a perimeter drain inside the basement, allowing water to
drain to a sump where it can be pumped out.
The basic approach for basement slabs is to
provide drainage (as needed); insulate the slab
with continuous, durable insulation (such as rigid
foam board or foam-glass); cover the insulation
with a vapor barrier (such as polyethylene); and
top it all off with new concrete or another type of
Basement walls typically are cool, so condensation can easily form on walls under the right conditions. Older basements may also leak bulk ground
water after it rains or due to high water tables. You
have two basic options for dealing with leaks: redirecting the water before it gets in, or accepting that
it will come in and direct it to a place where it can
be managed.
Ba s eme n t f l o o r s i n
Cross section of
a basement wall
and slab floor with
perimeter drainage,
sump pump, water
barrier membrane,
and insulation6
2" rigid foam insulation
Foundation wall
Interior drainage
trench to pump
Pump to outside
Poly vapor
Finished floor
2" rigid foam
Sump pump or
drain to outside
Walls will be covered with insulation and possibly
a finish material, but you do not want these materials to come into contact with a damp foundation
wall. One solution is to cover the foundation wall
with a waterproof drainage mat (such as a dimpled
polyethylene sheet) that directs water to a drain
and keeps any moisture away from finish materials. Products (such as Perimate; see Resources)
are being developed that can serve as both insulation and drainage plane. Once the water is managed, the wall and the perimeter band joist area
can be insulated, air-sealed, and finished.
Drying out a basement and providing means
for removing water that does get in not only helps
to control potentially damaging humidity levels
throughout the house, it also makes the space
more livable and versatile.
Above-Grade Walls
time to upgrade
walls is when you’re replacing the siding, but there
may be good reasons to do the work now rather
than wait. Of course, you’ll want to investigate
what your walls are made of and what’s inside
them before you start tearing things apart.
The main goal with wall improvements is to
prevent air and moisture from getting into the
wall while increasing its durability and insulating
value. Typically this involves removing the siding
and working from the outside. Following are the
basic elements and techniques for creating a
maximum-efficiency wall.
The most cost-effective
Insulating the
Interior Wall
Before insulating, seal up all air leaks in the
wall, including all penetrations in the wallboard
on the inside, through the siding on the outside,
and in the top and bottom plates. The conventional approach is to air-seal the wallboard from
the inside, using caulk, spray foam, and other
materials. With a few courses of siding removed
from the outside of the wall, you can install
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iBuilding Wrapi
In some cases it’s appropriate to install an air and moisture control barrier, such as building wrap,
over the sheathing. This is the common approach in standard wall construction, but may be integrated
into other products used in some high R-value wall designs. Building wrap must be taped at the
seams and lapped over window and door flashing to eliminate air leakage and to allow water to drain
consistently downward.
dense-pack cellulose insulation in the wall-stud
cavities, leaving the sheathing intact.
For a more complete approach, you would
remove the siding and sheathing, pull out all
the insulation, and use spray foam to seal leaks
from the back side of the wallboard and, as an
option, to insulate the wall cavities.
Sheathing Options
On most exterior walls, the studs are covered with
some kind of structural sheathing, typically plywood
or oriented strand board (OSB). This layer must be
air-sealed at all joints and at the top and bottom so
that no air can move behind the sheathing.
This can be accomplished in part with building wrap and/or rigid insulation taped at the
seams, along with spray-on urethane or latex
foam or caulk to seal the top and bottom of the
wall assembly to top and bottom plates. Peeland-stick roof underlayment material can be
used to seal the lower few inches of the sheathing to the top few inches of the foundation. The
goal is to integrate a durable air and water barrier into the wall.
Do the same thing at the eaves by air-sealing
the top of the sheathing (or building wrap) to the
top plate. This effectively ties the wall’s air barrier
to both the foundation and the roof air barrier to
create a continuous air barrier around the entire
building. (Note: If you’re working according to a
staged plan, be sure to make provisions for this
detail so you can easily seal the walls to the roof
when you get to your roof work.)
Exterior Foam Board
the joints staggered so that they overlap, and
with the outer panels taped at the seams to seal
out air and water. The continuous insulation layer
helps to control the thermal bridging effect of the
studs and should extend down over the foundation, if possible.
Depending on the materials and approach
you use, an additional waterproof membrane
may be needed to cover the insulation to drain
away water that migrates through the siding.
There are several such drainable building wraps
(such as HydroGap; see Resources) on the market designed for use as a “drainage plane.” Window and doorjambs must be extended to accommodate the added thickness of insulation on the
outside of the wall.
making connections
Vertical furring strips are nailed or screwed
through the foam insulation and into the studs.
These are used as a nailing base for the siding.
The windows (below) and doors are installed and
Windows are sealed over
the wall sheathing with
a waterproof membrane,
such as peel-and-stick
tape, that seals the window flashing to the wall
(typically overlapping the
air and moisture barriers), preventing air and
water infiltration into the
wall-to-window perimeter
junction. This is a critical
detail for all window
Over the sheathing goes a continuous layer of
rigid foam board insulation. Many installations
use two layers of 2" foil-faced foam panels, with
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C u r ta i n W a l l s
An alternative to tearing into and improving
existing walls is to build new “curtain walls” over
the old walls. The advantage to this approach
is that it can be less costly and intrusive than a
demolition of the existing exterior walls. Curtain
wall construction starts with dimensional lumber
(2x3 or 2x4) attached vertically to the existing
siding to create cavities for new insulation and a
nailing base for new siding. The stud cavities
are filled with expanding spray foam, then a
continuous layer of air-sealed insulation is added
over the studs, followed by a water control layer
or space, and, finally, the siding.
Exterior curtain wall retrofit. Walls are thickened, windows and doors trimmed as needed, insulation is
added, and new ­siding is installed. 4
flashed, with attention to both air leakage control
and water drainage. After the siding is installed,
there will be a gap at the bottom of the wall (and
perhaps the top, depending on the construction)
rigid insulation
Wall and roof assem­
blies, each with
con­tinuous exterior
insulation applied in a
deep energy retrofit.
Foam, caulk, insulation,
air and moisture barriers, tape and sealants
tie together both the
thermal and air boundaries of each assembly.
Note the small break in
the thermal boundary
where the wall insulation meets the roof
sheathing. This can be
considered a compromise to keep the roof
overhang intact. The
better energy performance solution would
be to cut off the rafter
tails, allowing for a
connection between the
roof and wall thermal
boundaries. 4
finished roofing
weather-resistant barrier
roof cavity
insulation in
rafter bays
strip nailing
wall cavity
rigid foam
wall cavity
house wrap
air barrier
created by the furring strips. This gap must be
covered with a screen that keeps out bugs and
rodents but allows water to drain.
The drawing at left illustrates how a roof and
wall retrofit connect the thermal and air boundaries of those assemblies. The basic approach
shown here uses an air barrier over the existing sheathing, followed by two layers of overlapping rigid insulation that is sealed at the seams.
The wall assembly uses furring strips as a siding nailer, and the air space created by the furring
strips allows water to drain away from the wall. On
the roof, additional sheathing is required as both a
nailing base for shingles and for additional durability. A weather-resistant barrier covers the exterior
roof sheathing, followed by the finished roof. Rigid
foam board sealed with spray foam or caulk can
be used to block the end of the rafter bays so that
insulation can be dense-packed into the cavity.
W h e n d ea l i n g w i t h windows in a deep
energy retrofit, there are two common options:
1) You may decide to keep the old windows if
they’re double-pane units and in good shape; or
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Storm window
installed over existing window.
The entire perimeter of the frame
is caulked before
installing to provide
a good air seal. 4
2) if the windows are older single-pane units, or
they’re damaged and in need of replacement, a
wall upgrade is the best time to replace them with
new high-efficiency, triple-pane windows.
With the first option, you might do well to simply add a storm window so that the windows are
now effectively triple-pane (having 3 layers of
glass, or glazing). Look for a high-performance,
Low-E coated window, and install for airtightness
to obtain maximum efficiency (learn more from
the Alliance for Low-E Storm Windows, and the
Efficient Windows Collaborative; see Resources).
In either case, installation details are extremely
important. The window must be flashed and
sealed to keep air and water out of the wall, while
allowing for rainwater to be drained away.
One decision you will need to make when
replacing windows in an upgraded wall is between
“innies,” where the windows are installed close
to the inside finished wall (providing a bit more
protection), and “outies,” where the window is
installed flush with the exterior siding (providing
a deep windowsill). This is primarily an aesthetic
decision, but in terms of energy efficiency, the windows are best placed in the middle of the thermal
boundary layer.
With the second option, it’s important to
choose windows based on performance ratings
that vary according to where the window is, which
direction it’s facing, and what you want the window to do. This is called an “orientation-tuned”
glazing approach, and it means that you choose
different performance characteristics for windows
on different sides of the house. If you’re in a
heating-dominated climate, you want to maximize
solar heat gain during the winter months, but perhaps minimize it during the summer. For coolingdominated climates, you will want to reduce the
solar heat gain. In both cases, you’ll want a high
R-value (low U-factor) to minimize heat transfer
between indoors and out.
It can sometimes take a fair amount of persistence from you (or your builder) to get what
you want, as it may not be a standard option in
your area. Talking directly with manufacturers can
help, since they are often able to supply a variety
of glazing types in their windows.
Window Performance
Before expanding on the idea of orientation tuning with examples, it will be useful to understand
how window performance is rated. Most windows are rated for thermal performance by the
National Fenestration Rating Council (NFRC; see
Resources). The NFRC sticker on a window states
all of the performance criteria you need to compare window efficiencies and make an informed
selection. The following are the performance criteria to look for on the sticker.
U-factor is a measure of the insulating value of
a window (including the framing material). Chapter
Sample NFRC window performance label
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Lo w - E Lo w d o w n
You’ve probably heard something about “low-E” windows or
coatings and wondered what
all the fuss and confusion are
about. The “E” is for emissivity.
This describes a material’s ability to emit, or radiate, energy.
Reflective materials have a
lower emissivity, while materials that absorb heat have a
higher emissivity.
Low-E coatings are used on
double- or triple-pane windows to improve their energy
performance. These selective
coatings allow visible light to
pass through the window, but
they reflect heat energy (infra-
red radiation) away. The Low-E
coating in a window is applied
to a single layer of glass that
faces the space between two
panes or (in the case of a
triple-pane window) to a thin
film in between panes.
Typically, the window is
oriented so that the glass with
the low-E coating faces the
warmer zone. For example, in
a heating climate the low-E
coating is on the outwardfacing surface of the inside
pane, so that heat radiating
from the house is reflected
back into the living space. For
cooling climates, the coating is
3 explains that U-factor is essentially the inverse
of R-value (see page 62), so a lower U-factor number indicates a better-insulated window. A single
pane of glass has a U-factor of about 0.91, translating to an insulating value of about R-1.1. Most
new double-pane windows have a U-factor between
0.50 and 0.30 (or an R-value between 2 and 3.3).
New high-performance windows with three or four
glazing layers can offer U-factors near 0.1 (R-10).
Solar heat gain coefficient (SHGC) is
a measure of how much solar radiation (heat
energy) is admitted through the window, via direct
transmission and absorption. An SHGC of 0.32
means that 32 percent of the solar energy falling on the window (including the framing material)
is transferred through it. Lower SHGC windows
(<0.30) can reduce the air conditioning requirements of a home in a warm climate.
Visible transmittance (VT) measures
how much visible light comes through a window
(including the framing material). VT is expressed
as a number between 0 and 1. A higher VT means
more light is transmitted. A VT of 0.51 means
that 51 percent of the sun’s visible light passes
through the window. Lower VT values are found
on tinted windows that can be beneficial in hot
climates to reduce solar heat gain.
on the inward-facing surface of
the outside pane, so that solar
heat is reflected to the outside.
There are two types of low-E
coatings, and windows from
different manufacturers differ
in the type, location, and number of surfaces with coatings.
Sputtered, or soft, coat is used
in windows with low or moderate levels of solar heat gain,
while pyrolitic, or hard, coat is
used in windows with higher
solar heat gain. One is not
better or worse than the other;
it all depends on how you want
your window to perform.
Air leakage (AL) is expressed in cubic feet
per minute of air passing through a square foot
of window area. Heat loss and gain also occur
by air infiltration through small air leaks in the
window assembly. A lower AL means less air will
pass through these cracks. A 15-square-foot
window with an AL of 0.2 means that 3 cubic
feet of air will move through the entire assembly
at the tested pressure differential (75 pascals)
in one minute. AL is an optional rating and is not
always included.
Condensation resistance (CR) measures
the ability of a window to resist the formation of
condensation on its interior surface. The higher
the CR rating, the better the window is at resisting condensation formation. CR is expressed as
a number between 1 and 100. CR is an optional
rating and is not always included.
How Orientation
Tuning Works
An orientation-tuned window strategy puts the
right glazing properties in the right place. An efficiency consultant can help with specifying the
right products and approach for your home and
climate. Generally speaking, in northern heatingdominated climates, the sun’s angle is low in the
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sun path
sun path
5Example of window tuning by orientation for a heating-
dominated climate: As the sun rises, high-SHGC glazing
in the east helps to warm the house after a cool night. As the sun moves to shine into the south-facing windows, high-SHGC glazing allows winter sun to warm the
house, while the higher summer sun does not shine as
deeply into the house. Low-SHGC glazing in the west
helps to reduce long summer afternoon heat gain. All
windows should have a low U-factor for maximum insulation value.
winter, flooding the south side of the house with
sunlight. Choosing a window with a high SHGC
and a low U-factor allows you to gain heat from
the sun without losing too much heat back out
the window. If the sun strikes floor and wall materials, such as tile or stone that have thermal
mass (meaning they can absorb and hold heat),
the stored heat will be released later as the sun
sets and the house cools.
The west-facing side of that same house will
be exposed to long afternoons of direct sunlight
in summer, potentially overheating the house.
Choosing a low SHGC window (again with a low
U-factor) can help reduce this overheating. In
cooling-dominated climates, windows with a low
SHGC can help control air conditioning costs.
Ceiling improvements follow the same
approach of thorough air-sealing and insulating
described in chapter 3. With a cathedral ceiling
over finished attics or living spaces, often the
approach is to create a deeply insulated, unventilated roof system, sometimes called a “hot roof.”
Unvented Roof
An unvented sloped, or cathedral, roof retrofit
can be very similar to the wall retrofits described
on pages 82–84. Think of a sloped roof as a
slanted wall. There will be insulation in the rafter bays, then roof sheathing, followed by continuous (taped and sealed) insulation over the
sheathing, and finally a moisture barrier (drainage plane) that drains away any water that gets
through the roofing. On top of all that go the
shingles or other roofing materials. The exception is that roofs may need an additional layer of
sheathing under the shingles.
As discussed in chapter 3, conventional roof
assemblies over unfinished attics must incorporate ventilation to keep the roof deck and
attic space cooler and to help prevent ice dams,
excess moisture, and other problems. With an
un­ventilated roof, aggressive insulating and
air-sealing creates a sufficient thermal barrier
between the roof surface and the living space.
How much insulation is enough? Lots. But it
depends. An energy consultant must be involved
to ensure a durable, efficient, condensation-free
Air Leakage
a building are often the largest
component of heat loss, and reducing air
leakage is generally a low-cost improvement with
substantial energy savings potential.
In addition to heat loss from outdoor air infiltrating a building, air movement from inside to
the outside of a building (exfiltration) can sometimes lead to moisture and mold inside the walls
or in the attic. This happens during the winter
when warm, moist air from inside your home
A i r l ea k s i n
The Roof
roofs vary significantly
depending on what’s directly underneath the roof:
If it’s unfinished attic space, the improvements
focus on the ceiling between the attic and living
areas below. If the roof directly covers living space,
such as with a finished attic or a cathedral ceiling,
the improvements are made to the roof itself.
D E R s t r at e g i e s f o r
air leakage 87
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travels into a colder wall cavity, where the moisture in the air condenses. The reverse is true in
the summer when hot, humid, outside air tries to
make its way into a cool, dry, air-conditioned interior (remember that heat moves from warm areas
to cold areas).
To achieve significant energy savings, adding
a continuous, durable air barrier is an extremely
important element in reducing air leakage. It also
serves to keep the spaces hidden inside walls dry
and mold-free. Air leakage control can be especially challenging in certain areas:
• Stone foundations
• Junctures between foundation walls and
above-grade walls
• Around windows
• Connections between roofs and walls
• Complex roof structures
Be Thorough
Air-leakage control and thermal boundary integrity are essential to any energy efficiency home
improvements, but with a deep energy retrofit,
you want air leakage to be at an absolute minimum. This requires thorough knowledge of the
correct products and how to install them, as
well as extraordinary diligence with the installation details. Every last crack, hole, or penetration
between conditioned space and unconditioned
space must be sealed — from the hose spigot in
the basement to the chimney chase through the
attic. Air leakage control products include building
wrap, caulk, expanding foam, rigid foam board,
high-quality tapes, peel-and-stick membranes,
and weatherstripping.
Heat loss calculations used to select the right
size heating and cooling sytems usually over­
estimate the air leakage of a home because they
are doing just that — estimating. Since air leakage
is such a significant factor when it comes to heat
loss and gain in a home, it’s important to quantify
the leakage rate accurately so that space conditioning systems can be properly sized. With a DER,
heating and cooling loads are so much lower than
a typical home that proper mechanical system
sizing becomes extremely important in achieving
maximum performance and comfort.
Quantifying air leakage can be done using a
blower door test (see page 53), typically conducted by a heating contractor or energy auditor. This test not only helps in sizing a heating
or cooling system, it also pinpoints air leakage
areas that need to be sealed.
Remember, the goal with a DER can be considered “end-game” planning. Go as deep as possible so that you don’t need to revisit or redo.
sealed house
is ideal in terms of energy efficiency, living in such
a home would not be pleasant. If the house is
too tight, both occupant and building will suffer ill
effects. So, how do you ensure a sufficient supply
of fresh air to create a healthy environment
and prevent physical damage to the building
materials? How much air is enough?
People need good air quality inside their
homes. This requires maintaining acceptably low
levels of allergens, humidity, and pollutants, such
as carbon dioxide (CO2) exhaled by people and
the off-gassing of nearly every manufactured product brought into the home. In a high-performance
building, uncontrolled air leakage is reduced to a
minimum through air-sealing; therefore, fresh air
needs to be provided by a mechanical ventilation
system that is controlled to optimize both indoor
air quality and energy efficiency.
As mentioned earlier, the builder’s phrase for
this is “build tight, ventilate right.” And for the
record: Ventilation systems do use energy, and
some conditioned air is lost to the outdoors. But
a tight, efficient building with good ventilation will
use far less energy than a leaky building with no
ventilation, and the energy cost is a good tradeoff for a healthy home.
The generally accepted standard for ventilation in homes is 15 cubic feet per minute (cfm) of
fresh air per person. This can vary according to the
activity level in the house. In addition, combustion
appliances (cooking, heating, water-heating), and
A l t h o u g h a h e r me t i c a l l y
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With a conventional
water heater (or other
combustion ­appliance),
combustion air is
drawn from inside the
home, and the burner’s
exhaust naturally flows
up and out of the flue,
taking conditioned air
from inside the home
with it. Backdrafting
occurs when exhaust is
directed into the home
by a pressure imbalance, flue blockage, or
outdoor wind currents.
So-called atmospheric
draft equipment needs
indoor air for both
combustion and chimney draft.4
vent pipe
appliances have
a sealed burner
chamber and pull
combustion air from
outdoors. Exhaust
gases are vented
directly to the
outdoors so there’s
no chimney or draft
damper, and no risk
of backdrafting. gas burner
air inlet
chimney drafts all require air. If all of the home’s
heating appliances are sealed-combustion (with
make-up air provided from the outdoors; see
below), then it’s safe to tighten up the house to
reduce heating and/or cooling energy use without
creating flue backdrafting.
Flue draft
Fossil fuel heat and hot water equipment needs
combustion air (air to burn fuel). In a typical
installation, this air comes from inside the house,
but there are better ways to address air requirements. In all homes — especially airtight, energyefficient homes — it is very important to consider
where the combustion air is coming from and
how the flue gases are getting out of the building.
Failure to pay attention to this simple detail can
result in poorly performing equipment or potentially deadly carbon monoxide poisoning.
Fossil fuel–burning equipment needs a chimney or other venting system to remove poisonous combustion byproducts from the house to
the outdoors. It is important to make sure the
chimney or venting system is in good condition
and properly sized for the equipment. There are
very strict codes for venting combustion appliances. To ensure both proper operation of combustion equipment and occupant safety, two considerations of venting exhaust gases must be
understood: draft and backdraft.
Draft is the flow of air into the fuel burner and
out the flue. As the fuel burns, air is drawn from
the surrounding environment into the combustion
chamber. The flame creates heat, and the hot,
buoyant combustion gases rise up the flue leading to the outdoors. Draft can be created naturally
by the combustion process, or it can be induced
by a fan in the venting system to ensure removal
of combustion byproducts.
Backdraft occurs when exhaust moves backward through the flue and into the home due to
inadequate draft. Inadequate draft can occur
when the interior of a house is under negative
pressure in relation to the outdoors, and the flue
gases reverse flow within the chimney: Instead of
flowing up and out, the gases flow down and in.
iBackdrafting in New Homesi
Building airtight new homes and upgrading older leaky homes have exacerbated the problem of
back­drafting. In a tightly constructed home, heat and hot-water appliances must get all the air they
need for combustion and draft from the outdoors, not from inside.
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This can result in continuous spillage of poisonous combustion gases into the house.
Backdrafting can be caused by several conditions: if the chimney is blocked or is the wrong
size for the equipment, if high winds force a backdraft down the chimney, or if the air pressure
drops in the area where the heating equipment
is. This pressure drop can be caused by exhaust
fans (including those in clothes dryers and highpowered kitchen vent hoods), or even from other
combustion equipment with a stronger draft.
Sealed Combustion
When selecting a space or water heating system
for your home, the best choice is to install sealed
combustion equipment. This means the entire
combustion process is sealed off from the surrounding indoor environment. All combustion air
is supplied by a duct from the outdoors, and the
exhaust is vented outside with a separate duct
or duct passage.
Cooking with Gas
The exception to venting the exhaust from fuelburning equipment has always been gas cooking equipment. Unless you cook for more than
a half hour a day, gas ranges, ovens, and cooktops typically do not cause problems with excessive moisture or combustion pollutants, but
it’s always a good idea to use a vent hood for
exhaust while cooking with gas. For very tight
homes, recirculating range hoods with filtration
are recommended, but again, if you cook more
than a half hour a day, you may need to investigate a custom approach to balanced ventilation
that allows fresh air into the home to make up
for the exhaust air that leaves through the fan.
Recirculating fans do not create pressure imbalances in the home, and they do not require a
hole to be cut in the wall for the fan’s exhaust
duct (any hole in the wall will always increase
air leakage). In conjunction with a well-designed,
balanced ventilation system (and average cooking skills), you should not experience any issues
with cooking-related pollution.
Types of Mechanical
Mechanical ventilation systems fall under two
general categories: exhaust-only ventilation and
balanced ventilation.
Exhaust ventilation includes kitchen vent
hoods and bathroom exhaust fans. They remove
stale air at the source and bring fresh air inside
by creating a slightly lower pressure inside the
house with respect to outside. This low pressure causes outside air to be pulled into the
house by way of the path of least resistance,
such as an open window, chimney, or leaks in
the house. A high-CFM fan (such as a downdraft
range fan or commercial range hood), used in a
very tight house with a fossil fuel heating system or hot water system that is not a sealed
combustion type, can present a very dangerous
backdraft situation.
Balanced ventilation offers separate
exhaust and supply ducting, and continuously
removes stale air from inside while introducing fresh air from outdoors. This is the best
option for effectively ventilating a home because
it removes stale air at the source (bathrooms,
kitchens, and bedrooms) and replaces it with
fresh air where it’s needed (living rooms and
bedrooms). It is called “balanced” because an
amount of air is supplied to the house equal to
that exhausted from it.
fresh air comes
in from outside
stale indoor air
goes outside
heat exchange core
in the middle
5An HRV allows air streams to exchange heat without
mixing the streams.
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A heat recovery ventilator (HRV) is the
most effective type of balanced ventilation system. An HRV allows heat energy to be transferred
from stale (conditioned) outgoing air to the fresh
(unconditioned) incoming air as both air streams
pass through a heat exchanger — without mixing
together. This heat recovery process minimizes
the energy penalty of introducing unconditioned
outside air into the home. HRVs have the following advantages over other types of ventilation
• The heat transfer process works in both
heating and cooling seasons.
• Effective ventilation occurs evenly throughout
the entire home, greatly improving indoor air
• Pressure imbalances are eliminated,
so there is a lower potential for ventilationinduced backdrafting of combustion
• The home can be significantly air-sealed,
offering maximum energy savings while still
providing adequate fresh air to occupants.
• Enhanced indoor air quality leads to
increased occupant health and comfort.
Another type of HRV is called an enthalpy recovery ventilator (ERV). An ERV does what an HRV
does but also allows for the transfer of water
vapor, thereby recovering both latent and sensible heat (see Sensible Heat and Latent Heat on
page 93). It accomplishes this with a permeable
heat exchange core or a desiccant wheel revolving between incoming and outgoing air streams.
An ERV may be the right choice if the home tends
to be too dry, or if the home is air conditioned and
you want to control the humidity.
Ventilation Control
Ventilation systems must be controlled because
they use energy and they remove conditioned air
from the house, so you don’t want to run them
more than you need to. Underventilating a home
compromises indoor air quality and can lead to
high levels of pollutants such as carbon dioxide,
which is exhaled by humans.
Exhaust Fans
For exhaust-only ventilation, choose a quiet,
low-wattage fan, coupled with a programmable
24-hour timer. The fan’s run time depends on
how tight the house is. Start with a timer setting
that allows the fan to run 20 minutes every hour
while the house is occupied (no need to provide
fresh air if nobody is home). Adjust the operating
time up or down from that setting depending on
the results. An efficient, quiet bathroom exhaust
fan can provide economical, reasonably effective
ventilation (50 to 100 cfm is required in most
average-sized homes). Install the fan on an upper
floor to take advantage of the building’s “chimney
effect” that makes air want to move upward.
If you have condensation problems on your
windows, it indicates that the window has
reached the dew point temperature. Poorly performing windows will have colder indoor glass
surfaces, exacerbating condensation. If condensation is a consistent problem on windows, ventilation will help by eliminating moisture at its
sources, such as showers.
Relative humidity can be an indication of ventilation or air leakage rates in your home. Humidity
levels below 25 or 30 percent in a northern climate heating season probably indicate too much
air movement between indoors and out. For most
of us, comfortable relative humidity in a home is
in the 35- to 55-percent range, but we can certainly tolerate a much wider range. Keeping an
eye on humidity levels with a hygrometer can help
you determine how long to run your exhaust fan.
Heat recovery ventilators include their own dedicated controls. Fan speed and run time can be set
with a timer, or they can be automatically adjusted
in response to indoor humidity or carbon dioxide
levels. This is called “demand-controlled” ventilation and is common in commercial buildings to
ensure a balance of good air quality and energy
efficiency. CO2 detection and demand control is
now making its way into the residential market.
Atmospheric (outdoor) CO2 levels are approaching 400 parts per million (ppm). For indoor
spaces with ventilation systems, a good balance
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between economy and efficiency is between 800
and 1,000 ppm. Poorly ventilated buildings may
have CO2 levels that exceed 2,000 ppm, a level
that will cause humans to feel drowsy.
Heating and Air
many types of heating
systems available that use various fuels, as well
as very efficient central and room air conditioners.
Typically, very large heating and cooling systems
are installed in homes, and often these are
oversized in terms of their space conditioning
Heating and cooling a low-energy-use home
requires an extra degree of care in the sizing of
mechanical systems to ensure comfort and efficiency. In other words, you will not be shopping for
conventional space conditioning systems. Rather,
you want systems that efficiently deliver low quantities of space conditioning and that allow you to
modulate those levels according to the weather
and indoor comfort needs.
T o d ay t h e r e a r e
Choosing a System
When researching and selecting the best heating and/or cooling system for your home, be sure
to assess the heat requirements of the house,
installation costs, and local fuel costs (and carbon content). Get help from a professional heating contractor or energy consultant to find an
Modern, high-efficiency
furnaces and boilers are
compact enough to hang on a wall. Some new systems incorporate
space heating, water
heating, and heat recovery ventilation into a single package.4
appliance that matches the new heating and cooling requirements of your improved home, or one
that can meet your needs now and still be appropriate after your next stages of energy improvements. Following are some popular equipment
options for low-load homes.
Gas-Fired Heating
Many highly efficient homes can be effectively
heated with a wall- or floor-mounted gas space
heater or with a high-efficiency, modulating gas
furnace or boiler. These heating plants adjust
their flame to deliver varying amounts of heat to
the air or hot water circulating in baseboard or
radiant floor distribution systems. Look for efficiency ratings in the mid-90 percent range.
Heat Pumps
There are two main types of heat pumps: ground
source and air source. Ground source heat
pumps remove heat from the ground by way of
a working fluid flowing through tubes that are in
contact with the ground. The fluid goes through
a compression and evaporation cycle to extract
heat from the ground and deliver it to the house.
One advantage of a heat pump is that it can
also work in reverse and act as a space-cooling
system, removing heat from the house and transferring it to the ground. Disadvantages of ground
source heat pumps are that they are quite complex, can be costly to install, and can use quite
a lot of electricity. They are generally most effective in cooling-dominated climates, and some
studies show that in heating-dominated climates
Mini-split air-source
system, showing
outdoor unit and indoor
unit with line set. Several indoor units
(evaporators) can
be operated from a
single outdoor unit
(­ compressor).
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S e n s i b l e H e at a n d L at e n t H e at
Air conditioning obviously helps
to manage summer heat,
sometimes referred to as “sensible” heat. Another important
function of air conditioning is
to control humidity, or “latent”
heat (heat held in water vapor).
Proper equipment sizing (in sensible Btus per hour), along with
a sensible heat fraction (SHF)
that matches your climate’s
humidity, will help to ensure efficiency and comfort.
SHF is a measure of the percentage of an air conditioner’s
total capacity that is available to remove sensible heat
from the air. This value ranges
from 0 to 1 (typical between
0.5 and 1.0). The remaining
capacity is available for the
removal from the air of moisture (in which the latent heat
is contained). When selecting
cooling equipment in humid
regions, knowing the SHF will
the actual efficiencies are somewhat less than
rated levels.
Air-source heat pumps can be efficient and versatile for both heating and cooling a home. They
operate by transferring, or pumping, heat between
indoor and outdoor air. Sometimes called “minisplits” or “ductless mini-splits,” these units are
similar in operation to central air conditioners,
but they do not use ductwork to deliver the conditioned air. Instead, one or more indoor units are
connected (via a refrigerant line set) to a single
outdoor unit. This setup allows for different temperature zones within the house. The absence of
ductwork eliminates the problem of leaky ducts,
a potentially large loss of energy.
Other Heating and Cooling Options
Additional options to consider for heating include
cordwood wood stoves, pellet boilers or stoves,
and masonry heaters. These options require
more frequent attention by the owner than automatic, fossil fuel systems.
Evaporative coolers work well in dry climates
by taking advantage of the same principle that our
bodies use to remove excess heat by sweating.
Evaporating water absorbs and dissipates heat
energy. When it’s humid, moisture can’t evaporate
from our skin, and we feel hot and sticky. In hot,
dry climates, moisture added to the air evaporates, absorbing heat energy and cooling the surrounding air in the process.
help you choose a system that
will properly cool and dehumidify your home. Work with
a knowledgeable contractor to
understand the regional recommendations for air conditioner
ratings. Generally, the higher
the efficiency, the higher the
SHF. Unfortunately, this means
that the highest-efficiency air
conditioners may not do a good
job of dehumidification in a
very humid region.
Evaporative coolers are sometimes called
“swamp coolers” because they use a steady
supply of water to cool the air while also making it more humid. Evaporative cooling equipment
requires no compressor and therefore consumes
much less electricity than a conventional air conditioner. Though not as effective as conventional
air conditioners, swamp coolers can provide sufficient comfort under the right conditions. Because
they rely on the evaporation of moisture, they
work only in dry climates where relative humidity
levels are below 40 percent.
More novel approaches to cooling very efficient
homes include a ground coupling system, where
fluid is circulated in underground pipes and then
through a “fan coil” (something like a car radiator) that lives inside the ductwork of a space
conditioning or ventilation system. Air blows over
the cool coil and delivers cool air to the house.
Another innovative system, called the NightBreeze
(see Resources), allows you to use cool nighttime
air to ventilate your home at night through a balanced ventilation distribution system.
Such systems can be found by exploring the
cutting-edge work being done to promote the
Passive House Institute U.S. efficiency standard, which primarily addresses new homes (see
Resources). This extremely efficient standard
has taken a strong foothold in Europe and is just
beginning to gain traction in the United States.
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Hot Water
DER may include getting your
house renewable-ready for a solar hot water system.
The basic efficiency improvements to start with
are getting the most efficient water heater, using
less hot water, and modifying your behavior around
waiting for hot water (see pages 44 and 45).
Here are some other equipment options for
highly efficient hot water heating:
Heat pump water heaters extract heat from
the surrounding air and “pump” it into the water,
much as a refrigerator removes heat from the
air inside its compartment and pumps it out into
the room. These systems have a coefficient of
performance (COP) of over 2, meaning that they
deliver twice as much heating energy to the water
when compared to the electrical energy required
to operate the heat pump. Because they remove
heat from the surrounding area, they also help
cool the room they are in.
Condensing water heaters are very efficient at getting every last bit of energy out of
natural or propane gas and converting it to hot
water. They have efficiencies in the mid- to upper
90-percent range.
On-demand water heaters, especially condensing models, can be extremely efficient when
used conscientiously. For example, if you need
Pa r t o f y o u r
only a small amount of hot water, you’re better
off using cold instead. This is because it takes a
minute or two for the heater to heat the water and
another minute to get it to the tap. If you shut off
the faucet right away, any unused heated water
ends up sitting and cooling in the pipes. An ondemand heater can also make it tempting to take
longer showers because the hot water will not run
out as with a conventional tank heater.
Drain water heat recover y system
(DWHR). When you shower, the water temperature is somewhere around 104°F. The heat contained in the water is used only briefly before going
down the drain. A DWHR device (see Resources)
allows you to capture that waste heat and reuse
it. The system consists of a length of copper drainpipe wrapped with a long coil of 1/2" copper plumbing supply pipe. Cold water is fed into one end of
the coiled pipe. As warm water travels down the
drainpipe, it warms the water in the supply coil,
and this preheated water is routed to the coldwater inlet of the hot water heater.
Smart Plumbing
A significant challenge in hot water efficiency lies
in transporting the heated water from the heat
source to the point of use (the fixture). Long or
indirect runs of pipe can sap a lot of heat from
the water, especially when the piping passes
through unheated areas, like basements and
crawlspaces, or within exterior walls. Here are a
few ways to minimize this energy penalty:
• Insulate all pipes with appropriately sized
foam pipe insulation.
Drain water heat
recovery system4
• Install direct plumbing runs from the water
heater to the fixtures (sometimes called
“home-run” plumbing).
• Plan the layout of plumbing runs so that all
(or most) rooms with hot water are backto-back or stacked. This keeps plumbing
fixtures close together for an efficient pipe
layout, with the water heater central to the
fixture locations.
• Use smaller pipe diameters, as appropriate,
to get water to fixtures more quickly.
cold in
drain out
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Home Energy
hile you’re probably already in the habit of tracking household
energy costs, prices change over time. A more meaningful and precise
indicator of energy use is consumption: how many units of energy you
use over a given period of time. You want to understand your usage in terms of kilowatt-hours, therms, cubic feet, gallons, pounds, or cords; you want to know how much
of each fuel you use and when. With this knowledge you can begin to see why you use
what you do and then make a plan of action to save.
The specifics of how you monitor your home’s energy use depends on the fuel
you want to measure, how much detail you want, how you will use the information
you gather, and your budget. The information you get from monitoring your energy
use can be invaluable in discovering energy wasters in your home and identifying
savings solutions.
This chapter introduces you to some of the popular products and approaches to
real-time energy monitoring and data logging. Keep in mind that this is a dynamic,
emerging market, and there are many additional options out there, as well as smartgrid products and applications used by electric utility companies.
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Electric Energy
T h r o u g h t h e h e l p of technology (and perhaps
your electric company, if the “smart grid” has come
to your neighborhood), you can monitor energy use
by the minute, day, week, month, or year. You can
look at whole-house information or just the use
of a single appliance. By far the most advanced
and user-friendly home-based energy monitoring
technology has been applied to electrical usage.
There are easy-to-use products for monitoring
electricity at the appliance (point of use or plugload) level and at the whole-house level.
Point-of-Use Monitoring
As discussed briefly on page 40, plug-in electric meters, such as the Kill A Watt and Watts
Up? (see Resources for chapter 2), have become
affordable and widely available. With these
devices you can record how much power (in watts)
an individual appliance is using in real time, as
well as how much energy (in kilowatt-hours) it
uses over a period of time.
There are even some power strips available
that let you monitor the electric use of everything
plugged into them, such as your home office
equipment or entertainment center. With this
information you can discover the most efficient
5A plug-in wattmeter records electrical energy used over
time, allowing you to evaluate consumption and cost.
operating modes of various plug-in appliances
and electronic equipment as well as determine
whether or not a more efficient appliance would
be cost-effective.
These meters accumulate the data and report
the electrical consumption over time in kilowatthours so that (with a little programming of the
meter) you can see how much that appliance is
costing you. The power draw of some appliances
varies depending upon what that appliance is
doing. For example, a refrigerator has a compressor and fans that cycle on and off, and periodically enters into defrost mode. Each of these
modes has a different power requirement. If you
want to know the energy consumption of a refrigerator, or anything else that cycles on and off, a
plug-in meter that measures kilowatt-hours offers
the most accurate reading.
You can sort out nearly all the electrical use
in your house with great specificity by moving a
point-of-use meter from one appliance to the next,
making notes, and adding things up. However,
one limitation of plug-in meters is that they are
limited to 120-volt appliances; they won’t work
with 240-volt appliances, such as electric clothes
dryers or water heaters.
Electrical Meters
Whole-house electrical meters measure and monitor real-time electric usage and report the information to a remote display that can be brought
to any room in the house. This allows you to see
how much power your entire home is using in real
time, as well as the immediate effects of your
conservation efforts.
One meter, the Power Cost Monitor (see
Resources), uses an optical sensor that attaches
to the outside of the utility’s electrical meter and
transmits data wirelessly to the display monitor indoors. Another, The Energy Detective (see
Resources), uses a current sensor attached to
the home’s electrical panel to sense the real-time
power consumption and uses the home’s electrical
wiring to transmit data to a wireless transmitter.
From there, the energy use information is sent to
a handheld display, computer, or smartphone.
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5Whole-house electrical monitors. Power Cost Monitor
(above) with outdoor sensor attached to meter, and
indoor monitor. The Energy Detective (below) with
transmitting unit and current sensors.6
monitoring and identifying savings opportunities
in the home. A current sensor is attached to each
wire in the main circuit breaker box, and each
sensor is connected to the monitor. The monitor
is connected to a router and sends data to the
company’s server, allowing you to view real-time
data on a Web browser.
If you have a renewable power system, the
eMonitor will display power production as well
as consumption. The monitor device has a very
basic display on the unit itself, but the Web-based
information center, or “dashboard,” offers many
layers of information. In addition, the system
allows you to view power use remotely and control
wireless electronic thermostats via a smartphone
app. A similar product called Agilewaves is made
by Serious Energy (see Resources).
Circuit-Level Monitoring
The eMonitor (see Resources) senses the electrical use of each individual circuit in your home so
that you can get a better idea of exactly how much
power is used and where. Circuit-level metering
takes a lot of the guesswork out of energy-use
5Web-based circuit-level energy monitor
iRemote Monitoring and Controli
Some whole-house monitors have the ability to extend monitoring and control to individual appliances
by interfacing with home automation and control software, often using the ZigBee Alliance wireless
communication standard (see Resources). A review of the ZigBee website will give you an idea of the
growing number and variety of products available for home automation, energy management, and
control. In addition, many information products have matching smartphone applications that allow
you to monitor and manage energy use from afar. See Resources for more products and companies
leading the way in the industry. For example, the folks at Plot Watt and Bidgely seek to take the
perceived nerdiness and complexity out of home energy monitoring.
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Gas Monitoring
propane gas use
is somewhat less user-friendly than electrical
monitoring. This is primarily because metering
gas usage for each appliance involves cutting the
gas supply line for that appliance and installing a
dedicated meter with a dial or pulse output.
For example, Itron (see Resources) manufactures various sizes of gas meters with integrated pulse output modules. Every turn of the
meter dial produces an electrical pulse that can
be captured, counted, and electronically manipulated, and the results can be displayed graphically on a dashboard or on a spreadsheet. There
are ultrasonic meter products that simply clamp
onto gas supply lines, but currently these are
quite costly.
For accurate metering of a specific gas appliance in your home, you can use a pulse-enabled
gas meter in conjunction with a pulse data collection logger. Many different kinds of sensors and
data loggers are available from data logging product manufacturers, such as Onset, Omega Engineering, and Campbell Scientific (see Resources).
M o n i t o r i n g n at u r a l o r
Reading Your Gas and
Electric Meters
Electric and natural gas utilities provide you with
a service meter that you can learn to use for
monitoring the various appliances in your home.
Contact your utility if you need help deciphering
dials and numbers, and the quantity of energy
each spin of the dial represents. Using gas as
an example, the concept is simple: Inventory all
the gas appliances in your home, and understand
what makes them turn on and off. Then turn off
all of the appliances. Read the gas meter’s dials
to get a starting point, then turn on the one gas
appliance you wish to monitor.
For example, if you want to know how much
gas your clothes dryer uses, make sure that the
heat (furnace, boiler, etc.) and hot water heater
are turned off, and don’t cook during the test.
Don’t worry about the pilot lights still being on;
they use a negligible amount of gas. Now, operate the clothes dryer, and when it’s finished,
read the gas meter again. Subtract the initial
reading from the final, and the result is the gas
consumption of drying a load of clothes. If the
meter reads in cubic feet, and the dryer used 30
cubic feet, you’ve used 30,000 Btus of gas (there
are approximately 1,000 Btus in a cubic foot of
natural gas). Multiply this by the number of dryer
loads you do each month, and that’s your total
Btu energy consumption for that appliance. Unfortunately, many gas meters read in increments of
100 cubic feet, so you might need to lengthen the
duration of the test.
Finally, you need to know how your gas company bills you. It charges for gas by volume (in
cubic feet, hundreds of cubic feet, or thousands
of cubic feet) or energy content (therms or Btus).
Once you know how many Btus are in one billable
unit of gas, a little more math will show how much
each dryer load costs. You can follow this routine
for any gas appliance in your home, or use the
disaggregation methodology described in chapter
2. This same approach works equally well with
electric meters.
Bottled Gas
If you use bottled gas, typically there is no meter
involved. Your only clue may be the percentfull gauge on the tank, and that’s not accurate
enough for the metering method described above.
If you’re determined to monitor bottled gas consumption, you can have a whole-house gas meter
installed for a few hundred dollars.
both indoor and outdoor
environments for any number of parameters.
Sensors are available to measure temperature,
humidity, water flow, rainfall, wind speed, solar
radiation, carbon dioxide, and volatile organic
compound levels, to name a few. You can assemble
a weather-monitoring station and integrate it with
your home energy data through products and
services from companies like Rainwise, APRS
World, and PowerWise Systems (see Resources).
Yo u ca n m o n i t o r
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Calculating Heating
If you want to meter heating energy use, it may be
useful to evaluate heating energy consumption in
the context of weather. Your heating energy consumption will likely change from year to year, and
this might be due to changes in occupancy, behavior, equipment, or weather. Assuming everything
else is equal and the only thing that changes is
the intensity of the heating season, you can compare your energy use based on seasonal heating
degree days.
A heating degree day (HDD) is the difference
between a balance point (usually 65°F), against
which calculations are based, and the outdoor temperature. As an example, if the average temperature over the course of a day is 50°F, then that day
has accumulated 15 HDD. If it took 1 therm of
D IY H o m e E n e r g y M o n i t o r i n g
For those of you who are inclined toward hands-on
gadgetry building, there are at least two options
for you to explore. For intrepid do-it-yourselfers, the
OpenEnergyMonitor explores interfacing various
input and output modules using the Arduino microcontroller platform (see Resources).
A less intimidating option (for most of us) is
the Web Energy Logger (WEL; see Resources).
This is a versatile data logger that reads temperature sensors, wattmeters, pulse inputs, contact
closures, and analog voltage. The WEL system
connects to the Internet (via your router) where
data is uploaded, stored, and managed on the
company website. There you can view and label
data, build charts and graphs, and manipulate
information to calculate things like Btus produced
by your solar hot water system or the efficiency
of your geothermal heat pump. You can even
load your own graphics to illustrate your system
for others to view.
Third-party software developers are able to
work with product manufacturers and even DIY
system sensor outputs to develop customized and
sophisticated dashboard displays so that you can
measure, record, view, and manage any number of
connected devices and systems in your home.
5Example of a home energy and environment dashboard developed by
PowerWise Systems (
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natural gas (1 therm is equal to 100,000 Btus) to
keep your house warm that day, the house has a
heating energy intensity of 6,667 Btus per HDD
(100,000 Btus ÷ 15 HDD). If you live in a climate
with a total of 5,000 HDD per heating season,
you can expect to use about 33 million Btus of
heating fuel each season (6,667 Btus x 5,000
HDD). If your gas company bills you in therms,
this translates to about 330 therms of natural
gas (33,000,000 ÷ 100,000) over the course of
the heating season.
In reality, there are many variables to all of this
fussing with numbers. Ultimately, if you want to
manage your energy use, you need to measure it;
otherwise, you’re just guessing. For example, the
heating energy intensity as described above will
increase as the outdoor temperature decreases
because your house will lose heat faster when the
temperature difference is greater.
Another potentially large variable is “internal
gains,” or how many heat-generating people and
appliances are in your home. Add this to the solar
heat gain you get through your windows, and you
may not even turn on your heat until it’s 50°F or
lower outside. You can find local weather HDD
data online at the Weather Underground and
Degree Days websites (see Resources).
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clo s e - up
My Hot Water Heating Story
u r 4 - k W s o l a r electric system keeps 50 kWh of batteries charged quite well when the sun shines,
with wind energy often picking up the slack when it doesn’t. Solar power generation is monitored through
the Outback Power MX80 charge controller, and wind data is collected with an anemometer feeding an NRG
Systems data logger. Happily, when we compare annual power production graphs of both solar and wind, they are nearly
mirror images, with wind providing more power in the winter and sun taking over in the summer.
M y Ex p e r i e n c e
I live off the grid with my
family, using solar and
wind for electricity, and
wood for heat. We have a
backup diesel generator
(often it’s biodiesel) for
those occasions when
the sun doesn’t shine
and the wind doesn’t
blow. My family uses
about 7 kWh a day, with
each electrical circuit
monitored through a
Powerhouse Dynamics
eMonitor (see Resources
for this and other
products mentioned).
Last summer, shortly after feeling quite
smug about having an electricity surplus,
I received a propane bill for over $1,000.
Most of that propane is used to heat water,
while some is used for cooking and some
as a source of backup heat if we’re away
from the house in the winter and can’t load
the wood stove. This presented a challenge
that I could not resist: how to get off the
propane “grid.” I knew that part of the
answer was efficiency and conservation, and
part lay in harnessing excess summertime
solar electricity production — at least for
now. Conventional solar hot water is not a
practical option for us due to the distance
between the water heater and a shade-free
place for the solar collectors.
To reduce hot water energy use, I
took out my 10-year-old, 40-gallon, sealedcombustion propane gas water heater (which
has an efficiency factor, or EF, of 0.59) and
replaced it with a Navien NR180 on-demand,
condensing propane water heater with an
EF of 0.98. Since most of our hot water is
used for showers, I also installed a GFX
(gravity film heat exchanger) drain water
heat recovery system (DWHR). I was thrilled
to put my hand on the coil and feel the 20°F
temperature rise in the water circulating
through it. Now the cold water entering the
Integrated water heating system incorporating
DWHR, on-demand water
heater, and solar electric
pre-heat option when
enough sun is available 
On-demand water heater heats water only
if incoming water is not hot enough
Hot water out
to faucets
Pre-heated water from
electric water heater
Preheated cold water
enters water heater
Electric heating elements
are used as dump load,
diverting solar power to
heat water when batteries
are full
supply feeding
water heater is
preheated by drain
Cooled drain water
M y hot water heating story 101
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c lo s e - up
My Hot Water Heating Story
Last summer, I
received a propane bill for over
$1,000. Most of
that propane is
used to heat water.
This presented a
challenge that I
could not resist:
how to get off the
propane “grid.”
water heater is about 70°F instead of 50°F,
saving on water-heating fuel use.
But I didn’t stop there. I did something I
would not necessarily recommend for anyone
else, simply because it is not terribly costeffective. However, in my case (off-grid with
too much power production) the numbers
worked a little bit differently, and it was in
fact quite cost-effective. Admittedly, I will do
things that get me off the fossil fuel mainline
even if they aren’t cost-effective — I can’t
help myself, I’m just wired that way, and I
won’t try to talk anybody into trying this at
home. But for those of you who are curious,
here’s how it went:
I needed a “dump load” for excess elec­
tricity generation. I considered a ductless,
mini-split air source heat pump for space
conditioning, but decided against it because
most of my excess power comes in the
summer. It doesn’t really get too hot here
in New England, so I didn’t need the cooling
benefit — I needed heat.
I also considered a heat pump water
heater (HPWH), but my off-grid power system
limits me to 120 volts, and the HPWH requires
240 volts. Also, HPWHs are a bit loud, and
since I don’t have a basement I wanted
something quiet. So I bought the most
efficient electric hot water heater I could find,
a 40-gallon Marathon, and swapped out the
240-volt heating elements with elements from
HotWatt (see Resources for this and other
products) that were suitable for use with the
48-volt battery bank that would now provide
electricity to heat water in the Marathon.
Marathon water heaters are not exactly
conventional, and I needed to have a couple
of bushings custom-machined to accept the
replacement heating elements. (Of course, the
lifetime warranty on the unit is now void.)
Finally, I put together a control system
that uses a signal from the solar charge
controller. This activates a solid-state relay
that connects the battery bank’s DC voltage
to the water heating elements once the
batteries are fully charged. Excess electricity
is automatically diverted to heat the stored
water in the Marathon heater.
Did I say finally? Since I know how much
propane gas I’ve used for the past 15 years,
and I will of course want to see the effects of
the changes I’ve made, the only choice (really,
it couldn’t be helped) was to install a data
monitoring system. This is not such a difficult
or expensive thing anymore with high-speed
Internet, nearly free online data storage, and
some neat innovative tech products.
An Itron gas meter with a pulse output
allows me to monitor how much gas is being
used in the home. In addition to the dials and
numbers indicating rate and quantity of use,
the meter delivers one electronic pulse for
every cubic foot of propane moving through it.
Cooking energy is almost negligible, so most
of the gas used in summertime is for water
heating. Therefore, I can establish a baseline
to which I add winter gas consumption
to determine the propane room heater’s
To monitor how much hot water the
family is using, I installed an Omega in-line
water meter with a pulse output. Half a dozen
temperature sensors complete the water
monitor sensor array. All these sensors are
plugged into a WEL (Web Energy Logger) data
logger that uses a Web interface, which allows
the user to see real-time and cumulative
data on a computer or smartphone. This
combination of monitoring devices allows
me to see how much, and when, gas and hot
water are being used. I can also determine the
energy contribution (in Btus) of the DWHR and
solar backup system.
The result is that we use about one-half of
the amount of gas we did before this retrofit,
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w e l t em p e r at u r e g r a p h : d h w s y s t em t em p s
• The cold water inlet temperature is 47°F,
represented by the gray line.
• Cold water feeds into the DWHR coil, and
you can see that the water temperature
drops as the water starts to flow through
the coil (it had warmed to the ambient
room temperature).
• The water is warmed in the coil by
shower water going down the drain. The
preheated water leaving the DWHR coil,
represented by the dark blue line, is 67°F.
• The outlet of the coil feeds the cold
water inlet of the storage tank, which
also serves as a dump load for excess
solar electric power. There was no solarpreheated hot water at this time.
• The light blue line shows the temperature
of the water leaving the storage tank and
entering the on-demand water heater:
66°F. Without any electricity supplying the
heating elements in the storage tank, the
temperature remains relatively constant
in the tank as the cold water inlet is fed
with water preheated by the DWHR unit.
• The black line indicates the temperature
of the water coming out of the on-
DWHR outlet temp
Hot water temp
Cold water temp
Tempered water temp
and even less during long sunny stretches
when the sun provides most of our hot water.
The financial payback is under 7 years, but
in terms of satisfaction, the payback was
immediate. On a sunny day, the batteries are
charged before noon and the water overheats
before dinner. It's nice to see the electrons
going to good use. I may soon be looking for
a dump load for excess hot water. Hot tub,
The graph at right, generated by the Web
Energy Logger, shows the hot water system
temperatures during a shower, with a DWHR
unit placed in the shower drain. Here’s how to
interpret the data:
History in Hours. 1 Min. samples
Hot water system
temperature graph
generated by the
Web Energy Logger
demand water heater and feeding
the shower as 114°F.
The WEL captures data at one-minute intervals
and can be downloaded to a spreadsheet for
further analysis. In this case, I was able to
determine that an 11-minute shower used
15.4 gallons of water and 0.11 gallons of
liquid propane gas. Propane gas contains
about 91,500 Btus per gallon, so my water
heating system requires 659 Btus to heat
one gallon of water. At $3.50 per gallon for
propane, each shower is costing me $0.385
in propane, plus the cost of a small amount of
power to run the water well pump. Since I know
my showerhead’s flow rate is 1.75 gallons per
minute, I’ve used just over 19 gallons for the
shower. To calculate the percentage of hot and
cold water is fairly straightforward:
15.4 gallons ÷ 11 minutes =
1.40 gallons per minute of hot water
So, hot water makes up 80 percent of the
water in the shower. (See another formula
for this on page 45.) This discussion could
go on for a very long time in many interesting
ways, but this should be enough to give you
the idea of the power of data collection and
The result is that
we use about
one-half of the
amount of gas we
did before this
retrofit, and even
less during long
sunny stretches
when the sun
provides most of
our hot water.
The financial payback is under
7 years, but in
terms of satisfaction, the payback
was immediate.
my hot water heating story 103
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Par t T wo
R enewable
E nergy
n c e yo u ’ v e t u r n e d your home into a comfortable, energy-sipping dwelling, it’s time to invest in renewables to offset a portion of your now smaller energy bill.
This section can help you to understand the opportunities you have
to generate energy for your home. When you’ve passed the decisionmaking, technical, and cost hurdles, living with renewable energy
becomes part of a lifestyle that involves a keen awareness of the
availability of those resources. Before you know it, you’ll be predicting the weather and looking at your garbage (and coveting your
neighbor’s garbage) as valuable energy sources. You’ll also find yourself taking advantage of times of abundance while conserving when
resource availability is low.
The value of producing your own energy goes way beyond dollar
savings and leads you to a place of empowerment, to a place where
you can actually take matters into your own hands and meet a good
part of your household needs without assistance from the energy
industry. Start slow, start small, gather parts and information. Think
about your energy future. Then take action.
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Hot Water
e at f r o m t h e sun can be used to heat water for your showers or
swimming pool, or to provide heat for your house. To be clear, solar thermal energy is an altogether different technology than solar electric power
(discussed in the next chapter), in which light from the sun is converted into electricity.
Using the sun is the easiest way to gain and use free heat and can be very costeffective. ­Simply leaving a garden hose out in the sun can provide useful hot water;
from there, it’s not such a big step to moving and storing that water with a simple
controller and a small pump. This chapter provides an overview of solar thermal systems for water heating.
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Types of Systems
water systems can
have many different configurations, depending
primarily on the climate, how much hot water
is needed, and when it’s needed. All systems
have one or more collectors (the “panels”
where the water is heated) and a storage
vessel that holds the heated water. The
stored water can be used directly, or it can be
delivered to a secondary water heater to boost
the temperature before use.
S o l a r t h e r ma l h o t
hot water
return (hot)
storage tank
cold water
supply (cold)
5Passive solar water-heater layout taking advantage of a
thermosiphon’s pumping action to move hot water from
collectors up to the storage tank. Hot water is less dense
than cold and naturally moves upward, while cooler, denser water sinks to the lowest level. The liquid in the
collectors and storage tank can be water or a working
storage tank is in the basement and the collectors
are on the roof. In this situation, hot water stored
in a tank in the basement will naturally want to
thermosiphon up to the collectors on the roof when
the collectors are cool. Unwanted thermosiphoning
must be stopped with a check valve in the plumbing, ensuring that water flows in only one direction.
Active Systems
Active systems use the sun’s heat to warm a
fluid in the collector, and the fluid is moved by a
pump so that the heat in the fluid can be used or
stored. Pumps are turned on and off by a controller that responds to the temperatures at the collectors and the storage tank. Active systems can
be directly or indirectly heated.
In a direct system, the water that’s heated in
the collectors is the same water you use at the
faucet, and it’s pumped between the storage tank
and collectors. Also called “open-loop” systems,
these are often used in climates where freezing temperatures are not a concern. Hard water
can be problematic for directly heated systems
because minerals in hard water build up on hot
surfaces, restricting or even stopping water flow.
In such cases, a water softener is used to reduce
mineral content in the water supply.
Passive Solar
Passive solar thermal can be described as simply allowing the sun to heat something. It could
be heating the air and floor in your living room, or
water held in a black barrel outside. A passive hot
water heating system often relies on a naturally
induced thermosiphon to transport heated fluid
between a solar collector and a water storage tank.
A thermosiphon requires a temperature difference to work: Hotter fluid (being less dense and
therefore more buoyant) will rise to the top of the
system, while cooler fluid is moved toward the
bottom of the system. This means that the storage tank must be at a higher elevation than the
collectors, since the collectors will be hotter than
the storage tank when the sun is out and you
want hotter fluid to move upward into the tank.
In practice, thermosiphon systems are somewhat uncommon, because typically the water
hot out
cold in
3Water heated in the
collectors is the same water used at
the faucets.
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Examples of directly heated systems include
integrated collector storage (see page 110) and
drain-down systems, where water is drained out
of the collectors at night and pumped back into
the collectors when solar energy is available.
With an indirect system, a heat transfer fluid,
or “working fluid,” is heated in the collectors and
circulated passively or actively in a closed loop
between the collectors and a heat exchanger. In a
separate loop, water that will be used at the faucets is circulated between the heat exchanger and
the hot water storage tank, taking heat away from
the working fluid in the heat exchange process.
Indirect systems are common in cold climates,
where the working fluid is an antifreeze solution.
Examples of indirectly heated systems include
active systems with antifreeze, and drainback
systems, where the working fluid (either distilled
water or antifreeze) is drained out of the collectors once the desired temperature is reached in
the storage tank. This prevents overheating and
deterioration of the working fluid caused by stagnation of the fluid. Stagnation occurs when the
storage tank is hot, the controller turns the circulating pump off, and the fluid stops circulating;
however, the sun is still shining on the collectors,
causing the working fluid to get hotter and hotter,
with no place for the heat to go.
Types of Heat
The heat exchanger is where heat is transferred
between the working fluid and the water in the
storage tank. The fluids exchange heat without coming into contact with each other. Heat
exchangers can be inside of the tank or external
3Tube-in-shell (“side-
arm”) heat exchanger.
Fluid is pumped from
the collector to the
heat exchanger, but a
thermosiphon provides
the pumping action
from the bottom of
the storage tank, up
through the heat exchanger, and out to the
top of the tank.
to it. Internal heat exchangers are in contact with
the water to be heated and offer the benefit of
a simpler installation that requires only a single
pump. External heat exchangers can be either
flat plate, where fluids flow through small holes
in flat plates, with the working fluid and water in
separate internal channels; or they can be tubein-shell, or sidearm, units in which a pipe (tube)
carrying the water to be heated lives inside a
larger pipe (shell) carrying the hot working fluid.
Flat plate external heat exchangers require two
pumps — one to pump working fluid between the collectors and the heat exchanger, and another to pump
water between the heat exchanger and the tank.
Tube-in-shell heat exchangers need only one pump,
because the circulation of cold water from the bottom
of the tank, through the shell, and out to the top of
the tank relies on a thermosiphon. Using an external
heat exchanger offers the advantages of more tank
choices and of being replaceable separately from the
tank, potentially reducing maintenance costs.
fluid return to
Flat plate heat
3Simplified active,
separate fluid
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cold water
hot water
fluid loop
closed-loop solar
hot water system
with internal heat
hot fluid from
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Solar Hot Water
E f f i c i e n t l y c a p t u r i n g a s much of the
available solar resource as possible requires
the right technology, proper installation, and
intelligent design. Choose the right equipment for
your specific needs and location, and install for
maximum efficiency.
Solar thermal collectors are designed to absorb
as much of the sun’s heat energy as possible and
transfer the heat to a liquid, heating it to 180°F or
more, depending on the available solar energy and
type of collectors. Collectors are ideally installed
on a shade-free roof or ground rack, facing within
30 degrees of south. More easterly or westerly orientations may be acceptable but will require more
collector area to meet the hot water demand.
The tilt angle of the collectors (the slope at
which they’re positioned) is set according to the
season that provides the best performance. For
example, if it’s always cloudy in your region during
the winter, you won’t have much production then,
so it might be best to set the tilt angle to maximize summer production. This may sound counterintuitive: Why not tilt the panels so that you
can gain more in the winter and maximize what
little sun there is? But the general rule is this:
Increasing a small amount of energy by a small
percentage will not amount to much, so focus
your efforts on where the energy is rather than
where it is not.
There are three common types of collectors —
flat plate, evacuated tube, and integrated collector storage (ICS) — any of which can be part of
either an active or passive system. Choosing the
best collector depends primarily on your climate
and how you will use the hot water.
Flat Plate Collectors
Flat plate collectors are insulated boxes covered
with low-iron, tempered, textured glass that provides a durable, highly transparent and absorptive solar window. Inside the box, to absorb solar
heat, are flat, dark-colored (usually nickel-plated)
copper plates to which copper tubes are fused.
The heat transfer fluid flows through the tubes,
bottom manifold
riser tubes
tempered glass cover
absorber plate
insulation on bottom
top manifold
3Flat plate collector,
cutaway view
removing heat from the absorber plates along the
way. Flat plate collectors are simple and compact
(typically measuring 4 x 8 feet or 4 x 10 feet and
several inches thick), and multiple units can be
plumbed together to increase the collector surface area. As they heat up, flat plate collectors
lose efficiency because they lose heat to the surrounding environment.
Evacuated Tube
Evacuated tube collectors do not hold fluid in the
same way as other collectors. They consist of a
series of annealed glass tubes, each covered with
a selective coating that absorbs solar energy while
inhibiting reradiation heat loss. During manufacture, air is evacuated from the tubes to create
a vacuum; like a Thermos, this eliminates conductive and convective heat loss. In the center of
each tube is a copper absorber plate.
From here, there are several variations on
the specifics of getting heat out of the tube and
into the working fluid. Often there is a heat pipe
attached to the center of the absorber plate.
This pipe contains a liquid that vaporizes when
heated, rising to a metal bulb at the top of the
tube. The bulb is immersed in the working fluid in
a header that is common to multiple tubes. Working fluid flows through the header, absorbing heat
from the hot bulbs along the way. This cools the
bulbs and condenses the fluid in them, allowing
it to flow down to the bottom of the heat pipe to
be heated and vaporized again.
The size of evacuated tube collectors is easy
to customize because each tube is separate, and
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ICS collector,
cutaway view
hot working fluid out
storage tank
cold working
fluid in
Evacuated tube
collector, cutaway
heat pipe
cutaway view of absorber plate inside evacuated tube
insulated box
with clear cover
hot out
cold in
heat exchanger
you can add tubes to the header to increase the
collection area, up to the maximum number of
tubes the header can hold. Evacuated tube collectors offer several potential advantages over
flat plate collectors; they are:
• Modular and lightweight
• Less sensitive to orientation
• Provide potentially hotter water (making them
a good choice for space heating)
• Tend to be more efficient in very cold
• Don’t reradiate heat
However, evacuated tubes are more fragile
than flat plate collectors, and they don’t shed
snow as well because they don’t reradiate their
heat. The vacuum in the tubes is a great virtue
but also a great liability because it’s difficult to
maintain a vacuum forever in the real world — so
look for a long warranty.
Integrated Collector
Storage (ICS)
ICS systems, sometimes called “batch” heaters,
heat a batch of water in a storage tank inside of
an insulated box with a clear cover. These simple systems heat the water to be used directly,
as cold water flows in and hot flows out, feeding
the faucets or another water heater used as a
backup. They are used in situations where there
5Indirect ICS with separate collection and storage
is no danger of freezing and are most effective if
hot water is needed primarily in the evening, after
the sun has had time to warm a large volume of
water. ICS systems are heavy, due to the weight of
the water they contain, and sturdy mounting structures are mandatory. One efficiency disadvantage
is that heat is lost from the water at night.
A variation on ICS integrates evacuated tube
collectors into an insulated water (or other working fluid) storage tank. A heat exchange coil is
immersed in the working fluid, through which the
water to be heated flows, making this an indirectly heated ICS.
Solar Collector
Solar hot water collectors are rated for thermal
output in terms of Btus per square foot per day.
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You can get this information from the manufacturer or from the Solar Rating and Certification
Corporation (SRCC). This nonprofit, independent,
third-party organization (formed by the solar industry, state energy officials, and consumer advocates) exists to certify and rate solar hot water
equipment. Performance is listed in a directory
published on the SRCC website (see Resources).
Note that a certified collector carries the SRCC
OG-100 label, while certified water-heating systems carry the SRCC OG-300 label. These certifications offer a level playing field for comparing the relative performance of collectors and
systems but may not predict actual performance
on your rooftop. Think of the ratings like the fuel
economy ratings for cars.
While you may be attracted to the most efficient collector, a more important factor is how
well the system will perform to meet your needs
in your specific situation and application. This
requires looking closely at the performance characteristics of various collectors.
Hot Water Storage
heater is typically set up as a
way to preheat water and deliver it to a secondary
(backup) electric or fossil-fueled heater to boost
the water to the desired temperature. The storage
tank for the solar-heated water can be the same
tank as the secondary heater, or a separate tank
can be used to provide greater storage volume.
A s o l a r wat e r
3Simplified view of an
active solar water
heater with collector
on roof, storage tank
in basement, and an
on-demand gas water
heater to boost the
temperature when
Typical storage capacity can range from 40 to
120 gallons for domestic hot water use (water
used at faucets, showers, and other fixtures or
hot water–consuming appliances) and 500 gallons or more for space-heating systems. The
appropriate storage capacity depends on collector output and hot water demand. Storage tanks
can be made of steel or fiberglass. Be sure the
tank comes with ample insulation, or add more to
the outside to keep the heat in.
Single- vs. Two-Tank
Whether or not you use a single water heater —
one that both stores solar heat and has an additional heat source — depends in part on your
So l a r P oo l H e a t e r s
Pool heating is the most popular application
of solar water heating. Pool heating collectors
are made of chemical-resistant, copolymer
black plastic with a header on each end, and
an absorber plate with integrated riser tubes
in between. Pool water is circulated directly
through the collectors. These simple and
inexpensive collectors perform well for their
intended purpose but are not designed for
freezing conditions.
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hot water usage patterns. A single tank may save
space and money, but you can use up all your
solar-heated water after the sun goes down, and
then the backup heat source will engage to heat
the water in the tank. In the morning, when the
sun comes out, the hot water produced in the collector will have nowhere to go.
With a two-tank system, the collectors heat the
water in a solar storage tank, which in turn feeds
a backup (fossil fuel or electric) water heater
with preheated solar hot water. The backup water
heater turns on when water is not hot enough. In
a strange twist of the right actions yielding the
wrong results, some research has shown that
where a two-tank system is used in a very efficient household, not much water is drawn from
the solar storage tank into the backup tank,
causing most of the water to be heated by the
backup heater. If this is your situation, a pump
can be used to circulate solar-heated water to the
backup tank depending on the water temperature
in each tank.
Hot Water on Demand
An on-demand (tankless) water heater can be a
good option to use in conjunction with solar hot
water. It’s important that the water heater has
an adjustable, or “modulating,” flame that can
change its heat output in response to the incoming water temperature. With the right tankless
model, there will be no additional heating energy
used if the incoming solar-heated water is hot
enough. When the solar water is not hot enough,
the on-demand unit will supply just enough heat
to bring it up to the set temperature.
Additional System
the collectors and storage
tank(s), a solar hot water system requires “balance
of system” components to make everything work
correctly and effectively. It’s important to note
that a quality installation is critical to ensuring
In addition to
the system performs as intended with minimal
maintenance over the long run.
Working Fluids
Working fluids include water (in direct systems)
and nontoxic antifreeze, such as propylene glycol solution rated for high-temperature (for indirect systems where freezing is a concern). Fluids
leak, and propylene glycol will deteriorate over
time, becoming more acidic with age and, if subjected to high temperatures, it stagnates. If the
fluid doesn’t stagnate, it should last for 10 to 15
years. Stagnation and deterioration are minimized
by allowing the antifreeze to circulate continually
when the sun is out; this requires having enough
storage capacity to accept the heat and thus not
overheat the working fluid in the collectors.
Collectors overheat when the water heater is
hot enough and the circulator pump stops operating while the sun is still shining on the collectors.
It is extremely important to remove all air from
the system when it’s being filled, or “charged,”
with working fluid, and to prevent air from getting
into the system. Air in the system can cause fluid
circulation problems that prevent the system from
Plumbing pipes should be copper for the hot
water leaving the collectors but can be PEX for
the cool water return. Avoid connecting PEX
directly to the collector; use copper pipe instead.
Some installers avoid PEX altogether because
it softens when heated. Don’t forget to insulate
the pipes with high-temperature–rated insulation,
such as fiberglass or Armaflex (see Resources),
and cover all exterior insulation with a PVC or aluminum jacket to protect it from UV radiation and
other environmental hazards.
Expansion Tank
An expansion tank contains an expandable air
bladder that responds to, and compensates for,
pressure changes in the collector loop as water
(or working fluid) alternately heats and expands,
then cools and contracts. The air inside the
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expansion tank compresses as pressure in the
system increases with temperature.
Without an expansion tank, pressure inside the
system would get too high, causing something to
burst. The size of the expansion tank depends on
the quantity and thermal expansion properties of
the working fluid, as well as the temperatures the
fluid will reach.
solar electric panel for
pump power
3Differential control-
Pumps can be AC (standard household current) or
DC (battery or solar-powered current), and should
be made of brass, bronze, or stainless steel suitable for high temperatures.
The pump size and required flow rate depends
on the collector area and the plumbing layout,
and must be sized according to system design.
As an example, flow rate through flat plate collectors typically is around one gallon per minute for
each 4 x 8-foot collector.
Some DC pumps (such as the Laing D5 series
and those made by El Cid, which are available
from plumbing suppliers or solar dealers) can
be powered directly from a small solar electric
panel mounted next to the solar thermal collectors. When the sun shines, the pump turns on
and moves fluid through the collectors. This is a
very simple and elegant solution to pump control
because if it’s sunny enough to make electricity to
operate the pump, it’s sunny enough to make hot
water. This approach also addresses the problem
of power grid failure, when an AC pump will stop
working. No circulation on a sunny day means
no hot water collection, leading to collector fluid
stagnation, overheating, and deterioration.
A controller is used with active systems to turn
the circulating pump on and off depending upon
the relative temperatures of the collectors and
storage tank. Responding to sensors that monitor
collector and storage tank temperatures, a differential temperature controller turns on the pump
when the temperature of the collectors is higher
than that in the storage tank, and then turns off
the pump when the collectors cool. A high-limit
setting prevents the tank from overheating.
ler operation. The
power supply can
be either a solar
electric panel or
household AC
power, depending
on what kind of
pump you use.
temperature sensor
temperature sensor
Gauges and Other
Additional parts and materials are required to
complete your system, and good plumbing knowledge and skills are essential for success. Gauges
for temperature and pressure are useful to monitor the system’s performance. Other parts you
may need include check valves, isolation valves,
air vents, an air eliminator, an aquastat (water
immersion thermostat), thermocouple temperature sensors, drains, temperature and pressure
relief valves, a tempering (mixing) valve, and a
vacuum breaker.
air valve
temperature sensor
hot fluid from
3Indirect solar
hot water system schematic
expansion tank
cold water
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Sizing the
a n d s t o r a g e must be
carefully matched so that the heat produced by
a solar hot water system can be used and stored
effectively. Too much collector area relative to
storage means that the water will overheat, the
pump will stop circulating, and the fluid in the
collectors will stagnate, causing it to overheat
and break down. Too little collector area means
that the stored water will seldom, if ever, get hot
Whatever you do, don’t undersize the system.
Doubling the size of a system doubles the output,
but it doesn’t double the cost. The best plan is
to design the system to meet your average daily
needs under sunny conditions.
Determining Your
Hot Water Demand
The average American uses about 15 to 20 gallons of hot water every day. Most system designers use 20 gallons per person as the design
requirement, while your actual use will vary
depending upon your needs and habits. From
this starting point, you can calculate the collector
square footage necessary to provide all the hot
water you need on a sunny day. This means you’ll
get what you need in summer but probably less
than you need in winter. Of course, the sunnier
your location, the less collector area you need to
satisfy your hot water load.
Calculating Btus
Here’s an example using a three-person household consuming 60 gallons of hot water each day,
in a location with lots of summer sun but cloudy
winters. A backup water heater provides hot water
during cloudy periods.
You can calculate water heating energy
requirements in Btus. Remember that a Btu is
the amount of energy it takes to raise the temperature of 1 pound of water by 1°F. A gallon of
water weighs 8.3 pounds. To calculate the Btus
required to heat our daily demand of 60 gallons, we start with the difference between the
cold water ground temperature and the desired
hot water temperature. We’ll assume the ground
water temperature is 55°F, and we want 130°F
water, yielding a temperature difference of 75°F.
The formula looks like this:
Temperature difference x weight of water
in pounds = Btus needed
75 (temperature difference) x 8.3 (pounds per
gallon) x 60 (gallons per day) = 37,350 Btus
Being realistic, we’ll add 10 percent to account
for system inefficiency, bringing our demand up to
about 41,000 Btus per day. This is what we need
our collectors to deliver to us each day.
Sizing the Collectors
Once you have a target Btu output for your system, you can research available collectors using
manufacturer and SRCC data. This will help you
to determine the total square footage of collector
area to meet your needs. To get there, we need
to dig a little deeper.
Knowing the solar resource available in your
location helps in sizing a system accurately. Solar
resource maps and data are available from the
National Renewable Energy Lab (NREL). Explore
the links listed in Resources to find the information you need.
Solar radiation data is often presented in
terms of kilowatt-hours per square meter per day
(kWh/m2/day). For solar thermal applications, it
iSolar Sweet Spoti
Depending on your climate, a solar hot water system typically provides about 50 to 75 percent of a
household’s annual hot water needs. This sizing scheme offers a reasonable compromise between
system size, cost, and energy savings.
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is useful to convert this to Btus per square foot
per day (Btus/ft2/day). To do this, multiply the
square-meter value by 317:
kWh/m2/day x 317 = Btus/ft2/day
For Instance . . .
Here’s an example using NREL’s “redbook” data
for Boston, Massachusetts, where we want to
install a solar water heater for a family of three.
We know that we need to heat 60 gallons of hot
water and that this requires 41,000 Btus every
day. The data indicates that for a flat plate collector mounted at an angle equal to Boston’s latitude of 42 degrees, we can expect a summertime
solar radiation average of 5.5 kWh/m2/day. That
converts to 1,743 Btus/ft2/day. Solar radiation,
and therefore solar hot water production, will be
somewhat less in the wintertime.
We’ve found a 32-square-foot, flat plate collector rated by SRCC to deliver 22,200 Btus per day,
given a solar radiation level of 1,500 Btus per
square foot. Two of these collectors (64 square
feet) will produce over 44,400 Btus, which would
more than cover our needs.
Sizing Storage Space
Regarding storage tank size, a very general rule
of thumb to prevent overheating is to provide 1.5
gallons of storage volume for every square foot
of flat plate collector area in an average seasonal
climate. For sunny regions, raise that to 2 gallons
for every square foot, and for cloudier regions,
lower it to 1 gallon. Applying the standard storage tank sizing rule to our Boston example, we
would need:
64 x 1.5 = 96 gallons of water storage
A properly installed solar hot water system using
high-quality components can last up to 40 years
and require only minimal maintenance. Spending
a little more up front for a better pump or hardware will be well worth it in the long run. Here are
some regular maintenance items to keep things
running smoothly:
• Inspect the system components and plumbing
once a month. Check for leaks, corrosion, and
missing pipe insulation. Listen for unusual
noises from the pumps.
• Keep the collectors free from debris and shade.
• Check the temperature gauge to confirm the
collector fluid is hot on a sunny day.
• Check the pressure gauge to confirm the
• Check the controller to confirm the system
is operating in accordance with the indicator
lights. If the controller tells you the pump
should be running, but the temperature is low
and you don’t hear the pump, you may have
a damaged pump or controller, poor wiring
connection, or faulty temperature sensor.
• Plan on replacing the circulator pump about
every 10 years, and expect to replace the
expansion tank every 15 to 20 years.
• Test the antifreeze solution after 10 years of
use or after any significant stagnation events.
Check for proper pH (no lower than 7.5) with
litmus paper, and check for freeze protection
using a tester that is suitable for propylene
glycol (not an automotive antifreeze tester).
system is maintaining pressure.
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clo s e - up
Homemade Hot Water
for a while, Lori was already in tune with her daily
energy use and was motivated to improve the 100-plus-year-old farmhouse she’s
lived in for 14 years. She heats her house with wood and has made many efficiency
improvements, including adding insulation, air-sealing, and drying out the dirt-floor basement.
av i n g l i v e d o f f - g r i d
L or i B a r g
is a small-scale hydroelectric power devel­oper
and consultant. She
is the founder of
Community Hydro (see
Resources) and works
with communities to
identify hydropower
opportunities and develop
appropriate solutions.
Lori is personally driven
to reduce her home’s
energy use and produce
her own energy using
simple techniques and
accessible resources.
While working in her berry patches one
summer, Lori became intrigued with the idea
of capturing the solar heat that was just lying
around inside the hoses she used to water
her gardens. The water inside those hoses
always ran hot for the first few minutes.
This inspired her to develop a simple waterheating scheme using her existing water
heater, an additional water heater, the sun
in the summer, and the wood stove in the
winter. She succeeded in her goal of putting
something together herself for under $1,000,
having less than a five-year return on the
The solar hot water collector Lori built
consists of an old 3 x 10-foot tin roof panel
painted black, with 75 feet of 3/4" flexible black
hose laid out in a serpentine pattern on the
panel and fastened to it with UV-resis­tant
black plastic cable ties (zip ties).The collector
is secured to two pressure-treated 2x4s
mounted on the roof. To avoid penetrating
the roof (to eliminate the possibility of leaks),
Lori extended the 2x4s beyond the ridge
and added two more boards that extend
down the opposite side, so the pieces “hook”
over the top of the roof. A third 2x4 spans
across the joined ends of the two boards on
each assembly to strengthen the hook. (Lori
chose the roof for better solar access, but a
ground-mounted rack would work equally well).
An old 30-gallon electric water heater
serves as a storage tank that provides
solar-preheated water to feed a 40-gallon
propane water heater. If the water coming
out of the solar preheat tank is too cold,
the propane fires up the heater. The electric
heating elements of the preheating tank
were removed and replaced with adapters
that connect 3/4" copper pipe to the heating
element ports on the side of the tank. Both
tanks are on the second floor of the house,
higher than the solar collector.
To deal with the inevitability of leaks, each
tank is set in a drain pan, with drains plumbed
down to the basement sump pump. The sun
heats the water in the collector, and as long
as the collector water is hotter than the
water in the preheating tank, a thermosiphon
effect passively circulates water between the
collector and the preheating tank. Because
there is water (rather than antifreeze) in the
collector, the system has valves to isolate
the collector loop so it can be drained in cold
The top pipe of the solar collector leads
to the port of the former top heating element
of the preheating tank (which has been
removed). Another pipe leads from the
bottom port of the tank to the bottom of the
solar collector. As the water in the collector
heats up, it rises to the top of the collector
and continues to move upward into the water
heater, while cooler water at the bottom of
the tank feeds the collector. As long as there
is a temperature difference, thermosiphoning
provides continuous circulation between
the collector and the heater. The greater
the temperature difference, the higher the
flow rate.
Next, Lori built an air-to-water heat exchanger for the wood stove out of tube-­and-­fin
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Lori became intrigued with the idea of ­capturing the solar heat that was just lying
around inside the hoses she used to water her gardens. The water inside those hoses
always ran hot for the first few minutes.
baseboard radiators, the kind used for boilerbased (hydronic) home heating. She cut
several lengths of fin tube to the width of
the stove, then plumbed them together in a
serpentine pattern and backed them with a
shroud to retain the heat and to support the
heat exchanger. This “reverse-radiator” heat
collector is fastened to the chimney (which
won’t move), not the wood stove (which will).
The fins fit snugly against the stove to absorb
its heat and transfer it to the water inside the
pipe. A thermosiphon is created between the
fin-tube collector and preheating hot water
tank upstairs.
In operation, cold water from the main
house water supply feeds the preheating
tank, and that water is heated with solar or
wood heat when available. Water from the
preheating tank feeds the propane water
heater, where it is further heated if needed.
If the preheated water feeding the gas water
heater is hot enough, then no gas is needed
to heat the water. Hot water from the gas
heater feeds the home’s hot water fixtures.
After the first year of operating the
system, Lori provides this report:
“The thermosiphon works. I put some
inexpensive temperature sensors on the
inlets and outlets, and water is preheated
[by the solar collector or wood stove] to
around 105 or 110°F by each system. While
I still use some gas to heat the water, I like
that I don’t have to worry about the water
getting too hot or building up high pressure.
I added a check valve to the solar loop to
keep the hot water from recirculating at night
and cooling off. When I drained the system
for winter, I propped open the check valve to
let that pipe drain. Otherwise, the pipe could
possibly freeze and burst with the first hard
“Overall, I am quite pleased. I had
thought of solar hot water for a long time
but could not afford it. I had looked at ways
of preheating hot water off my wood stove
and discarded most of them. I did not want
to take heat off my chimney, and possibly
increase creosote and the risk of chimney
fires; I did not want to take heat off the top
Lori’s solar collec-
tor mounted to her
roof with the 2x4
hook system
Homemade hot water 117
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c lo s e - up
Homemade Hot Water
of my wood stove, because I like to cook
on it in the winter, keep a teakettle on, and
allow water to evaporate to keep the house
from being so dry. The chimney-mounted,
serpentine, high-Btu fin tubing used in typical
baseboard hot water systems works great.
“I am thinking of adding additional sup­
ports to my rack and mounting some photo­
voltaics above the hot water panel.”
hot water out
cold water in
Water circulation
diagram. Shutoff valves
allow each system to
be isolated, drained,
and turned on or off
according to the season
and which heat source
is active. 
pressure relief valve
hot water collector
storage tank
propane gas
water heater
fin-tube heat
wood stove
iSafety Considerationsi
When the water in both the preheating tank and collector loops are very close in temperature,
the thermosiphon action slows or stops. If heat continues to be collected in this situation,
it’s possible for pressure in the system to reach dangerous levels. For this reason, it’s critical
to have a temperature and pressure relief valve (TPR valve) in both the solar and wood stove
preheat loops to eliminate the potential for a burst pipe, which could release scalding hot
water or steam. A small expansion tank would be required in any isolated loops, such as for
an indirectly heated system with a heat exchanger, or if there is a chance that a fluid-filled
preheat loop would be isolated from the rest of the system by valves.
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his is a very simple design for a batchtype solar water heater that uses a thermosiphon loop to move water between
a solar thermal collector and a storage barrel.
While it’s not the most efficient solar water heater and works rather slowly, it effectively demonstrates the operation of a thermosiphon and its
connection to hot water storage. Better yet, the
system can provide useful amounts of hot water
for an outdoor shower, washing garden produce,
keeping a biogas generator warm (see chapter
13), or any number of other uses you can think
of. Because it uses water, the system must be
drained when the weather turns cold.
Buying all new parts for this system might
cost around $300 or $400, but there are many
ways to modify the design to incorporate salvaged parts or for enhancing the system; see
Ideas for Upgrades on page 122. For longevity
and durability, the parts should be rated for UV
exposure and high temperatures. Most plastic
(PVC and polyethylene) will start to deform above
140°F, and typical garden hose will not hold its
shape much over 100°F.
The parts list includes recommended materials and temperature ratings. Use materials
that can withstand temperatures up to 180°F,
such as metal, CPVC, or polypropylene fittings,
as well as high-temperature water hose material,
such as EPDM rubber. Black-colored hose will
assist in absorbing solar heat. If you can’t find
what you need at your local hardware store,
plumbing supplier, or home center, shop online
through industrial supply companies (such as
Grainger or McMaster-Carr; see Resources).
Build a Solar Hot Water Batch Heater
M at e r i a l s
Four 8-foot 2x4s
Five 8-foot 1x4s
21/2" deck screws
3/4" roofing screws or galvanized sheet metal screws
Two 2 x 8-foot corrugated metal roofing panels
High-temperature, flat black spray paint
One 100-foot, black EPDM rubber garden hose, 3/4"
I.D. (inner diameter), rated for 200°F
One hundred 8" black plastic cable ties, UV-resistant,
heat-stabilized, rated for over 200°F
One 55-gallon barrel, black plastic, preferably with
wide-mouth top
Two 3/4" NPT (National Pipe Thread) /GHT (garden
hose thread) brass faucets, rated for 180°F
Teflon tape
Two 3/4" polypropylene bulkhead fittings, rated for
Two 3/4" brass garden hose-to-tubing adapters
Two hose clamps
One 36" length foam pipe insulation
5Completed collector frame with panels installed
(rear view)
iSolar Educationi
A smaller version of this system makes an excellent science project. Use clear plastic tubing for the
collector loop and add food coloring to the water to demonstrate circulation.
B u ild a so la r hot water batch heater 119
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Build a Solar Hot Water Batch Heater
1. Build the collector structure.
Construct two A-frame supports using 2x4s and
21/2" deck screws: Position the front leg of each
support at the desired tilt angle for the collector
panel (your latitude angle is a good starting point),
and attach the rear leg at an opposing angle for
stability. Join the two legs (front and back) of each
side with a horizontal cross piece.
Space the A-frame supports about 6 feet
apart, and join the two back legs with two diagonal 1x4s to keep the frame from racking.
Install three 8-foot pieces of 1x4 horizontally
across the supports. Locate one piece at the tops
of the supports, one 24" down from the tops,
and one with its bottom edge 48" from the tops.
Fasten the 1x4s to the supports with the deck
Mount the roofing panels to the wood frame,
using 3/4" roofing screws or sheet metal screws.
Install the lower panel first, fastening it to the
bottom 1x4. Install the upper panel so it overlaps
the lower panel, then fasten through both panels
into the center 1x4. Fasten the upper panel to
the top 1x4.
Paint the top surface of the roofing panels
with high-temperature, flat black spray paint (the
kind used for painting wood stoves). Let the paint
dry completely.
2. Install the collector hose.
Lay out and mark the hose path on the collector
panel, using full-length horizontal runs back and
3Detail of bulkhead
adapter and faucet
forth, working from the bottom of the panel to
the top. Do not exceed the bending radius of the
hose at the ends, as kinks in the hose will stop
the flow and can lead to trapped air bubbles. A
3/4" I.D. hose should allow for eight horizontal
runs across the 4-foot-tall panel. Be sure to leave
extra hose at the beginning and end for connecting both ends to the storage barrel.
Note: As the water in the hose heats up, air
will be released from it. Keeping the hose runs
reasonably level, with no kinks or sags, allows
the thermosiphon to work effectively, eliminates
trapped air bubbles, and facilitates draining the
Secure the hose by drilling pairs of holes
through the collector panel, one above and one
Collector panel, front view, with hose secured
with cable ties (right)
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below the hose, then loosely fastening the hose
with a plastic cable tie (zip tie). Add a tie about
every 12" along the entire path of the hose. Make
sure the hose is in full contact with the collector
panel for best heat transfer. You will tighten the
ties later, after the hose is connected to the barrel and all fits well.
3Hoses connected
to barrel with a
smooth rising
3. Prepare the water storage barrel.
The barrel gets two threaded bulkhead fittings to
provide a watertight connection through its side.
The fittings receive the tapered threaded ends
(not the garden-hose ends) of the faucets that
will connect with the collector hose. Make sure
the faucets are compatible with the bulkhead fittings and the adapters for connecting the collector hose.
Cut a hole through the barrel for each fitting,
using the appropriate size of hole saw. Position
the lower hole as close to the bottom of the barrel as possible, and locate the upper hole about
one-third of the way down from the top of the
barrel. Choose areas with no raised markings
and little curve in the barrel surface to ensure a
watertight seal.
Wrap the threaded end of each faucet with
Teflon tape, and thread it into the exterior half of
a fitting. Fit each fitting into its hole and secure it
inside the barrel with its nut.
3A sagging hose
with downward
sections can
interrupt the
4. Set the barrel and connect
the hose.
Position the barrel on a sturdy stand that is tall
enough so that the faucets on the barrel are
higher than their corresponding hoses mounted
on the collector. Position the collector close to
the barrel. Extend the lower end of the hose to
the lower faucet, and cut the hose to length so it
makes a smooth upward arch toward the faucet.
Make sure the hose doesn’t sag, which can trap
air or create a “heat trap,” stopping the thermosiphon action. Cut the upper hose end to connect
to the upper faucet.
Install a tubing-to-faucet adapter on each
end of the hose, securing it with a hose clamp.
3Detail of cut hose
end with faucet
adapter installed
B u ild a so la r hot water batch heater 121
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Build a Solar Hot Water Batch Heater
Thread the hoses onto the faucets. Tighten the
cable ties on the collector panel so they hold the
hose securely in place. Put a piece of foam pipe
insulation on the hot water (top) hose to help reduce heat loss and increase the effectiveness of
the thermosiphon.
5. Get started making hot water.
Open the faucet valves, and fill the barrel to the
top, leaving 1" or 2" of air space for expansion.
You want to be sure that there is no air in the collector loop. Tilt the collector back and forth (one
tilt for each hose bend) after the barrel is filled to
be sure that all the air is out of the hose.
You’ll start making hot water as soon as
the sun comes out. Cold water sinks to the bot-
tom of the barrel and continues down the hose
to the bottom of the collector. As the water is
heated it rises up through the hose, through the
top faucet, and into the barrel, where it rises to
the top. There will be a noticeable temperature
stratification within the barrel until the water is
completely heated.
As an example, on a sunny 45°F day, I
achieved a 40°F temperature rise through the
collector loop using about 75 feet of 3/4" hose
laid out on the collector, plus another 8 feet
leading to and from the storage barrel. This
was at a fairly low flow rate, and resulted in
a 10°F per hour temperature rise within the
stored water during the hours just before and
just after noon.
Ideas for Upgrades
With some additional effort,
you can increase the efficiency of the system and even
bring the hot water you make
into your home, where it can
preheat the water in your
existing water heater. Check
local plumbing codes before
modifying your water heater.
Using a heat exchanger in
between your solar collector
and water heater means you
won’t be putting potentially
nonpotable water into the
water heater.
• Insulate the water storage
barrel to keep the water
hotter for longer periods.
• Enclose the collector in
a box for hotter water.
Insulate the box on
the bottom, and cover
it with a piece of UV
resistant clear Plexiglas
or flexible fiber-reinforced
plastic (FRP).
N ote : Enclosing the
collector may make
temperatures exceed the
materials’ ratings, requiring
the use of all metal
• Collect and store more solar
energy by increasing the
collector area and the length
of the circulation hose.
• Switch to an active system
with the addition of a
small solar-powered 12volt DC pump that moves
less than 2 gallons per
minute; this frees you
from the constraints of a
thermosiphon system.
Optional equipment for water
circulation is available through
local and online renewable
energy dealers. This includes
a low-wattage, 12-volt DC
circulator pump that can
operate from a 5- or 10-watt
solar panel. If you make this
investment, you will also want
to spend a bit more to insulate
the storage barrel and enclose
the collector.
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Solar Electric
h o t ov o lta ic (P V ) d e s c r i b e s the electrochemical process of
using the energy delivered in photons of light to create an electric current.
Photo means light, and voltaic means related to producing electricity. (A
photon is a particle of electromagnetic energy.) When a photon of light strikes one
side of a solar cell, the photon’s energy causes an electron to jump to the other side
of the cell. From there, the electrons travel through a circuit to where the electricity
performs the desired work, such as lighting a lamp or charging a battery.
A PV panel, or module, is made up of many small PV cells wired together to produce the desired voltage and power. The cells are assembled into a sturdy frame and
covered by a strong, clear, waterproof elastomer or thermoplastic layer that is resistant to breakdown by UV rays from the sun. Each module can range in power output
from 10 to over 200 watts.
Two or more PV modules wired together are called an array. The size of the array
needed for any given task depends upon the power requirements of the particular
site. Arrays can be installed on a roof or a ground-mounted rack.
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Solar Power
technology and materials
used, commercially available PV cells convert
light energy to electrical energy with an efficiency
rate of between 8 and 18 percent. Current work
in laboratories is producing cells with efficiencies
of over 30 percent.
The material in PV cells that converts the
energy of photons to electricity is called a semiconductor. The most common semiconductor
used in cells today is the element silicon (as
in Silicon Valley; not silicone, as in tub and tile
caulk). However, other materials, such as germanium, gallium, and cadmium can also be used.
Organic solar cells using polymers are also
being developed.
Semiconductor materials can be formulated
in a solid crystal for use in rigid cells, or in sintered form, where powdered semiconductor material can be sprayed onto flexible products, such
as roof shingles (see Space Requirements, page
134) and clothing. Each technology has advantages and disadvantages in terms of cost, efficiency, and flexibility. Multicrystalline silicon
PV cells are the most common type used for
De p e n d i n g o n t h e
stationary residential and commercial installations and have an efficiency of about 16 percent.
Assuming an average efficiency of 15 percent,
a PV panel can deliver about 14 watts per square
foot (150 watts per square meter). Keeping your
panels aimed directly at the sun throughout the
year and throughout the day will increase overall
output. You can adjust panel position manually, but
an easier and more reliable way is to incorporate a
tracking system that automatically moves the array
to the optimum position (see pages 131 to 132).
3Multi-layered silicon
wafers are assembled
into photovoltaic cells.
Cells are assembled
into modules, and modules are wired together
into arrays to produce
the desired voltage and
Ho w M u c h P o w e r ?
On average throughout the
world, solar energy striking
Earth from directly overhead
delivers about 1,000 watts of
energy per square meter, or
about 93 watts per square foot.
In reality, though, how much
energy your solar collector
“sees” and absorbs depends
on several factors:
• Your location on the planet
• Season
• Temperature
• Level of cloudiness
• Light reflection from the
ground to the solar panel
• Angle of incidence between
the collector and the sun
(see page 130)
• How much light the panel
reflects away from itself
On a clear day, you can expect
the sun to deliver between
700 and 1,400 watts of raw
solar energy to each square
meter of solar collector area
that is aimed directly at
the sun.
iAC vs. DCi
The power produced by PV systems is direct current (DC), not the alternating current (AC) you need
to power your home. The conversion from DC to AC is handled through an electronic device called
an inverter. See chapter 10 for more information about inverters and other components common to
renewable electricity generation.
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summer solstice
Planning for
a PV System
how much electricity
you use simply by looking at your electric bill,
which tells you how many kilowatt-hours (kWh) you
used during the past month. Some bills present
daily usage, and some utilities let you look at how
much energy you’re using at any given time by way
of a “smart meter” that may even have a Web
interface. You can also learn to read your own
electric meter on page 98, and see chapter 5 to
learn about focused monitoring of specific power
users in your house.
As you examine your electrical use, you may find
patterns where consumption during certain times
of the year is greater than at other times. But the
general rule is to size your PV system for average
daily use, knowing that you will make more than
you need on some days and less on others. Solar
electric systems can be expanded over time, so
you can start small and add more as your budget allows. Making your home ready for renewables requires long-term planning; if you prepare
for future expansion, there will be less work and
expense when the time comes to upgrade.
winter solstice
Yo u ca n d e t e r m i n e
Assessing Your Site
Let’s say that your home uses an average of 20
kWh of electricity each day, and you want to supply
50 percent of that electricity using solar power.
Your solar-generating capacity needs to provide
10 kWh per day. Depending upon where you live,
there are some months when you can count on
the sun more than other months. It would probably not be practical to size your system to generate 10 kWh on cloudy days, because on sunny
days you would have far more than you need. So
let’s keep things simple and use a sunny day as
an example to design a solar power system.
How Much Sun?
Once you’ve determined how many kilowatt-hours
you want to generate, the next step is to understand how many hours of sunlight you can expect
each day at your location. The greatest power
output occurs during peak sun hours, when the
3Seasonal sun
sun is high in the sky, typically spanning the three
hours on either side of noon (that is, 9:00 a.m.
to 3:00 p.m.). Outside of that ideal “solar window,” power production starts to fall off unless
you have a tracking system that allows the array
to follow the daily movement of the sun across
the sky. The intensity of sunlight will vary throughout the year (unless you’re on or near the equator), so the actual power output of your PV panels
will vary further with the seasons.
You can find average daily sun hours from a
local weather station, or you can research weather
data online through the National Climate Data Center or the National Renewable Energy Lab’s Renewable Resource Data Center (see Resources). The
latter website includes an analysis tool called PV
Watts that helps you predict the output of a PV
system in your area. These tools are a good place
to start, but you still need to perform a solar site
survey to assess the daily and seasonal solar
resource available at your specific site.
trajectories show
the sun’s path
across the sky at
winter and summer
solstices. Any
obstacles between
the sun and the PV array will cast shadows and
reduce power.
Solar Site Survey
A site survey takes a close look at the path
the sun takes across the sky at different times
throughout the year. There are two tools commonly used by professional solar installers for
site surveys and power production analysis (see
Resources for websites).
Solar Pathfinder. This tool lets you see where
the sun will be at any given time in any season.
It also provides a visual indication of when and
where the panels will be shaded. Shaded PV panels produce power about as fast as you get a suntan sitting under a shade tree, so this is an important part of any solar site assessment. The user
(typically a professional solar installer) sets up the
BackyardEnergy_Final_Pages.indd 125
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cast by trees
early in the
the year
The math required is simple:
Watt-hours needed ÷ daily sun hours =
PV system size (in watts)
10,000 watt-hours ÷ 5 hours = 2,000 watts
Map Estimating
A Solar Pathfinder
is used to identify
your solar window
and highlight obstacles that might
shade the solar
Pathfinder at the prospective PV site and observes
the sun’s path (along with shadows) against a grid
that shows latitude and longitude. The company’s
software helps to predict annual power output and
modify the results, should the homeowner decide
to eliminate some of the shading.
SunEye. Made by Solmetric, the SunEye is an
electronic analysis tool that may be used by professional solar installers. It does everything the
Pathfinder does but with the accuracy and additional bells, whistles, reporting, charting, and
computer interface that you would expect from
this professional electronic analysis tool.
Sizing a System
There are two ways to determine how many kilowatt-hours a PV array of a given size will produce
over the course of a year.
Math Estimating
This sizing method starts with learning how many
hours of sunlight you can expect each day, on average, throughout the year. Then, factoring in how
much power you need, you can work backward to
estimate the capacity of your PV array in watts.
Back to our example, to deliver 10 kWh (10,000
watt-hours) per day. Your site survey indicates you
can expect an average of 5 hours of unshaded sunlight each day of the year. This average includes
cloudy days and seasonal variations; your actual
daily power production will vary quite a bit.
The second way to estimate the size of a PV system is to find the average annual power that can
be produced for each watt of PV installed at your
location. Most solar estimating maps (such as
those available from the National Renewable
Energy Lab) present solar insolation (exposure to
sunlight) in terms of raw solar power available in
kilowatt hours (kWh) per day. This represents how
much solar energy can be harvested by a solar
collector and does not account for the efficiency
of the PV cells. In terms of system design, it’s
more useful to convert available solar insolation
into kWh (energy produced over time) that can be
produced for each kilowatt (kW) of installed PV
power (rated electrical power production). This is
expressed as the kWh/kW factor.
Refer to the solar energy estimation map (see
facing page) to see the approximate daily kWh of
solar energy available at your site for conversion
to solar electricity. The value shown is for each
square meter (10.7 square feet) of PVs installed
on a fixed-mount (non-tracking) rack with a tilt
angle equal to the latitude. The sun shines more
frequently and intensely in some places of the
world, and less so in other places. Solar electric panels are tested and rated at a light level
of 1,000 watts per square meter (93 watts per
square foot). At 14 percent efficiency, one square
meter of PVs will produce 140 watts (13 watts
per square foot) under equivalent sunlight.
A more meaningful interpretation of the chart
for our purpose is to understand that the kWh per
square meter per day figure is the same as the number of available daily sun hours, adjusted for insolation intensity. Using this value as our guide allows
us to more easily estimate how many kWh can be
produced for every kW installed. Here’s an example:
Let’s say you live in a place where the sun
delivers 5 kWh each day for every square meter
of PV array or, in other words, the sun shines
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N o t e : The uncertainty of the contoured values is
generally ± 10%. In mountainous and other areas of
complex terrain, the uncertainty may be higher.
less than 2 hours per day
less than 2 hours per day
Average Daily Solar Insolation
United States and Southern Canada
Average Daily Solar Insolation
United Hours
Solar power estimation. Map of the
United States showing
approximately how
many kilowatt-hours
can be produced each
year for each kilowatt
of solar electric system capacity. Source:
U.S. Department of
Energy 
5 hours on average each day. Every 1 kW of PV
capacity can deliver:
1 kW x 5 hours per day x 365 days =
1,825 kWh per year
The kWh/kW factor in this case is 1.825
Keep in mind that this map is highly generalized
and does not account for local conditions, system
inefficiency, or tracking rack adjustment factors,
but it gives you a general idea as to what you can
expect in terms of annual power production. As a
comparison, the 2,000-watt PV array calculated in
the math example above will deliver approximately
3,650 kWh per year (2,000 x 1.825).
Accounting for Inefficiencies
The above examples do not account for any inefficiencies in the system. You may experience up
to 25 percent power loss through wiring, connections, power handling equipment, panel derating (they don’t always operate in factory-test
Hours per Day (kWh/m²/day)
2 to 3
2 to 3
3 to 4
4 to 5
5 to 6
3 to 4
4 to 5
5 to 6
6 to 7
6 to 7
7 to 8
7 to 8
8 to 10
8 to 10
conditions), temperature (cooler panels deliver
more power), and dirt on the panels (even a little
bit of shading hurts a lot). A 15 percent reduction from the published PV panel rating is a good
value to use when estimating net power delivered
from your PV system. Dividing the power needed
by the total efficiency brings our 2,000-watt PV
contribution requirement up to an array size
of 2,353 watts (2,000 ÷ 0.85 = 2,353). This
lowers the effective kWh/kW factor from 1.825
to 1.55.
Bigger Is Usually Better
Now you can choose your PV panels. PV panels
are rated in watts of power output, as well as voltage (volts) and current (expressed in amperage,
or amps). Larger panels typically are a bit less
costly (in terms of price per watt) than smaller
panels. They also require less wiring because
fewer panels are needed in the array. Years ago,
PV arrays were assembled from 50-watt ­panels,
but today 200-watt panels are common.
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On-grid solar electric
system with utility
intertie. Electricity
can flow in either
direction, depending
on how much power
the house needs
relative to how much
is being produced by
the solar panels. 4
can flow
in either
PV array
PV array
Off-grid system where
electricity is stored in
batteries and no utility
power is available.4
battery bank
Hybrid solar electric
home power system
that is grid-tied. Batteries provide backup
power in the event of a
power outage.4
battery bank
backup generator
can flow
in either
PV array
PV System Wiring
produce a nominal
12 volts of DC electricity, while current (amps)
depends upon how many cells are in the panel
and how bright the sun is. Power output is
expressed in wattage, which is a product of volts
and amps (volts x amps = watts). In reality, a
12-volt PV panel will produce up to 20 volts in
full sunlight with no load, meaning that the wires
are not connected to anything. This is known as
open-circuit voltage.
Nominal voltage is used in system design to
match voltage output with other components.
Open circuit voltage is higher than nominal voltage because the electrons need to overcome wiring losses, along with other voltage-derating factors, such as heat. As an example, a 12-volt battery may require 15 volts to charge fully, and this
voltage can be expected from a nominal 12-volt
panel. To prevent overcharging of ­batteries, a
charge controller is used.
A PV system can be designed to charge batteries or feed power to the utility grid, or to do
both. Each approach requires different voltages
to maximize the efficiency for each scenario and
to match the needs of the power handling equipment. Higher-voltage equipment generally is more
efficient and allows for the use of smaller diameter (and less expensive) wires without significant
voltage drop — loss of power resulting from low
voltages over long wire runs.
PV p a n e l s t y p i c a l l y
Wiring Configurations
It’s acceptable to combine different panels
in a system, but for best efficiency and performance the panels in each array should be closely
matched for voltage, while individual current output can vary. In order to deliver the desired voltage and power, the panels can be wired in three
configurations: series, parallel, or series-parallel
In a series circuit, the positive wire of one
panel is connected to the negative wire of
another, and the remaining positive and negative wires are connected to the load. A serieswired array produces a voltage that is the sum of
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12 V
24 V
24 V
3PV panels
3PV panels
wired in
12 V
V module
V module
each individual panel’s voltage, while its current
(amperage) is the average of all of the panels’
currents. The diagram above shows two PV panels wired in series. Each panel produces 12 volts,
6 amps, and 72 watts (12 x 6 = 72). The total
output is 24 volts, 6 amps, and 144 watts (24 x
6 = 144).
In a parallel connection, all positive wires are
connected together, and all negative wires are connected together. With this configuration the voltage stays the same, and the total amperage is the
sum amperage of all of the panels. Our two 12-volt,
6-amp panels are now producing 12 amps at 12
volts, with the same total output of 144 watts.
Series-Parallel Combination
Let’s look at an example of a battery-charging PV
system that’s wired for 48 volts. Higher voltage
helps to increase equipment efficiency and to
reduce the cable size between the PV array, charge
controller, and batteries. There are several brands
of 200-watt PV panels that produce 24 volts each
(and thanks to Home Power magazine’s Solar
Electric Module Guide, we know there are several
choices for power inverters that meet our needs).
We will need to wire these in a series-parallel
combination in which every two panels are wired
in series to produce 48 volts. Each set of two
panels is then wired in parallel with other sets
of two. Using our example system design, we’ve
wired in
12 V
V module
12 V
V module
determined that our desired power output (wattage requirement) is 2,353 watts. To find the number of panels required, we divide the total wattage
requirement by the wattage per panel:
2,353 watts ÷ 200 watts per panel =
11.7 panels
We must have an even number of panels for our
48-volt configuration, so we’ll round up to 12 panels, yielding a total output of 2,400 watts. For the
practical purposes of mounting location, future
maintenance, and troubleshooting, we’ll split the
system into two separate arrays of 1,200 watts
System wired with
series-parallel combination, including
combiner and main
PV disconnect 
+ – + – + –
– + – + – +
– + – + – +
+ – + – + –
combiner box
main PV
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Because we have more than one PV array, the
arrays must be electrically connected, or combined, in a combiner box (see chapter 10). Here,
each of the array wires is connected to a common
electrical distribution block for positive, negative,
and ground, so that only a single wire runs to the
charge controller (for an off-grid system) or to the
inverter (for a grid-tied system). Each array has its
own circuit breaker inside the combiner box so that
individual arrays can be disconnected as needed
without interrupting the entire PV power supply.
The drawing on page 129, bottom, shows
our two separate PV arrays feeding into a single
combiner box. The positive PV feed wires from
each array are connected to a dedicated circuit
breaker. The output side of each circuit breaker
is connected to a junction block, as are each of
the negative PV feed cables. The junction blocks
have one large supply cable that carries all of the
PV current to the power management center that
includes the charger controller and inverter.
The PV supply feed coming from the combiner
box is next run to the main PV disconnect switch.
The disconnect is required both for electrical protection and servicing and can include a master
fuse or circuit breaker. In the case of a grid-tied
system, a disconnect is mandatory to protect the
line workers, should they need to work on power
lines fed by your PV array.
F o r ma x i m u m p o w e r output, the PV
array should live in an unshaded location at a
perpendicular angle to the sun’s rays for 4 or more
hours each day. Even the shade of a single leaf
can eliminate most of the power output of the
affected panel and the series-connected part of
the array it’s wired into. Maximizing the time of full
sun exposure maximizes the power output and
increases the rate of return on your investment.
If you’re in the northern hemisphere, the sun
will be in the southern half of the sky (unless
you’re within 23 degrees of the equator, in which
case the sun will cross over to the north for the
summer), and PV panels should therefore face
south. When orienting your PV array, be sure to
account for magnetic deviation, an effect that
causes a compass needle to indicate other than
true north. The amount of deviation depends
upon where you are in the world, and it changes
over time. Consult a geomagnetic map (see
Resources) to find the adjustment you need to
apply to your compass.
However, a fair amount of offset from true south
can be tolerated without substantial loss of power.
For example, a fixed PV array facing southeast or
southwest will produce about 85 to 90 percent
of the power of an array that faces due south. In
fact, some utility-sponsored programs support PV
installations oriented specifically to help offset
peak load conditions (periods of maximum power
demand) on the utility. In such cases, you may find
PV arrays facing due east or due west. The array
orientation is based on where the sun is during the
time of the utility’s peak demand.
As the earth travels around the sun throughout the year, the sun’s altitude changes with the
seasons (see How Much Sun? on page 125). At
the time of summer solstice, the sun is at its
highest point in the sky, which is your latitude
iPV and Peak Demandi
Peak demand is the period of time when the utility needs to deliver the greatest amount of power
to its customers. For example, if peak demand is at 5:00 p.m. in the summertime — when everyone
comes home to air conditioning, electric cooking, and water heating — a west-facing PV array will
help offset the demand on other power plants that may be close to full production capacity. The
overall power output of the PV system may be substantially less than with a south-facing array, but
the utility’s objectives (which are likely different from yours) are achieved. This approach is often a
better solution than building a new power plant which would be needed for only a few hours a day.
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plus 23.5 degrees (the tilt of the earth on its
axis). So if you live at a latitude of 42 degrees,
the sun will reach a maximum latitude of 65.5
degrees above the horizon.
At winter solstice the situation is exactly the
opposite, and the sun will be at a latitude of
18.5 degrees (42 minus 23.5) above the horizon. When mounting solar panels on a permanently fixed rack, the best tilt angle is the latitude
of your location. You may decide to increase or
decrease the tilt angle to gain a bit more power
in the winter or the summer, depending on either
your seasonal needs or on the season that delivers the most sun. If your system is grid-tied, you’ll
want to orient the array for maximum annual average power production.
Racks and
mounted on a rack to
assemble an array, and the racked array is then
mounted on supports either on the ground or
on a roof. A ground-mounted PV rack requires a
sturdy foundation, typically either a concrete pier
supporting a steel pole or multiple pressuretreated posts anchored firmly in the ground. A roofmounted rack can lie flat against the roof over the
shingles, or it can be tilted to a specific angle.
Before mounting panels on your roof, be sure
that the roof construction is capable of holding
the additional weight. Also consider future shingle replacement: You don’t want to have to take
down your PV system in 5 years just to replace
the shingles.
You can buy commercial racks designed for
simple assembly and installation, but you can also
make your own with 2" slotted steel or aluminum
angle stock. Regardless of the rack you use, don’t
skimp on the foundation, which must support the
weight of the PV array as well as keep it from sailing away in high winds.
Consult with an engineer and/or mounting system manufacturers (such as Direct Power and
Water; see Resources) for specifications on pole
pa n e l s
and foundation requirements based on the size and
weight of your array and the type of soil you have.
Tracking Racks
The previous examples of power production
assume a fixed PV array, where the array is permanently mounted in a fixed orientation. If the
array is mounted on a pole, the tilt can be manually adjusted a few times each year to match the
seasonal angle of the sun, but essentially this is a
fixed installation. A tracking rack automatically follows the sun throughout the day and year.
Tracking extends the number of hours during
which you can capture peak sunlight by adjusting
the horizontal and vertical orientation of the array
throughout the day as the sun moves across the
sky. For a tracking rack to make economic sense,
you must have clear access to the sky from shortly
after dawn to nearly dusk; no more than a couple
of hours of light should be lost in either direction.
Tracking racks require space for the array to pivot
around the pole upon which they are mounted and
are not suitable for roof-mounted arrays.
Single-Axis vs. Dual-Axis
Tracking racks are available with single- or dualaxis tracking capability. Longitude, or azimuth (east
and west), is the most important axis to track for
maximum power collection. A single-axis, longitudinal tracking rack can increase your average annual
power production by 24 to 33 percent over a fixed
rack. A dual-axis tracker (adding altitude to azimuth
tracking) will increase output by 7 to 9 percentage
points over a single-axis tracker. The lower ranges
of these power increases occur in locations with
relatively less sun.
Power gains are always greater in summer, when
the sun is in the sky for longer periods. This can be
particularly beneficial for grid-tied systems, since
excess summer power generation can help offset
winter use, should your utility offer net metering
(which allows solar power to, in effect, turn your
electric meter backward; see page 175).
Is Tracking Worth It?
You may wonder whether it’s worthwhile to spend
money on a tracking rack to increase power, or
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Various options for
installing PV panels
pole mount, fixed
ground rack
if it’s more cost-effective to increase the size of
your fixed PV array. The chart on page 133 presents a comparison of three options using the
same baseline cost to buy PV panels and install
them on a rack. The costs shown do not include
any other system components because these
would be common to each system regardless of
rack type. A tracking rack uses the same foundation and supporting pole as a fixed rack, so the
only variables are the cost of the rack (based on
the size needed to hold the panels) and whether
it is fixed or tracking.
Tracking Rack Mechanics
pole mount with
dual-axis tracking
PV shingles
Tracking racks can use electric or hydraulic
motors, controlled by an integrated clock drive or
photo sensors that detect variations in light level
and provide feedback to the motor drive. Zomeworks (see Resources) manufactures a thermally
operated, passive solar tracker using a refrigerant
that changes phase when heated by sunlight. As
the sun’s heat vaporizes the liquid refrigerant, the
vapor moves to the high side of the rack, where it
cools and becomes denser, increasing the weight
on one side of the rack and causing it to tilt. Thermally operated racks tend to be a bit more sluggish to respond than motorized trackers (especially in colder weather), and therefore not quite
as accurate, but they are simple, maintenancefree, and a bit less expensive, and they require
no energy.
roof mount
Yo u may wa n t to use solar power for many
reasons: to avoid connecting to distant power
lines, to be independent of power companies,
to “go green,” to reduce your exposure to risky
energy markets. As an investment, solar power
will yield predictable returns for many years.
If you are considering the long-term economics
of renewable energy as an investment, you’ll probably want to dig a little deeper. And remember,
using less electricity means that you can meet
more of your needs with fewer solar panels, so be
sure to invest in efficiency first. Efforts to reduce
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energy use are almost always less expensive
than buying more solar power capacity to support
inefficient habits and old energy-hog appliances.
Plugging In the Numbers
Our sample 2,400-watt PV array will produce
about 3,840 kWh per year. If electricity costs
$0.10 per kWh, you’re saving $384 each year.
As electricity prices rise, your solar dividend pays
even more. Over a useful life of 25 years, the system will have produced 96,000 kWh (or $9,600
worth) of electricity at today’s rates. If electricity
costs rise just 2 percent annually above the rate
of inflation (a 2 percent escalation rate), you’ll
save about $12,600 over the life of the system.
To figure your return on investment, you need to
subtract the installation and lifetime maintenance
costs from this lifetime savings amount.
At the time of writing, a complete, professionally installed solar power system costs anywhere from $4 to $8 per watt of DC-rated capacity, depending on the size and complexity of the
system and whether or not there are batteries
to buy. Federal, state, local, and utility incentives
can help to bring installation costs down, and
sometimes utilities offer a payment for power
produced. Maintenance costs with PV are minimal, but you may want to consider potential
inverter replacement approximately every 10 to
15 years, and, if it’s an off-grid system, batteries
will need replacing every 5 to 10 years.
If the PV system costs $5 per watt installed,
the 2,400-watt system totals $12,000. Without
incentives, lower installed costs, or increasing
energy prices, this system just about breaks even
over its lifetime with the 2% escalation rate. If you
are building a new home far from existing power
lines, compare the costs of PV to those of bringing in utility power. Additionally, as I mentioned
in the introduction, there are many noneconomic
reasons to buy energy efficiency or generation.
How much is energy autonomy worth to you? Only
you can put a “payback” value on that.
The Shelter Analytics website (see Resources)
includes an energy-improvement analysis tool
that allows you to enter details about PV systems
and costs, incentives, utility costs, and escalation rates, as an aid to understanding lifetime
economic and carbon impacts of a renewable
energy system.
Comp a r i s o n o f f i x e d a n d t r a c k i n g r a c k s
In the chart, the Fixed column assumes
a 2,400-watt PV array on a fixed rack.
The Tracking column assumes the same
size of array on a dual-axis tracking
rack. The Fixed Plus column shows how
many watts a fixed array would need to
be if it were sized to provide the same
power as the tracking rack. Keep in
mind that, in reality, costs and power
output will vary widely based on your
situation and location, so be sure to
get accurate costs and solar insolation
(solar radiation) data for your particular
site and project. Be sure to read Living
with Solar (and Wind) Power (page 135)
for another perspective on tracking.
In the example here, a dual-axis
Type of Rack
Fixed Plus
Array size, watts
Rack cost
Annual power output, kWh
Adjusted kWh/kW
Installation price per watt (array and rack) $5.91
Lifetime kWh (25 years)
Lifetime cost per kWh generated
tracking mount delivers 38 percent
more power at a slightly lower cost
when considered in the context of
lifetime power production. Both higher
PV prices and larger system sizes
improve the economics of tracking
racks. With larger, multi-array systems,
there’s potential for significant savings
if tracking increases power production
enough to eliminate the need to install
an additional rack with foundation
and supporting structure.
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Sp a c e R e q u i r e m e n t s
If you’re using PV panels made
with multicrystalline silicon cells,
you’ll need about 1 square foot
of rack space for every 10 watts
of PV capacity. The panels don’t
need to be contiguous, but the
electrical wiring layout needs to
work with the physical layout. You
can electrically combine several
arrays mounted in various locations to feed a common load. The
2,400-watt array from our sample
system will require about 240
square feet, along with a roof and
rack that are sturdy enough to
carry the weight.
Alternatively, if you use thinfilm PV technology, you’ll need
about 50 percent more area,
since these panels are generally less efficient than those
made from crystalline cells.
Thin-film PV is used in some PV
roofing shingles, such as those
M o d e r n e q u i p me n t ma k e s it fairly easy
for a skilled do-it-yourselfer to install a solar
power system safely and successfully. This does
require working around potentially lethal voltage
and current levels, so it’s critical to take all
possible precautions for the installer’s safety and
the safety of others affected by the work, such
as utility line workers. In all cases, national and
local codes must be adhered to. Plan on hiring a
licensed electrician to advise you along the way.
Here are just a few of the essential safety considerations for any solar power installation:
• Improperly selected or installed equipment
can be a shock and fire hazard.
• Cables that are not in conduit present serious
hazards for anyone digging holes in the
ground or driving nails or screws into walls.
• Ungrounded or improperly grounded
equipment can be troublesome at best,
deadly at worst.
PV panels produce high voltages when exposed
to sunlight, with enough energy to kill a human
who touches the bare conductors. During installation and wiring, cover the panels with a tarp to
decrease or prevent electrical generation, and cap
available from Dow Solar (see
Resources). A solar-shingled
roof costs a bit more per watt
than framed PV modules, but
the shingles have a much lower
profile, blend in well with a dark
roof, take the place of standard
shingles, and provide power for
your home. This makes your
roof a real asset, rather than
just another maintenance item
for your home.
the conductors so that no bare wire is exposed.
PV power is a “soft” power, in that the panel’s
electrical output connections can be shorted (positive and negative terminals connected together)
without hurting anything. The electrons simply continue on their way around the electrochemical process. Just don’t get in their way!
It’s important to remember that PV produces
DC power, and all electrical components must
be rated for use with DC power. Using electrical
equipment that is not DC-rated fails to provide
suitable electrical protection, resulting in early
(if not immediate) failure of the components and
possibly creating extreme hazards. This is especially true for circuit breakers and fuses. Solar
electric power system installations must follow
the National Electrical Code (NEC) Article 690
safety standards. The NEC covers all requirements for wiring, grounding, fuses, batteries, and
grid-tie systems.
Proper system grounding requires connecting the
frame of every PV panel in each array to a grounding rod driven into the ground. Grounding hardware
should be bronze or stainless steel, rather than
aluminum, for best weather resistance. All electrical equipment must be grounded as well. This is
required for system safety, and it also helps to protect components from getting fried by lightning.
Solar electric systems rely primarily on electronic components to do most of the work and therefore
require minimal attention. In the case of solar electric modules, the only maintenance you may ever
need to do is check the electrical and mechanical connections every few years to be sure they are
clean, free of corrosion, and secure.
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clo s e - up
Living with Solar (and Wind) Power
day delivers about 10 percent of peak output, but a sunny day with snow on the
ground may increase peak output by about 10 percent. When the sun shines for 5 hours, I gain 4,000 watts
x 5 hours = 20,000 watt-hours, or 20 kWh. However, since my panels are on a fixed (nontracking) rack, peak
output happens only for a couple of hours either side of noon. Since I live in the North, wintertime output is much less
than summertime output because the sun doesn’t deliver as much energy to the northern hemisphere in the winter, there
are more cloudy days, and, of course, the days are shorter.
dark and overcast
M y Ex p e r i e n c e
The second question
people ask me about
living with solar electricity
(right after “Does it
really work?”) is, “How
many panels do you
have?” It’s not how many
panels that matters (they
come in all sizes), but
rather how much power
those panels produce. I
have 4,000 watts of peak
solar electric generating
power; in other words,
when the sun shines, the
modules produce about
4,000 watts of power.
We also have a wind generator, and the
question I get most often is, “How big is
it?” I never know exactly how to answer
this because “big” is a subjective term,
and it depends on who’s asking. So I
provide multiple answers, and that’s
probably why most people’s first question
is often their last.
• The tower is 115 feet tall (tall is one
kind of big); tall enough to get the
turbine 30 feet above the treetops,
which is necessary to avoid wind
• The blade diameter (another kind of big)
is just under 10 feet.
• What blade diameter really tells you is
the bigness of the “swept area,” which
essentially is the wind collection area —
in my case about 76 square feet. This
is the kind of big that really counts when
it comes to wind energy.
• The final “bigness” quotient is how
much power it can generate, and of
course that depends on the wind speed.
My Kestrel e300 will start to spin in a
7 mph wind, producing only a few tens
of watts, and produces a maximum of
1,000 watts in a 25 mph wind. (See
chapter 8 for more about wind power.)
Our household uses about 7 kWh per
day, with storage capacity of about 50 kWh
in batteries. That gives us about one week
of power storage if there is no sun or wind.
“No sun” conditions occur for us about two
months out of the year. During that time,
our wind generator helps to cover some of
the loss, but we usually need to rely on a
backup generator to keep the batteries
fully charged. It would not be cost-effective
to add more PV panels to meet our needs
during those two months because “no sun”
is just that; it wouldn’t matter if we had one
watt or one megawatt.
You may wonder what we do with 20
kWh of daily power generation when the
household only uses 7 kWh per day. The
answer is “dump load.” Also known as
a “diversion load,” this is a place to use
excess power that keeps coming in even
after the batteries are charged. Normally,
this power is simply not used, and not to
use available solar power feels like wasting
it. For us, an electric water heater is the
recipient of excess electrons. On a bright
summer day our batteries are charged
by lunchtime, and by dinner we have 40
gallons of 120°F water. Of course, this only
works during sunny periods, so during the
winter months most of our hot water is
heated by gas.
I decided not to install a tracking rack
because being at 45 degrees north latitude,
the main benefit would be reaped in the
summertime, when we don’t need extra
power. During the winter, the sun angle
is so low that tracking would not provide
appreciably more power. After crunching
the numbers, I found that it would be more
cost-effective to buy more PV panels than
living with solar ( and wind) power 135
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c lo s e - up
Living with Solar (and Wind) Power
to invest in a tracking rack. This argument
works only because we are off-grid. If we
were on-grid and able to sell electricity
back to the utility, the extra summer power
generated would be beneficial. A careful
examination of local conditions for solar
power generation, utility costs, and the
incremental costs and benefits of a tracking
rack will tell you which racking system is
more cost-effective in your situation.
The best thing about PVs is that they
simply sit in the sun and quietly do their job
with no moving parts, requiring little or no
attention for years at a time. Sometimes I
go outside just to look at them — it’s quite
amazing to see something that does so
much work with so little fuss.
The real maintenance for us is in the
batteries. They’re heavy, corrosive, and smelly,
and they need regular care and attention.
For best operation, they need to be kept
between 60 and 90°F, they must be filled
every couple of months with distilled water,
and the terminals need to be checked for
corrosion (and cleaned, if needed). If they’re
not charged just right, batteries don’t last.
The best thing about
PVs is that they simply sit in the sun and
quietly do their job
with no moving parts,
requiring little or no
attention for years at
a time. Sometimes
I go outside just to
look at them — it’s
quite amazing to see
something that does
so much work with so
little fuss.
M o n t h ly e n e r g y r e s o u r c e ava i l a b l e f r o m s u n a n d w i n d
Solar kWh/kW
Wind Power Density W/sq M
Our batteries live in a shed next to
the house, in a well-insulated box that has
a vent fan to remove hydrogen gas that is
released during charging. Make-up air for the
fan comes from inside the house, through
a wiring conduit, allowing for warm air to be
moved around the batteries during colder
weather. I keep a remote thermometer in the
box so I know if they’re too hot or too cold.
Before the box was well insulated, I
used a couple of 100-watt electric battery
heating pads during the coldest part of
winter. These were only marginally effective
on subzero nights, and of course they came
with an energy penalty when we could
least afford the power. Once the box was
insulated and air-sealed against drafts, I
found the heat generated by the batteries
during sunny-day charging to be far more
substantial than what the heating pads
could provide. With the insulated and
ventilated box, the battery temperature is
acceptable without the heating pads.
In general, I’m really happy with our
current system. The wind and sun complement
each other quite well, in that the windiest
months are also the least sunny, and sunny
summer months are not very windy at all.
The chart here shows the relative monthly
energy resource available from both sun
and wind monitored at our site. Solar
power is expressed in how many kilowatthours of energy we collect over the course
of a month for each kilowatt of charging
capacity. Wind energy is expressed in terms
of power density, or how many watts are
generated for each square foot of swept
area (wind collector area represented by
the area covered by the blades as they spin
in a circle), based on the average monthly
wind speed. The chart shows at a glance
how PV and wind power can be seasonally
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Wind Electric
i n d m i l l s h av e b e e n around for a very long time. Relatively
short towers once hosted very large rotors with many blades to produce the power and torque needed for things like grinding grains and
running machinery. During the 1930s, wind electric generators made their way into
rural areas where there were no electric power lines. These low-voltage machines
were primarily battery chargers and were used to power low-voltage DC home appliances. Some were dedicated to pumping water.
Today there are a handful of manufacturers producing electricity-generating
wind turbines for both grid-connected systems and off-grid battery-charging applications. The term turbine generally refers to the combination of blade set and
generator assembly, while the term generator refers specifically to the electricityproducing unit.
Modern wind machines use high-efficiency generators or alternators and highly
refined blade designs and materials for maximum efficiency. There are also some
interesting and novel devices on the market that can capture energy in the wind.
These range from small rooftop wind machines to vertical axis wind turbine (VAWT)
designs. While there are niche markets and encouraging research in some new areas
of design, current best practices for harvesting wind energy center on the horizontal
axis wind turbine (HAWT). This chapter will focus on wind fundamentals and how
they apply to the tried-and-true HAWT.
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Using Wind
Energy at Home
electricity by
capturing the wind’s energy as it moves around
two or three propeller-like blades. The blades are
attached to a generator that produces electricity
when it spins. The turbines sit high atop towers,
taking advantage of the faster, stronger, and less
turbulent wind at 100 feet or more above ground.
Many locations have some potential for capturing wind energy, but the resource varies widely with
location, season, and time of day. Your neighbor
down the road may have more wind available than
you do, due to local conditions such as elevation,
exposure, terrain, and trees or other obstructions.
Most small wind turbines employ an “upwind”
configuration, meaning the rotor (the blades)
points into the wind and spins in front of the
tower, and the assembly is oriented by a tail vane
that is downwind of the rotor. A notable exception
are the Kingspan (formerly Proven) wind products
W i n d t u r b i n e s g e n e r at e
(see Resources), which are downwind and do
not have a tail. Downwind turbines may have an
unconventional look, but they can perform just as
well as their upwind counterparts.
Large, utility-scale generators and residential
grid-tied systems produce alternating current
(AC; the same current used by household electrical systems), but there are a number of direct
current (DC) wind generators that can be used
as battery chargers for off-grid applications. In
either case the power must be managed and
manipulated before it can be used. Residential
wind generators range in peak power generation
from 50 watts to 10 kilowatts or more and may
cost between $3 and $5 per peak “rated” watt
to buy.
As you’ll see, however, while the peak power
rating of a wind generator may help you get your
head around the relative size and capacity of the
unit, it’s not the best measure for comparing different machines because it has little bearing on
how much energy will be delivered over time.
Wind turbine
designs. Top row: upwind
HAWT, downwind
HAWT; bottom
row: two VAWT
makes up
the rotor
Basic parts of a small wind
electric machine
iWind Testi
My friend Hilton Dier III, a renewable-energy teacher and consultant, uses his own “Sound of Music
test” as a crude indicator of wind potential: “If the breathtaking, panoramic view of the valley below
makes you want to sing like Julie Andrews in The Sound of Music, the site may have possibilities.”
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iUnits of Measurementi
Keeping measurement units clear and consistent is extremely important when assessing wind
equipment. Mixing meters and miles or pounds and kilograms quickly leads to trouble. Wind power
has been long established in the European market, so many wind equipment manufacturers use
metric units when describing their machines, while some U.S. manufacturers also give values in
imperial units. Just be careful not to mix them up.
Before buying and installing a wind machine you
must assess your site for wind power potential,
determine how much energy you hope the wind will
produce, and research which models will deliver
what you need based on your site and the generator specifications. You will likely find a few options,
and you’ll need to compare differences in cost,
quality, durability, sound level, and ability to produce the most energy at your site.
Also be sure to know what’s covered by each
manufacturer’s warranty, as this is a good indicator of a company’s trust in its own products.
Home Power magazine publishes a wind turbine
buyer’s guide every year or two that surveys units
worth buying in North America (see Resources).
Estimating Energy
in the Wind
p o w e r r e l at i v e t o s w e p t a r ea
relative power output
Assess Your Site
30 40
50 60 70
80 90 100 110 120 130 140
swept area
For example, if your wind turbine has a rotor
diameter of 10 units (the units may be any measure of length), the radius is 5 units. Therefore,
the swept area is:
3.14 x 52 = 78.5 square units
energy that can be captured
from moving air is a function of wind speed, wind
“collector” area (called the swept area), and (to
a lesser extent) air density. Swept area is the
circular area covered by the blades as the rotor
spins. It can be expressed in square feet (sq. ft.)
or square meters (sq. m).
T h e am o u n t o f
Swept Area Trumps All
Longer blades mean a greater swept area, allowing for more wind energy collection. Doubling the
length of the blades quadruples the area from
which the wind’s energy can be captured. Swept
area is reported on manufacturer specifications,
but you can calculate it yourself using the rotor
diameter and applying the formula for the area
of a circle:
3Swept area
Swept area = π x radius2
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Swept area increases exponentially with rotor
diameter. Compare the above value for a 10-unit
rotor with the swept area of a 12-unit-diameter
cubic foot (lb/cu. ft.) or kilograms per cubic meter
(kg/cu. m). Manufacturers rate the output of their
machines at a standard temperature of 59°F and
air density at sea level.
3.14 x 62 = 113 square units
Air density has a relatively small effect on available energy when compared to wind speed, but
for a basic understanding, there’s more energy
available in a flow of cold, dry air at low altitude
than from warm, humid air high in the mountains.
All other things being equal, change in air density
is roughly 3 percent for every 1,000 feet in elevation change.
As these examples show, a 20-percent increase
in rotor diameter results in a swept area increase
of 44 percent. In terms of evaluating potential
performance of a wind turbine, swept area is
the most important factor. Simply put, the greater
the swept area, the more energy a wind generator
will produce, given the same wind resource. The
chart below shows that doubling the swept area
doubles the potential power output.
Air Density
Designated by the Greek letter rho (ρ), air density decreases with increasing altitude, temperature, and humidity. It is expressed in pounds per
A i r De n s i t y Va r i at i o n s
This table shows a few examples of air density variations. The
difference in air density between 0°F at sea level and 70°F at 2,000
feet is 24 percent, translating into about a 15-percent change in the
power of a moving air mass.
Air Density (pounds
per cubic foot)
Air Density (kilograms
per cubic meter)
relative power output
10 12 14 16 18 20 22 24 26
wind speed
Wind speed is the air velocity and is expressed in
either miles per hour (mph) or meters per second
(mps). When working with formulas, the values must
be in the same units (metric or imperial) as the density and swept area. 1 mph is equivalent to 0.447
mps; conversely, 1 mps is equivalent to 2.24 mph.
Power increases as the cube of velocity, so
doubling the wind speed increases the available
energy eightfold. Small changes in wind speed
yield dramatic changes in energy produced. The
Power Relative to Wind Speed graph (at left)
shows how power output increases cubically compared to wind speed. Keep in mind that the actual
power output of a turbine varies with the swept
area and generator capacity, but the relative comparison between wind velocity and power always
follows the same relationship.
Useful Range of Wind Speeds
p o w e r r e l at i v e t o w i n d s p ee d
Wind Speed and Power
28 30
Many wind turbines do not start turning until the
wind speed reaches the point of overcoming the
inertia of the system, often between 7 and 10
mph. This is called the cut-in speed. There is very
little energy in wind speeds below 6 to 8 mph,
so it’s not worthwhile to try to capture them. On
the other end of the spectrum, most turbines will
not produce additional power when wind speeds
increase beyond 25 or 30 mph, having mechanisms to limit speed and protect themselves in
high winds. Be wary of advertising that shows
energy performance values in winds below 6 mph
— it just isn’t going to happen! Likewise, performance claims above about 30 mph indicate that
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someone wants to sell you a machine that may
end up tearing itself apart in high winds.
P o we r Re l at i v e t o W i n d S p ee d
e300i (48v) Annual Harvest
Wind Energy
Energy, expressed in watt-hours for our purposes,
is a quantity of power (wattage) produced over
time. The energy produced by a wind generator is
a function of:
• Average wind speed at the tower location
• Wind speed frequency distribution, based on
data showing how many hours during the year
the wind blows within a certain speed range
(this range of combined data points is called
bin data)
• Wind turbine power curve, indicating the
power produced by the generator at various
wind speeds
Kinetic energy, or power, available in the wind
can be can be expressed by the following
• Tower height (taller towers provide access to
higher and more consistent wind speeds than
those available closer to the ground)
Wind speed ms -1
Average energy produced as a function of average annual wind speed for a
Kestrel e300i. Image courtesy of Kestrel Renewable Energy,
Power = (air density ÷ 2) x
swept area x (wind speed3)
Power Curve and
Energy Curve
Manufacturers publish power curves showing the
power output, in watts, at various wind speeds.
However, this information will not tell you how
much energy (watt-hours) the machine will produce at your site given your wind resource. Some
important information a power curve does provide
is whether, when, and to what extent the machine
will protect itself in high winds. Look at the wind
speeds over 25 mph on the curve and notice if
they drop off or flatten out. A steep drop-off indicates that the wind may have reached a speed
where the turbine’s over-speed protection mechanism has activated, and the rotor furls, or turns
itself out of the wind, and stops producing. A
small drop or flattening of the curve may indicate
at what speed the blades pitch, limiting the rotor
to a maximum speed.
More useful than a power curve is the energy
curve. This is the real nugget of information you
want to use when estimating the value of a wind
turbine at your site. The energy curve indicates
how many kilowatt-hours are produced over a
specific period of time given the average wind
speed at the turbine’s location. The Annual Harvest chart (above) shows how many kilowatthours are produced at various average annual
wind speeds.
estimating energy in t he wind 141
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Wind Speed
to getting power out of the
wind, it’s all about how fast the air is moving. A
wind generator’s maximum output power is rated
at a specific speed, usually about 25 mph, give or
take 5 mph, depending on the manufacturer (until
recently, this number was even more arbitrary). This
lack of consistency is important to understand
when comparing wind machines.
One manufacturer might rate the output of its
machines at 24 mph, while another might rate
output at 28 mph. The additional power produced
at higher wind speeds might make the 28 mph
machine look somehow “better” than the other.
However, the rated power output is not an indication of energy delivered!
Until recently, there was no standard for small
wind turbine performance ratings. A new American
Wind Energy Association (AWEA; see Resources)
performance and safety standard specifies 24.6
mph as the speed at which output power is rated.
The Small Wind Certification Council (SWCC; see
Resources) is working independently to verify test
results and to certify and label wind machines
to the AWEA standard so that consumers have a
better understanding of performance ratings and
W h e n i t c o me s
Rated Annual Energy
Rather than being overly concerned with the maximum power (watts) rating, what you want to know
is how much energy (kilowatt-hours) a generator
will deliver at your site and in your wind conditions. For this reason, it’s best to compare wind
machines on the basis of swept area and the
manufacturer’s (or SWCC’s) test results of energy
production at various average wind speeds, rather
than the “rated” power output. When using the
SWCC ratings to compare machines, the important value is the rated annual energy.
Lower average wind speeds produce less
energy than higher average speeds. It’s worth
repeating that the cubic relationship between
wind speed and watts means that doubling
the wind speed available to your wind turbine
increases the available power eightfold. Therefore, cutting the wind speed in half results in oneeighth the performance.
Increasing the turbine’s height above ground
offers access to faster, more consistent, less turbulent wind streams. In general, a minimum average annual wind speed of 10 to 12 mph is the
point at which wind power generation makes economic sense, depending on the cost of electricity in your area. (There are, of course, other values you might want to place on wind power.) This
does not mean that the wind blows 10 mph or
more all the time; it is an average of the various
wind velocities occurring at each hour throughout
the year. Sometimes the wind is at 0 mph, while
other times it may blow at gale force.
Wind Speed Data
Before building an expensive addition to the list
of things you need to maintain, it’s important to
understand the wind resource available at your
site. This is best done by obtaining long-term (at
least one year) wind speed data for the specific
site under consideration. There are several ways
to get this information, and they vary in ease and
Internet tools. The U.S. Department of
Energy’s Wind Powering America website (see
Resources) offers a wealth of information about
wind power. The National Climatic Data Center (NCDC) maintains long-term records of wind
speeds in various locations around the United
iWhere’s the Wind?i
When planning a solar electric system, the sunny spot is fairly easy to find, and shadows are obvious.
Wind being both invisible and variable, siting is not so easy. It may not be windy where you stand, but
100 feet in the air, above the treetops, the situation changes. Not only is it windier up high, but there
is less turbulence and variability created by obstacles that the wind needs to move around.
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T h e Tro u b l e w i t h T u rb u l e n c e
Buildings, crops, and trees
create drag and turbulence in
the wind. Local wind speed depends in part upon the “roughness” of the surface below
the wind turbine. For example,
smooth water and ice have
a very low roughness coefficient, which means little drag
is created as the wind blows
across these surfaces. Every
doubling of turbine height can
increase the wind speed up
to 7 percent over water, while
over woodlands or typical
suburban areas, this increase
can jump to nearly 20 percent.
To see turbulence in action, all
States In addition to this historical data, there are
a few Internet resources that can get you started
with a reasonable estimate of wind energy availability in many places around the country. The
National Renewable Energy Laboratory (NREL)
has produced some excellent wind resource
maps that others are using to build estimating
tools. One such effort is the Distributed Wind Site
Analysis Tool that guides you through selecting
your site and a wind machine to predict energy
production. See Resources for links to NREL’s
maps and the wind assessment tool. It’s important to note that data for these maps are estimated for a turbine height of 80 meters above
the ground. For most residential systems, a more
common tower height is about 30 meters, where
the wind speed will be somewhat lower.
Subjective assessment observations,
such as use of the Beaufort scale, show how the
wind affects your surrounding environment, and
these observations give you clues about available wind energy. Of course, this works only in
the moment, while effective wind power assessment requires long-term observation. Subjective
scales are more recreational: they can help you
get a feel for what the wind speed might be at any
given moment, but they are not at all useful at
predicting annual wind generator energy output.
The Griggs-Putnam Index of Deformity illustrates average wind speed based on the wind’s
flagging effects on trees and shrubs. Conifers are
especially susceptible to permanent growth deformations in consistently strong winds. If you have
class 3 flagging or better, you probably have a reasonable wind resource. However, if you don’t see
you need to do is fly a kite and
watch how the tail behaves at
different heights. Turbulence
is very hard on wind turbines,
creating lots of stress on bearings and the tower without
much power to show for it.
any flagging, you don’t necessarily have a poor
wind resource. There is only one way to be sure
of your wind resource, and that is to measure and
Recording anemometer. The most accurate way to measure site-specific wind resources
is to use a recording anemometer. This device
measures wind speed along with the duration of
specific speed ranges (bins) and stores the data
electronically, allowing you to quantify the “wind
regime” at your site accurately to estimate longterm energy production. To ensure accurate measurements, the anemometer must be located at
the same height as the proposed wind generator.
Data logging systems, such as the NRG Systems
Symphonie data logger, are available from professional wind equipment suppliers. Recreationallevel equipment includes products from Horizon Fuel Cells Technologies, Inspeed, and Talco
5Windswept trees. If you’re driving down the road and see trees that look like
they’ve had a bad haircut, it could indicate a good site for wind energy.
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iWind Monitoring Is Priceyi
One drawback to installing wind monitoring equipment is cost. A wind data acquisition system can
cost from a few hundred dollars up to $2,000, a price tag approaching that of a small wind machine.
Depending on the height and design, the cost of buying and installing a tower can range from a few
thousand to tens of thousands of dollars. A few places in the U.S. offer anemometer loan programs.
Ask your local Extension service, technical college, or wind equipment installer whether they provide
such a service. Another option might be to install a small wind machine on the tower and keep tabs
on power produced over the course of a year.
Efficiency and
things, harnessing energy in the
wind is not without its inefficiencies. There are
limitations to how much wind the rotor blades can
capture, along with losses in wiring and controls.
As with all
A fundamental limitation that applies to all
wind collection devices, known as the Betz limit,
states that a wind turbine cannot harness more
than 59.3 percent of the energy in the wind as a
theoretical maximum. To understand this limitation, imagine the wind blowing at a brick wall. The
wind speed abruptly drops to zero, and any energy
not absorbed by the wall is diverted as wind in a
different direction. A wind turbine’s rotor is not a
brick wall, but wind velocity on the downwind side
of the rotor will be slower than on the upwind
side, due to the energy harvested out of the wind
stream by the rotor blades.
Capturing 100 percent of the energy in the
wind stream would require reducing the wind
velocity to zero. Stopping the wind is impossible
if you want it to blow through and spin a set of
turbine blades. In reality, modern small wind turbines will capture 20 to 40 percent of the maximum energy in the wind. This “capture” efficiency
varies with the blade design and wind speed. Of
course, the generator, wiring, and electronic controls in the system are not 100 percent efficient,
so there are additional efficiency penalties inherent in the rest of the system.
How Much Power
Can You Make?
We have enough information and understanding
now to put the power equation together with an
example using my own wind turbine, a Kestrel
e300i. According to the manufacturer specifications, this turbine will produce 1,000 watts at a
wind speed of 10.5 mps. The rotor diameter is
3 meters, resulting in a swept area of 7 square
meters. We’ll assume a capture efficiency of 25
percent and an electrical efficiency of 85 percent.
When metric units are used, this formula result is
power expressed in watts. When using imperial
units, multiply the answer by 0.134 to obtain watts.
Here’s the equation written out and then with the
metric units (from the example) plugged in:
(air density ÷ 2) x swept area x (wind speed3)
x capture efficiency x electrical efficiency
(1.191 ÷ 2) x 7 sq. m x (10.53) x 25%
x 85% = 1,025 watts
How Much Energy
Can You Make?
Instantaneous power generation (watts) is only a
small part of the picture. The useful number you
need when considering a wind power system is
an estimate in kilowatt-hours of annual energy
output (AEO) that can be produced. Manufacturers have charts that present this data at various
wind speeds. There are also several methods for
calculating this yourself. All AEO values should be
considered estimates. The wind and the operating characteristics of turbines are far too variable
for anything better.
One simple AEO calculation comes from Mick
Sagrillo, in the American Wind Energy Association’s newsletter, and is attributed to Dean Davis
of Windward Engineering:
A x V3 x 0.085 x OTE = AEO
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The formula is the product of the swept area in
square feet (A), the average annual wind velocity
(V) in mph cubed, the density of air in pounds per
cubic foot, and the overall efficiency of the turbine (OTE). OTE accounts for the efficiency of the
blades, generator, wiring, and controls — everything between the wind and the electricity that is
ultimately used. Most residential turbines operate at somewhere between 15 and 25 percent
efficiency in typical wind distribution patterns.
Commercial machines used on wind farms typically achieve 35-percent overall efficiency.
Here’s an example using my Kestrel turbine,
with an average wind speed of 6 mph, where OTE
is the capture efficiency multiplied by electrical
75.4 x 63 x 0.085 x 21.3% = 294 kWh per year
Applying Wind Speed Data
Understanding average wind speed is useful
in determining how much energy can be produced at your site and will help you in choosing
the most suitable turbine for your wind regime.
Higher average wind speeds mean that a higherpower generator would be cost-effective. Lower
average speeds call for a smaller (lower power
output) generator with a larger swept area to
capture more of the available wind. But average
wind speed only tells part of the story. Knowing
how wind speed is distributed over time brings
you closer to a more realistic estimate of annual
energy production. A speed distribution assessment indicates not just the speed of the wind, but
how much time the wind spends blowing at that
speed over a period of time.
Wind speed distribution assessment.
This assessment methodology is often built into
more expensive recording anemometer software.
Despite the expense, it is the most useful way
to quantify the available wind resource and the
energy produced by a specific combination of
wind regime and wind machine. This assessment
is especially important where costs and risks are
high and there is a need for detailed technical
and economical evaluation of the wind resource.
The occurrence and duration of various wind
speeds can be assembled graphically as a wind
speed distribution pattern. The Weibull distribution curve describes this annual variation in
wind resource. It indicates the number of hours
each year during which you can expect the wind
to blow at a specific speed (or range of speeds)
and distributes this information in data “bins.”
For example, if the wind blows at 10 mph at your
site for 600 hours (out of the 8,760 total hours
in a year), you can use the manufacturer’s output power data to calculate how much energy (in
e x am p l e o f w e i b u l l w i n d s p ee d d i s t r i b u t i o n
annual hours at speed
Weibull Wind
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
wind speed, MPH
Speed Distribution graph. The
number of hours
in each bin add
up to the total
number of hours
in a year.
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iPower Densityi
The Kestrel’s cut-in speed (the speed at which the rotor starts to spin and produce power) is about
6 mph. If my average speed is only 6 mph, then how can there be any useful power in the wind at
all? The answer lies in the wind speed distribution, which can be used to quantify the wind’s power
density. Power density is a measure of how much wind energy passes through the swept area. It
is the average of all wind speeds weighted by the duration of each speed “bin” (as per the Weibull
distribution), which is different from the simple average wind speed.
kilowatt-hours) will be produced in that 10 mph
wind during those 600 hours.
A variation on the Weibull distribution curve is
known as the Rayleigh distribution. This is simply
a mathematically derived “shape” of the Weibull
curve that is commonly used to estimate wind
speeds and thus energy production. The shape
changes based on the average wind speed and
variability. As average speed increases, the bell
on the curve moves to the right, indicating more
overall wind energy.
The Proof is in the Wind
As you can see, there are many ways to estimate
wind power and energy that give you an idea of
what you can expect from the wind resource at
your site. While these offer some level of comparison, such methodologies are very rough estimates, and manufacturers’ engineering data are
not the same as real-world results. Be aware that,
as with all things, your “actual mileage” will vary.
Despite manufacturer’s claims, tests, and charts,
there is no way to predict exactly how much
energy your wind generator will actually deliver
given your particular site characteristics. If you
have a high-cost project in a questionable location, it’s especially important to remember that
nothing will take the place of real-world, long-term
Co s t - E f f e c t i v e n e s s a n d Hybr i d E n e rgy Sy s t e m s
Your goal is to maximize renewable kilowatt-hours, so any
comparing of cost must include
the total value of the energy
produced over the lifetime of
the machine, compared to the
money invested over the lifetime,
including maintenance costs. If
I’m only producing 294 kWh per
year, and I’m paying $0.15 per
kilowatt-hour for electricity from
the power company, I’m earning only $44 per year. That’s a
227-year payback on a $10,000
system (not including maintenance costs or any monetary
incentives). Worse, it can’t begin
to cover my annual electrical
energy needs. However, if my
average wind speeds were
doubled, I’d generate eight times
more energy, and the payback
falls to under 30 years.
In reality, I harvest about
1,000 kWh per year from the
wind. This is not a lot of energy,
but there are five factors that
change the payback equation
for me:
1.I am off-grid with no utility
power available at all.
2.I have a solar electric power
3.At my location, there is more
sun in the summer and more
wind in the winter.
4.If I don’t get the power I
need from nature, I need to
run my generator, at a cost
of about $0.75 per kWh.
5.I have a strong desire to
reduce my reliance on fossil
fuels, and I understand that
comes at a cost, which I am
willing to pay.
In terms of economics,
small wind does not make
sense at my location. But
in terms of practicality and
personal goals, it’s a good
option and the perfect seasonal complement to solar
electric. The graph on page
136 shows the relative available solar and wind resources
and how they complement
each other seasonally.
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Wind Machines
and Controls
W i n d p o w e r s y s t em s require a good
deal of management and control, and most
manufacturers provide the required electronic
controls as a package with their turbines. All
wind generators — whether permanent-magnet
generators or high-frequency AC alternators —
produce AC power.
Grid-tied generators must be synchronized to
match the voltage, frequency, and power quality of
utility power. This task is handled by the inverter.
For battery charging, AC power must be rectified
(at the controller or in the generator) to the DC
power required by batteries.
When the batteries are full or the grid is down,
any excess power generated needs a place to go.
If the wind blows when there is no load on the
generator, the fast-spinning rotor can be damaged
itself or cause damage to generator bearings. For
most wind turbines on the market today, controlling speed in these conditions requires a diversion,
or dump load, to absorb the energy. (Read more
about controllers and dump loads in chapter 10.)
Wind generators typically have rotors with two
or three blades made from fiberglass, wood, carbon fiber, or composite material. Fewer blades
3Rotor and blade design is engineered
for efficiency, balance, and the wind
regime for which the
turbine is intended.
yields higher aerodynamic efficiency, but more
blades offers better rotor balance and may start
spinning at lower wind speeds. A well-balanced
rotor reduces mechanical strain on bearings for
greater longevity. Modern turbines are commonly
available with two or three blades, offering a good
compromise between efficiency and balance.
System Cost
When it comes to wind energy, there’s no such
thing as cheap. Your goal is to achieve costeffective energy generation over the lifetime of
the wind machine and system components. In
terms of overall cost of your wind project, the
price of the turbine will probably be small compared to the complete system, which includes the
cost of the tower, cabling, labor, and site work
(crane, excavator, and so forth) that are required.
If you buy an inexpensive wind machine, you will
likely spend more on maintenance over the long
run, unless it is installed at a site with only lightto-moderate winds. More costly models tend to
be heavier and more durable. They also spin more
slowly, which reduces noise.
Turbine Noise
Small wind machines may be relatively quiet,
or they can be quite noisy, depending on their
design. Often the sound they produce is just a
little bit louder than the surrounding wind noise.
However, at certain speeds or in certain kinds
of winds, a whirring or whooshing can be heard,
even to the point of roaring at times. When the
wind speed is high and the turbine is furling out
of the wind, the noise can be quite loud, depending upon the machine and the mechanism it uses
to protect itself.
When shopping for a wind turbine, it’s a good
idea to listen to the models in operation, preferably in both low winds (when noise often is more
noticeable), and high winds (when speed governing can be loud), to be sure it won’t bother you
or your neighbors. Like a crying baby, if the wind
generator is your own, it doesn’t sound so bothersome — but if it’s not yours. . . . Taller towers
improve performance and move the noise farther
away but may create a visual encumbrance for
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the neighbors. Tower height will likely be subject
to local zoning regulations, so be sure to look into
this issue first.
Speed Controls
High wind speeds can damage a generator by
causing it to spin too fast, so turbines include
speed-governing mechanisms to deal with excessive speed. These are automatically engaged,
mechanically activated controls that change the
pitch of the blades as wind speed increases, or
they furl the entire rotor out of the wind (vertically or horizontally) so that the blades do not
accept all of the wind’s force. Pitch adjustment
may allow the turbine to continue to produce maximum power in high winds, while rotor furling may
cause the rotor speed to slow, reducing output.
Sometimes it’s necessary to stop the rotor
from spinning, to facilitate maintenance or simply to turn off the wind generator in the event of
an approaching storm. This can be done mechanically, either with a rotor braking disc or a manual
furling mechanism that pulls the tail parallel to
the blades. Braking may also be accomplished
with an electric, or “dynamic,” brake that shorts
the electrical output wires together, putting the
machine under maximum load. Dynamic braking
is effective at slowing the rotor, but may not stop
it under heavy winds. Such electronic braking may
be handled through the charge controller, and is
as simple as throwing a switch.
Area of wind turbulence around a
building of height
H and the relative
heights and distances required
to avoid turbulent
W i n d t u r b i n e s t y p i c a l l y are mounted
atop tall towers so that they can access large
quantities of turbulence-free moving air. The
towers must be sturdy enough to hold their own
weight plus the deadweight of the machine
mounted on top, and they must be stable enough
20 H
to withstand the lateral forces delivered to both
the tower and turbine during the highest wind
speed that may be experienced at the site.
Turbine manufacturers offer data on the maximum lateral thrust developed by their machines.
Commercial towers and turbines often are able
to withstand hurricane-force winds of 140 mph or
more, but only when proper design and installation techniques are followed.
There are several very good reasons not to
mount a wind machine on a rooftop or attach it in
any way to a building:
• Location with very low wind resource
• Wind turbulence created by objects near the
• Thrust forces acting upon — and developed
by — generators that will be transferred to
the building
• Vibration created by a spinning turbine
Tower Power
You wouldn’t put a solar panel in the shade and
expect it to generate much power; don’t make
the equivalent mistake with a poorly sited wind
generator. The absolute minimum recommended
tower height is 30 feet above any ground feature within 500 feet. If the turbine is located in
a wooded area, it must be at least 30 feet above
the tops of the trees. In addition to height, there
must be no obstructions within a minimum 500foot radius around the turbine. These are minimums, but winds are influenced by the ground surface at heights up to 300 feet. More tower means
more power, because wind movement is faster,
more consistent, and less turbulent farther above
ground-level influences.
Tower Design
Towers can be made from a single, heavy-gauge
steel pipe, or from steel lattice interlaced between
three or four legs. They can be freestanding or
guyed (secured by guylines, or guy cables) and
are usually assembled on the ground and then
stood up using either a crane or a tilt-up kit. In
order for the turbine to yaw (rotate horizontally
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to meet the wind), the tower must be reasonably
plumb. A guyed tower can be adjusted somewhat
for plumb using the guy cables to take minor
twists out of the tower. A freestanding tower must
have a level foundation and plumb base section,
which might require the use of leveling nuts or
shims between the foundation and base.
Guyed Towers
Guyed towers can be two types: fixed or tilt-up.
Tilt-up towers and kits are made by the likes of
Bergey and NRG Systems (see Resources) and
can be used with either pole or lattice towers. Tiltup towers require four sets of guy cables, while
fixed towers generally use three sets, with each
set consisting of two or more guys, depending on
the tower height and thrust loads. Each set of guy
cables will extend out from the tower for a distance of between 50 and 80 percent of the tower
height and are attached to a common anchor.
As you can imagine, guyed towers require a
fairly large footprint on the ground, with lanes
cleared for each guy cable run. Lattice towers can
be climbed, and therefore do not necessarily need
to be tilt-up. A tubular pole tower is often tilt-up,
but it is possible to weld steps onto the pole so
that it can be climbed, giving it the flexibility to be
a fixed guyed, tilt-up, or even a freestanding tower.
Guyed towers rely upon proper wire tension
to stay vertical while maintaining some flexibility to react to the wind. Cable tension is often
adjusted by way of a turnbuckle on each cable,
located near the anchor. The type of cable and
required tension are specified by tower manufacturers. For example, Rohn specifies that
stranded EHS cable (extra-high-strength; the
only type you should consider for guys) be used
for their lattice towers and tensioned to 10 percent of its breaking strength (see EHS Cable
Breaking Strength at right).
The cable tension will increase under wind load.
Too little tension means a wobbly, unstable tower,
while too much tension can put excessive compression force on the tower, causing the legs to
fail. The combination of guy cables on your tower
must be able to withstand the maximum possible
forces created, with an additional safety margin.
3Guy cable
Crosby clamp
cable thimble
wire grip (open)
wire grip
3Connecting multiple
guy cables to the
anchor through an
equalizer helps to
equalize the tension
in all cables.
anchor rod
E HS Ca b l e B r ea k i n g S t r e n g t h
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Working with guy cables requires some specialized tools and equipment. Crosby (saddle)
clamps or wire grips can be used to secure the
cable as it wraps around the tower and anchor
attachment points. Thimbles are important to
prevent the guy cables from crimping under
stress as they bend around connecting points.
An equalizer plate can be used to attach multiple guy cables to a single anchor.
Tower Installation
Tilt-up towers are assembled on the ground,
and a gin pole (a pole with a pulley on one end),
attached to the tower at a 90-degree angle, is
used as a lever to raise the tower with a winch or
a griphoist. A griphoist is a hand-operated hoist
that is anchored on one end and pulls the gin
pole cable through it as you crank the ratcheting
handle. The advantage to tilt-up towers is that
they can be lowered for maintenance or to protect
the turbine from a potentially damaging storm.
Tilt-up towers do not require climbing and are
quite popular for this reason.
Lattice towers, such as those made by Rohn,
are available from wind dealers or equipment
suppliers, such as Tessco, Sabre Industries, and
Cable and Wire Shop (see Resources for websites). These typically are supplied in triangular, 3-tube (or -rod), 10-foot sections that can be
assembled on the ground. They can be lifted by
crane, raised with a tilt-up kit, or hoisted up one
section at a time using a vertical gin pole, pulleys,
and a tag line to steady the section as it is lifted.
A griphoist offers
mechanical advantage to pull the
hoisting cable.4
Gin Poles
A gin pole for lifting sections of a lattice tower
can be made using suitably engineered brackets,
pulleys, and a sturdy pipe. The brackets attach
to both the tower and the pipe, and the pipe is
moved up with the addition of each new section.
During this slow process (but less expensive than
a crane, if you do it yourself), a climber wrangles
each tower section into place while the ground
crew pulls the section up with a rope. This rope is
attached to the tower section to be moved, runs
up to the gin pole pulley, then down to a pulley at
Raising a tower section
with a gin pole. Pulleys
at the top of the pole
and bottom of the tower
keep the direction of pull
vertical, thus avoiding a
potentially pipe-bending
angular force on the
tag line
hoisting rope
rope pulled by
3Raising a tilt-up tower
anchored strap
winching handle
gin pole
hoisting cable
gin pole
to hoist
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Gin Pole
Used in: All tilt-up and some
guyed and freestanding wind
tower installations
A.K.A.: Lever arm, lifting pole,
falling derrick, davit
What it is: A lever to raise a
tilt-up tower or a temporary
crane for a non-tilt-up tower
What it ain’t: A liquor survey
The phrase “gin pole” is used
to identify two very different
structures associated with wind
generator towers.
In reference to tilt-up towers,
the phrase refers to the lever
arm that is used to lift the
tower off the ground. Usually
it is a steel pipe of the same
diameter as the tubular tower
pipe, and can be as long as the
guy wire radius.
A gin pole makes it easier to
raise the tower. Try tilting up a
pipe or pole by pulling along the
length of it, and you’ll find that
something may break before
anything lifts. Adding a lever at
90 degrees makes it easy to lift
the pipe.
In reference to non-tilt-up
towers, a gin pole is a temporary “crane” that sticks up
above the tower. It allows you
to lift additional tower sections
and the wind generator without
hiring a $200-per-hour crane.
Generally, two brackets
are attached to a tower leg with
bolts, providing a sleeve for
the base of the tower, where the rope changes
direction for the crew to pull on.
Freestanding towers can be pole or lattice type
and must be anchored in a concrete pier, or foundation, engineered to withstand the design loads
of the tower, turbine, and prevailing winds. These
the gin pole, which is pulled up
through the brackets. A davit or
block is added on the top, and
a lifting line is threaded through
before the pole top is raised out
of reach.
The gin pole is then bolted
securely in place before any
lifting is done. After each section is in place, the gin pole and
brackets are moved up to the
next section. Temporary guy
ropes are necessary to keep the
tower stable.
— Ian Woofenden
Reprinted with permission.
© 2012 Home Power Inc.,
are more costly than guyed towers because of
the amount of steel in the tower and concrete in
the foundation, as well as greater site preparation costs. However, freestanding towers require a
much smaller footprint because there are no lanes
to clear for guy wires.
guyed tilt-up
pole tower
guyed lattice tower
Types of towers
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Foundations and
must have a solid, stable
foundation and must be well anchored to withstand
the lateral, compressive, and uplift forces of
the wind. Freestanding towers require a single,
massive, well-engineered concrete foundation
that also acts as an anchor. Guyed towers need a
foundation under the tower to resist compressive
forces and an anchor for each set of guy wires.
Anchors and foundations must extend below
the frost line (the depth to which the ground
freezes in winter) to prevent heaving or shifting. A
few other critical design factors include:
A wind tower
• Weight and thrust of the turbine
• Wind load on the tower at the design wind
• Weight and strength of the tower
• Soil into which the anchor is placed
• Anchor angle (its position in the ground)
Turbine and tower load specifications and anchoring requirements are available from manufacturers and must be consulted for proper anchoring
system design.
Types of Anchors
Several types of anchors are available to suit various soil types and tower requirements. Chance,
a subsidiary of Hubbell Power Systems (see
Resources), manufactures a variety of suitable
anchors and is a good online resource for information on anchoring. Soil types are classified
according to the table below.
Concrete anchors buried underground can
provide the weight needed to counteract horizontal and uplift forces, but only if the weight of
the anchor is sufficient and the soil is cohesive
enough to hold the anchor in place. One cubic yard
(volume of a cube with 3-foot sides) of concrete
weighs about 4,000 pounds.
Screw-in anchors are rated for use in soil
classes 3 through 7. They are available with
varying diameters and numbers of helixes, all
S o i l C l a s s i f i c at i o n s
Common Soil-Type Description
Geological Soil Classification
Sound hard rock, unweathered (bedrock)
Granite; basalt; massive limestone
Very dense and/or cemented sands; coarse gravel
and cobbles
Caliche (nitrate-bearing gravel/rock)
Dense fine sands; very hard silts and clays (may be
Basal till; boulder clay; caliche; weathered laminated rock
Dense sands and gravel; hard silts and clays
Glacial till; weathered shales, schist, gneiss, and siltstone
Medium-dense sand and gravel; very stiff to hard silts
and clays
Glacial till; hardpan; marls
Medium-dense coarse sands and sandy gravels; stiff
to very stiff silts and clays
Saprolites, residual soils
Loose to medium-dense fine to coarse sands to stiff
clays and silts
Dense hydraulic fill; compacted fill; residual soils
Loose fine sands; alluvium; loess; medium-stiff and
varied clays; fill
Flood plain soils; lake clays; adobe; gumbo, fill
Peat, organic silts; inundated silts, fly ash, very loose
sands, very soft to soft clays
Miscellaneous fill, swamp marsh
(a) Note: It is advisable to install anchors deep enough (using extensions) to penetrate into Class 5 or 6 soil when the soil layer above it is Class 7 or 8
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anchor rod
With expanding
anchor closed
5An anchor can be embedded
in concrete and buried in
cohesive soil.
contributing to holding strength. Some can be
screwed into the soil by hand with a lever bar,
while harder soils or anchors with more and
larger helixes may require the torque of a handor machine-operated hydraulic drilling tool. Screwin anchors are most commonly used for temporary anemometer towers and other light-duty
Expanding anchors allow you to auger a hole
into the ground, then place the anchor into the
anchor open
hammer drill. The hole should be at least 3 feet
deep so that enough rock is above the anchor. If
the anchor is too close to the surface, a piece of
rock could crack under pressure or if water enters
the hole and freezes. The anchor is inserted into
the hole and tightened so that the split wedge is
forced against the wall of the hole. As more tension is put on this anchor, the split bolt will want
to expand, wedging it more tightly in the hole. The
hole should be sealed with brick mortar to keep
out water. Epoxy is not recommended because it
can prevent the anchor from expanding as it pulls
under tension.
anchors, a hole
is drilled into the
soil, the closed
anchor and rod
are dropped into
the hole, anchoring helix blades
are unfurled,
and the hole is
3Screw-in anchors with
various numbers and sizes of
helixes are chosen according to anchoring strength
requirements and soil type.
hole. Expanding leaves at the end of the anchor
are unfurled, wedging themselves into the surrounding soil, and the anchor hole is then backfilled. These are advantageous in dry, solid soils
because the anchor leaves expand into undisturbed (and therefore stronger) soil, but strength
of the anchor is also dependent upon the quality
of the backfill tamping.
Rock anchors are used when the soil is not
deep enough for any other anchor to make sense.
A hole is drilled into bedrock using a pneumatic
A rock anchor
slides into the
drilled hole with its
split wedge closed,
then is tightened
to force the split
wedge against the
rock inside the
foundations and anchoring 153
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require regular
service — they don’t sit idly on your roof like
solar panels with no moving parts. And while
maintaining a wind generator is nothing like
changing the oil on your car (which almost anyone
can do), maintenance, like oil changes, must be
done to get the most out of your investment and
to avoid catastrophic failure. For this reason, you
need a plan and a tower design that allow you to
access the generator for required service.
Annual inspection of tilt-up towers requires lowering the tower, and any maintenance can be performed on the ground. For fixed towers, access
requires climbing gear and the skills, strength,
and nerve to work 100 feet or more in the air. If
you drop a tool from up there, it can be at best
a 20-minute round trip to retrieve it and at worst
a deadly mistake for someone on the ground.
Tether your tools!
M o d e r n w i n d ma c h i n e s
Maintenance Matters
The turbine manufacturer will have a maintenance
schedule that you should follow closely to get the
most out of your machine for a long time. The following are some general maintenance concerns
to keep in mind.
Environmental Exposure
Consider the elements and their effects on the
wind turbine and its tower. Depending on your
climate, both of these critical components may
need to withstand turbulent thunderstorms, lightning, intense sun, subzero temperatures, pouring rain, sleet, snow, ice, gale-force winds, blowing sand, and dust. Despite this constant abuse,
maintenance of modern wind machines is generally minimal (but, as mentioned, mandatory). Turbines that operate in higher average wind speed
regimes require more frequent maintenance.
Turbine Sound
Make a note — or even a recording — of the
sounds your turbine makes when it’s new. As the
machine ages, the sounds may change as bearings and blades wear. Notice the vibrations in
the tower at various wind speeds. Vibration will
worsen if the blades become unbalanced.
Pay attention to how the turbine behaves in various wind conditions. If it starts to wag its tail (an
unbalanced condition), an out-of-plumb tower or
excessive turbulence might be taking a toll on
yaw or rotor bearings.
Blade Inspection
Get out your binoculars or climb up to the turbine
to check the blades for stress cracks or other damage. Also make sure they spin in exactly the same
plane. Examine the leading edge of each blade for
signs of wear or damage. If water gets into the
blades (especially if they are wood), balance will be
affected. Be sure that furling mechanisms are still
working in high winds; you often can detect a problem by the sound the turbine makes in high winds.
Tower and Hardware
Inspect the tower twice a year to make sure all nuts
and bolts are tight and anything attached to it is
properly secured. New guy cables will stretch and
should be checked every few months for the first
year after installation, and once a year after that.
If a guy wire becomes loose, the tower can rock
back and forth in higher winds, stretching the other
cables and eventually bringing the tower down.
A tension gauge, such as one made by Loos
& Company (see Resources), makes checking
guy wire tension fast and easy. Be aware that a
guy cable that continues to loosen may indicate
a failing anchor.
iThinking Aheadi
Unless you have a tilt-up tower, maintenance will include climbing, so consider whom you might hire
to climb the tower when you have arthritic knees in 10 years. Okay, hopefully you won’t have arthritic
knees in 10 years, but you should have a backup plan that relies on something more concrete than
your friends’ goodwill (pizza and beer go only so far).
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cable tension is
read on scale
tension spring pulls
back and guy wire
placed into upper
chart on tool
indicates tension
as a percent of
breaking strength
for various cable
guy wire placed
between two lower
5Loose cable tension gauge
are tall, and wind
machines are heavy. Wind can be unpredictable,
trees can fall, and hardware can fail, while gravity
never fails.
Working on and around wind energy systems
requires a hefty “tool kit”:
W i n d g e n e r at o r t o w e r s
• Well-researched information
• Great attention to detail
• An experienced crew leader
• Mechanical and electrical skills
• Steady nerves
• Quality tools
• Professional climbing gear (if you’re not
installing a tilt-up tower)
A tower that is properly designed, anchored,
and maintained should not fall. And if you’ve
cleared around the tower and guy cable runs, no
trees should fall on them. Towers are everywhere
in our society today; they should not be feared,
but they must be well engineered to withstand the
forces of nature and machines.
Basic Safety Precautions
Protecting yourself when working on towers is just
as important as proper system design and maintenance. Here are the essentials:
Tie off the turbine. Be sure to put the brake
on the rotor to prevent it from spinning while you’re
on the tower. Even with the brake on, assume the
turbine can spin or yaw unexpectedly until you have
it safely and securely tied off. View the entire turbine as a heavy, two-dimensional spinning weapon
ready to knock you off balance when you least
expect it. Tie off both the blades and the turbine
assembly to stabilize them before doing any work.
Watch the weather. Tower work is safest
during calm, pleasant weather. Don’t work on the
tower when it’s too windy, or when it’s snowing
or raining.
Dress properly. Wear boots, gloves, and a
hard hat with a chin strap. Remove all jewelry,
tuck long hair inside clothing, and don’t wear
loose clothing. Wear a full-body harness attached
to the tower at at least two different points.
Know your gear. Learn about tower climbing
gear and make use of snap hooks, harness shock
absorbers, slings, and lanyards. Assume that at
some point in your climbing history you will slip
and fall; never be at risk of hitting the ground
when you do.
Most professional tower workers won’t work
on a tower unless it has a tower-integrated fall
restraint system consisting of a vertical lifeline,
running the height of the tower and to which a
harness can be hooked (in addition to hooking it
to the tower). A locking slider glides up the lifeline, but if you slip the slider catches the lifeline
and stops your fall.
Don’t work alone. Communicate well with
those working around you, using two-way radios
for talking with the ground crew. To protect others
from dropped tools or parts, make sure no one is
working on the ground or tower below you.
Check yourself. Do not climb when you’re
tired. Never assume you know everything and
don’t need to double-check.
Plan for everything. Ask yourself how many
different ways things can fail and plan for all of
them. It is, after all, your life that is at stake.
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Wiring and
now have their
own section in the National Electrical Code (NEC).
Article 694 covers all aspects related to wiring,
fuses, disconnects, grounding, battery charging,
utility interconnection, and signage. Refer to the
NEC for specific electrical requirements. See
chapter 10 for more information on the NEC.
W i n d e l e c t r i c a l s y s t em s
Supporting and
Connecting Cables
Electrical cables leading from the wind generator down the tower must be firmly supported so
that they don’t pull on the wires coming from the
generator. The heavy-gauge copper cables can
be quite weighty, requiring a strain relief at the
top of the tower to support them. One example
of a suitable strain relief is a wire net. Remember that a wind generator tower — and anything
attached to it — will vibrate, so be sure to use
crimp connectors for electrical connections and
Off-grid wind
system. A wind
generator system also includes
many of the same
and control elements
as a solar-electric
setup, such as
disconnects, charge
controller, inverter,
system monitor, and
possibly a backup
generator. 
cable strain reliefs that will not loosen with vibration over time. Cover all connectors with weathertight, double- or triple-wall heat-shrink tubing
with adhesive inside. See chapter 10 for more
information about wire sizing.
Lightning protection is imperative for a wind generator tower. While no grounding system can prevent damage from a direct lightning strike, there
are many ways to reduce the static charge surrounding your tower, making it much less attractive to lightning.
Grounding should follow NEC requirements.
At a minimum, the tower must be grounded by
attaching a wire between the tower and at least
one ground rod driven 8 feet into the ground (or
other suitable buried grounding array). Guyed towers should have one ground rod at each anchor,
and each guy cable must be connected to that
rod. Ideally, all ground rods are then tied together
with buried copper wire.
power cables
Wind generators create high-voltage electricity. It does not take very much electrical current to kill
a human. Be sure the generator is disconnected from the wiring before performing any work on the
turbine or tower.
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clo s e - up
Wind Wisdom from an Expert
with wind electricity formally began in 1984, when I installed my first machine. An 8foot-diameter Wincharger on a 112-foot homebuilt tower at my off grid home got me hooked on making
kilowatt-hours with wind.
y l o v e a f fa i r
Ian Woofenden
has been working with
wind for more than 30
years. An independent
consultant and recognized
expert in the industry, Ian
is also an instructor for
Solar Energy International, senior editor for Home
Power magazine, and the
author of the book Wind
Power for Dummies, along
with numerous wind power articles and equipment
reviews (see Resources
for Ian’s website).
Since then, I have owned and operated
multiple machines, learning by successes
and failures what works and what doesn’t.
I had the benefit of informally testing a
variety of machines and running up to three
machines at once, because of my position in
the wind industry, as well as my compulsion
to experiment and learn. I’ve been involved
in dozens of installations for others, working
with wind contractors and as a workshop
coordinator and instructor.
I love the feeling of harvesting free
natural forces. When people complain about
the weather, I suggest that they harvest
it! When it’s rainy, my rainwater tanks are
filling up. When it’s sunny, the solar-electric
modules are charging my batteries, and the
solar hot water collectors are heating up the
tank of water. And when the wind blows, my
wind generators charge the batteries, too,
staving off fossil-fueled generator use.
Living with wind electricity takes
awareness and persistence. It is not for
the faint of heart. All wind generators need
regular maintenance, which means lowering
or climbing a tall tower. Almost all wind
generators have “issues” at some point in
their lives — it’s rare to find a residential
wind project that has been trouble-free for
decades. If you go into it thinking it will be
simple and cheap, you are very likely to be
disappointed. If you go into it planning for
maintenance and bracing for trouble, you’ll
be able to maintain your excitement and
not get discouraged, while keeping your
machine running for years.
Living off-grid changes the way you
think about energy use (unless you have an
unlimited bank account). It helps you focus
on ultra energy efficiency and on shifting
your loads to the times when you have
energy coming in. Adding wind electricity
to a solar-electric system balances out the
low times and also brings you seasonal
surpluses that are fun to enjoy.
In my part of the planet, winds come
in winter, so I can use the surplus energy
for cutting more firewood with an electric
chainsaw, moving heat around the house
with fans, keeping the fridge cool even
though the wood-heated house is warmer
than in summer, doing the laundry on windy
days, and running plenty of lights during
those long winter nights and rainy days.
When the calm, dark times come, I have to
conserve energy by changing my lifestyle, or
turn on “the noise” — the propane-powered
generator — to charge the batteries.
Changing usage and behavior with the
weather is an acquired taste, but one that
I enjoy.
How can you figure out if wind energy
is right for your site and for you? Those are
two different questions with two sets of
answers. A good-to-excellent wind energy
site will have these characteristics:
I love the feeling of harvesting free natural forces. When people complain about the
weather, I suggest that they harvest it!
wind wisdom from an ex pert 157
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c lo s e - up
Wind Wisdom from an Expert
Living with wind
electricity takes awareness and persistence.
It is not for the faint of
heart. All wind generators need regular maintenance, which means
lowering or climbing a
tall tower.
• Adequate space and permission to put
a tall tower well above all obstructions
for years
• A reasonable (8- to 14-mph) measured or
accurately predicted average wind speed
• Reasonable wire-run distance from the
tower to the utility service or battery bank
• Neighbors who are at least happy, if not
excited, to have a wind generator in the
The perfect wind-electric system owner
has these characteristics:
• Adequate education before the fact, to
understand siting, basic system design,
and performance estimating
• Adequate budget to install a robust
system on a very tall tower
• Commitment to lower or climb the
tower once a year at a minimum (or hire
someone to do it) and perform whatever
maintenance is needed
• Awareness of the system and a
determination to address any changes
you notice before they become
catastrophic problems
• Patience to deal with the almost
inevitable problems that come with
being a wind-electric system owner
From my perspective as a 30+-year user
of wind-electric systems, student, teacher,
climber, and journalist in the residential
wind industry, there are some basic lessons
that could save you a lot of time, money,
and anguish:
• Try to capture the wind only if you can
put the wind generator on a very tall
tower, well above all obstructions in the
area. This is where the good fuel is;
trying to capture anything less than the
good stuff will only disappoint you.
• Put up a large enough rotor (blades and
hub) to generate a significant portion
of the energy you need. For most North
American homes, this means a rotor
diameter of 12 to 50 feet. Small rotors
capture only a small amount of energy.
• Ignore “wattage” ratings of wind
turbines, and get accurate estimates
of how many kilowatt-hours (kWh) the
machine you are looking at generates
in your average wind speed. Get a
second opinion.
• Buy turbines from manufacturers that
have been around for a while, have a
good reputation, offer a solid warranty,
and have a track record of good
performance and service. Run, don’t
walk, away from “new,” “improved,”
“exciting,” “breakthrough” products
— these companies will likely have
vanished or be in bankruptcy before
too long. If no one else is doing it, ask
yourself why. Or, to quote wind geek
Dan Bartmann, “Before you ‘think
outside the box,’ find out what’s in the
box, and why.”
• Install your system carefully and
don’t cut corners. “Cheap” now will
turn into expensive later. Build robust
infrastructure — wind is a powerful
resource that doesn’t fool around.
• Maintain your system very regularly,
once or twice a year.
Have fun with your wind-electric system!
Life is short.
Living off-grid changes the way you think about energy use (unless you have an unlimited bank account). It helps you
focus on ultra energy efficiency, and on shifting your loads to the times when you have energy coming in.
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Hydro Electric
f yo u l iv e near falling water, a small-scale hydro system may work well for
home electricity production. With micro-hydro systems, power generation can
range from 100 to 2,000 watts of electricity production from streams or small
rivers, with minimal damming and water diversion.
A dam serves as a way to create both a reservoir and a flow diversion. The
diversion sends water to an inlet pipe at the top of a vertical drop, which is required
to develop the necessary pressure to spin a water-powered generator. The reservoir
also helps provide a relatively constant flow of clean water with no air pockets. You
will need such a reservoir, but substantial dam construction is beyond the scope of a
typical home power project and therefore is not covered here.
Most rivers and streams flow all day long and year-round, making hydropower
more consistent — and often more cost-effective — than solar or wind energy. Of
course, seasonal flow variations, and freezing or drying of the water, may be real
issues in your situation. This chapter will help you to evaluate and understand the
potential for hydroelectric power at your site.
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Home Hydro
rare to find a location that
meets all of the practical requirements to make
harnessing water power worthwhile. You need
access to enough moving and falling water that
is reasonably close to a dwelling that can use
the power (or to grid power for grid intertie), and
you need to secure the required local, state, and
federal permits and rights to access the water
and harness its power. If such a site is yours,
you have struck your own little oil well, and
opportunity awaits!
Large-scale, alternating current (AC) hydro systems are generally not practical for homeowners due to cost, complexity, regulations, and the
volume of water needed to make the investment
worthwhile. Micro-hydro systems don’t require
much alteration of the stream and so have a minimal impact on waterways and ecosystems.
The power generated by a micro-hydro system
may be AC or direct current (DC) but will often be
converted to DC so the energy can be stored in
batteries. In fact, most micro-hydropower systems
can be considered battery chargers. One significant advantage to energy storage is that the generator can be much smaller than your peak power
I t i s s o me w h a t
The reservoir
upstream supplies
a steady water flow
through the penstock,
which carries water
down to the turbine
in the powerhouse.
Water flows through
the tailrace and back
into the river. 
demand, relying on batteries and a power inverter
to manage and deliver any power surges required
by the loads that exceed the output capability of
the generator.
The iconic image of an old-style water wheel
is not the modern way of generating electricity
that we’ll explore in this chapter. Water wheels
collected water’s energy as it flowed through a
river or over a relatively short dam at high flow
rates, low pressures, and low speeds. The energy
harvested was used for mechanical power, such
as grinding grain. Today’s modern hydro-power turbines require water to be delivered at high pressure through a nozzle that focuses a jet of water
onto a fast spinning wheel, or runner, which in
turn spins an electric generator.
The most common way to capture the water
energy in micro-hydro systems is to divert part
of the stream through a pipeline, or penstock,
downhill to the power-generating turbine, which
may be sheltered in a small shed or powerhouse
along with the required controls. After the water
has done its work, it flows back into the river,
often through another pipeline, called a tailrace.
How Much Power
Can You Make?
There must be enough energy in the water to justify installing a hydro energy system, so quantifying water resource is the first order of business. To estimate the available power of a stream
requires the understanding of a couple of key performance factors:
• How much water is flowing over a given period
of time (flow)
• How much pressure (head) can be delivered
to the hydropower generator
Head and flow will determine everything else
about the design of your hydropower system, so
you must capture these two parameters first —
and with reasonable accuracy. Accuracy cannot be
overemphasized: If you want to make the most of
the time, money, and labor invested in your power
system, you must take accurate measurements.
Once you know how much potential energy is
available in the water, you can begin to design the
16 0 H Y D R O EL EC TR I C G E N E R AT I O N
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systems to collect, control, and store this energy.
Those details include:
• Determining the type of turbine that best
suits your site
• Working with manufacturers to tailor the
turbine specifications to your site
• Sizing the generator capacity — usually a
compromise between meeting your power
needs, what the water can support, and cost
• Determining how much water must be
diverted to support the generator
• Sizing and layout of penstock pipe and wiring
• Determining requirements of controls
When you have some understanding of your water
power site and requirements for harnessing that
power, it’s time to contact a water turbine manufacturer to begin fine-tuning the design, based on
the specific equipment you choose. Working with
a manufacturer is important because there are
many turbine variables that can be customized
based on your specific site. Manufacturers, along
with experienced installers, can offer a wealth of
information and can custom-tailor a system to
suit your site.
Hydro Energy
to the details, I offer one
caveat: There are many different ways to express
the values we will be talking about, and it’s
important to keep the numerical units consistent
and clear while performing your measurements
Be f o r e m o v i n g o n
and calculations. Keep this in mind as you work
to evaluate the energy in the water by accurately
quantifying the head, the flow, and the resulting
pressure available for the turbine to generate
Head is the pressure generated by falling water. It
is dependent upon the vertical distance that the
water falls from the penstock inlet in the stream
bed to the turbine. Twice the head means twice
the power, so take advantage of all of the vertical
drop you can reasonably gain access to. Head is
often described simply in terms of feet or meters
of vertical drop, or it can be described in terms of
pressure. Pressure can be expressed in pounds
per square inch (psi), or in kilograms or newtons
per square meter.
Each vertical foot of drop creates 0.433 psi of
pressure. Therefore:
Total pressure (in psi) = Feet of head x 0.433
Expressed another way: 27.72" (2.31 feet) of elevation drop produces 1 psi of pressure. More head
means more power, but useful head for a homebased micro-hydro system ranges from 25 to 200
feet. With less than that, you may not have enough
power; with more, the costs to manage long pipe
runs and high pressure begin to take you out of the
micro-hydro realm.
Measuring Head: Method 1
You can evaluate head even if you don’t have
surveyor’s tools, but note that most barometric
or GPS-based altimeters often are not accurate
enough for head measurement. With two people,
a long board or 20-foot section of PVC pipe (much
iWater Weight + Elevation Drop = Pressurei
Why does a vertical drop create 0.433 psi per foot of head? One gallon of water weighs 8.345
pounds. There are 7.48 gallons in a cubic foot. One cubic foot of water weighs 62.4 pounds. There are
144 square inches in a square foot. Now we can calculate the weight of water in psi:
62.4 pounds ÷ 144 square inches = 0.433 psi
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lighter than wood), a level, and a tape measure
you can make a reasonably accurate measurement of vertical drop over uneven terrain. Here’s
1. Set one end of the long board at the high
point of your future penstock location and hold
the board straight and level.
2. Measure
and record the distance between
the raised end of the board and the ground. Mark
the ground where you took the measurement.
3. Move
down the slope and place the board
end on the ground at the measurement mark.
Hold the board level, measure to the ground as
before, and add this dimension to the first measurement.
4. Continue in this manner until you reach the
proposed turbine location, adding up all of the
heights that you measured; this is the total head.
Measuring head
with a level and
measuring stick
requires moving
downhill from the intake to the turbine.
Total head is found
by adding all of the
vertical measurements taken along
the way: H1, H2, H3,
and so on. 
Tip: You can use a hand-held sight level in place
of the pipe and spirit level, allowing you to get a
level line of sight over a longer distance.
Measuring Head: Method 2
Another way to measure head is to run a hose
from the top of the stream where your penstock
inlet will be, downstream to where the generator
will be. The diameter of the hose does not matter because there is no flow through the hose
measuring stick
with this test. Allow water to fill the hose, avoiding high spots that could trap air bubbles. Screw
a water pressure gauge with an appropriate scale
(0 to 30 psi is a good place to start) onto the
end of the hose, and read the pressure: each psi
indicates 2.31 feet of head. Accuracy is imperative; you will probably be traversing a very long
distance, so when you connect hoses, there must
be no leaks. Even small leaks can greatly affect
accuracy in measuring pressure.
Interpreting the Test Results
What you have measured in these tests is called
static head, or gross head — the pressure of
the water in the pipe when the water is not flowing. Friction losses will reduce water pressure as
it flows through piping between the inlet and the
power generator. Pipe diameter and length, and
each twist, turn, and elbow all increase pressure
drop (meaning the pressure will be reduced).
The pressure you end up with after these friction losses is called net head. Net head is the
pressure that the turbine has to work with (in
terms of useful power) and will be used for system design.
Flow is the volume of water that moves during a
specific period of time. It is expressed in any combination of a unit of volume over time, such as
gallons per minute, liters per second, cubic feet
(or meters) per minute, etc. Don’t confuse the
flow rate of volume with the flow rate of speed,
or velocity. Velocity is a surface-level measure of
speed in feet (or meters) per second.
Water flow will likely vary during different times
of the year, and power production varies with
water flow. Twice the flow means twice the power.
It’s important to assess your water resource and
size your system components for average stream
iBypass Flowi
A certain amount of water needs to remain in the stream to support aquatic life. Bypass flow is
determined by your state agency responsible for issuing the Environmental Protection Agency’s Clean
Water Act Section 401 Water Quality Certificate. Bypass flow must be subtracted from the total
stream flow to determine the flow that is available to you.
16 2 H Y D R O EL EC TR I C G E N E R AT I O N
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conditions, not the peak water flow after a heavy
rain. The maximum amount of water flow that can
be reasonably counted on is called the design
flow. Design flow, along with net head, will guide
your system design and component selection.
Measuring Flow
and Estimating
able to find information about
stream flow at your site from the U. S. Geological
Survey StreamStats data online (see Resources).
If not, there are three ways to measure flow
yourself: bucket measure, weir measure, and
cross-sectional flow measure.
Y o u ma y b e
Bucket Measure
For small streams, start with a bucket or barrel
of known volume. Find or create a narrow place
in the stream where you can capture most of the
water in the container, and use a stopwatch to
time how long it takes to fill. For example, if you
have a 5-gallon bucket and it takes 4 seconds to
fill, your flow rate can be calculated in any number of ways:
Weir Measure
In this case, a weir is a temporary dam that
allows all the water to flow through a rectangular opening of a known size. A weir needs to be
set up carefully but is fairly accurate in small- to
medium-sized streams. With a weir, you can easily
make flow measurements anytime throughout the
year with a simple depth measurement.
The goal is to create an opening, or gate,
that allows the stream water to back up into
a reservoir behind it, increasing the height of
the water in the reservoir while allowing some
water to flow through the gate and not over the
top of the weir. For accuracy, the bottom of the
gate should be level, and the water should flow
freely and smoothly through both the reservoir
and the gate.
Drive a stake into the reservoir area of the
stream, far enough upstream of the weir (4 feet
or more) so that the stake is not in the area just
behind the weir (where the level may be lower
than the rest of the reservoir as the water crests
over the gate). The top of the stake should be
level with the bottom of the weir gate. With water
flowing through the gate, measure the depth
of the water from the surface to the top of the
stake. The gate width should allow the water to
build up some head behind the weir, allowing for
a good depth measurement.
5 ÷ 4 = 1.25 gallons per second (gps)
Using a weir to
estimate flow by forcing water through a
known gate area and
measuring the water’s
height above the bottom of the gate. The
top of the stake must
be level with the bottom of the weir.
5 ÷ 4 x 60 = 75 gallons per minute (gpm)
5 ÷ 4 ÷ 7.48 = 0.167 cubic feet per second
5 ÷ 4 ÷ 7.48 x 60 = 10 cubic feet per minute
iMetric Conversions for Volumei
1 cubic foot = 7.48 gallons
1 gallon = 3.79 liters
35.31 cubic feet = 1 cubic meter
1 cubic meter = 1,000 liters
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Finding the Flow Rate
We i r F l o w Ta b l e
Once you know the width of the gate and the
water depth to the top of the stake, you can use
math or a weir table to find the stream’s flow rate.
Here’s the math to measure flow in cubic feet per
second (cfs):
CFM flow per inch of gate width
Depth in
D = depth from surface of water to top of stake,
in inches
W = width of weir gate, in inches
3.33 x D1.5 x W ÷ 500 = flow rate in cfs
Let’s say we have a 12"-wide weir gate and
we’ve measured 61/2" of depth. The formula now
looks like this:
3.33 x 6.51.5 x 12 ÷ 500 = 1.324 cfs
Multiply cfs by 60 to get cubic feet per minute
(cfm): 1.324 x 60 = 79.4 cfm
Multiply cfm by 7.48 to get gallons per minute
(gpm): 79.4 x 7.48 = 594 gpm
To use the Weir Flow Table (right) to determine
flow, find the depth by looking down the left column; if you measure an additional fraction of an
inch, find the nearest fraction in the top row. The
+0 column means that you have measured the
depth to an even inch. Move across the inch row
to the correct fractional column to find the flow
in cfm per inch of gate width. Multiply the value
in the table by your gate width in inches to find
the flow through the gate.
For example: You measure 61/2" of depth, and
your gate is 12" wide. Go across row 6 to the + 1/2
column, and you land on the value of 6.62. If your
gate were only 1" wide, that’s how much water in
cfm would be moving through it. Since your gate
is 12" wide, multiply by 12 to find your flow rate:
6.62 x 12 = 79.4 cfm
additional fraction of an inch, depth
Cross-Sectional Flow
This flow measurement is useful for assessing
larger streams. It involves measuring the average
depth of the stream and the speed of an object
floating on the surface. To do this, you’ll need to
find a 10- to 50-foot section of the stream that is
reasonably accessible.
To determine the average depth, find a relatively flat section of stream that you can walk
through. Mark a board or pipe with 1-foot increments along its length and lay it across the
stream from bank to bank. You can also use a
rope with a knot tied every foot. The actual distance between measuring points is not critical;
what matters is that the distances are the same.
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Measure the depth of the water across the
stream at equal intervals using the board or rope
as your guide. Calculate the average depth by
adding up all the measurements and dividing the
total by the number of measurements you made.
You can increase the accuracy by doing this at
several locations across the stream.
Measuring Velocity and Flow Rate
To measure the water’s velocity, mark a line
across the stream by throwing a rope across to
the other side. Do the same thing 10 to 50 feet
downstream, and include the section that you
used to measure the average depth. Measure the
distance between the two ropes.
Next, find something with some weight that will
float down the stream (fruit or vegetables work
well since they are relatively heavy, they float, and
they’re biodegradable) and measure how much time
it takes to travel from one marker rope to the next.
Repeat the test a few times to get an average.
Divide the length of travel (in feet) by the time
(in seconds) to compute the velocity of the water
in feet per second. However, because the stream
bed creates friction, the top of the water will be
moving faster than the bottom. An adjustment
factor of 0.83 helps compensate for this effect
for better accuracy in the velocity calculation.
Here’s an example:
We measure that it takes 15 seconds for an
orange to float 25 feet downstream.
The velocity of the stream is 25 ÷ 15 x 0.83 =
1.38 feet per second (fps), or 83 feet per minute
(fpm) (1.38 x 60).
You now have the three things you need to calculate flow volume: average water depth, stream
width, and water velocity. Use the following formula:
Flow (cfm) = Area (square feet) x
Velocity (feet per minute)
1. Multiply the width of the stream by the average depth to get the cross-sectional area. Let’s
say it’s 10 feet wide and 2 feet deep, so the area
is 20 square feet.
5Measure the cross-sectional area of a stream by
averaging the depths at various locations. Mark off
a known distance between two points to estimate
stream velocity by timing how long it takes a floating object to travel the distance.
2. Multiply the cross-sectional area (20 square
feet) by the velocity (83 fpm) to find the flow:
20 x 83 = 1,660 cfm
3. If you want your answer in gallons per second, multiply cfm by 7.48, then divide by 60:
1,660 x 7.48 ÷ 60 = 207 gps
Rough Power
Power output is a product of water flow, pressure,
and the efficiency of the entire hydropower system. To roughly estimate the system’s potential
for power generation, multiply head (in feet) by
flow (in gallons per minute) and divide by 10:
Head (feet) x Flow (gallons per minute)
÷ 10 = Watts
This simplified approach will give you a very
rough expectation of the system’s power output
in watts; it is based on installer’s experience but
is not a substitute for thorough analysis of your
project. In systems with lower component efficiencies, the “divide by” value may increase somewhat, indicating a loss in power.
As an example, if you have 40 feet of head and
a flow of 75 gpm, this works out to 40 x 75 ÷ 10
= 300 watts of power that can be generated continuously, as long as the water is flowing at that
rate. Multiply 300 watts by the number of hours
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of flow you can expect daily (or seasonally) and
divide by 1,000 to arrive at the potential kilowatthours the site can produce for you:
300 watts x 24 hours ÷ 1,000 =
7.2 kilowatt-hours per day
Intake Site
where the water is diverted
from the river and channeled into the penstock
leading to your turbine. The intake’s job is to
provide a constant flow of clean water. This
requires a debris screen (see Resources), or trash
rack, to catch particles that can clog the penstock
and damage the turbine. To prevent a plugged
nozzle or equipment damage, the filter system
must catch anything larger than the size of the
nozzle orifice. This also means the debris screens
must be cleaned frequently.
Sedimentation, caused by small particles (such
as sand and dirt) washing down the stream, can
quickly cover over your dam and block the intake.
Sediment must be removed and the trash rack
cleared regularly. To help avoid intake blockage,
T h e i n ta k e i s
the intake can be positioned on the downstream
lip of the dam, or upstream of the dam if there is
a sizeable reservoir.
A quiet pool of water around your intake allows
for smaller particles to settle out of the water
before entering the penstock. The inlet pipe
needs to be under water that is deep enough and
replenished at a rate that is fast enough to keep
the intake underwater, so that air does not enter
the system. Air in the penstock not only reduces
power but can also cause damaging shocks to
the turbine as it’s intermittently pounded by water.
Consider durability at every step when assembling
your hydropower system, keeping in mind that it
will be exposed to the forces of nature year-round.
Penstock Pipe
T h e p e n s t o c k p i p i n g must be sized to
provide the required flow and pressure to the
turbine without too much friction loss. Even
though a pipe may be able to carry all the water
to the turbine, if its diameter is too small, the
water flow will be restricted and slowed on the
way down, losing power along the way.
penstock intake with debris screen
debris screen
5The goal of the water intake at the top of the penstock is to provide a constant flow of clean water. Set up your intake system so that water flows through a trash rack or debris screen. The intake on the left requires a constant flow of water
from a reservoir above. The intake on the right is submersed in the reservoir.
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The variables to consider in penstock sizing
are head, flow, generator capacity, and pipe length
and layout.
A good design goal for your penstock is to limit
total friction losses to 10 or 15 percent, so you
can achieve a net head of 85 to 90 percent of
gross head. Once again, pipe size and material
will likely be a compromise between pressure
drop, ability to work with a given material at your
specific site, and cost. It will be important to discuss the finer details of your penstock design
with the turbine supplier or manufacturer.
Friction Loss
Most micro-hydro systems call for PVC pipe diameters between 2" and 8", depending upon head
and flow. You probably don’t want to exceed half
a mile in total pipe length unless the value of the
site in delivering power can justify the costs of
pipes and wires.
The Hazen-Williams equation offers an accurate method for calculating friction loss based on
pipe diameter and water flow. You can use the
Hazen-Williams Friction Loss table (page 168) to
find the head loss of several common pipe sizes.
Or you can calculate the friction head losses in
your specific piping configuration by applying the
Hazen-Williams equation when you know:
If you have 75 GPM flowing through a 2" ID
PVC pipe, the formula looks like this:
[0.2083 x ((100 ÷ 145)1.852)] x (751.852)
÷ (2.0674.8655)
To break it down further looks like this:
0.105 x 2969 ÷ 34.2 = 9.1 feet
In this example, every 100 feet of penstock
length results in a loss of 9.1 feet of head pressure. Therefore, for every 100 feet of pipe, you
would subtract 9.1 percent from the gross head
to find the net head value.
Accounting for Bends
The Hazen-Williams equation values are for
straight pipe. You will also want to account for
the effects of each elbow. It’s best to use longsweep 90-degree elbows or 45-degree elbows
wherever possible to reduce friction losses due
to bends and turns. The head loss for each longsweep elbow is roughly equal to 3 times the nominal pipe diameter in inches, but expressed in
feet of straight pipe. For example, a long-sweep
90-degree elbow on a 4" (nominal) pipe has a
pressure drop equivalent to about 12 feet (3 x 4)
of 4" straight pipe. A 45-degree elbow has a pressure loss of about half that of a long-sweep 90.
1. Type of pipe and its roughness coefficient (c)
Inside pipe diameter (ID). Note that the ID is
not the same as the pipe’s nominal size. Measure or research on manufacturer’s website.
3. Flow rate (in gpm)
For this exercise, we’ll assume a 75 gpm flow,
and the use of 2" (nominal) PVC pipe with a
Hazen-Williams roughness coefficient (c) of 145.
PVC is about as smooth as you can get, but pipes
with a rougher interior will have lower values (corrugated steel has a coefficient of 60).
Friction loss in feet of head per 100 feet of
pipe =
[0.2083 x ((100 ÷ c)1.852)] x (flow in gpm 1.852)
÷ (ID4.8655)
Choose long, smooth curves to use in the penstock to
reduce friction losses inside the pipe; the 90-degree
long-sweep elbow above is better than the standard
90-degree elbow below.
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Penstock Design
Let’s say you have 200 feet of head and 100 gpm
of flow, and the total length of the penstock is
500 feet, including four long-sweep 90-degree
elbows. With 200 feet of head, your penstock
loss might range from 20 feet (10 percent loss)
to 30 feet (15 percent loss). In this case, you
don’t want to exceed 6 feet of head loss for every
100 feet of penstock length (30 ÷ 500 x 100 =
6). Using the Hazen-Williams Friction Loss table
Ha z e n - W i l l i am s F r i c t i o n L o s s
The table below uses the Hazen-Williams equation to present friction
head loss for various combinations of PVC pipe sizes and flow rates.
Values are expressed as feet of head loss for every 100 feet of
penstock length. The values can also be read directly as percentages.
Find your penstock diameter along the top row, and your flow rate in
the left column.
F r i c t i o n Hea d L o s s f o r 1 0 0 Fee t o f
S c h e d u l e 4 0 PVC P i p e
Pipe size, nominal inches
234 68
Flow in gpm
Head loss (in feet) of water per 100 feet of pipe
(or the Hazen-Williams equation), you can see
that at least a 3" pipe diameter is required to
keep losses below 6 feet (or 15 percent). In this
case, the losses amount to 2.26 feet per hundred, for a total head loss of 11.3 feet.
Now let’s add in the elbow losses. Four 3"
elbows are approximately equivalent to 48 feet (4
x 3 x 4) of straight 3" pipe, for a total effective penstock length of 548 feet. Fifteen percent head loss
in this pipe is equal to 30 ÷ 548 x 100 = 5.5 feet
of acceptable loss per 100 feet of pipe. Therefore,
the 3" pipe selection is still a good choice.
Note the huge jump in loss between 2" and
3" pipe sizes. If you have a borderline situation,
contact the turbine manufacturer for guidance on
penstock pipe sizing. You want to be sure that the
additional cost of larger pipe is worth it in terms
of power output.
To calculate your net head, subtract the pipe
loss from the total head:
Total head = 200 feet
Pipe loss with 548 feet of 3" pipe and a
flow of 100 gpm = 12.6 feet (2.26 feet of
loss per 100 feet x 548 feet ÷ 100)
Your net head is: 200 – 12.6 = 187.4 feet
Converting that to pressure available at the
187.4 x 0.433 = 81 psi
iPipe Maintenancei
Moving water represents a potentially huge amount of energy. It’s important to support the penstock
well, especially at turns, where thrust blocks may be needed to counteract the water’s force. When
it comes time for maintenance, you must have a means to remove and/or divert the water from the
penstock. Often this is provided by a valve at both the top and bottom of the penstock, with the top
valve providing an air inlet (just below the shut-off valve) to allow the water to flow smoothly out the
bottom. Always turn valves gently to avoid potentially damaging forces created by sudden changes in
water pressure.
16 8 H Y D R O EL EC TR I C G E N E R AT I O N
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thrust block
lower penstock
water valve
for vacuum
pressure gauge
5Micro-hydro system
have determined net head
and design flow of your stream, it’s time to think
about the kind of turbine that is best suited to
your site. Specifically, the turbine is the piece of
the hydropower system that collects the energy
input; it’s the interface between the water in the
penstock and the shaft connected to the power
Turbines are different from water wheels of
old because water is delivered at high pressure
and velocity through a nozzle that focuses a jet
of water onto the runner. The runner rotates to
transfer energy to the generator power shaft. Different turbines have different types of runners,
N ow t h at yo u
components and layout.
and the turbine’s housing design is integral with
the runner in terms of how the water impacts and
reacts with the runner and flows through the turbine and down into the tailrace.
Choosing a Turbine
Choice of the best turbine design for your site
depends upon the site’s characteristics, as well
as the head and flow. Most small hydro systems
employ direct drive between the runner and the
generator, meaning that there are no efficiencyrobbing belts, gears, or pulleys. Belts and pulleys
may be required in larger systems so that both
the turbine and generator can run at their respective optimal speeds.
iHydropower Resourcesi
There are many local, state, and federal guidelines and laws surrounding the use of water, water rights,
and alteration of streams and wetlands. Due diligence is required to identify all of the legal issues that
apply to your site. For larger, grid-tied hydro systems, you will need to look into licensing, permitting,
design specifications, and fees that may be required. Here are some places to start your research (see
Resources for websites):
• The Environmental Protection Agency’s Clean Water Act Section 401 Water Quality Certificate
provides guidance on water quality standards that may be required by your state for projects that
impact streams or wetlands.
• The Federal Energy Regulatory Commission’s responsibilities include licensing of new or existing
power generation projects and oversight of all ongoing project operations, including dam safety
inspections and environmental monitoring.
• The U. S. Army Corps of Engineers has jurisdiction over most U. S. waterways and wetlands, and
offers some useful design guides.
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There are two basic approaches to small-scale
hydro turbines, categorized by how they capture
the energy in water. You may have a very small
stream with a very high head that creates lots of
pressure but perhaps relatively little flow. Or you
may have access to a river meandering through
your property, powerful and high-flowing but without much head. Each situation requires a specific
approach to capturing the available resource, and
each turbine can be customized by the manufacturer, and by your control of the water flow hitting
the turbine, for best efficiency at a specific site.
impulse turbine from
Harris Hydro. A pipe
from the intake feeds
the four nozzles that
spray water into the
runner cups. The runner spins the generator,
and the water spills
down and away from
the runner. 
Impulse Turbines
An impulse turbine
focuses one or more
water jets onto the
runner cups. 
water flow
5Cross-flow turbines allow water to flow across the runner
blades, so that the water hits the blades at the top, falls
through the runner, and hits the blades again adding
energy. The distributor guides water through the turbine
so that it hits the runner at the proper angle.
Impulse turbines work well in situations with high
water pressure (head) and low-to-medium water
flow. Impulse turbines are not submersed in
water; they operate in the air and receive water
from an inlet pipe, sending it through one or
more nozzles to create a focused, high-velocity
spray. Additional nozzles may be used to increase
the power output, but this can be achieved only
when there is enough supporting water volume.
The water jet(s) hits the runner’s paddles, causing it to spin. Two common (and similar) turbine
designs use Pelton and Turgo runners. These runners have a number of cups around the perimeter
to catch the jet of water.
A good example of an impulse turbine is the
alternator-based micro-hydro generator made by
Harris Hydro. Beneath the housing is a Peltonwheel runner connected to the shaft of the alternator. These micro-hydro systems can produce up
to 2,000 watts of DC power, depending on the
water flow rate, pressure, and output voltage.
Useful power output starts at 25 feet of head
and a water flow rate of 15 gpm, a configuration
that will yield about 25 watts of power.
Crossflow Turbines
A crossflow turbine is a sort of modified impulse
turbine where water flows in high volume and
with low pressure through a large opening, rather
than through small, high-pressure nozzles. Water
passes over the runner blades in a somewhat
similar fashion to a water wheel.
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5Two different versions of reaction turbines. They both take advantage of water flowing through the turbine blades in a
stream or under a boat.
Reaction Turbines
Reaction turbines are best suited for low-head
and medium-to-high flow situations. A reaction
turbine sits fully immersed in the water in a way
that allows water to flow through it, causing it to
spin. A wind generator is another good example of a reaction turbine in that it spins in reaction to a fluid force (air) moving through it. Large
hydropower installations use reaction turbines,
but there are a few small units on the market for
home or recreational use.
Power Generators
systems, the power
generator is a specially designed alternator.
Older-style alternators require brushes that need
periodic replacement, while newer alternator
designs use more efficient brushless, permanentmagnet technology. An alternator is used
because it efficiently and affordably generates AC
electricity. However, this is unregulated, variablefrequency electricity and is not the same as the
AC power used in your home. The output of an
alternator is ultimately rectified, or converted,
into DC power.
Generating high-voltage AC power has a significant advantage over low-voltage DC generation.
Low-voltage systems require very large (read:
expensive) power cabling if there is significant
distance between the generator and the battery
In many micro-hydro
bank, which typically is located in the home.
High-voltage AC power can travel long distances
in small wires without much power loss, and it
can be transformed to higher or lower voltage, or
it can be rectified to produce DC power that can
be stored in batteries.
power management
There are a few critical design factors and control features needed to ensure power quality and
prevent damage from overspeed, in both grid-tied
and off-grid systems.
Utility Power
Grid-connected hydro systems must deliver
utility-quality power in terms of voltage, frequency, and power quality. The voltage and frequency of an AC generator depend upon its
speed, and the speed depends on how much
water is hitting the runner and how much load is
on the turbine. Power conditioning is handled by
the electronic components.
Preventing Overspeed
Whether grid-tied or off-grid, the generator cannot
be allowed to spin too fast, or damage can occur.
Overspeed can result from situations where you
don’t need the full power output at the same time
the stream feels like delivering it.
Speed control is often accomplished by
sending excess power to a diversion, dump, or
ballast load (all the same thing) in order to
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maintain a constant load on the generator, resulting in a constant speed. This function is performed by an electronic controller. Diversion
loads are usually electric air- or water-heating elements. In a battery charging system, once the
batteries are fully charged, the controller sends
the power to the dump load while providing just
enough power to the batteries to keep them fully
In a grid-tie system, the grid serves as the full
load . . . until the grid goes down, and then the
dump load takes on the burden.
Additional controls are required to ensure safe
conditions for the generator and any people working on it. These include the following features:
• Electrical safety disconnect that cuts off the
generator output power
• Shutoff valves to halt water flow
• Electrical brake (shorting the output to apply
a maximum load to the generator), which
prevents the generator from freewheeling
or runaway in case the load is accidentally
removed from the generator
PowerHouse Design
You will probably want a box or small shed to
mount and install hardware, make connections,
and protect the generator and controls from
the elements, including freezing temperatures,
animals, and unauthorized personnel. Plan this
power­h ouse with turbine efficiency in mind:
Don’t make too many efficiency-robbing penstock
twists and turns away from the ideal turbine site
to get to the ideal powerhouse site. Be sure to
provide a large enough water outlet at the turbine
so that “backsplash” (when the water splashes
and bounces around inside the turbine housing,
impeding efficient runner operation) does not
affect the turbine. The powerhouse also must
include adequate space and access for servicing
the equipment.
System Efficiency
efficiency you can expect — in
getting the energy from water to wire — from
a micro-hydro system can range from 40 to 70
percent. Efficiency depends upon all the little
details of each component in the system, with
each piece affecting overall efficiency.
You will need to work with the turbine manufacturer for specific numbers to estimate efficiency and expected power production at your
site and with the equipment you choose. The
efficiency will vary depending on flow and head
throughout the year.
System efficiency is calculated by multiplying
the efficiencies of each component within that
system. The Hydropower Component Efficiencies table (facing page) shows some approximate efficiency values you can expect for the
various components in a well-designed microhydropower system. Turbine efficiency will vary
quite a bit over the seasonal range of water
power hitting the runner. As flow changes, the
nozzle size can be changed (either by switching
out fixed nozzles or using an adjustable nozzle)
in order to maintain the optimum velocity for
maximum efficiency, even though the power will
drop off.
The kind of
iElectricity Transmissioni
Proper transmission cable selection, installation, and layout are as important as penstock design.
Once you generate the electricity, you’ll want to get it to the power control center as efficiently as
possible. See chapter 10 for more information on power management, controls, and wire sizing.
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H y d r o p o we r S y s t e m C o m p o n e n t
Permanent-magnet alternator
Wiring and controls
Total System Efficiency
Maintenance Checklist
Maintenance for a hydro system includes the
following basic procedures:
Lubricate generator bearings and replace
brushes as needed.
Inspect generator periodically for wear,
vibration, damage, cracks, leaks, or
Keep the turbine’s water intake clear of
debris and ice.
Adjust the water flow into the turbine
according to seasonal fluctuation in water
Check the penstock for leaks, and reset
pipe anchors as needed.
Inspect electrical connections periodically
for tightness and corrosion.
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r e v i o us c h a pt e r s d i s c uss e d a variety of resources for generating electricity from renewable resources. Each collection technology has its
own set of specific equipment and site requirements, but there are some
common components among home power systems. This chapter offers a brief introduction to those commonalities, including wiring considerations, controllers, inverters,
batteries, battery chargers, generators, system monitoring, and other important “balance of system” components needed for a complete, safe renewable-energy system.
We’ll go over some terms that are important to understand, and you’ll get an
idea of what’s significant from an electron’s point of view, as it travels through your
system doing its job while avoiding trouble. By paying attention to the details, you can
wrangle maximum benefit out of every last electron.
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Grid-Tie vs.
chapter 7, the primary
distinction between various home-based
electrical generation systems is whether they
are interconnected with utility power (grid-tied) or
are stand-alone (off-grid). Grid-tied systems come
without the cost and hassle of storage batteries,
but one big disadvantage is that if the grid fails,
you are out of power, too. It is possible, though,
to have a hybrid system that is grid-connected
but includes battery backup. This approach can
provide power for critical loads, or even the entire
home, when the power goes out. However, such a
system adds cost and complexity.
A grid-tied renewable energy system provides
power (when available) to your home and diverts
excess electricity to the local utility. In this way,
the grid is used as a kind of storage facility for
your power. For instance, if you have a solarelectric grid-tie system and the sun is shining,
the photovoltaic (PV) modules contribute to the
power needed by your home. If the PVs are generating more power than you need, the electrons
actually flow into the power company’s lines,
spinning your electric meter backward as they
go. In some cases, the amount of solar energy
produced is tracked using a separate meter. At
times when you need more than your own system is producing, the power company provides
you with all the electrons you need from the grid.
The details of accounting for electrons sent
back and forth vary by state and utility. At worst,
you can expect to offset, or receive a credit on, your
power bill through a system called net metering. If
grid power
critical loads
As discussed in
main power
you produce a surplus of electricity this month, and
next month is cloudy, you can draw on your electrical “storage account” to meet your needs at no
cost until you’ve used up your banked electrons.
Of course, the power company will continue to provide all the power you need as you offset what you
can with what you produce. At best, you might earn
money for the power you produce by way of a feedin tariff. This policy mechanism allows you to earn
money as a small power producer.
5Hybrid grid-tied PV
system with battery
backup for critical
loads in the event
of a power outage.
In this case, the PV
system is optional
because the batteries can be charged
with grid power
when it returns.
Options for
Backup Power
You can use renewable energy on a scale that
is appropriate for your needs. Many homeowners have gas-powered generators that can be
used as a source of backup electricity in the
event of a power outage. Another option is a
iDistributed Generationi
Having lots of small power generators, such as home PV systems, distributed throughout a utility’s
service territory, serves to decentralize power generation, a strategy appropriately called distributed
generation. Relying on just a few large power plants makes everyone on the grid more vulnerable
to power outages should one generator fail or the fuel supply be disrupted. Distributed generation
offers a measure of diversity and resiliency to the power grid that will be better utilized as smart-grid
technologies are used more widely. If you want to connect your renewable power generator to the
grid, start by contacting your power company.
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battery-and-inverter–based backup system, which
can be used to provide electricity to critical loads,
such as heat and refrigeration. One huge advantage to this approach is that the switch from utility grid to inverter power can be done automatically without any need for human management.
This provides some peace of mind if you’re away
from home when the power goes out.
In this system, the critical load circuits are separated from the home’s main circuit breaker box
(service panel) and brought to a subpanel. The
subpanel is fed by the inverter, and while the grid
is active, the inverter merely allows grid power to
pass through it and on to the subpanel. Meanwhile, the batteries are kept charged by either utility power or some renewable source. When utility
power is not available, the inverter senses this
and immediately draws power from the batteries, providing its own AC power to the subpanel.
When utility power returns, the inverter automatically and instantaneously makes the switch back
to grid power, and the batteries recharge.
Definition of
generation and
consumption, there are several terms that require
clear definition.
When discussing energy
Volts are a measure of electrical pressure, or
how much force is pushing the electrons through
the wire.
Amperes (amps) are a measure of the flow
of electrons, or current. The way that electrical
current is produced can be divided into two categories. Solar, wind, and hydroelectric generating
systems usually produce direct current (DC). Batteries store and deliver electricity as DC. Alternating current (AC) is how electricity is supplied to
your home by the power company. It is difficult to
generate the high-quality AC power produced by
the power company with residential-scale renewable sources because the inconsistency of the
resource means that the voltage and frequency
will vary too much to be used by your home’s
appliances. Additionally, AC power cannot be
stored, while DC power can be easily stored in
batteries and used later. DC power can be converted to AC with an electronic inverter, and AC
power can be converted to DC with an electronic
Resistance is the opposition to the flow of
current and is measured in ohms. This will be
important to understand when determining the
wire size required to move electricity efficiently
from one place to the other.
Power is the product of volts and amps and
defines the rate at which work is performed. One
horsepower is the amount of work required to
move 550 pounds of weight a distance of 1 foot
T h e O f f - G r i d R oom
I bought my first solar electric
panel back in 1988 (a Solarex
MSX53). I walked out of the
store feeling like my own power
company. It was as if the solar
panel was a magic carpet that
would take me to many exotic
new places. And it did. That
purchase eventually led to a job
with the solar energy company I
bought it from.
I used that first PV module
(at the rental house I shared)
to power an electric garden
fence and to charge a small
motorcycle battery that kept
the fence operating at night.
Soon, the battery had lots of
wires hooked up to it, powering a clock, a radio, and DC
lights in one room, creating an “off-grid” room in the
house where everything was
solar-powered, even when the
utility power failed. I learned
a lot from that simple system
— from battery care to the
effects of tilt angle on the
PV panel. Living with solar
electric power makes you
hyperaware of when the sun
is out and how much power
you’re getting.
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N a t i o n a l E l e c t r i c a l Co d e a n d S a f e t y
The National Fire Protection
Association (NFPA) develops,
publishes, and disseminates
more than 300 consensus codes
and standards intended to
minimize the possibility and
effects of fire and other risks.
One of these codes is the
National Electrical Code, or NEC.
The NEC is updated every three
years and contains all the practical and engineering requirements for safe and efficient
electrical installations, including
specific sections for renewable
energy systems and batteries.
Most states adopt the latest
NEC as law, and building code
enforcement agents follow it
when inspecting for violations.
Licensed electricians are required
to install all things electrical
according to the NEC. Building
codes such as the NEC contain
highly technical information and
use very specific language —
they are not for the faint of heart
or average amateur.
over a period of 1 second. When working with
electricity, power is commonly expressed in units
called watts. One horsepower is equal to approximately 746 watts.
Energy is a quantity of work performed. In
terms of electricity, energy is expressed in kilowatt-hours (kWh). A 100-watt light bulb consumes
power at a continuous rate of 100 watts. If that
light bulb is left on for 10 hours, it will have consumed 1 kWh (100 watts x 10 hours) of energy.
British thermal unit (Btu) is another quantity of energy. When comparing fuels and their
energy content, we need to find a common
denominator for all energy measurement units,
regardless of fuel, so we can compare apples to
apples. The energy “apple” (at least in the United
States and Britain) is the Btu. By definition, a Btu
is the amount of energy required to raise the temperature of one pound of water (about a pint) by
1°F. For perspective on energy equivalents:
• 1 Btu is approximately the amount of energy
released by completely burning a wooden
kitchen match.
You can buy a copy of the
NEC from the NFPA’s website
(see Resources) or read it online
for free after registering with
NFPA. You can also find help
with understanding and interpreting NEC information through
online tutorials and books.
Always remember that there are
no shortcuts around safety and
electrical wiring. If you’re unsure
about electricity, wiring techniques, or safety, seek the advice
of a licensed professional!
• A gallon of gasoline contains the equivalent
of about 31,000 food calories. This is
equivalent to the energy in more than 50
McDonald’s Big Macs!
• It takes 320 pounds of lead-acid batteries to
deliver the equivalent energy in one 6-pound
gallon of gasoline.
Electrical Wiring
the proper conductors for it to move through.
The tasks of cutting, stripping, and connecting
wires are fairly simple, and you may be able to
work with your electrician to wire and connect
your renewable energy system’s components.
However, do not attempt this on your own if you
are not an electrician.
An experienced electrician will know all about
the importance of the following:
m o v i n g E l e c t r i c i t y e f f i c i e n t ly
• Wires need to be properly sized to carry a
specified current over a certain distance.
• There are about 125,000 Btus in a gallon of
gasoline and 5.8 million Btus in a 42-gallon
barrel of oil.
• Fuses and circuit breakers must be carefully
chosen to protect both conductors and
• One kilowatt-hour of electricity is equivalent to
3,413 Btus.
• Connectors and switches must be properly
rated, sized, and placed within the system.
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• Grounding and lightning protection are of
utmost importance to ensure personal safety
and prevent failure of electronic components
due to power surges.
• A main disconnect switch is required to
remove your renewable power generator
from the system, for both service and safety
Wind-, solar-, and battery-powered electrical systems now have their own sections in the National
Electrical Code (NEC; see National Electrical Code
and Safety on page 177). Specifically, NEC Article
690 relates to photovoltaics, Article 694 relates
to wind, and Article 480 relates to batteries. Several additional sections of the NEC are also applicable to renewable systems. At present, there is
a proposal to consolidate these articles, so these
references may change in the future.
You can find all the specialty tools, suitable
wires, connectors, and insulation at your local
electrical supply store or renewable energy
dealer. One excellent online resource for electrical cable, connectors, and tools is Del City Wire
(see Resources).
Wire Sizing
While not a substitute for code requirements or
the skills and experience of a professional electrician, there are some basic guidelines for properly sizing wires. Wire size is important to get
right because a wire that is too small will not
deliver the full power of your renewable energy
system; a wire that is too big will be more difficult to work with and add to the cost, sometimes
Wires are not perfect conductors because they
offer some resistance to the flow of current. For
example, a 10 AWG (American Wire Gauge) wire
has a resistance of 1.29 ohms per thousand
feet. A 2/0 (“2-aught”) cable has a resistance of
0.1 ohms per thousand feet. These may sound
like small numbers, but they have a big effect on
the electricity flowing through the wires. Shorter
wires, fatter wires, and higher voltages help to
increase electrical transmission efficiency. The
wire must be able to carry the required current at
a specific voltage over a distance with a minimum
of the loss known as voltage drop.
Acceptable voltage drop for renewable energy
systems is generally 3 percent or less. To ensure
minimal voltage drop and maximum current transfer, the wire must be sized based on the supply
voltage, the current (or amps) flowing through
the wire, and the distance between the source
(solar panels or wind generator, for example) and
the storage (batteries or grid tie-in). The currentcarrying capacity (ampacity) of wires can be found
by using the Wire Size and Ampacity chart on
page 179.
Calculating Wire Size
To estimate the wire size you need, look up the
ampacity based on the maximum amps your
power source will deliver. Next, calculate the voltage drop index (VDI) of the wire. To do this you
need to know the one-way distance between the
power supply and the battery bank, as well as the
acceptable voltage drop percentage. Use the following formula:
VDI = (amps x one-way distance in feet)
÷ (% voltage drop x voltage)
Here’s an example using a 24-volt solar electric system that delivers 50 amps of charging current to the batteries. The total distance of the
actual wire run between the charge controller and
the solar panels is 100 feet, and we are willing
to accept a 3-percent voltage drop. If you look
only at the ampacity of a wire as the sole sizing
requirement, it would appear that an 8 AWG wire
would be sufficient. The voltage drop index tells
us something different:
VDI = (50 x 100) ÷ (3 x 24)
The calculated VDI is 69. Look up the nearest
VDI from the chart and round up. Our example
shows that we need a 3/0 copper wire. If you
decide that this cable size is too big or expensive to work with, an alternative might be a
higher-voltage system that allows for the use of
smaller conductors. Many modern charge controllers manage the voltage and current so that
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W i r e S i z e a n d A m pa c i t y C h a r t
There is an important distinction to make between the ampacity of wires and the gauge required to keep
power loss to a minimum. This chart shows the current-carrying capacity of both copper and aluminum
wires, based on the wire gauge in both AWG and metric units. These ratings should be used only for direct
current (DC)–carrying wires. Also listed in the table is a voltage drop index (VDI).
Wire Size
Area mm2
you can wire your PV panels at a higher voltage
than the batteries require, thus minimizing wire
size and cost.
Balance of System
required to complete your renewable electric
power system. Some are optional; some are not.
Here is an overview of the main items.
Many additional components
An inverter converts the DC power — produced
by the power source and stored in the batteries — into the AC power required by lights and
appliances in your home. Most modern inverters deliver clean, pure sine wave AC power that
don’t use
allows you to operate everything you would normally use in a utility-powered house. Older or
less expensive inverters may produce a “modified sine wave,” which can be problematic with
some types of appliances but fine for recreational use.
Power-handling capacity of the inverter can
be increased by connecting two or more units
together electronically, a configuration sometimes
called stacking. Since inverters typically provide
120 volts of AC power output, another advantage
to stacking is that the voltage can be doubled,
providing 240 volts to high-power loads, such as
well pumps.
Inverters used in grid-tied systems accept
the renewable power source input and, through
electronic manipulation, condition and synchronize that power with the grid to deliver the correct voltage, frequency, and phase. Off-grid inverters must match the battery voltage, and many
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Inverters convert DC
power produced by
renewable electricity
sources and stored
in batteries, into 120
volt AC power ready
for use in your home.
Their capacity can
range from a few tens
of watts to several
thousand watts.4
Inverters can be
electrically connected to increase
power delivery,
and to double the
voltage if 240
volt service is
inverters also act as battery chargers when power
from another source (utility or generator) is available. Some inverters can be used in both battery-based and grid-tied scenarios, allowing for
a hybrid system that enables batteries to supply power to critical loads when grid power is not
available. A few of the more popular brands of
inverters are Outback, Xantrex, SMA, Fronius,
Solectria, Apollo Solar, and Exeltech, to name a
few (see Resources for websites).
Charge Controller
A charge controller is an electronic device that
regulates the amount of power flowing from the
power source into the batteries while preventing the electrons from flowing back to the power
source. The primary function of the charge controller is to prevent overcharging, which can damage the batteries. To keep the batteries properly
charged, the controller can be adjusted to manage the charge current and hold the voltage at
a specified level. It can also help to protect the
batteries by disconnecting them from the load
at a specified voltage. Choose a charge controller based on the system voltage and maximum
amps delivered by the power source. All controllers have a display meter or lights indicating voltage, current, and/or charge status.
Many modern charge controllers use maximum power point tracking (MPPT). This technology optimizes charging by managing and manipulating the voltage and current available from
the energy source to match the battery voltage
and charging requirement. It’s a bit like shifting
gears in your car to deliver maximum power to
the wheels from the same engine. One benefit of
MPPT controllers is that you don’t need to match
PV voltage with battery voltage. Sending highvoltage electricity from the panels to the charge
controller can increase efficiency by lowering line
Not all charge controllers are alike, and not
all energy-generating technologies are alike.
The charge controller must be suitable for the
generating source. Solar panels can be disconnected from the load, or the output wires can be
connected together (shorted) without damage.
Most wind and hydroelectric generators should
not be allowed to “freewheel” in an open-circuit
condition or they could be damaged from overspeed. These systems require a charge controller that can transfer the power to an alternate
load (a dump, or diversion, load) when the batteries are full but the generator keeps producing
power. Most wind and hydroelectric controllers
are available from the manufacturer as part of
a system package. Many inverter manufacturers
also produce charge controllers, but some additional brands include Midnight Solar, Morningstar, Blue Sky Energy, and SCI (see Resources
for websites).
System Monitoring
A good system meter will show the battery voltage,
the charge and discharge currents, and the state
of charge of the batteries. A meter also facilitates
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5Charge controllers range from
simple on/off switching to sophisticated power management
with MPPT and metering.
se ld SE
nd LEC
s to T
monitor from Tri-Metric
(see Resources)
Power system
system troubleshooting, making it easier for you
to know exactly what’s happening throughout the
Diversion or Dump Load
This provides a place for excess power to be
dumped or diverted away from the usual load. It
can serve two purposes:
1. Once the batteries are charged in an off-grid
system, any excess power generated has no place
to go, so it’s effectively wasted when the charge
controller disconnects the power source from the
batteries. If that power can be diverted to some
“opportunity load” and put to good use, the renewable energy source can be more fully utilized.
2. A dump load can prevent a wind or hydro generator from spinning too fast once the batteries
are charged and the controller disconnects the
source from the load. In a grid-tied system, the
load is the grid. If the grid goes down, the load
disappears and the electrons need a place to go
to keep the spinning generator under control and
prevent it from tearing itself apart.
The most common diversion loads are electric
resistance heating elements, such as those used
for heating air or water. The load must be electrically matched to the power source to handle
the voltage and current effectively. Renewableenergy equipment dealers and manufacturers
offer products for specific applications. HotWatt
(see Resources) offers a wide variety of air and
water heaters suitable for diversion loads.
The electrical transfer from the charging load
to the diversion load is normally handled through
a charge controller that senses that the battery bank has reached a set voltage, or that grid
power is not available. Power from the source is
then diverted to the dump load.
Lightning Arrestor
Also called lightning protection devices or surge
protectors, lightning arrestors should be installed
as close as possible to the power-generating
source. On a PV system, it would be mounted
on the combiner box. It is wired in parallel with
the power cables, with one wire connected to
a ground rod; if the voltage surges, the excess
energy is quickly shunted to the ground.
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Typical dump
loads: low-voltage
water heater element (top) and electric resistance air heater (bottom)4
5Lightning protection devices. Two different kinds from
Delta and ETI; see Resources
Lightning arrestors can handle surges of
10,000 amps or more in a matter of a few nanoseconds, but they should be replaced after taking
a hit. Some devices provide visual indication that
they need replacing, such as LED lights, and may
also show visible signs of damage. Good grounding and a quality lightning protection device go a
long way toward preventing damage to your power
system from close lightning strikes. However,
nothing in the world can withstand a direct lightning strike without damage or total destruction.
Backup Generator
Having a backup generator in an off-grid system
allows the use of high-power equipment without
draining the batteries, or if the inverter doesn’t
have the power capacity to handle a large load. A
generator also provides a source of power for battery charging during prolonged periods when the
renewable resource may not provide enough power
to meet your needs.
Generators can be powered by gasoline, diesel, kerosene, liquid propane gas, natural gas,
wood gas, or biogas (the latter two with modifications to the engine). Lower-speed (1800 rpm)
engines and generators are quieter and often last
longer, though they are more expensive than the
more common high-speed (3600 rpm) engine/
generators. Northern Lights and Kohler (see
Resources) are just two manufacturers offering
low-rpm, durable generators.
Battery Charger
Off-grid power systems are essentially battery
chargers. However, when the renewable resource
is not available, a separate battery charger can
be operated by a source of AC power, such as
a fossil fuel–powered generator. A hybrid power
system (one that is grid-tied and includes battery backup) can use utility power to charge batteries. Battery charging also may be integrated
with the inverter, as many inverters have builtin battery chargers. Before choosing a battery
charger, read the following section on batteries
and make sure to use a charger that is smart
enough to charge batteries effectively. When
using a fossil fuel–powered generator, be sure
the generator can deliver the full power required
by the charger.
Additional System
A variety of additional components are required
for your renewable energy system. Some are
specific to the resource being harvested, many
are common to power management. All must be
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properly designed and rated to handle the job at
hand. This equipment includes:
in the form of
DC electricity, for use when the power source may
not be producing power. When the sun shines, the
water flows, or the wind blows, the batteries are
being charged. The stored electrons are available
to supply DC electricity during times of low or no
power production, smoothing out an otherwise
inconsistent supply of electricity. Sufficient energy
storage allows for lower-capacity (less costly)
energy-generating equipment because the energy
stored over time in the batteries can be released
at the desired rate, providing the required power
to electrical loads.
meaning that they can be consistently and deeply
discharged without significantly shortening their
life span. Deep-cycle designation generally means
that the battery can consistently withstand a depth
of discharge (DOD) of up to 80 percent of its full
rated capacity, meaning that 20 percent of the
stored energy remains in the battery.
When a battery has delivered its rated amphours to a load (thus achieving its rated DOD) and
is then recharged, it is said to have undergone
one charge cycle. Cycle life drops dramatically
with improper charging and poor maintenance,
such as allowing the electrolyte level to drop too
low or terminal connections to become corroded.
In addition to use in off-grid homes, deep-cycle
batteries may be used in forklifts, golf carts, and
wheelchairs. The most common technology used
for home power storage is the flooded lead-acid
battery, meaning that the lead-based electrodes
are immersed in a liquid electrolyte (hydrochloric acid). Lead-acid batteries are used primarily
because of their relatively low cost, availability, and
familiarity. They are similar to the battery used in
your car, but because conventional car batteries
are designed for only about a 10-percent discharge
before they require recharging, they would not perform well in a home power system.
Battery Rating and Type
Choosing Batteries
Batteries are classified by voltage, and their
energy storage capacity is rated in amp-hours.
Amp-hours are a measure of how many amps of
current can be supplied to a load over a period
of time. Mathematically, a 200-amp-hour battery
should deliver 200 amps for one hour (or some
combination of amps and time leading to the
same number of amp-hours) before its charge
is depleted.
In reality, the faster a battery is discharged, the
less overall energy it will deliver due to its internal
electrochemical efficiency. The amp-hour rating
of batteries typically is based on a 20-hour discharge rate, meaning that the battery can deliver
a certain number of amps over 20 hours, at which
time the battery has been fully discharged.
Batteries used in a renewable energy system
must be specifically designed for deep-cycle duty,
Batteries are likely to be the biggest maintenance item in your renewable energy system
and represent a substantial part of the cost,
so they’re worth careful consideration. There
are many battery brands and several technologies to choose from. When selecting batteries for renewable energy systems, compare the
following performance factors so that you can
determine their lifetime cost and maintenance
• solar panel
mounting racks
• disconnect boxes
• wind towers
• circuit breakers
• water sluices
• weathertight cable
• dams
• electrical grounding
• fuses
• box to hold the
Ba t t e r i e s s t o r e e n e r g y
• storage capacity — rated in amp-hours
• depth of discharge (DOD) — 80 percent DOD
is typical
• cycle life — number of charge cycles that
can be endured before the battery must be
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• electrolyte reservoir capacity — a larger
reservoir means less frequent watering is
Lead-acid batteries have a low cost per amphour and generally survive through 500 to 1,000
charge cycles. Flooded lead-acid batteries have
a liquid electrolyte that must be checked and
filled periodically. As batteries charge, the electrolyte is depleted as gases are produced and
released into the air. These gases are poisonous
and must be removed from the house. Industrial
lead-acid batteries are big, heavy, and costly, but
when properly cared for they can last quite a bit
longer than smaller batteries. Another consideration is how to dispose of the batteries at the
end of their life. Lead-acid batteries are almost
completely recyclable, while other types of batteries utilizing heavy metals may require disposal as
hazardous waste.
Sealed lead-acid batteries utilize electrolyte
that is gelled or absorbed into a substrate. They
have no liquid electrolyte to fill or spill and do
not off-gas while charging. This can be desirable
in cases where low maintenance is desired, but
care must be taken when charging so as not to
boil off the gelled electrolyte, which cannot be
replaced as with flooded batteries.
Nickel-cadmium (ni-cad) or other, advancedtechnology batteries using exotic materials are
quite a bit more expensive and often less forgiving in their charging requirements when compared to lead-acid batteries, but they hold great
promise in terms of capacity and longevity.
Batteries need periodic inspections (every two
or three months) to ensure adequate electrolyte
level and clean, solid, corrosion-free cable connections. Other maintenance requirements include:
• Paying attention to the voltage and charge
level on your system monitor to avoid heavy
discharge or overcharge
• Keeping the batteries warm (70 to 90°F)
• Following a regular charging regime according to
the manufacturer’s charge profile, to maximize
performance (see pages 186 to 189)
Battery life can range from 1 to 25 years,
depending on the type of batteries you choose,
how deeply they are discharged, how closely you
follow the recommended charge regime, and
whether you keep them filled with the proper
amount and type of electrolyte (add only pure distilled water to lead-acid batteries).
Some battery brands made for use with renewable energy systems include Rolls, Surrette,
Interstate, Trojan, and Deka (see Resources for
Sizing Your
Battery Bank
Once you’ve determined how many kilowatthours (kWh) are required to power your home
each day, decide how many days you want your
batteries to last between charging cycles. This
depends primarily on the consistency of the
charging resource. For example, if you need 3
kWh each day and you want the ability to go 3
days without the need for charging, then your
batteries should have 9 kWh of storage capacity.
Batteries rated for 6 volts and 220 amp-hours
are commonly used as a building block in smallto-medium-size battery banks, or groups of batteries. The amp-hour capacity rating typically
reflects the battery’s storage capacity over a
period of 20 hours, during which time it is completely drained. If you have a 24-volt power system you will need to wire four 6-volt batteries in
series (positive to negative) to achieve 24 volts
(see pages 128 to 129 for information on series
and parallel wiring).
Figuring Battery Capacity
Converting from the amp-hour ratings of batteries
to kilowatt-hours of electric use requires a little
volts x amps = watts
6 volts x 220 amp-hours = 1,320 watt-hours,
or 1.3 kWh of energy storage
Because you don’t want to discharge the battery
all the way — only to no lower than 80 percent for
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a deep-cycle battery — adjust the rated storage
value to find the battery’s useful capacity:
1,320 watts x 0.80 = 1,056 watt-hours,
or just over 1 kWh
Four of these 6-volt batteries (wired in series to
produce 24 volts) will store approximately 4 kWh
of electricity. Connecting two of these serieswired battery strings in a parallel configuration
will store 8 kWh of electricity. However, keep in
mind that mixing and matching batteries of different voltages, capacities, or ages is not recommended because the older batteries will waste
energy by constantly draining the newer batteries
(but without having the capacity to accept and
hold the charge). Batteries of different capacities
will recharge at different rates, leading to inefficiencies in charging.
Figuring Charge Rate
The greater the charging capacity, the faster your
batteries will recharge. For example, if you have
a 1 kW (1,000 watts) solar array (group of solar
modules wired together) and a 10 kWh battery
bank, here’s how long it will take to recharge the
dead batteries (assuming full sun reaching the
solar array):
10,000 watt-hours ÷ 1,000 watts = 10 hours
As with all things, batteries are not 100 percent efficient. A typical lead-acid battery is about
75 percent efficient, meaning that 75 percent of
the energy that went into it will be available for
use. Therefore, you need to give a battery 25 percent more energy than what came out of it for it
to be fully recharged.
Figuring Bank Capacity
Battery Charge
The amp-hour capacity in a series string is the
same as that of a single battery, but both the
voltage and available energy (watt-hours) have
increased. The amp-hour capacity in a parallel
wiring arrangement is a multiple of the number
of batteries in the battery bank. In this case,
the voltage stays the same, but again, the available energy has increased. To determine the
watt-hour capacity of the entire battery bank,
multiply the watt-hours per battery by the number of batteries in the bank, regardless of wiring
Ensuring your batteries achieve a full charge and
have a long life requires charge profile optimization. This is the optimal pairing of power generation to storage capacity, ensuring that the correct
voltage and current are delivered to the batteries
for the correct period of time. Manufacturers have
recommendations specific to each battery so that
it absorbs as many electrons as possible for a
certain period of time, then is held at a set voltage until the charge current (in amps) reaches a
certain level, after which the battery is held at a
lower, float-charge voltage.
iBattery Balancing Acti
The size of the battery bank must be matched to your rate of power consumption and your need for
periods of autonomy when no charging occurs. Equally as important is the electrical supply capacity
of the charging system (i.e., how much power the PV system can deliver). It’s important to recharge
the battery bank fully in a reasonable amount of time when the charging resource is available. If there
is not enough charging capacity, the batteries will never be fully charged. Too much charging capacity
relative to battery size only results in wasted energy (and money) because batteries can accept a
charge only as fast as their chemistry allows. A charge controller regulates the battery charge rate to
prevent overcharging, but there is nothing that will compensate for too little charging capacity.
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A battery has three basic charging stages, plus
a periodic, controlled overcharging stage called
equalizing. A high-quality charger automatically
manages these stages and allows the user to
adjust the parameters to meet the specific needs
of the batteries. Voltages required are very precise values, and while this may seem nitpicky,
these details are important if you want to maximize battery lifetime and efficiency. I offer some
reference values below, but always follow your
battery manufacturer’s recommendations when
setting up your charger.
The four charging stages are:
1. Bulk charging, during which the battery will
accept as much current as it can take from the
charging source, limited only by the battery’s
chemistry and the capacity of the charger. Empty
batteries can accept a huge amount of current
to fill them up, but more current than the chemistry can manage will lead to heat buildup in the
battery and wasted charging energy. During bulk
charge, the battery’s voltage will rise until it has
reached the voltage set by the charger. The bulk
charge voltage is usually set at or slightly above
the point at which the batteries cannot accept
additional charge and the electrolyte begins to
bubble and off-gas, as the electrolyte separates
into hydrogen and oxygen. For flooded lead-acid
batteries, the gassing voltage is around 2.37
volts per cell, or 14.2 volts for a 12-volt battery.
2. Absorption
charge begins when the bulkcharge voltage set point is reached. The voltage
is held constant for a period of time, and the
charge current drops off as a result of the battery’s increasing internal resistance as the state
of charge rises. The absorption charge cycle can
last for a preset period of time or until the current
falls to a specified level.
3. Float charge starts after the absorption charge
criteria have been met. Float charge can be considered a “maintenance” charge, where the voltage
is held to a minimum and current is reduced to a
trickle. Float voltage for a 12-volt flooded lead-acid
battery is usually between 13 and 13.5 volts.
4. Equalization charging is a high-voltage, controlled overcharge that is performed periodically
(perhaps monthly) and for a period of several
hours. Equalize voltage for a 12-volt battery is
over 15 volts. The purpose of an equalization
charge is to break up sulfation, a buildup of lead
sulfates on the electrodes. A battery left in a low
state of charge for an extended period of time
may develop excessive amounts of sulfation
that cannot be removed. Sulfation reduces the
amount of current a battery can deliver.
The Battery Charge Profile chart on the following
page shows the recommended charge profile for
certain Interstate brand, 12-volt flooded lead-acid
batteries (see Resources). Note that it specifies a
charge current of C/10, where “C” is the battery’s
20-hour capacity in amp-hours. C/10 means that
the capacity is divided by 10. For example, for a
220 amp-hour battery, the recommended charge
current would be 22 amps. Faster charge rates
result in excess heat buildup, and the battery may
not absorb all the energy it needs to be “filled”
even though it has met the voltage set point.
Lower charge rates may not be able to overcome
the cells’ internal resistance. An ideal charge rate
for renewable energy systems is between C/6 and
C/12, or between 18 and 36 amps for our 220
amp-hour battery.
Adjusting Battery Temperature
Battery performance is rated at a specific temperature, usually 77°F. A cold battery will not
accept or deliver its charge as readily as a warm
battery, and a hot battery can suffer plate damage and a shortened life. A lead-acid battery,
for example, does not want to be more than
95°F. To match the charge profile, the temperature must be compensated for by adjusting the charge voltage. For a lead-acid battery,
charge voltage is increased by 0.028 volts per
cell (0.17 volts for a 12-volt battery) for every
10 degrees below 77°F. If the battery temperature is greater than 77°F, the charge voltage
is decreased by the same amount. Some battery chargers automatically adjust the charge
voltage based on the battery temperature. Such
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T e s t i n g B a t t e r i e s U s i n g Sp e c i f i c G r a v i t y
Testing the state of charge of a wet-electrolyte
battery can be done by measuring voltage with
an accurate voltmeter, or (more accurately)
with a hydrometer to measure the specific
gravity of the electrolyte. Voltage correlates
with the specific gravity, but to be accurate in
either case requires that the battery rest for
several hours after being charged, and with no
load, so that the chemistry stabilizes, and in
turn so does the voltage.
To test the charge level with a hydrometer, draw electrolyte into the hydrometer
and read the value on the floating scale
inside the tube. The specific gravity readings
between cells should not vary by more than
0.05 points. If they do, it’s time to perform an
equalizing charge. Specific gravity changes
with temperature, so be sure to use a hydrometer with a temperature compensation scale.
The table here shows the state of charge of
both 6- and 12-volt batteries as indicated by
a voltmeter and a hydrometer, at a temperature of 77°F.
Bat t e r y V o lta g e Re l at i v e t o
S p e c i f i c G r av i t y
State of
Hydrometer with built-in
temperature compensation
1 2 - v o lt Bat t e r y C h a r g e P r o f i l e ( s am p l e )
Battery Voltage
Current (1)
Bulk Charge
Time, hours
Float Voltage Equalization
Voltage (3)
Time, hours
C / 10
2 to 4
1. C = 20-hour capacity in amp-hours
2. Float condition is for long-term storage (several weeks).
3. Equalize every 4 to 8 weeks. temperature compensation requires a temperature sensor that’s attached to the outside of a
battery and connected to the charger.
Battery Safety
As useful as batteries are, they are also very
dangerous. Always take great care when working with and around batteries. Keep the following information and guidelines in mind to prevent
• Batteries contain an enormous amount
of energy. If you drop a wrench across the
terminals of a battery, sparks will fly, the
wrench will be welded to the terminals, the
battery will heat up and may even explode.
• Remove all jewelry, wear insulating gloves,
and use insulated tools.
• Cover all exposed battery connections and
terminals that are not being worked on with
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B a t t e ry B o x B a s i c s
and 1/4" epoxy-coated (or other acid-resistant
treatment) plywood on the inside. Caulk the
interior joints and install a hinged, tight-closing,
insulated, and gasketed top.
A sturdy box made with acid-resistant interior surfaces, such as epoxy-coated plywood, offers many
benefits to protect and house your battery bank,
• Providing protection against unauthorized or
• Removing gases with an exhaust fan. The
untrained access.
• Keeping battery tops clean. When you remove
the batteries’ vent caps to add water, you
don’t want dust and debris (or anything other
than distilled water) falling into the batteries,
which can wreak havoc with the electrolyte and
shorten the battery life.
• Controlling battery temperature. Battery
temperature rises while charging and
discharging, but the batteries tend to cool
off in places like unconditioned basements.
An insulated box helps maintain the desired
temperature: Sandwich a layer of 2" rigid foam
board between 3/4" plywood on the outside
box must be reasonably airtight with a suitable
exhaust fan to move air through and out of the
box to the outdoors. An air inlet is cut into the
box near the bottom (the gases naturally rise up)
and screened against debris and bugs. A PVC
vent fan designed for battery boxes is available
from Zephyr industries (see Resources). This
unit has an internal damper to prevent backflow.
Some charge controllers offer an auxiliary output
that allows the fan to be automatically turned
on and off based on battery voltage. This control
is quite useful, as batteries only off-gas once they
reach a certain voltage.
Tip: Make the box a bit larger to store your
hydrometer, gloves, a funnel, and baking soda.
and downwardpointing air
2" PVC pipe
from the
box to the
exhaust vent
fan in PVC pipe
Vented battery box
2" screened air inlet
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wind turbine
wind charge
wind charge
dump load
PV array
array charge
array DC
main DC
AC breaker
A hybrid wind and
solar electric power
system that is
grid-connected with
battery backup
backup generator
a nonconductive material, such as plywood, a
rubber mat, or a durable PVC apron.
• Batteries contain deadly poison. Electrolyte
in lead-acid batteries is hydrochloric acid. If
you spill it on yourself or your clothes, it will
burn them. If you get in your eyes, it could
blind you. Keep water and baking soda handy
while working around batteries. These can
neutralize acid spills. Water (or a mix of
water and baking soda) can be used to wash
acid off skin or clothes; baking soda can be
sprinkled on electrolyte spills.
• Batteries generate poisonous and explosive
gases while being charged. Never smoke
around batteries. Always ventilate the area
where the batteries are located. Avoid sparks
near batteries.
• Always disconnect the charging source(s) and
the load(s) before working on batteries.
• Batteries are heavy, weighing anywhere from
60 to 120 pounds; be sure they reside on a
sturdy, well-supported floor. Use straps to lift
and carry batteries to avoid back injury.
• Build a sturdy, ventilated, insulated box to
house your batteries (see Battery Box Basics
on facing page).
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clo s e - up
Mapping Motivations . . .
and Watts
because I like to solve problems and make things work
better. While getting my mechanical engineering degree, I learned how to calculate
the efficiency of mechanical and electrical systems and how to design them so they
operate as efficiently as possible.
C hr i s K a i s e r
is an industrial and
commercial building
efficiency consultant,
sustainability enthusiast,
and cocreator and
principal contributor to
the Map-a-Watt blog
(see Resources). Here’s
his perspective on efficiency, sustainability,
pain, and gain.
b e c ame a n e n g i n ee r
I learned about companies taking steps
to increase efficiency and operate more
sustainably — and I thought all companies
operated that way. Then I entered the real
world. I saw inefficiency all around me.
My first job was selling automation
and electrical control products to industrial
customers. I wanted to sell them more
efficient motors, new efficient lighting, energy
monitors, and variable-speed drives that
control motors better. I had a whole bundle
of products to help with efficiency, but in
most cases the customers would buy only
the cheapest motor, not the most efficient.
Most purchasing managers I encountered
cared about the up-front cost, not the lifetime
operating costs of equipment. Most plant
managers had no clue about how energy
efficiency translates into financial gain and
focused only on how many widgets can get out
of the door with the least amount of financial
pain. They didn’t care about energy efficiency
because the managers and accountants
rewarded short-term economic goals instead
of long-term savings. But now I work fulltime selling energy efficiency solutions to
companies that have realized that increasing
efficiency improves their bottom line — and
the beneficial environmental impacts are just
icing on the cake.
One thing I’ve realized in sales is that
people buy things that reduce their pain or
offer a direct gain. If the purchasing agent or
maintenance person isn’t graded or doesn’t
receive some sort of incentive related to how
much energy they save, they don’t have any
pain around energy costs and don’t have any
desire to save it. If energy is cheap, then
costs haven’t risen to the point where it
causes management any pain. All companies
love talking points on the environment or
sustainability, but the majority of companies
aren’t going to act on operating more
sustainably unless it solves a specific pain
(such as with reduced operating costs) or
increases gain (such as with more sales to
environmentally conscious consumers).
It’s not just companies that act this
way; so do families and individuals. If we
see no value or realize no gain in living more
sustainably, we probably aren’t going to do
it — unless not doing it is so painful that we
have no other choice. But if saving energy
puts more money in your bank account each
If we see no value or realize no gain in living more sustainably, we probably aren’t
going to do it — unless not doing it is so painful that we have no other choice. But if
saving energy puts more money in your bank account each month, it has a greater
chance of happening.
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month, it has a greater chance of happening.
If your child has asthma that’s triggered by
poor air quality, you have pain around his or
her suffering. If you tie that pain to realizing
that smog is caused by air pollution from
coal-fired power plants and gas-guzzling cars,
you will be more likely to care about turning
off the lights or consider buying a hybrid
Living more efficiently and sustainably
isn’t a quick-and-easy, one-time deal or a
gimmicky marketing campaign; it’s a way of
life. It’s a way of operating, both personally
and in business, that reduces the negative
impacts of waste on our society. I try to live
sustainably because it reduces the pain I
feel when I see, smell, or feel pollution in
my lungs, or I realize I’ll have less money
this month due to a high energy bill. Most
importantly, living sustainably means living
with less pain, which coincidentally provides
the ultimate gain of living happier.
Living sustainably is all about happiness.
I’m happy when I have more money. I’m
happy when I’m hanging out with friends and
family and helping my community. I’m happy
when I’m enjoying the clean outdoors while
hiking or biking. I’m happy when I’m eating
good food from local farms and drinking good
beer from my local brewery. I’m happy when I
get a new car that has excellent gas mileage,
which lowers my nation’s dependence on
foreign oil, saves me more money, and
improves my local air quality. I’m happy when
I learn something new and when I can share
it with my extended online community. When
people are happy, great things happen for
everyone and everything.
Living more efficiently and sustainably isn’t a quick-and-easy, one-time deal or a
gimmicky marketing campaign; it’s a way of life. It’s a way of operating, both personally
and in business, that reduces the negative impacts of waste on our society.
mapping motivations and watts 191
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t’s c o m m o n k n ow l e d g e to anyone who’s spent time around a kitchen
that vegetable oil is flammable. What’s not so commonly known is that when
Rudolf Diesel developed his engine back in the 1890s, it was designed to burn
multiple fuels, including vegetable oil. He was under the impression that someday
farmers would be providing both food and fuel. Now that the fossil fuel heyday is
mostly behind us, his prediction is being fulfilled.
Somewhere around 2001, I caught the biodiesel bug. It seemed like the perfect
way to offset my energy costs and reduce my reliance on fossil fuel. I had a diesel
generator for backup power and was thrilled when my first batch of biodiesel burned
with the smell of French fries in the exhaust, providing electricity for my house. All it
took was a little time. Okay, it took a lot of time. But the fuel was nearly free and I
could hardly resist.
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Venturing into
dozen local restaurants and asked
the managers what they did with their waste
fryer oil. At first, I suspect they might’ve thought
that I was the state health inspector. But when
I explained what I was doing, they were very
interested. The fact that I was offering to take
their garbage away for free was an added bonus,
since they usually paid to have this hauled away
in barrels or waste bins.
Different restaurants have different qualities
of grease. Some use the oil for so long that it’s
practically rancid and sometimes unusable even
as a fuel. However, one high-end vegan restaurant in my area used its oil for only one day —
it was practically new and made great fuel. I
can’t eat fried food now without thinking about
Collecting waste grease can be fairly clean and
simple if the restaurant pours its waste oil into a
5-gallon container that you can carry away. Otherwise, it can be quite a disgusting job. You never
know what you might find in the waste oil bin:
rainwater, beer cans, cigarette butts, food waste
— so wear old clothes when you go to collect
Next I had to find a source of methanol and lye.
To start, I used Red Devil brand lye from the supermarket. My propane gas supplier was able to part
with a gallon of methanol, which is often used as
an additive to keep propane lines from freezing in
I visited a
the winter. That was enough to experiment with.
My father-in-law happens to be a chemist at a
local university, and he was happy to join me in the
experiment. This gave me a great excuse to buy
my own set of chemistry tools, including a digital
scale, glassware, hydrometer, and viscometer.
Back home, I set up a process that used an
extended length of hose from the cooling system
of the VW (see below) to heat the oil before mixing with it methanol and lye. This allowed me to
use biodiesel burned in the car’s engine to make
more biodiesel. The electric mixing pump was
powered from my home’s solar electric system.
After settling and filtering, the biodiesel worked
great in both the generator and the VW. This gave
me the confidence to use my homemade biodiesel in my daily driver, a newer VW Jetta TDI.
Even at 40 miles per gallon, it takes a fair amount
of time to gather and process the 375 gallons of
fuel to travel 15,000 miles every year.
Every 50-gallon batch produced about 8 gallons of waste glycerin. The better oil produced a
decent-quality glycerin, out of which I could make
soap that proved to be an excellent degreaser.
The lower-quality oil made a vile sort of goo that
was best burned in a good, hot bonfire. I had read
that glycerin could be composted and would readily biodegrade, but I didn’t have much luck with
that. Perhaps in an ideally mixed, hot compost
pile it would have worked better. Over the years,
I’ve ended up with many 5-gallon jugs filled with
waste glycerin that have been disposed of in various ways, including compost, soapmaking, bonfires, and landfill.
iCalamari Cruiseri
I bought a beat-up 1985 VW diesel Golf so I could experiment with driving on vegetable oil. I modified
the car by taking out the backseat and all the carpet, so it would be more like a pickup truck. It held
a 55-gallon drum and a 12-volt fuel pump so I could transfer grease from the restaurants’ grease bins
to the barrel in the back of the VW. It worked great — and always drew stares and questions during
the grease transfer. The car was dubbed the “Calamari Cruiser” because calamari was the main fried
food of my favorite restaurant for collecting oil.
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What Is
B i o d i e s e l i s v e g e t a b l e oil that has
been chemically modified to remove the heavy
glycerin portion of the oil. This allows it to flow
freely at temperatures down to around freezing,
while straight (unmodified) vegetable oil must
be heated to 120°F to flow freely through filters,
injectors, and burners.
Both vegetable oil and biodiesel can be used
in place of diesel fuel, home heating oil, and
kerosene for use in diesel engines and oil-fired
heating equipment. Using biodiesel requires
processing the vegetable oil, but no changes
to the vehicle or burner are needed. Straight
vegetable oil (SVO) requires modification to the
fuel system.
Biodiesel is chemically described as a mono
alkyl ester. It can be used in its pure form or
blended in any concentration with petroleum
diesel. It can be made with vegetable oil, animal fats, or recycled (waste) fryer oil from restaurants. The oil is filtered and mixed with methanol (methyl or wood alcohol) with the aid of a
lye (sodium hydroxide) catalyst to complete the
chemical process known as transesterification.
Transesterification is the chemical transformation
of one type of ester to another.
Other alcohols, such as ethanol, can be used
in place of methanol, and potassium hydroxide
can be used in place of sodium hydroxide. These
ingredients are less hazardous to work with, but
the reactions are more sensitive, and the biodiesel yield is generally lower. Most commercial
biodiesel makers and home brewers use methanol and sodium hydroxide.
DIY Biodiesel
In the interest of ease of use for the biodiesel
home brewer, this chapter describes the basecatalyzed production method using methanol
and sodium hydroxide. The products of transesterification are methyl ester (used as fuel)
and glycerin (soap). About 20 percent of vegetable oil is glycerin, which will be removed during
the chemical process and replaced with alcohol.
You’ll need a plan to dispose of the waste so you
don’t end up with dozens of plastic pails full of
glycerin scattered around the yard.
Benefits and
of fossil diesel
presents many benefits to both environment
and engine, but it’s not without quirks and
peculiarities. All of these need to be addressed
to achieve success in using biodiesel as a fuel.
U s i n g b i o d i e s e l i n s t ea d
Biodiesel biodegrades about four times faster
than fossil diesel. Its lack of sulfur eliminates
the sulfur oxides (responsible for acid rain) produced when fossil diesel is burned. Because
biodiesel is an oxygenated fuel containing 11
percent oxygen by weight, combustion is more
complete and overall emissions are reduced by
up to 90 percent when B100 (100-percent biodiesel) is used instead of fossil diesel. These
emissions include carbon monoxide, carbon dioxide, unburned hydrocarbons, and particulate matter (soot).
iSoy Mileagei
An average acre of soybeans grown in the U. S. produces about 42 bushels, at about 60 pounds per
bushel. Each bushel of soybeans can produce about 1.5 gallons of soy oil, adding up to 63 gallons
of oil per acre. In terms of heating energy value, if a gallon of soy oil contains 130,000 Btus, that’s
8.2 million Btus per acre. A modern diesel passenger car gets about 45 miles per gallon, while a
semitruck might get 6 miles per gallon. That works out to between 380 and 2,800 miles per acre.
19 4 B I OD I ES EL
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Oxygen content in fuels effectively increases
the volumetric efficiency of the engine as a result
of more complete fuel combustion. This increase
in combustion efficiency helps overcome the
slightly lower energy content of biodiesel: You
may not notice a significant difference in engine
performance or fuel economy when using B100,
but you can expect to experience some loss of
each. Biodiesel’s higher cetane number (a measure of the fuel’s ability to ignite under pressure)
translates to better fuel ignition. Increased lubricity means less wear and tear on engine and fuel
system components, and it has a detergent effect
on the entire fuel system.
Biodiesel is produced from recently grown biomass, rather than biomass that grew millions of
years ago and has remained sequestered for that
time (as is the case with fossil fuels). Therefore,
no net increase in atmospheric carbon dioxide
(CO2) results from burning biodiesel because the
same amount of carbon dioxide is released when
that biomass decays naturally. Of course, in most
cases, producing biodiesel requires the use of
fossil diesel, but a net CO2 reduction of over 75
percent can be realized when using B100. Finally,
tailpipe emissions smell like fried food, which
is considered a benefit by most people driving
behind a biodiesel-powered vehicle.
Shortcomings of biodiesel include a possible
increase in nitrogen oxides (NOx) when burned,
depending on the type of engine. Nitrogen
oxides contribute to smog and ozone. Given the
lower energy content of biodiesel, you may experience a 10-percent reduction in fuel economy if
you’re driving on B100. Biodiesel will dissolve
any rubber in the fuel system, such as gaskets
or seals, so all rubber parts that may come into
contact with biodiesel must be replaced with
synthetic materials.
Biodiesel has some cold-weather limitations.
It begins to congeal (reaches its gel point) at
around 45°F and must be mixed with fossil diesel
when the temperature drops below this gel point;
see Mixing Biodiesel with Other Fuels on page
204. Be aware that biodiesel acts as a solvent
that will dissolve the fossil diesel deposits that
have accumulated inside of your fuel tank and filter. Ideally, you should flush the fuel tank with a
few gallons of biodiesel (let it sit for a day or so),
drain, and repeat, until all of the gunk is gone.
You should also replace the fuel filter after flushing the tank. If you don’t flush the fuel tank, you’ll
quickly go through several fuel filters, as they will
become clogged with sludge. Biodiesel will leave
its own residue in the fuel tank that will build up
over time. Should you switch back to fossil diesel
after using biodiesel for a while, flushing the tank
may again be needed.
are required to
make biodiesel: vegetable oil, methanol, and a
catalyst. Here’s some information on each one
and where best to find them.
O n l y t h r ee i n g r e d i e n t s
Vegetable Oil
New, virgin vegetable oil is ideal for making biodiesel. You can also use oil left over from restaurant fryers. Waste fryer oil will yield a bit less biodiesel than fresh oil, but you can often find it for
free at local restaurants, where they usually pay
to dispose of it.
Restaurants, food manufacturers (salad dressing companies), and food processors are good
sources for finding free or cheap vegetable oil. You
can also buy it new in large quantities from restaurant food suppliers. Oil quality varies depending
on how used it is. Older, more heavily cooked oil
generally yields more waste in the biodiesel reaction than newer, less-used oil. Canola and soy oil
are common, but you may find other types. Most
cooking oils will make a suitable biodiesel.
Avoid using lard or anything else you can’t
pump at room temperature. Waste fryer oil often
is available for free, but you may find that competition for the oil — from other biodiesel brewers like yourself — has made it a more valuable
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Methanol (CH3OH) technically is wood alcohol but
generally is derived from fossil fuels. It is required
for transesterification, the basis of converting
vegetable oil to biodiesel. The amount of methanol required for a successful reaction varies a bit
but typically is around 20 percent of the initial
volume of oil in the recipe.
This fossil fuel is available in 55-gallon drums
from chemical supply companies. You might be
able to find smaller quantities at your local car
racing track or from a propane gas supplier. For
test batches, you can use “dry gas” gasoline
additive that contains a high percentage of methanol. Do not use this type with ethanol or other
Sodium hydroxide is also known as caustic soda
or lye, or chemically as NaOH. Potassium hydroxide (KOH) also may be used, but 40 percent more
is required in the recipe. The catalyst is required
to chemically combine the oil and methanol to
form biodiesel. The amount of catalyst varies
based on the acidity of the oil.
Oil that has been heated, burned, or used
for cooking is more acidic than new oil and will
require more catalyst (a base) to neutralize the
acid and create the chemical bonds. Liquid catalyst mixes better than dry or crystalized products,
Sodium hydroxide generally is more widely available than potassium hydroxide, and the recipes
in this chapter are based on using dry sodium
Lye is available in various quantities from
chemical supply companies or, for small batches,
use drain cleaner that is 100-percent sodium
hydroxide, found at hardware and grocery stores.
Keep the lye dry in a tightly sealed container.
T o ma k e y o u r own biodiesel, you will need
equipment for collecting, storing, pumping,
mixing, and heating the oil, as well as some basic
chemistry equipment, and, of course, appropriate
safety gear.
Collection. If you plan to collect waste fryer
oil from local restaurants, first talk to the manager and find out how they currently dispose of it.
It may go into a garbage bin in 5-gallon buckets,
or it may go into 55-gallon drums or 300-gallon
receptacles to be picked up by a waste oil hauler.
If they dispose of it in 5-gallon jugs, your job is
easy. If not, you’ll need to transfer the oil from
their storage vessel to a collection tank or buckets on your pickup truck. You can do this with a
hand or motorized pump. If the oil normally is collected by a waste hauler, you may need to enter
into a contractual agreement.
Pumping. If you’re making only small quantities of biodiesel, an inexpensive, hand-cranked
barrel pump works well. For moving a lot of liquid, a 12-volt DC-powered diesel-fuel transfer pump is a good solution. Just attach the
power cable to your truck battery and run hoses
between the collection vessel on your truck and
the restaurant’s oil storage bin. When you’re
back home, use the same pump to off-load the
oil from your truck into your storage barrels.
The same pump can be used to:
• Fill the reactor, or mixing, tank with vegetable
• Pump the glycerin out of the bottom of the
reactor and into a waste collection container
(after mixing and settling)
• Remove wastewater mixture from the tank
after washing
iTip: Draw from the Middlei
Water and debris settle to the bottom of the waste oil bin. When using a transfer pump to collect
waste fryer oil, adjust the length of the intake tube so that it won’t sit on the bottom of the barrel.
Debris and scum water accumulate on top of the grease, so also avoid pumping off the top. Water
in the oil will ruin a batch of biodiesel.
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O i l - G at h e r i n g E t i qu e t t e
Gathering waste restaurant oil
can turn out to be a sociable
experience. Be sure to ask the
restaurant manager if it’s okay
to take the waste oil they produce; managers are generally
appreciative of the free service
you offer. Be prepared to talk
it up with the staff — they’ll
be interested in the idea of
biodiesel, and you want to stay
on their good side. Be respectful
of the restaurant’s busy times.
If you spill any oil, be sure to
clean up after yourself. Be
sensitive to the fact that some-
• Transfer the biodiesel from the reactor to the
fuel storage or settling tank
• Pump biodiesel through a filter and into your
car’s fuel tank
You can get by with a single pump, but it’s handy
to have two. Diesel fuel pumps are not designed
for use with water, but you should be able to avoid
problems by making sure the last liquid through
the pump is oil or biodiesel. This keeps the seals
lubricated and prevents rust from forming inside
the pump. Good sources for fuel-handling equipment include large auto supply shops and the
online retailer Northern Tool and Equipment (see
Mixing tank. A suitable mixing tank for the
home brewer can be made from a 50- to 200-gallon plastic barrel with a conical bottom, which
facilitates pumping out the glycerin after processing. Such tanks are available from specialty
agricultural supply stores, such as PolyDome. or
industrial plastic manufacturers, such as U. S.
Plastic Corporation (see Resources).
Heat. You will need to devise a way to heat
the vegetable oil to 120°F for mixing. This can
be done in an old water heater, in a barrel with a
submersible electric heater, or using another heat
source and heat exchanger of your own design.
Good places to find heaters suitable for this task
include farm stores; agriculture supply outlets;
auto parts stores; and online resources, such as
Diesel-Therm and Jeffers Pet (see Resources).
body probably already picks up
the restaurant’s oil, and that
may be someone who earns a
living hauling waste. If you suddenly come in and take that oil
without permission, it could be
tantamount to stealing.
Mixing motor. If you’re making only a few gallons of biodiesel, you can get by with a portable drill and a paint-mixing attachment. A 3∕8" drill
will do fine for starter batches, but you may soon
find yourself upgrading to a 1/2" drill with a larger
motor. For mixing larger quantities, you’ll want to
use a 1/2-horsepower (hp), 1800-rpm motor and a
good mixing blade attachment to provide vigorous
hand-crank pump
Basic equipment
needed to mix a batch of biodiesel
submersible heater
motor and mixer
Never use a diesel fuel pump for pumping methanol or gasoline! Methanol forms explosive vapors at a
temperature of 52°F, and sparks from a pump motor could easily ignite the fumes.
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agitation. Remember that methanol is flammable.
Sparks from motor brushes can ignite methanol
vapors, causing an explosion. Use only Class
1-rated “explosion-proof” motors around flammable vapors. A Class 1 motor is constructed to
contain an explosion within itself without rupturing. A suitable motor-mixer combination, designed
for use with drums and barrels, is available from
Neptune Chemical Pump Company (model F-3.1;
see Resources). These are costly but will pay for
themselves the first time they prevent an emergency-room visit.
Lab ware. Some basic lab equipment is
required for measuring and weighing the ingredients and determining the proper amount of lye
to use for the biodiesel reaction. The more often
and longer the grease was heated for cooking,
the greater amount of lye is needed for a complete reaction. The process for determining this
is called titration (see Making a Test Batch with
Used Vegetable Oil, page 203).
For lab ware, Frey Scientific is a good source
(see Resources). Order extra; glass breaks. A
basic lab kit to get started converting waste vegetable oil to biodiesel includes:
Filtering. Biodiesel must be filtered before it
goes into your fuel tank. You can use a “sock”-type
filter (a filter bag that looks like a big sock) or standard automotive fuel filters in line with the fuel pump
to filter out particles greater than 10 microns.
Storage. Biodiesel can be stored for over a
year in a clean, dark, dry environment. Use only
containers suitable for liquid storage, made from
black mild steel, stainless steel, fluorinated polyethylene, or fluorinated polypropylene. Keeping
the biodiesel cool helps it last, but longer-term
storage may result in fungal growth within the
biodiesel (especially if any water is introduced
into the fuel), requiring treatment with a chemical biocide. Keep in mind that there may be state
or local regulations governing storage of large
quantities of fuel or vegetable oil, so check with
your city or local health department for more
measuring beaker
• Electronic scale for weighing quantities of
lye up to 2 kilograms (kg), with a minimum
resolution of 1 gram (g)
• Calibrated, 1.5-milliliter (mL) pipettes for
measuring small quantities of oil and alcohol
for titration when waste vegetable oil is used
• Hydrometer to measure the specific gravity of
the biodiesel
• Glass beaker or wide-mouth jar
• 2-liter (L) beaker to measure your lye
• 1-L bottle to store your 1-percent solution of
sodium hydroxide
pH paper
• Two 10-mL graduated cylinders
• pH paper
• Funnels for pouring various wet and dry
• Scoop for measuring out lye
• Stirring rods
stirring rods
small beakers
Lab ware required for titration, measuring, weighing,
mixing, and testing biodiesel
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but much less
so than diesel fuel. It has a minimum flash point
(the temperature at which vapors will ignite when
exposed to a spark or flame) of 266°F, compared
to about 165°F for diesel fuel. Biodiesel is
relatively safe and less toxic than fossil fuels,
and it’s not difficult to make and use, but it does
require close attention to detail and respect for
the materials and equipment you will be working
with. Don’t get lazy with safety.
It is extremely important to use personal safety
equipment when working with methanol and lye.
Obtain, read, and understand the material safety
data sheet (MSDS) from the supplier of any chemicals you use. Handle biodiesel as you would any
other fuel, and always take steps to prevent personal and environmental contamination. Biodiesel must be made outdoors or in a very wellventilated area, using great care to protect yourself from hazardous materials and conditions. At
a minimum, you will need:
B i o d i e s e l i s f l amma b l e ,
• Chemical-resistant goggles
• Organic vapor respirator
• Nitrile gloves
• Chemical-resistant apron
• Clothing that completely covers all of your skin
• Ground-fault circuit interrupter (GFCI) — use
this type of electrical outlet (receptacle or
extension cord) for plugging in any electrical
devices used in your processing operation
• Vinegar and water to neutralize spills of the
corrosive lye and sodium methoxide
Many of these supplies are available at hardware
stores or online through such places as Industrial
Safety equipment
GFCI extension cord
Safety Company, Grainger, and Direct Safety (see
Methanol is an alcohol, and the vapors are
flammable when mixed with air in concentrations
between 6 and 36.5 percent. It has a flash point
(the temperature at which it will begin to evaporate, forming explosive vapors) of 52°F. Methanol
is poisonous and can cause blindness and internal bodily damage; a quantity of only 2 ounces is
enough to kill a human if swallowed. It is readily
absorbed into blood through the skin, with exposure reactions similar to those from ingestion.
Inhaling the fumes can make you sick in many
ways: Always wear a respirator.
Sodium hydroxide, or lye, has a pH of 12
and will burn your skin, eyes, mouth, lungs, and
clothing. It can be fatal if swallowed.
Sodium methoxide (methanol-lye mixture) is
highly toxic, flammable, and explosive. Exposure
iA Cautionary Talei
A farmer friend of mine made several successful batches of biodiesel during the summer months so
that he could heat his greenhouses during the winter. When the weather turned cool in the fall, he
moved the mixing operation into a greenhouse. After starting a batch by mixing the methanol and
lye, he returned a short time later to find all his tomato plants dead; they had been burned by sodium
methoxide fumes. When he entered, not yet knowing what had happened, his eyes, nose, and lungs
were instantly burned. It took weeks for the burns to heal. Making biodiesel is an outdoor activity!
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to this extremely strong base will burn your lungs,
skin, and eyes.
Glycerin contains both unreacted methanol
and catalyst, and therefore is somewhat caustic.
(This is why it makes such a good soap.) Depending on what you want to use it for, and how complete your biodiesel reaction was, you may need
to clean and neutralize your glycerin.
Biodiesel and vegetable oil can spontaneously combust under the right conditions. Do
not leave oil-soaked rags in enclosed containers.
Also, vegetable oil is slippery! If you spill it, clean
it up immediately. This is especially true if you
spill it at the restaurant where you are picking up
the oil (ask me how I know).
Basic Steps for
Making Biodiesel
I f y o u ’ r e f o r t u n a t e enough to be using
fresh, new vegetable oil (as opposed to waste
fryer oil from a restaurant), you will be reacting a
quantity of carbohydrates in the form of vegetable
oil with 20 percent (by volume) methanol and a
small amount (0.35 percent) of sodium hydroxide
as a catalyst.
I highly recommend that you start your biodiesel experiments with a small blender batch
using fresh oil, and work your way up to more substantial volumes and converting waste oil. This
will give you some practice with the process and
equipment before moving on to larger batches.
During the process, the bonds of the triglycerides that make up vegetable oil will be broken by
the catalyst. Glycerin is replaced with alcohol to
form methyl ester, and the catalyst then bonds
with the glycerin, which will settle out as waste.
The result will be 80 to 90 percent fatty acid
methyl esters (biodiesel) and 10 to 20 percent
glycerin (a carbohydrate). As a point of reference,
new canola oil weighs about 7.6 pounds per gallon, but used oil will weigh a bit more. Methanol
weighs 6.63 pounds per gallon. Your finished biodiesel will weigh about 7.4 pounds per gallon.
The Basic Process
First we’ll cover the basic steps of making biodiesel, followed by the specific processes for
making test batches with new oil and waste oil.
Make sure to do all of your mixing with mechanical mixers or pumps suitable for use with caustic
and flammable chemicals.
1. Gather your oil. If using waste oil, strain it to
remove bits of food and other debris. Try not to
use oil that has been burned or has gone rancid.
You can make decent biodiesel from some pretty
nasty oil, but higher-quality oil means a better reaction and more usable fuel for your efforts. The
oil quality varies depending on the source and
on whether it is fresh-pressed or waste from restaurant cooking. Do not attempt to use oil that
has any water in it — it will ruin the entire batch
(again, ask me how I know). If it smells like something that died and rotted, find another source
(you can ask me about that, too).
2. Perform a titration (see Making a Test Batch
with Used Vegetable Oil, page 203) if you are using waste fryer oil, to determine how much lye to
use for a complete reaction.
3. Mix methanol with the correct amount of lye
Collecting oil
from a restaurant
with the Calamari
Cruiser 
for about 15 minutes to form sodium methoxide.
This is an exothermic chemical reaction, meaning heat will be created.
2 00 B I OD I ES EL
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iManaging Waste Glycerini
The waste glycerin resulting from making biodiesel can be cleaned and made into soap, or it can be
composted as with other organic materials. Be aware that the pH of the waste glycerin will be quite
high due to the lye used in the mix. The pH will neutralize when combined with other organic matter.
There will also be unreacted methanol in the glycerin, which you don’t want on your skin, but this will
evaporate over time.
4. Heat the oil to 120°F. While you can have a
successful reaction at temperatures above 70°F,
the mixing time will be longer and you may end
up with more unreacted byproducts, along with
lower-quality biodiesel.
5. Add the vegetable oil to the sodium meth­oxide
mixture, and mix for about an hour. Avoid splashing
the methoxide.
6. After mixing, allow the glycerin to settle to the
bottom of the mixing tank (this should take 4 to
8 hours).
7. Pump or drain the glycerin into a waste container after it has settled. If you wait longer than
12 hours, the glycerin will begin to solidify and
cleanup will be more difficult because the glycerin will be too thick to be pumped.
8. Pump the biodiesel immediately into a holding
tank and let it settle for a week or so, during which
time excess methanol will evaporate and smaller
particles will fall to the bottom. If necessary, you
can “wash” the biodiesel before storing it by mixing it with water to remove impurities, such as
small glycerin particles and any excess methanol
(see Washing Biodiesel on page 205). If you’re
making large amounts of biodiesel, it’s a good
idea to recapture the methanol by boiling it off the
biodiesel and capturing it through distillation for
reuse. This is prudent from both an economic and
environmental standpoint.
Making a Test Batch
with New Vegetable Oil
Starting off with a small blender batch using new
vegetable oil is a good way to get your feet wet
with making biodiesel. First, get a cheap or used
blender; the plastic and rubber parts will likely
disintegrate after a few batches, and you won’t
want to use the same blender for food. If you’re
working indoors, be sure to protect yourself, your
B i o d i e s e l Q u a l i t y a n d M e e t i n g AST M S t a n d a r d s
Professionally made and commercially sold biodiesel needs
to meet the American Society
for Testing and Materials (ASTM)
D6751 specification. It must be
registered with the U. S. Environmental Protection Agency under
40 CFR Part 79. Homebrew
biodiesel often does not meet
those high quality standards but
is useful as a fuel if properly
made and thoroughly reacted.
Commercial-grade biodiesel
meets the following standards:
• Glycerin content of less than
0.24 percent
• Methanol content of less
than 0.2 percent
• Water content of less than
0.05 percent
• pH of 7
• Specific gravity between
0.86 and 0.90
Unless you have a friend who
works in a chemistry lab, most
of these tests (other than pH
and specific gravity) can be
quite expensive if you want the
accuracy required by ASTM.
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clothing, and all work surfaces from splashing
or spilled chemicals. Heed all of the advice in
the safety section (pages 199 and 200), regardless of batch size. Basic solutions will burn skin,
clothes, and finished surfaces just as quickly as
acidic solutions.
This recipe is for 1 quart of biodiesel (with
metric units for making 1 liter shown in parentheses) but the process and proportions are the
same regardless of how much you’ll be making.
You will need:
1 quart (1 L) of NEW vegetable oil
3Sample of mixed
biodiesel showing
separation of glycerin (bottom) and oil
esters (top)
6.4 ounces (200 mL) of methanol (20 percent of
the amount of vegetable oil)
7. Slowly pour the vegetable oil into the sodium
methoxide and blend at medium speed for 15
0.11 ounces (3.5 g) of sodium hydroxide (0.35
percent of the amount of vegetable oil) from a
fresh, unopened container
8. Pour the biodiesel into a glass container and
let it settle.
Safety gear (see pages 199–200)
If all has gone well, you should see two layers start to form in the container after about 10
minutes. Depending on the type and quality of oil
and the completeness of the reaction, anywhere
from 75 to 95 percent of the product will be biodiesel. After 8 hours or so, much of the settling
has occurred and you can pour the biodiesel off
the top, filter it, and use it as fuel. Once the biodiesel is drawn off, you can dry out the bottom
layer of glycerin by leaving the open jar outdoors
in a protected area for a week or two, so that the
alcohol has a chance to evaporate, then use the
glycerin as soap. To purify the glycerin for other
uses, further processing may be required.
Pot and thermometer for heating oil
1.5 quart (or larger) glass container
Here’s what you do:
1. Put on your safety gear.
2. Measure all ingredients.
3. Heat the vegetable oil to 120°F.
4. Carefully pour the methanol into the blender.
5. Gently
pour the lye into the methanol and
close the top tightly. Blend at low speed until the
lye is completely dissolved, a few minutes, to
make sodium methoxide.
6. Stop
the blender and — keeping your face
away from it — take off the top.
iTesting the Mixi
To determine if your mix is a success, dip a jar or beaker into the reactor immediately after the mixing is
completed (step 5, page 201), and draw off a pint or so of the liquid. Within 15 minutes, you should see
two layers begin to form in the mixture. The top layer is biodiesel; the bottom layer is a slurry of glycerin,
lye, and particles that may have been in the oil. After 8 hours, most of the settling has occurred. If you
use a beaker, you can easily see how much glycerin was produced compared to biodiesel. Cleaner, lessused oil will produce less (and cleaner) glycerin.
202 B I OD I ES EL
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Making a Test Batch
with Used Vegetable Oil
The only difference between making biodiesel
with used oil instead of new oil is the amount
of lye added. All other processes are the same.
To determine the quantity of lye required, you
will need to perform a titration — a process to
determine the concentration of an acid or a base
— of the oil. This is necessary because oil that
has been heated will be more acidic than fresh
oil and require more catalyst (a base) to neutralize. Over time, you may find that oil from a single
source has a fairly consistent quality, and experience may teach you how much lye to add without
performing a titration, but otherwise a titration is
always required for best results.
You’ll need the following materials for the
Sample of the vegetable oil you wish to use
Fresh bottle of isopropyl (rubbing) alcohol, at least
90 percent pure
1 L distilled water
1 g sodium hydroxide
1 L bottle (glass or chemical-resistant plastic) with
tightly closing cap
Pipettes to measure 1-mL increments of liquid
4. Using
a clean pipette, add 1 mL of the
1-per­cent sodium hydroxide solution to the oil/
alcohol solution, and stir.
5. Test the pH of the solution by dipping the pH
paper into it.
6. Repeat steps 4 and 5, as needed, until the
pH reaches 9; this completes the titration.
To apply the titration result, note how many mL
of sodium hydroxide solution were added to reach
a pH of 9, then add 3.5 to that number; this is
how many grams of lye are required for each
liter of vegetable oil in your biodiesel reactor. For
example, if you add 3 mL of sodium hydroxide
solution to reach a pH of 9, you would need 6.5
g/L of catalyst for your biodiesel recipe. Use the
Lye Quantity Table below to determine the total
amount of lye to add to your recipe.
For the record, the more lye that’s required,
the greater the percentage of waste: If you need
to add 7 mL of NaOH to your titration, the waste
glycerin will be about 25 percent of the total
batch quantity.
Ly e Q u a n t i t y Ta b l e
Glass mixing containers
If you have to add
this many milliliters
of NaOH solution for a
successful titration
You’ll need this
many grams of
lye for a 10-gallon
Or this
Mixing rod
1. Pour 10 mL of rubbing alcohol into a small
2. Add 1 mL oil, using a pipette.
pH paper
To begin, make a 1-percent sodium hydroxide
solution by adding exactly one gram of lye to the
1-liter bottle, fill it with 1 liter of distilled water,
and mix thoroughly. This solution becomes the
basis for many titrations. Complete the following
steps for a titration of used vegetable oil:
3. Mix the oil and alcohol thoroughly (they mix
more easily when warm). A well-mixed solution
will be cloudy and will not separate quickly.
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Mixing Biodiesel
with Other Fuels
kerosene, and diesel fuel
essentially are the same thing. Kerosene is almost
identical to heating oil and diesel fuel, but it’s
slightly more refined, has a lower gel temperature,
is slightly lighter in weight, and is slightly lower in
energy content. There are also differences in the
federal standards for allowable sulfur content of
each fuel, and they are taxed differently. Kerosene
and heating oil are considered “off-road” fuels
and are not subject to the same taxes as diesel
engine fuel.
Due to the highway tax imposed on motor
fuels, it is illegal to use untaxed biodiesel or kerosene in place of diesel fuel for highway vehicles,
though you may be able to apply for a research
permit to have taxes waived for personal use.
Kerosene is dyed red so that it is readily identifiable and distinguishable from diesel fuel and
home heating oil. When using biodiesel on the
highway, off-road, on a farm, or in your generator or heating system, check with your appropriate state agencies regarding taxes, use, storage,
waste disposal, and fire codes.
Mixing fuels requires no special process; simply filling the fuel tank with the desired amount
of each fuel allows the liquids to mix and stay
mixed. Any amount of biodiesel mixed into fossil
diesel, kerosene, or heating oil will perform well
in your diesel engine or oil burner, provided there
are no rubber gaskets or seals or other materials
that will be degraded by biodiesel (check with the
engine or burner manufacturer to ensure the suitability of biodiesel for your equipment).
Be aware that you may void all warranties if you
use mixed fuel or straight biodiesel (B100). Some
engine manufacturers offer specific warranties
when fuels are used that contain small amounts
of biodiesel. Diesel engines and oil burners have
been optimized for best performance with fossil
H o me h eat i n g o i l ,
Cold Climate
Below a certain temperature, diesel fuel begins to
congeal, or gel, and the particles become too big
and the fluid too thick to flow through the fuel system. Pure fossil diesel has a gel point of around
20°F, while biodiesel has a gel point of around
45°F. In cold climates, refineries mix anti-gelling
agents into diesel engine fuel. Once the temperature drops below the gel point, biodiesel should
be mixed with fossil diesel. A mix of 20 percent
biodiesel with 80 percent fossil diesel — called
a B20 mix — will raise the gel temperature of
the fossil diesel by 3 to 5°F, and should work well
at temperatures down to –20°F (in areas where
anti-gelling additives are used in the fossil diesel
fuel). With B20, you should not notice any difference in equipment performance.
a way to remove
any unreacted methanol, lye, and glycerin after
mixing. Unless you plan on selling commercialgrade fuel, it is not mandatory to wash biodiesel
before using it, though you will find varying
opinions regarding washing. Impurities in your
fuel may lead to fuel system problems in the long
Allowing the biodiesel to sit for a week or two
is generally enough time for most of the unreacted ingredients to settle, leaving a clear biodiesel fuel with a neutral pH. Before washing, you
may want to run a few simple tests. Put a sample
of your biodiesel in a clear jar so that you can
observe it over time. The particles that settle to
the bottom of the jar can be seen, and the pH can
be easily measured with pH paper.
Testing for methanol content is a bit more
difficult but is important because if too much
methanol remains in the biodiesel it can damage
an engine, burner, or fuel system. The easiest
method to test for methanol content is to weigh a
sample of biodiesel, heat it to above methanol’s
Wa s h i n g b i o d i e s e l i s
2 04 B I OD I ES EL
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boiling point of 148°F (aim for 165 to 200°F),
then weigh the sample again. The difference in
weight is the amount of methanol that has boiled
off. Methanol weighs 6.63 pounds per gallon. You
can use the same process to determine water
content, by heating the biodiesel to above the
boiling point of water (212˚F).
How to Wash Biodiesel
You can wash your biodiesel after mixing and the
initial settling by adding water to it so that you
have about a 50/50 mix of water and biodiesel.
Operate the mixer for about 2 minutes, after
which time the whole slurry should be a milky yellow color. After settling (24 to 48 hours), there
will be three layers in the tank. A milky water
mixture will settle to the bottom, a soapy layer
may form in the middle, and biodiesel will be on
top. Pump or drain the bottom layers and discard
them. Repeat this process 2 or 3 times until the
water at the bottom of the tank is clear, and the
biodiesel is a clear, amber color.
Environmental Care
Biodiesel is fairly nonreactive and will biodegrade over time. However, the ingredients used
to make biodiesel can create serious environmental impacts if not handled properly. Both methanol and lye are toxic to all living things. Avoid
spills and fumes. Better biodiesel kits and largerscale manufacturing plants use sealed reactors that keep vapors contained and are able
to recover methanol from the biodiesel. They
can also recover glycerin through the process of
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clo s e - up
Veggie Oil Conversion
a diesel pickup on straight vegetable oil (SVO) for a few years now.
I decided I’d rather convert the vehicle once than convert the fuel forever. Vegetable oil is
much thicker than diesel fuel, and so won’t flow through fuel filters or injectors unless it
is heated to reduce its viscosity.
H ilto n D ie r III ,
my friend and renewable
energy consultant, has
been a renewable energy
wrench-twister, consultant, and advocate for
the many years that I’ve
known him. Together, we
began an electric
car conversion business
back in 1990, and today
we continue to practice
what we preach, with a
twist: We traded electricity for waste vegetable
oil as a transportation
fuel. I prefer biodiesel
because it’s less worry
for me about engine
damage, I don’t have to
hack my car, and I can
use the fuel I make in
both my car and diesel
generator. He runs his
diesel pickup truck on
straight vegetable oil.
Here’s what he has to
say about it.
’ v e b ee n d r i v i n g
An SVO vehicle has an extra fuel tank just
for the vegetable oil, plus a series of heaters
to get the oil up to a temperature (150 to
190°F) where it flows as well as petroleum
diesel. An SVO system also has valves and
controls for switching between diesel and SVO.
This can be done manually with dashboard
controls or automatically with microprocessors
under the hood. It’s a good feeling, driving
down the road fueled by an organic waste
product rather than a petroleum product, but
it isn’t a perfectly convenient thing to do. Here
are a few important things to think about
before buying or converting an SVO vehicle.
• Figure out your vegetable oil supply first.
You’ll be using waste vegetable oil (WVO,
generally interchangeable with SVO),
probably from a restaurant, maybe from a
food processing business. Get an idea of
the type of diesel vehicle you’ll want, its
fuel efficiency, and the miles per month
you’ll want to drive it. This will give you a
monthly vegetable oil budget. The beauty
of a dual fuel (SVO/diesel)-system is that
you can always fall back on diesel, but
it’s pointless to spend the money on a
conversion if you can only run it on SVO
now and then.
• In some areas where SVO vehicles are
popular, you’ll find out just how limited
supplies of WVO are. In other places
you’ll be competing with professional
companies that earn a living picking up
and recycling WVO from restaurants and
food processors. Make the situation
convenient for your supplier and don’t
step on any toes.
• Not all WVO is created equal. Fast-food
chains and burger joints generally use
hydrogenated oil, which turns to sludge
at room temperature. You can’t use
that. Some restaurants use and reuse
the oil until it is brownish-black and full
of impurities. This will be more acidic,
which will abuse your injection pump,
and it will be full of particles that will
clog your filters. High-quality restaurants
generally have high-quality oil.
• Make sure you have an appropriate,
heated space for processing and storing
your WVO. It is a messy process, and the
oil won’t flow well in cold temperatures.
Your kitchen is not a good place. Oh, and
mice love the stuff. They will leave little
souvenirs in your bag filters, and they
will drown themselves in any container
of oil you leave open. Make sure you can
close everything up. Also make sure that
you are willing to handle a sticky, slightly
pungent liquid on a regular basis.
• Set up your filtering and storage to avoid
lifting heavy containers. I get my WVO
in 5-gallon jugs, which weigh about 35
pounds each. Holding one carefully in
midair to pour into a funnel gets old.
I built a hinged jug holder with a long
handle so I could decant WVO into the
bag filter with one hand. The filter, set up
next to and halfway up a flight of open
2 06 B I OD I ES EL
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stairs, gravity-feeds into a repurposed
fuel oil tank, which has a hand pump
installed to fill my truck. I never have to
lift a jug above knee height.
• Let your WVO sit at room temperature
for a couple of weeks so that the water
and food waste can settle out. Then
decant the good stuff through stacked
sock filters: 100 micron, 25 to 50
micron, then 5 micron. McMaster-Carr
is a good source for filters and other
hardware (see Resources). The stacked
arrangement means that you’ll end up
replacing the 5-micron filter less often.
I made my filter holder by cutting circular
holes in the tops of two tall, five-gallon
buckets, bolting them together top to
bottom, and sealing the seam between
the two. I cut the holes slightly smaller
than the 8" diameter of the ring in the
top of the filter. The lower bucket has
a hose fitting at the bottom. An old pot
lid keeps the mice out when I’m not
using it.
• If you buy a vehicle that has already been
converted, be extra cautious. A diesel
engine can run well on SVO for a long time,
if the owner has done a proper conversion.
If not, the injection pump can get clogged
and etched, the piston rings can get
carbonized and stuck, and much mayhem
can be inflicted on the fuel system in
general. Have a competent mechanic
check out the vehicle thoroughly.
• If you are doing the conversion yourself or
are having it converted, spend the extra
money on a flat plate heat exchanger.
These are identical to those used as
hot water heat exchangers (described in
chapter 6). They are available for around
$100 online. The standard conversion
kits have a fuel tank heater and a fuel
filter heater. Add the finishing touch
of the heat exchanger, just before the
injector pump, and you’ll have hotter oil
and better combustion. This is especially
important in northern climates. Insulate
every part of the SVO system.
Veggie oil bag
filter using two
5-gallon buckets.
The top bucket
holds the filter
in place over the
bottom bucket,
which holds the
filtered oil.
valve switch
heated vegetable oil tank
heated and
insulated fuel
line and filter
Basic diagram of a
fuel line and filter
dual-fuel system for a diesel vehicle.
The heat for the
fuel filter and
fuel lines can be
provided by engine
coolant, or they
can be electrically
fossil diesel tank
veggie oil conversion 207
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c lo s e - up
Veggie Oil Conversion
• With an SVO system, you start out driving
on diesel and then switch to SVO when
the engine (and SVO heating system)
is up to temperature. During a belowzero winter cold snap, the oil may never
get warm enough. Cold oil will lead to
injector pump damage. When you are
near your destination you will hit a switch
that flushes out the SVO system with
diesel. This prevents clogging and leaves
the whole fuel system full of diesel for
starting. Don’t push your luck. Flush the
system early.
pieces of clear tubing connected to the
fuel filter’s send and return lines, with the
other ends sunk in the bottle of cleaner.
Then, sit in your driveway revving the
engine until the cleaner is almost used
up. It takes maybe 15 minutes to make
your diesel engine run much cleaner and
Running on SVO isn’t the most convenient
way to drive, but for someone willing to put in
the occasional bit of work, it’s a cheap and
eco-friendly alternative. (See Resources for
SVO conversion kit manufacturers.)
• Clean your injectors. I neglected this at
first, and it cost me a set of injectors.
This means getting a couple of cans of
diesel injector cleaner and running it
through the system every 3,000 miles
or so. Don’t just use the kind you pour
into the fuel tank but rather something
like Lubro Moly Diesel Purge that can be
used undiluted to clean injectors. You
can do this by emptying the SVO filter
and filling it with the cleaner, or by rigging
a temporary fuel “tank” made from a
quart-size plastic bottle with a couple of
2 08 B I OD I ES EL
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Create a Biodiesel Kit
nce you achieve consistent success with small
batches of biodiesel, you
may be inclined to start making
enough to power your diesel vehicle
or oil-fired heating equipment. You
can have some success with a fivegallon bucket and drill mixer attachment, but when you’re ready to make
batches of 40 gallons or more, it’s
time to get serious about automation, durability, and safety. The processor described here has served
me well in making dozens of batches
of biodiesel suitable for use in diesel
engines. This is a fairly expensive kit
(my total was over $2,000) but will
last a very long time when properly
cared for, and it could very well be a
good investment as fuel prices continue to rise.
Before we get to the steps for
building the biodiesel kit, let’s look at
each of the main components:
Motor. At over $1,000, the
most costly item by far is the
explosion-proof mixing motor. This
Class 1, Group D motor is required
because it operates in an environment that may include explosive concentrations of methanol vapors, and
a standard motor could easily ignite
these vapors and cause an explosion (see page 198).
Mixing tank and stand. My
conical tank and lid from Polydome
(see Resources) work quite well
for mixing. This tank is made with
∕16"-thick, medium-density polyethylene and is designed for acid and
caustic chemical storage. It is UVstabilized and has a useful working
temperature limitation of 140°F.
The tank normally comes with a
discharge pump on the bottom,
which may work well for pumping
out sludge and biodiesel; however, I
have not employed this feature and
ordered the barrel without the pump.
You may find tanks of other sizes
and materials through U.S. Plastics
(see Resources).
The tank stand is welded steel,
with a white, baked-enamel finish
and integral motor mount. The mixing
paddle (included with the motor) is a
two-bladed propeller with a 5∕8"-diameter stainless steel shaft that’s long
enough to extend into the 8 gallons
of methanol/lye mixture — a typical
quantity for the first part of the batch
My tank has a 55-gallon capacity. Larger tanks and stands are
available at additional cost. All other
kit parts remain the same with the
larger tanks. Keep in mind that the
tank, stand, and motor may involve
significant shipping costs due to
weight and size.
Fuel pump. The 12-volt DC fuel
pump has a telescoping suction tube
with strainer, a 10-foot hose, and a
nozzle. It’s a magnetic-drive pump
that can be used to transfer vegetable oil and biodiesel at up to 10
gallons per minute (gpm). I needed a
longer hose, so eventually replaced
it along with a nozzle with automatic
shutoff. Do NOT use the pump for
pumping methanol!
I use the same pump for moving
vegetable oil from the barrel at the
restaurant into a transfer tank on the
pickup and back into larger storage
tanks at the shop. Then I use it to fill
the reactor tank with vegetable oil,
and finally to pump the liquid glycerin
out of the bottom of the reactor and
into a waste collection tank or jug
after mixing and settling. It can also
be used to pump waste water from
the tank after washing, but always be
sure to pump biodiesel or oil through
it before storage to prevent the internal parts from rusting. You may want
a second pump that can stay put,
along with an in-line filter to fill your
car’s fuel tank.
Heater. The thermostatically
controlled heater in the parts list on
page 210 is safe for use in plastic
i Warning!i
Follow all necessary safety precautions and don’t take shortcuts! See pages 199 to 200 for detailed information on
safety and safety equipment for working with biodiesel. Always read and understand all safety warnings on equipment,
along with the precautions spelled out in material safety data sheets (MSDS) supplied with the chemicals required.
You must protect yourself by using safety equipment properly and practicing common sense. If you find that any task —
including electrical work — is confusing or unfamiliar, please consult someone who is knowledgeable in this area.
create a bi odi esel ki t 209
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Create a Biodiesel Kit
M at e r i a l s
tanks and turns itself off when the
oil reaches 100°F. You should strain
the vegetable oil to remove larger
bits of food and other debris before
preheating. While you can have a
successful reaction at temperatures
above about 70°F, lower temperatures yield unpredictable results,
longer mixing times, and possibly
more unreacted byproducts —
meaning lower-quality biodiesel. It’s
best to heat the vegetable oil to at
least 100°F before adding it to the
Lab ware. The lab equipment
is used for titration (see page 203).
Remember, this is required only
when using waste fryer oil. If you
plan to use virgin vegetable oil, you
need only a scale to weigh the lye,
as the quantity will not vary from
batch to batch.
Parts note: Manufacturers
change prices, part numbers, designs, and availability without notice,
so no prices are given in the parts
lists, and there is no guarantee of
availability. However, similar products
to those listed should be available
locally or online. You can download
motor/mixer specifications from
Neptune Chemical Pump Company.
See Resources for suppliers and
products noted in these plans.
Mixer Parts
Safety Equipment
One ½ hp Class 1, Group D motor/mixer,
1750 rpm (Neptune F-3.1; includes
2-bladed folding, 316SS mixer)
One tank stand (Polydome PT-304S;
specify stand that includes motor
One 55-gallon conical tank, graduated
(Polydome PT-304; graduated tank
with gallon markers; specify without
the optional pump motor)
One tank cover (Polydome PT-304C;
specify split hinged inside cover with
motor slot cut out)
Nitrile gloves
Splash-proof chemical goggles
(preferably antifog; it’s worth it!)
PVC apron
Full-face respirator with carbon filter
cartridge for organic chemical vapor
Electrical Supplies
One dozen 1.5-mL pipettes (to measure
fluids for titration)
pH paper
One 1-L narrow-mouth HDPE bottle
Two 10-mL graduated glass cylinders (to
measure alcohol and lye solution for
Two 30-mL glass beakers (to measure
and mix for titration)
One 1-L polypropylene beaker (for
measuring and pouring lye)
One hydrometer and jar (to test specific
gravity of your biodiesel; avail­able
through brewing suppliers)
One 1-g resolution, 2 kg max. scale
(Ohaus CS2000)
Three waterproof, strain-relief cable
connectors (Del City Wire #2612)
One weatherproof switch box with
weatherproof cover
One 10-foot length 14-3 SJOOW
electrical cable (oil-, acid-, abrasion-,
and flame-resistant)
Two 14 AWG, #8 stud spade connectors
Three 14 AWG, #8 stud ring connectors
Four yellow wire nuts
One 120-volt, 15-amp AC plug (NEMA
5266 style)
2" length ¼" heat shrink tubing
One 120-volt, 15-amp switch
One 14 AWG (minimum) portable GFCI
extension cord (use if your AC outlet is
not GFCI-protected)
Two 3∕8" x 1" #16 hex head bolts
Two 3∕8" lock washers
Two 3∕8" flat washers
One 5∕8" loom clamp
Lab Equipment
(for titration; see step on page 213)
N o t e : Much of this equipment is available
from school science or lab supply outlets,
such as Frey Scientific (see Resources).
Miscellaneous Equipment
One barrel-mount pump with telescoping
suction pipe, hand crank or electric;
use to pump oil and biodiesel
(Northern Tool)
One 1,000-watt submersible heater
with thermostat control (Jeffers
W-449; must be safe for plastic tanks)
One thermometer
2 10 B I OD I ES EL
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switch box with
A ssemb l i ng the
B i od i esel K i t
heat shrink
ring connectors
wire nuts
1. Wire the motor, switch, and plug.
Remove the electrical connection plate from the
motor. Screw one waterproof, strain-relief cable
connector into the threaded hole in the motor’s
electrical connection box. Screw two more of the
connectors into the threaded holes on each end
of the weatherproof switch box.
Cut a 7-foot length of the 14-3 cable. Strip
about 3" of the cable jacket and 1/4" of insulation
on each individual wire, at both ends of the cable.
Insert one end of the cable through the connector
on the motor’s electrical connection box. Crimp a
ring connector onto the green wire and screw it to
the hole inside the motor’s electrical connection
box. Connect the black and white wires as shown
on the wiring diagram on the inside of the motor’s
electrical connection box cover, using wire nuts.
Attach the box cover. Insert the other end of the
cable through one of the waterproof connectors
on the switch box.
Using the remaining 3-foot length of the 14-3
cable, strip the jacket and wires at both ends,
as before. Attach one end of the cable to the
5266 AC plug. Insert the other end of the cable
through the remaining open waterproof connector on the switch box. Slip about 1" of heat-shrink
tubing over the black wire ends, leaving the tubing loose. Crimp a spade connector onto each
black wire in the switch box, making sure it’s secure. Heat-shrink the connection, then attach the
connectors to the switch.
Crimp a ring connector onto each green wire
in the switch box, then screw them to the box.
Mount the switch and install the box cover.
Double-check all your work, making sure
there are no frayed wires or loose crimps. With
the motor on a workbench or floor, block it so that
it will not roll either way. Turn the switch to the off
position, plug in the power, and test the motor.
cable connector
7-foot cable
3-foot cable
Wiring assembly
for motor, switch,
and plug
Detail of motor
mounting frame,
with holes drilled
to attach to stand
Fully assembled
and wired mixing
Create a b i odi esel ki t 211
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Create a Biodiesel Kit
2. Mount the motor to the tank stand.
N o t e : You will need a helper for mounting the motor to
the tank stand.
If you’re using the Polydome PT-304S tank stand,
cut off the two horizontal supports and remove
the threaded clamp from the Neptune motor
mount frame. If you’re using a standard barrel
or drum for the mixing tank, you’ll need these
pieces to secure the motor to the barrel.
Drill two ½" holes into the motor mount
frame to match the mounting holes on the tank
stand as shown. Secure the motor mount frame
to the motor using the four 7∕16" bolts, nuts, and
washers included with the motor/mixer kit and
following the manufacturer’s instructions.
Stabilize the mixing tank in its stand and attach the mixing motor using two 3∕8" x 1" bolts,
washers, and lock washers, orienting the lock
washers so they face the bolt head. Have a helper hold the motor in place while you tighten the
bolts securely into the captive nuts on the mixing
tank frame (torque to at least 25 foot-pounds).
Attach the loom clamp to one of the motor frame
mounting bolts; the clamp holds the power cord
out of the way and provides strain relief. Make
sure the mixing tank is stable and reasonably
3. Install the motor shaft and
mixing paddle.
Attach the mixing paddle to one end of the mixing shaft, using an Allen wrench. Secure the
con­necting barrel to the other end of the mixing
shaft, then attach the open end of the connecting barrel to the motor shaft (follow the instructions included with the motor mount). Be sure to
make these connections very tight so they won’t
loosen while in operation. Add a little thread-lock
to be safe.
N o t e : Retighten all fasteners after mixing your first
batch of biodiesel.
4. Set up the transfer pump.
Attach the suction tube or hose to the transfer
pump as directed by the manufacturer. Be sure to
install a screen filter to prevent large debris from
clogging the pump.
If you’re using the DC pump, set up the
pump and nozzle as directed by the manufacturer. Attach the red clip to the positive terminal
of a 12-volt car battery, and attach the black
clip to the negative battery terminal; be sure
the power switch is in the OFF position before
connecting to the battery to avoid sparks and
unintended pumping. You may want to use an
auxiliary battery to avoid draining the starting
battery while you are pumping vegetable oil or
Motor, motor mount,
mixing shaft and paddle, power cable and
switch assembly4
Dress in full safety gear and wear a respirator when handling or mixing methanol and lye, and
during the biodiesel mixing process. Be sure to use the appropriate filter cartridges, and follow the
manufacturer’s instructions to ensure the respirator fits properly.
2 12 B I OD I ES EL
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M ix i ng a B atch of
B i od i esel
• Titration is complete, and the test batch is
1. Heat the oil.
• Oil temperature is 100°F (37.8°C)
Note : The mixing tank holds a total of 55 gallons. It
is recommended that you mix 48 to 50 gallons (including methanol) at a time for best results. Using too little
means the mixing paddle won’t extend far enough into the
methoxide to give a good mix; using too much could result
in some spillage over the side once the mixer is turned on.
Heat the oil in an open-top storage barrel before
pumping it into the mixing tank: Drop the submersible heater into the storage barrel and plug the
heater into a GFCI-protected extension cord or wall
outlet. It will take about 2 hours to heat 50 gallons
of vegetable oil from 60 to 100°F. The heater will
turn itself off once it reaches 100°F, then back on
again if the oil cools below 80°F. Hotter oil helps
improve mixing, yielding a better biodiesel. An insulated barrel speeds heating. Use a thermometer to be sure the oil is hot enough.
• Mixer is plugged into the GFCI outlet and
tested to be sure it works
• Methanol and lye are scaled up to your batch
size and ready to add
• Transfer pump is ready to pump the heated oil
into the mixing barrel
• You are dressed in old clothes and protective
gear (respirator, goggles, gloves, apron).
To begin the mixing process, place the cover
on the mixing tank and open the lid. Be sure the
mixer is OFF. Carefully and slowly pour methanol
into the mixing barrel; avoid splashing! (If you’re
transferring the methanol from a 55-gallon tank,
use a hand-crank or other suitable pump.) Close
the tank cover and turn on the mixing motor.
2. Perform a titration (for used oil).
Perform a titration to determine the proper amount
of lye to use; see page 203. It’s also a good idea
to mix a small test batch in a blender to be sure
you have a good recipe; see page 202. Generally,
you will use 8 gallons of methanol, 40 gallons of
vegetable oil, and a quantity of lye (sodium hydroxide). If you’re using new vegetable oil, you’ll
need 530 grams (18.7 ounces) of lye. If you’re
using waste fryer oil, the quantity of lye is based
on your titration results.
Note : To increase success and reduce waste, avoid using fryer oil that requires more than 3 grams of NaOH for
a successful titration.
3Pouring lye into
3. Mix the biodiesel.
When mixing a batch of biodiesel, do it straight
through with no breaks between steps. Lay out
all of the equipment and measured ingredients
you will need to make sure everything is ready
to go. You don’t want to be fumbling around for
things with a pound of lye in one hand. You are
ready to mix a batch of biodiesel when:
create a b i odi esel ki t 213
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Create a Biodiesel Kit
Once the methanol is done with its initial
splashing around inside the tank, open the hinged
cover and very slowly and carefully pour the lye
into the methanol. Close the lid, turn on the mixer,
and let it run for 15 minutes. Turn off the mixer
and let the methoxide stand for a few minutes
until the fumes dissipate.
Pump the heated vegetable oil into the mixing barrel. Turn on the mixer and let it run for at
least 45 minutes. Depending on your recipe, the
temperature, and the quality of your ingredients,
you may find that you need to mix for longer or
shorter times. Actual mixing time may vary from
30 to 60 minutes.
Turn off the mixer and immediately take a
sample of your biodiesel in a clear jar. If the mix
is successful, it should begin to separate within
15 minutes.
Allow the mix to settle for at least 4 hours
(but no more than 12) in the mixing tank. There’s
no need to disassemble the mixer or remove
the paddle. Once the mix has settled, use the
you wait too long to pump off the glycerin, it will
solidify and you will not be able to pump it. If
this happens, pump the biodiesel off the top and
scoop out the sludge from the mixing tank.
N ote : The biodiesel will continue to settle for several
weeks. If you pump fresh biodiesel into a storage tank,
pump fuel for use from the middle of the storage tank
rather than from the bottom. Periodically drain or pump
the settled glycerin off the bottom of the tank and dispose
of it.
4. Clean up the equipment.
Remove any unreacted ingredients, sludge, or
other debris from the mixing tank before mixing
another batch of biodiesel. The sooner you clean
up, the easier it will be. Clean all lab equipment
used for titration and measuring.
Pumping heated
vegetable oil
to the sodium
methoxide mix6
transfer pump to pump the glycerin layer from
the bottom of the mixing tank: Extend the suction tube or hose all the way to the bottom and
pump the sludge into a waste container. When
all the sludge is removed, stop pumping. You can
let the biodiesel settle further in the mixing tank,
if desired, or pump it right into a storage tank. If
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Wood Gas
u r n i n g wo o d i n an open fire produces light, some heat, and lots and
lots of smoke — as you know if you’ve ever forgotten to open the fireplace
flue. The process isn’t terribly efficient, and it obviously doesn’t do wonders
for our air quality. But when you burn that same wood in a very hot, oxygen-restricted
environment, you break down the compounds of the wood into clean-burning combustible gases, along with ash or charcoal. Those gases — wood gas — can be used
to heat a cook stove or even power a car, and their emissions consist of carbon dioxide and water vapor. There’s no smoke.
Gas produced from wood and other carbon-based materials (primarily coal) has
been used since the beginning of the industrial revolution. It’s had many names —
synthesis gas, syngas, producer gas, gengas, town gas — and has been used variously
to provide heat, light, and transportation fuel. During World War II, over one million
European cars and trucks traveled with onboard gasifiers that provided fuel for their
modified gasoline engines. In this chapter, we’ll look specifically at making and using
wood gas.
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Doesn’t Burn
How Wood Gas
Generators Work
and look at the flame. Notice
that the flame is not actually in contact with the
match but rather surrounds it. Likewise, wood in
a fire does not actually burn; it is being heated to
the point where combustible gases are released.
When the hot gases combine with oxygen in
the air, they oxidize (combine chemically with
oxygen) and burn. It is the liberated gases that
are burning while the wood becomes carbonized,
turning to charcoal, and eventually the charcoal
burns to ashes. Charcoal is wood that has been
reduced mostly to carbon. Ashes are minerals
that are left over after all the carbon has been
burned off the charcoal.
Gasification works by
S t r i k e a ma t c h
burning soot
burning carbon
carbonized wood
burning hydrogen
pyrolysis zone
5Stages in the combustion process
The blue part of the flame is burning hydrogen
gas (oxidizing to form water vapor); the orange
flame is carbon monoxide oxidizing to produce
carbon dioxide (CO2); and burning soot and tars
produce a yellowish flame. With the addition of
more oxygen to support further combustion, the
carbon is reduced to ash. The ashes cannot be
further oxidized. If you choked off the air from hot
wood coals and stopped the burning, you would
be left with charcoal suitable for use in a charcoal
barbecue grill. When making charcoal, combustion is controlled so that no additional oxygen will
further oxidize the carbon coals.
heating the biomass
fuel — wood or almost any other carbonaceous
material — to nearly 500°F, releasing flammable
gases from the fuel without immediately burning
them. The combustible gases produced are
hydrogen (H2) and carbon monoxide (CO). When
burned, they create only carbon dioxide and water
vapor (H2O). The gases can either be burned
within the unit (as with a gasification cook stove)
or pulled off for external use as a gaseous fuel.
A wood gas generator consists of a chamber
for holding and heating the fuel to create flammable gases in a controlled environment, a system for cooling and filtering the gases, and a system for distributing the gases to where they will
be burned. Each of these pieces must be carefully designed to create an integrated system for
managing the thermochemical decomposition
of biomass.
Not a Wood Stove
A wood gas generator is different from a wood
stove. A wood stove burns chunks of wood, using
lots of air to allow for complete combustion. It creates heat, coals, and ashes and lets the smoke
go up the chimney. Most stoves are not very efficient at capturing all the heat in the wood. However, some modern wood stoves increase their
efficiency by preheating incoming air to 400°F
or more and injecting it into the exhaust stream,
supporting more complete combustion.
A typical wood gas generator uses smaller
chunks of biomass (or most any other material
containing carbon, hydrogen, and oxygen) as a
fuel. Such materials include:
• coal
• nuts
• wood chips
• seed shells
• wood pellets
• dry animal dung
• pinecones
• agricultural waste
• corncobs
• almost any other
material that
contains carbon
• rice husks
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These fuels are burned in an oxygen-restricted
environment to produce flammable gases through
the staged combustion process of gasification.
A wood gas generator can be as simple as a
small cook stove utilizing the efficient wood gas
production and combustion process. You can
build a simple gasifier cook stove (see plans
later in this chapter) or buy one ready-to-use from
Spenton LLC (see Resources). In a gasification
stove, wood is not burned directly, but rather the
wood gas is contained after it’s liberated from
superheated wood, then it’s burned separately.
Gasifier Cook stoves
Here’s how a gasifier cook stove works: A starting fire is lit on top of the wood fuel, and a controlled amount of “primary” air is forced through
the fuel by the unit’s integral fan. The heat liberates gases from the incandescent (but not flaming) fuel, and they rise to the top of the stove
where additional, preheated “secondary” air is
introduced by the fan through a series of holes at
the top of the stove; here, the hot gases are oxidized by the incoming oxygen and ignite, producing a flame. The combustion zone moves downward toward the unburned fuel, leaving charcoal
and ash on top.
These gasification stoves burn wood very efficiently, with little or no smoke, and produce very
high temperatures. Heat output can be controlled
by adjusting the airflow through the stove. Wood
gas cook stoves produce charcoal, which can be
In this gasifier
cook stove, the
fire is lit from the
top and primary
combustion air
is supplied from
underneath the
fuel load. Pyrolysis
gases are released
from the hot wood
and burned with
the addition of
secondary air supplied through the
top holes.
further burned in the stove or removed to use in
a charcoal grill or as biochar (see Biochar on
page 218).
Challenges of Wood
Gas Generation
At the other end of the scale from cook stove
units are large, combined-heat-and-power gasifiers that provide efficient, renewable heat and
electricity for homes and businesses. This may
sound like a simple engineering and marketing
task, but significant technical challenges remain
in the design of a turnkey wood gas generator.
Despite its long history of use, gasification technology that can support a wide variety of fuel
qualities and user savvy is still in its early stages.
Making and using wood gas is a very hands-on
approach to energy generation.
Unlike biogas and compost, wood gas doesn’t
just want to happen. It’s not waiting around for
you to take advantage of its hidden bounty. Managing combustion and capturing the resulting
gases is difficult to manage in a practical sense.
Two small companies that are making a big difference in this area are Victory Gasworks and All
Power Labs; see Resources.
The basic challenges in developing a successful wood gas generator and harnessing wood gas
• Creating an airtight gas system with a
pressure relief function that manages and
moves air, fuel, gases, coals, and ashes to
the right places at the right time, and for the
correct amount of time
• Creating a suitable combustion chamber and
reduction zone
• Controlling the oxygen supply to the
combustion zone
• Capturing and filtering the combustible gases
released during pyrolysis
• Delivering the gas to where it will be burned
• Modifying equipment to burn the wood gas
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Biochar is charcoal that’s used as a soil amendment. Because charcoal is primarily carbon, when it
burns it releases lots of carbon dioxide, a potent greenhouse gas. But instead of burning the charcoal,
it can be crushed and put back into the soil. This process is one way to sequester carbon in the ground,
while helping to improve soil, rather than release it into the atmosphere as CO2. See Resources for
more information on biochar, including a source for NASA’s Biochar Activity Kit: instructions, plans, and
a teaching guide for building and using a three-can, top-loading, updraft (TLUD) gasifier cook stove.
Four Stages of
a combustible material to burn,
it needs to be hot enough, and there must be
enough oxygen to feed the combustion process.
The intent of gasification is to create combustible
gases in an oxygen-restricted environment and
capture the gases before they burn. They can
then be shunted or piped away to be used as fuel.
Think of wood gas generation as a controlled,
multistage combustion process. In fact, what you
are doing is taking apart the combustion process
and controlling each phase within that process to
your advantage. The amount of air allowed into
the combustion zone is less than what is required
for complete combustion, and this is the key to
controlling each phase of the process.
The following four stages are presented as a
way to understand the activity inside a gasifier.
Managing these processes is the goal of successful wood gas generator design. While each
stage occurs in a specific place in the gasifier, the
processes don’t happen in isolation but rather
in equilibrium with one another in a complex yet
elegant thermochemical process.
Stage One: Drying. The fuel must be as dry
as possible before it’s loaded into the generator, ideally with a water content of less than 20
percent. Further drying will occur when the fuel
warms in the gasifier and as air or fuel gases
move through it. Drying consumes energy and
keeps things cool until enough moisture is
removed to allow the required pyrolysis (see
stage 2) temperature to be achieved. If the fuel is
too wet, it will take more energy to evaporate the
In order for
water before combustion processes can occur.
Excessive water vapor also increases the formation of organic acids, which can lead to corrosion
within the gasifier and poor-quality gas. All water
vapor must be removed from the fuel before moving on to Stage Two.
Stage Two: Pyrolysis. An igniting fire is lit to
heat the fuel. Once the fuel is heated to around
500°F in the absence of oxygen, the volatile solids decompose and release gases and liquids.
The exact composition of these gases and liquids is related to the fuel being burned, but they
will contain some combination of hydrogen, oxygen, and carbon. When biomass is used as a
gasification feedstock, an acidic, tar-like pyrolytic
oil is also produced. Pyrolytic oil is the result of
moisture content and resins contained in woody
materials. In a well-designed and properly managed gasifier, it will be burned as fuel. If the oil
escapes into the fuel gas stream, it must be
removed because it can gum up gas plumbing
and engine parts.
Stage Three: Combustion. When carbon
and hydrogen (contained in most feedstocks or
organic material) combine with oxygen, the result
is heat, carbon dioxide, and water vapor. After the
igniting fire dies out, combustion in a wood gas
generator is perpetuated by the biomass fuel,
tarry oils, and hot carbon coals, along with just
the right amount of air. The heat of combustion
(approximately 2000°F) drives further pyrolysis
and sets the stage for the final phase of wood
gas generation, named for its chemical action of
Stage Four: Reduction. In chemical terms,
reduction is the opposite of combustion. Combustion occurs when a material is oxidized by
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the addition of an oxygen atom, which releases
heat. Reduction occurs when an oxygen atom is
removed from a molecule by adding heat. In a
gasifier, the fuel is oxidized (burned during combustion), forming (in part) CO2 and H2O, which
come into contact with the hot carbon coals in
the gasifier. The oxygen in the gases is strongly
attracted to the carbon in the charcoal, and the
heat gives it the energy needed to create new
chemical bonds.
This is the point where the thermochemical
magic happens in a gasifier. Through reduction,
CO2 gives up one oxygen molecule to the carbon in the coals to become carbon monoxide
(CO). Water vapor (H2O) gives up one oxygen
molecule to become hydrogen gas (H2), and the
remaining oxygen is free to further oxidize the
carbon. Carbon and hydrogen also react to form
methane (CH4). The processes of oxidation and
reduction continue in equilibrium until there is
no fuel left.
A wood gas generator must be tightly
sealed so that any air entering the system is
intentional and controlled. In many designs,
fuel storage, combustion, and gas production
all can take place within the same container.
The drawing on page 217 shows a gasifier
in which the dry biomass is loaded into the fuel
chamber from the top of the container and covered
with an airtight lid. The fuel slowly dries and moves
downward toward the combustion zone, then to
the reduction zone, where it is consumed. Finally,
ashes collect at the bottom of the barrel. The fuel
moves by gravity and/or mechanical action to feed
the carefully controlled combustion zone.
Some fuel material can get stuck in the barrel,
causing combustion to stop for lack of fuel. This
also can increase the possibility of channels developing within the fuel bed that can allow enough
4 P r o c e s s e s i n g a s i f i c at i o n
Charcoal and Tar
H2O and CO2
H2 and CO
biomass (C H O)
biomass (C H O)
tarry gas or charcoal
hot charcoal (C)
The four processes
heat, controlled air
controlled air
H2O and CO2
in gasification can be broken out
for illustration, but all processes
are happening
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oxygen into the unit to reach flammable or explosive levels. To reduce the potential for this effect,
the fuel storage must be agitated to keep it moving. Small fuel materials (such as pellets, chips, or
shells) may need to have recirculated gases blown
through them to prevent the fuel from settling into
a solid mass that is too dense for air to move
through. This approach is called a fluid bed — as
opposed to a fixed bed, where there is no intentional agitation. Gasifiers mounted on vehicles
actually benefit from the bouncing, which keeps
the fuel moving down to the combustion zone.
Firing Up
The combustion zone is at the bottom of the generator container and is accessed through a small
airtight door for lighting and cleanout. A starting
fire is lit in the combustion zone to ignite the fuel.
Once started, air supply is choked off. As the fuel
moves from storage to the combustion zone, it
burns on a cone-shaped metal hearth with lots
of holes in it, which allows ashes to drop down
to the cleanout area. Air supply to the combustion zone is limited so that combustible gases
released from the fuel do not burn. There’s only
enough air to keep the coals hot enough for pyrolysis to occur.
The movement of gases through the generator,
including the amount of air drawn into the combustion zone, can be facilitated by the vacuum
produced within an internal combustion engine,
or with a fan that pulls gases through the gasifier and blows them into a burner. The induced
flow forces the combustion gases through the
hot coals, where the reduction of those gases
occurs to make the wood fuel gases. The flow of
air into the generator, and the flow of gases out
of it, keeps the entire system under a slight negative pressure. This is important: If there is a leak,
allowing too much air into the generator, the system will cease to function or, worse, all of the fuel
will burn uncontrollably.
Cleaning and
Filtering Wood Gas
Ga s
r e q u i r eme n t s
vary based on how the wood gas will be used.
Wood gas produced in a gasifier includes ash,
tar, and water vapor. These impurities may
cause problems in a simple gas burner, but
they all must be removed if you plan on using
the gas in an engine; engines are more sensitive
than gas burners and require cleaner fuel.
The gas can be initially filtered using a centrifugal canister, or cyclone separator. This is a coneshaped chamber through which the gas swirls. In
the process, ashes and larger particulates drop
Woo d G a s Compo s i t i o n
In addition to hydrogen gas and
carbon monoxide, there also
are small amounts of carbon
dioxide and methane present
in the wood gas. Nitrogen gas
(N2) amounts to about one-half
of the gas volume and does
not add to its energy content.
The actual components and
amount of each gas depend
upon the feedstock and the completeness of each stage in the
gasification process. A typical
makeup of gas produced from
wood might be:
• 50 percent nitrogen gas (N2)
— air is used as a source
of oxygen, and nitrogen is
the main ingredient in air.
Nitrogen passes through the
gasifier with no effect other
than to take up space and
reduce the overall energy
content per volume of wood
• 20 percent carbon monoxide
(CO) — a flammable gas
• 20 percent hydrogen (H2) —
a flammable gas
• 5 percent methane (CH4) —
a flammable gas
• 5 percent carbon dioxide
(CO2) — a nonflammable
byproduct of combustion
2 2 0 WOOD GAS
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cleaner gas
gas outlet tube
dirty gas
Inside a cyclone inlet
cyclone body
Cutaway view
separator. “Dirty” gas enters
through the side
inlet and swirls
around as particulates fall to the
bottom. Cleaner
gas exits through
the top.
of secondary
particulate filter
using drum
filled with fine wood chips or
conical section
to the bottom and, as the gas cools, some of the
water vapor will condense out of the gas stream.
After the cyclone separator, the gas can be
passed through a low-tech filtering container
of wood chips or even hay for further filtering, assuming the temperature can be reduced
enough to prevent the filter medium from burning. This simple but effective filtering system can
last for several years in a reasonably well-used
gas generating system. Some commercial filter
units use glass-fiber filters capable of withstanding high temperatures.
The hot gas is then cooled in a heat exchanger.
Reducing the temperature causes the water
vapor, tar, and oils to condense out of the gas
stream, increasing the volumetric energy density
of the gas. The gas can then be further filtered
through a paper or cloth fine-particulate air filter
before going into the engine or burner.
Using Wood Gas
gas can be used
in place of, or mixed with, natural gas, liquid
propane gas, gasoline, fuel oil, or diesel fuel. It
can be used for heating or in gasoline- or dieselpowered engines.
A f t e r f i lt e r i n g , w o o d
When replacing liquid fuels (which are generally delivered to engines in a gaseous or vaporized
state, by way of fuel injectors or a carburetor), wood
gas is supplied through the engine’s air intake.
Using an automotive throttle body to open and close
the wood gas supply, and a fuel shutoff valve to
open and close the original fossil fuel supply, each
system can be isolated and used independently.
On average, wood gas has an energy content
of about 150 Btus per cubic foot. This is a relatively low value because one-half of the fuel volume is noncombustible nitrogen. For comparison,
that’s about 15 percent of the heating energy in
a cubic foot of natural gas. In order to burn, wood
gas is delivered to an engine or burner using an
air-to-fuel ratio (measured in terms of mass, or
weight, not volume) of approximately 1:1, in contrast to gasoline combustion, which requires an
air-to-fuel ratio of 14.7:1.
Wood gas–powered engines tend to be a bit
more sluggish than their gasoline counterparts
and lose about 20 to 30 percent of their power
due to the lower energy density (heating value per
unit of fuel by weight) of wood gas, along with a
greater pressure drop in fuel delivery created by
the gas generating system.
With a flame temperature of around 3,600°F,
wood gas can be used in a heating or cook stove
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shutoff valve
blower fan
Gasifier system cyclone separator
to produce gas
for an engine
In addition to achieving the proper air-to-fuel
ratio, using wood gas as an engine fuel requires
advancing the ignition timing to compensate for
its slower flame. Carbureted engines have the
advantage of being able to use both wood fuel
and gasoline simultaneously. Modern fuel-injected
engines will likely have a computer control that
must be modified or reprogrammed to adjust the
timing and turn off the injectors. Combustion can
be controlled manually with cable controls from
throttle-body valves, or electronically using an oxygen sensor as a feedback control in the exhaust
stream; this in turn adjusts the air-to-fuel ratio.
Powering Diesel
burner, but the gas must be under a small amount
of pressure. A high-temperature centrifugal blower
can be used to pull the wood gas out of the generator to the burner, and the air-to-fuel ratio will
need to be adjusted at the burner (see chapter
13 for more discussion about burners).
Powering Gasoline
To use wood gas in a spark-ignition (gasoline)
engine, the engine typically is started on gasoline. The wood gas generator is ignited using an
external blower to start the combustion. Once
the fire is burning and wood gas is flowing, the
gasifier’s blower is turned off; the gasoline flow
is reduced while the wood gas flow is increased,
and the vacuum from the engine pulls air into
the gasifier, driving the gasification process.
Compression-ignition (diesel) engines typically are operated in a dual-fuel mode. This is
because the wood gas will not ignite under the
normal diesel compression ratio. In a typical scenario, the engine is started on diesel fuel, then
the flow of wood gas into the engine’s air intake
is increased, which has the effect of automatically decreasing the diesel fuel flow as the energy
requirements are met with the wood gas to maintain the desired rpm.
Diesel fuel flow can be reduced by about 80 percent while increasing the wood gas flow. Injector
timing must be advanced, and the injector pump
may need to be adjusted for a lower fuel-flow rate
to accommodate the additional energy input of the
wood gas. In some cases, fuel injectors may need
to be changed or modified to avoid overheating
and fouling during dual-fuel mode. Power output is
typically reduced by 15 to 20 percent.
iImproving Accelerationi
As a wood-powered vehicle accelerates, more fuel is required by the engine and more wood gas is
drawn through the system using the vacuum generated by the engine. As more air is drawn through
the gas generator, the rate of combustion increases in the gasifier. However, it takes some time
for the combustion process to respond and deliver the required amount of fuel. The result is poor
acceleration. This can be overcome by installing a small volume of expandable gas storage: When
you’re stopped at a red light, the storage container fills with wood gas. When you accelerate on
the green light, the fuel storage is drawn down while the combustion builds once again.
2 2 2 WOOD GAS
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Storing Gas
sense, wood gas cannot be
stored and should be burned as it is produced.
Its low volumetric energy content makes any
storage scheme quite bulky. Compressing the gas
requires energy and can change the chemistry of
the gas — carbon monoxide is not very stable
and may devolve into a potentially explosive
combination of carbon and oxygen.
The best way to store wood gas is in wood!
The next best ways are to generate electricity and
store it in batteries or to use it to heat water.
Some World War II-era vehicles used expandable gas bags for storage, but the obvious dangers of fire or explosion make this an impractical
In a practical
How Much Gas Can
You Make?
In terms of energy output, 1 pound of perfectly
dry wood releases approximately 8,500 Btus
when completely combusted. (The actual energy
content released when burning wood in the real
world is based on the wood’s density, moisture
content, and combustion management.) By comparison, 1 gallon of gasoline (just over 6 pounds)
contains about 125,000 Btus. So in reality, about
18 pounds of wood with 20 percent moisture content contains approximately the same heating
energy potential as one gallon of gasoline. This
gives dry wood an energy density of about onethird that of gasoline.
The wood gasification process is in the range
of 60- to 75-percent efficient at converting energy
stored in biomass to the energy released by the
gas produced on combustion. The exact makeup
and amount of gas produced, and the energy contained in the gas, vary according to the fuel’s characteristics. For example, coconut shells and charcoal produce relatively high-energy gas compared
to rice hulls and wheat straw.
On average, one pound of wood converted to
gas in a gasifier produces approximately 40 cubic
feet of gas. Each cubic foot contains about 150
Btus, or about 6,000 Btus of energy produced
for each pound of wood fuel consumed. A general fuel consumption rule of thumb for driving
a car on wood gas is about 1 mile per pound of
wood. That’s over 4,000 miles on the equivalent
of a cord of hardwood. If a cord of wood costs
$300, your fuel cost is about 7.5 cents per mile
— about the same cost per mile if you paid $2
per gallon for gasoline and your car gets 25 mpg.
Of course, gasoline is more convenient, but there
are many more value propositions to consider
than cost and convenience.
Quantifying Your Gas Needs
When designing a wood gas generator, start by
determining how much gas you need to produce,
and at what rate. Assuming you want to power
a gasoline engine with wood gas, here’s an example of how much gas you’ll need for each horsepower (hp) of engine rating:
1 hp = 746 watts (or 2,546 Btus)
With a typical internal-combustion engine efficiency of 20 percent, you’ll need to increase the
Btu output by a factor of 5:
2,546 x 5 = 12,730
Therefore, you’ll need to produce 12,730 Btus of
wood gas each hour.
At 150 Btus per cubic foot, that’s about 85
cubic feet of gas production per hour. Since each
pound of wood yields about 40 cubic feet of gas,
that works out to just over 2 pounds of wood
burned for each horsepower-hour. However, this
doesn’t mean that if you have a 200-hp engine
you’ll need 400 pounds of wood to drive for an
hour, but you would if you were pushing the engine
to produce maximum power for that hour.
This rule of thumb can help you think about
maximum required gas production rate. Your gasifier will produce only as much as you ask it to produce, based on how much air is moving through
it. But keep in mind that oversizing can create a
set of problems. Therefore, it’s best to determine
how much gas you require under the most typical situation and adjust the design accordingly to
meet short-term peak-load requirements.
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iThe Importance of Proper Sizingi
To ensure maximum efficiency, the gas generator must draw in air at the correct volume and rate to
support all gasification processes that meet the demand of the load. More air increases the rate of
combustion, but if too much air is moved through the system, the pyrolysis gases won’t spend enough
time in the reduction zone to be fully converted, or the reduction zone could cool off. The result is
poor-quality gas and increased amounts of tar. Proper sizing and good design are essential to good
performance and quality gas production.
Types of Gasifiers
T h e r e a r e t h r ee basic gasifier designs,
named according to how air and fuel gases are
moved through them. The design choice depends
primarily on the type of fuel to be used, according
to its energy value, moisture and ash content,
density, and charring properties.
Downdraft gasifiers bring air into the combustion zone that resides in the lower-middle half of
the unit. Air enters into the combustion zone and
is drawn downward, away from the fuel into the
reduction zone, then is channeled out. Heat radiating upward evaporates moisture from the feedstock, and as charcoal beneath is consumed, the
feedstock sinks closer to the combustion zone.
Downdraft gasifiers generally are the most
common design for fueling engines on wood
gas because they typically have relatively low tar
production and respond well to changes in gas
requirements where the load varies. Downdraft
gasifiers are best suited for fuels with low (less
than 25 percent) moisture content.
The biomass cook stove described on page
217 is an example of an inverted downdraft gasifier, which has a container of biomass that is
lit from the top with tinder. The pyrolysis reaction moves from top to bottom, where the gas is
drawn off and burned.
Updraft gasifiers admit air into the bottom
of the unit at the combustion zone, drawing the
heat and gases up through the fuel (preheating
and drying it) and out the top. This design is relatively efficient but generally produces more moisture and tar, so it’s best suited for low-moisture,
low-tar fuels, such as charcoal, rather than resinous biomass, like wood.
Crossdraft gasifiers bring air into the combustion zone toward the bottom of the gasifier
to feed the gasification process, with the fuel
gas outlet on the opposite side of the fuel load.
These are often used for gasification of charcoal,
in which very high temperatures are generated.
Drying Zone
Drying Zone
Ash Pit
Drying Zone
Pyrolysis Zone
Combustion Zone
5Schematic of downdraft gasifer
Pyrolysis Zone
Reduction Zone
Ash Pit
5Schematic of updraft gasifer
Combustion Reduction
Ash Pit
5Schematic of crossdraft gasifer
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Working Safely
around Wood Gas
fuels contains a high proportion of carbon
monoxide. This colorless, odorless gas is harmful
or fatal in very small doses. Any experiments you
do must be done outdoors, and all gas produced
must be captured and channeled away from living
Do not pipe the gas indoors for use with a
cook stove, heating appliance, or any other purpose. Natural gas and propane gas have the odorant ethyl mercaptan added for leak detection. The
pungent smell alerts occupants of a gas leak or
if a pilot light has gone out. Wood gasifiers may
smell a bit smoky, but pure wood gas is odorless, so leaks and gas accumulation are not easily detectable, creating a potentially dangerous
If you experience symptoms such as drowsiness, headache, or nausea while working around
wood gas, you are likely being poisoned by carbon
Ga s s y n t h e s i z e d f r o m
monoxide and should move immediately to fresh
air and seek medical attention. Wherever you are
using wood gas, you should have a personal CO
meter and alarm, as well as a stationary alarm
for your shop. Spend a little extra on these safety
devices and get models that read low concentrations, such as those available from CO Experts or
Pro-Tech Safety (see Resources).
The main combustible gases produced by a
wood gas generator are hydrogen and carbon
monoxide. Each is flammable when mixed with air
in a very wide range of concentrations. For hydrogen, the range is between 4 and 75 percent; for
carbon monoxide, the range is between 12 and
75 percent.
Always take great care when working around
such flammable gases. Air leakage into a gasifier could cause a fire or explosion when oxygen comes into contact with hot fuel. Remember: Generating wood gas involves high temperatures and combustion. Take suitable precautions
against fire and have a fire extinguisher available
near the gasifier.
E n v i ro n m e n t a l Imp a c t s o f Woo d G a s
Both carbon monoxide and hydrogen gas are
clean-burning fuels. When burned, they each
combine with oxygen to form carbon dioxide (CO2)
and water (H2O). Engines powered by wood gas
are much cleaner in terms of emissions than
fossil-fuel engines. This is partly due to catalytic
converters in the exhaust systems of wood gas
vehicles that control nitrogen oxides produced
when the nitrogen present in wood gas is oxidized
in the engine.
When biomass from the current generation of
feedstock is used to produce wood gas, there is no
net increase in global warming potential of the carbon dioxide released as exhaust. The CO2 produced
on combustion is equal to the amount that would
be released by the biomass decomposing naturally
over time. Ideally, that CO2 is absorbed by the next
generation of biomass. Of course, the process is
accelerated with combustion; it takes many years
for a tree to break down naturally and completely
release the equivalent CO2.
Tar produced by wood gas can be problematic to
dispose of because it is caustic. It’s best to use dry
fuel and design your generator so that tars and acids
are burned and reduced to ash. Ash production and
disposal generally are not a problem. Volume ranges
from 1 to 20 percent depending on the fuel material
Cooking and human health. When using the
gasification process for cooking, there is almost
no smoke and a much hotter flame than that of a
conventional wood fire. This means fewer particulates, faster cooking, and, importantly, healthier
humans. This last point has been the focus of several organizations bringing clean, efficient cooking
options to developing nations. Considering that
nearly one-half of the world’s population cooks
daily meals on open fires, efforts of organizations
such as the Aprovecho Research Center and the
Global Alliance for Clean Cookstoves (see Resources) have greatly increased the quality of life
for many families throughout the world.
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c lo s e - up
Two Men and a Truck
an energy geek, car fanatic, or science expert. He is a cut-from-the-cloth DIY man with practical and
relevant skills to make things work. He was looking for a hands-on project and admits that he didn’t do as much
research as he could have before building the gasifier. This led to a few mistakes but resulted in a useful, working
gasifier that powered his truck on wood chips for many satisfying, gasifying miles.
ohn is not
Joh n D u n h a m
got the alternative energy
bug in college. He looked
into converting a diesel
car or truck to burn waste
vegetable oil or biodiesel
but could not find a
suitable and affordable
diesel vehicle. When
John was scratching his
head for senior project
ideas, it was his father
who first stumbled onto
the thought of running an
engine on wood gas.
The idea intrigued
both of them. Using plans
dating from the 1970s —
from Mother Earth News
— along with information
gathered from online
forums such as those
hosted by All Power Labs
(see Resources), they
embarked together on a
project to build a stratified, downdraft wood gas
generator and use it to
power a pickup truck.
They scavenged barrels, pipes, and scrap
metal. With their plans, welding skills, and
ingenuity, the project started to take shape:
Two stacked 55-gallon drums make up the
fuel hopper (on top) and combustion chamber
housing (on the bottom). The fire tube is
12"-diameter snow-making pipe (scavenged
from a local ski area) that drops from the
bottom of the top barrel, through and to the
bottom of the bottom barrel. The combustion
zone is ideally in the middle of the fire tube
(it can be in the wrong place if not properly
designed), and the reduction zone is at the
bottom, where hot coals drop onto a grate
made from a stainless steel colander. A small
door cut in the bottom barrel provides access
to light the fire in the combustion zone and
also serves as an ash cleanout.
Once the fuel in the gasifier is burning,
the lighting door is closed, and air is drawn
through the entire system via a blower motor
on the outlet of the gasifier that pulls air
through it. This creates negative pressure
inside the gasifier and provides enough draft
to get the fire going. After about 15 minutes,
wood gas is generated and can be burned
in the engine. The blower also serves for
testing whether the gas is ready to burn: If a
fire can be lit at the outlet of the blower, the
gas is ready. Once the flame has stabilized,
the blower is turned off and wood gas is
diverted to the engine.
Here’s how John describes the system:
1. Air enters through the top of the top barrel. Its quantity is determined by the draft
created by either the blower or engine vacuum and ultimately is restricted by the size of
the air entry port.
2. The air moves through the stored chips
and down into the fire tube, along with chips,
which fall into the tube by gravity to the combustion zone.
3. The combustion gases are pulled down
the tube, through the reduction zone, and
through the open space in the barrel surrounding the tube, which cools them as they
exit the barrel and enter the “cyclone” particle separator.
4. The gas moves into a barrel filled with
wood chips that act as a filter and further
cool the gas. (After a period of time, the filter
chips can be replaced with fresh chips and
the old chips used for fuel.)
5. The gas flows through pipes (made from
car exhaust pipe) to the front of the truck
and into a series of metal tubes, where it
cools, releasing moisture and tar through
6. Finally, the wood gas enters the engine
through the air intake. Individual throttle bodies are used to control both the wood gas intake and air intake by way of cables operated
from the cab of the truck. This allows John
to manually adjust the proportion of wood
2 2 6 WOOD GAS
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There does come a time when you really need to just go out, get your hands dirty, and
try it for yourself.
gas and air for best engine performance. A
carbon monoxide detector lives in the truck
at all times.
John uses a plug-in electronic tuning module
(a unit made by Tweecer; see Resources)
to access the truck engine’s computer and
adjust spark timing to compensate for the
slower burn of the wood gas, and to turn off
the fuel injectors to stop the flow of gasoline
when wood gas is flowing. This approach
allows the truck to operate on either wood
gas or gasoline with the turn of a dial.
The switchover can’t be done on the fly,
however, because there’s a manually operated
valve on the outlet of the condenser that
must be opened for wood gas operation and
closed for gasoline operation. With additional
controls for independently regu­lating gasoline
and wood gas flow, the truck could run on a
combination of both wood gas and gasoline.
At some point, John will hook up two hot-wire
anemometers — one located in the wood
gas intake, the other in the air intake — to
receive visual feedback on the quantity of
both air and gas flowing into the engine. This
feedback can allow for more precise control
of the fuel-to-air mixture when running on
wood gas.
As mentioned, many lessons were
learned, including discovering that the com­
bustion zone in the fire tube can move up and
down the tube depending on the draw of air
through the system. This led to a problem
with lighting the fuel because the draft wanted
to pull the igniting fire away from the fuel. A
wood chip
blower for
fan shutoff valve
pipe from filter
to condenser
condenser /
gas cooler
wood gas filter
(wood chips)
John’s gasifier truck
5Schematic of the truck’s parts and processes
pipe from
condenser to air
two men and a truck 227
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c lo s e - up
Two Men and a Truck
carefully designed combustion zone helps to
control this situation. As for preferred fuels,
John has used both hardwood and softwood
chips and feels that the former provided
better performance.
The initial gasifier design was oversized,
which means that the combustion and
reduction processes were not ideal. This led
to excessive tar in the fuel, which can damage
or ruin an engine. Since the ideal air-to-wood
gas ratio is 1:1, the gasifier needs to be
sized to provide about half the displacement
volume that the engine requires at the most
typical (or desired) rpm. John remedied this
by reducing the outlet below the combustion
zone from the full 12"-diameter pipe to a
6" opening. This constricted the airflow and
increased the air velocity, making a much
hotter combustion zone.
After learning this the hard way, John
discovered that others have covered the same
ground and have published tables online that
could have helped with the initial sizing (there
are some excellent Internet forums for wood
gas users and experimenters, and this DIY
community is happy to share information).
With his system designed to operate best at
an engine speed of 3,000 rpm, the truck will
stall if it idles for long periods.
John is already planning his next gasifier
project, complete with better combustion
zone design, an insulated combustion
tube, improved gas filtering, and preheated
combustion air. He also plans to incorporate
mass airflow sensors to provide feedback
for automatic mixing of air and wood gas
for optimum ratio, as well as temperature
monitoring of both the combustion zone and
the downstream gas temperature, to be sure
that it’s cool enough to condense the tar out
of the gas. John shares the following thoughts
for anyone thinking of taking on a similar
“Despite the mistakes I made and prob­
lems I encountered in this project, I had an
enormous amount of fun while learning many
things that I would not have been exposed to
otherwise. While I would encourage anyone
interested to read the articles and books on
the subject (certainly more of them than I did
before I started), there does come a time
when you really need to just go out, get your
hands dirty, and try it for yourself. Be safe,
and keep that CO detector close.”
Despite the mistakes I made and problems I encountered in this project, I had
an enormous amount of fun while learning many things that I would not have been
exposed to otherwise.
2 2 8 WOOD GAS
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ooking with wood gas allows
you to move away from oldschool, smoky wood fire to
modern, clean-burning pyrolysis fire.
This project shows you how to build a
top-loading, updraft (TLUD) stove that
not only helps you understand biomass gasification, it’s also useful for
cooking. All you need is a coffee can
(or any other tin can, preferably unlined; the size does not matter much),
some hardware cloth (metal mesh),
and some fuel.
The fuel can be almost any dry
biomass — from twigs or wood pellets to cherry pits or dry corncobs. Try
different fuels and experiment with
can sizes and air-hole diameters. It
may take some trial and error to find
the optimum design, but the materials are inexpensive, and the project
takes only about 15 minutes.
This simple cook stove design
belies the full potential of clean cooking. Larger stoves employing this
basic design can be used to build a
complete cooktop and oven arrangement with a single fire.
M at e r i a l s
One tin can (unlined)
One piece hardware cloth
(wire mesh) with 1/4" grid
Handful of dry biomass:
twigs, nutshells,
wood pellets, etc.
1. Make the bottom air inlets.
3. Add the fuel screen.
Remove any paper from the can, then
if you haven't already, remove the lid
from one end of the can with a can
opener and empty the can of its contents. Turn the can open-side down
and drill or punch eight evenly spaced
∕8" holes around the perimeter of the
bottom lid, about halfway in from the
edge, then make one hole in the center; these are the primary air inlets to
support fuel combustion.
Cut a square piece of 1/4" hardware
cloth or similar metal mesh the same
width as the interior diameter of the
can. Bend down the edges of the
mesh to create a shelf that will keep
the fuel about 1/2" above the bottom
air inlet holes.
Build a Simple Wood Gas Cook Stove
5Holes in bottom lid of can
2. Make the side air inlets.
Position the can with the open end up
and mark a line around the perimeter
of the side, about one-third of the way
down from the top. Drill eight evenly
spaced 1/4" inch holes along this line;
these are the secondary air inlets and
will provide oxygen to burn the pyrolysis gases before they leave the stove.
Can with side
inlet holes 
5Fuel shelf made with 1/4" hardware cloth
4. Fire up the stove.
Set the stove on top of a fireproof surface that allows air to enter the primary air inlets on the bottom of the can;
an open barbecue grill works well for
this. Fill the can about one-third full
with dry biomass. Put some paper or
tinder on top of the biomass and light
it from the top. A little fuel soaked in
alcohol makes a good starter, too.
After a few minutes the biomass
should start to burn from the top down
as combustion air is drawn upward
due to the draft created by the hot fuel
on top. The fire may be a bit smoky
at the start and again at the end of
the burn, but once it settles down the
bu ild a simp le wo o d gas cook stove 229
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Build a Simple Wood Gas Cook Stove
smoke will subside, and you’ll see blue flames appear at the inside of the secondary air inlets; this
is the pyrolysis gas being burned with the addition
of more oxygen.
To use the stove for cooking, balance two pieces of angle iron (so that the angles are over the
center of the can) on top of the stove to rest a pot
on for cooking. A more stable design would be to
cut a notch halfway through the center of two 1"tall pieces of thin metal bar stock. Slide the bars
together at the notch and lay it across the top of
the can. Allow 1" or 2" of space between the top
of the can and the bottom of the pot.
If desired, you can improve the stove’s cooking
performance by adding a metal wind guard made
from a larger can or a piece of metal roof flashing;
cut this to the same height as the stove and encircle it around the stove can, leaving a few inches
of space between the two.
A chimney added on top of the stove will
improve draft and create a hotter fire. You can
make a suitable chimney from another can that
rests on top of the stove can, or from roof flashing encircled tightly around the stove can (above
the secondary air inlet holes) and secured with a
metal hose clamp.
Experiment with different hole sizes and loca­
tions. Different fuels behave in different ways.
Cutaway view
of completed
cook stove 
2 3 0 WOOD GAS
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i o g a s i s a mixture of gases formed anywhere organic material decomposes in the absence of oxygen, such as underwater, deep in a landfill,
bubbling out of municipal solid waste, or in the guts of animals (including
you). Sometimes called swamp gas, biogas is produced through the biological and
chemical process of anaerobic digestion (AD). This is a natural process that happens
without any assistance from you or me.
Simply put, anaerobic digestion is the microbial decomposition (digestion) of
carbohydrates in an oxygen-free (anaerobic) environment. It begins with a process
similar to the fermentation of alcohol, but AD occurs in the absence of oxygen and
continues past fermentation. In fact, oxygen is toxic to the process, in that it inhibits
the growth of methane-producing microbes, also known as methanogens, which are
ultimately what we want to encourage for the production of biogas.
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The Basics
of biogas made in
a controlled environment is methane. Methane
(chemically known as CH4) is a hydrocarbon made
up of one molecule of carbon and four molecules
of hydrogen, and is lighter than air. Methane is also
the primary component of natural gas, commonly
used for cooking and heating, although biogas is
not as energy-dense as natural gas. The methane
content of the biogas you make will probably
range from 50 to 80 percent, compared to about
70 to 90 percent with utility-supplied natural gas.
Natural gas also contains up to 20 percent other
combustible gases, such as propane, butane, and
ethane, while biogas does not.
The exact makeup of biogas depends in part
on the source of the gas, which is based on what
is fed to the digester, and in turn what was fed
to the producers of those ingredients. Noncombustible components of biogas can be considered
T h e ma i n i n g r e d i e n t
Organic materials
mixed into a slurry
and put in an airtight
container produce
combustible gases,
nitrogen-rich liquids,
and compostable
gas storage
organic material
impurities. These will be primarily carbon dioxide
(CO2), along with small amounts of water vapor,
nitrogen (N2), and possibly trace amounts of hydrogen sulphide (H2S). If air contaminates the process, nitrogen can dilute the biogas. Other trace
impurities may be formed as well. You can remove
these impurities if desired, but depending on how
you intend to use the biogas, you may not need to.
Producing Biogas
To produce biogas, you first mix water with organic
material (often called feedstock) such as animal
manure or vegetable material, add a starting culture, then close it all up in an airtight container.
You maintain a temperature within the container
that is close to the temperature inside an animal
(around 100°F) and, in about a week, you should
be generating biogas.
The airtight container where this process is
captured and controlled is called an anaerobic
digester or methane generator. I prefer the term
generator for the system in general, because it
implies the intention of producing something,
while anaerobic digestion is a process that happens with or without our intention or intervention.
While design specifics can vary, a methane
generator usually contains a filler tube for feeding
the digester vessel; an effluent outlet to remove
digested solids and liquids (also called digestate);
and a gas outlet. You can make a small generator
from a single 55-gallon barrel, but any digester vessel smaller than 200 gallons should be considered
experimental because it will not make enough biogas to be useful for any practical purpose.
Keeping Things Simple
The biological and chemical processes of AD,
along with all the nuances of feedstock variables,
are complex. However, if you dwell on the complexity of the science, you may never get started.
iTalkin’ Biogasi
Throughout this chapter, biogas refers to the gas produced by the generator, impurities and all, while
methane refers specifically to the chemical compound methane, which is the combustible component
of both biogas and natural gas. They are not the same.
2 3 2 B I OGAS
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T h e W i s d om o f S t a r t i n g Sm a l l
I highly recommend starting with small batches and
systems, so you can experiment
and get a feel for the process.
Having a biogas generator is
like having another mouth to
feed — it takes time and attention, and without food the
microbes will die and no gas
will be produced. Other practical
challenges include:
• Controlling the gas flow to
• The availability of (and ability
You may also need to modify
your cook stove burner so that
it can handle gas with a higher
level of impurities.
to collect) enough local
organic material to make a
useful amount of gas
deliver the correct pressure
to the gas burner
• Storing the gas
Save that step for when you turn professional.
Anaerobic digestion is a natural process of decay
that wants to happen by itself — any encouragement you offer can only be helpful.
In fact, you could probably ignore the rest of
this chapter and find a sealed container, put a
home brewer’s airlock on top, fill it halfway with
water and halfway with any sort of organic material you can find, and have some success in making biogas within a week. But if you want to understand the process and be reasonably efficient
about it, read on.
How It Works
Once your digester is filled with organic material
and water, biochemical processes begin to happen. First, the ingredients will break down and
ferment, then acids will begin to form, followed
by the desired methane production. There are
four stages in the breakdown of organic material within a biogas generator. These four stages
can be separated into two phases: acid formation
and methane formation. The waste of one stage
feeds the next. Once a generator is operating and
producing gas, these processes happen simultaneously rather than as discrete sets of chemical
Hydrolysis starts when water is mixed with
organic material. Hydrolysis is the enzymatic
breakdown of complex proteins, carbohydrates,
fats, and oils into amino acids, simple sugars, and fatty acids. The broken-down (depolymerized) material is in a chemically accessible
form and ready to be fermented by acid-forming
Acidogenesis , or fermentation, happens
when acid-forming bacteria oxidize the simple
compounds formed during hydrolysis to create
carbon dioxide, hydrogen, ammonia, and organic
Acetogenesis is the conversion of organic
acids into acetic acid. Acetic acid is the main
ingredient in vinegar and is the food for the final
stage of decomposition within the generator. Acidforming bacteria are fast-breeding and hearty, producing lots of CO2.
Methanogenesis is the creation of methane-producing microbes, or methanogens
organic material
and water
airtight biogas
biogas (methane
and co2)
Four stages of
anaerobic digestion occur
simultaneously in a single container
nutrient-rich liquid
ph as e 1 :
pha se 2 :
Aci d f o r mati o n
Methane fo r mati o n
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(single-celled, nonbacterial microorganisms from
the group Archaea). Methanogens combine hydrogen and CO2 produced during the acid-forming
phases to create methane. In contrast to the acid
formers, methanogens are slow to reproduce and
extremely sensitive to temperature, pH, and the
presence of oxygen.
How Much Biogas
Can You Make?
There are many variables in all processes of generating biogas. These include the type and quality
of feedstock, the type of generator and how well
it is maintained and fed, and other factors that
you will read about later. I point this out because
it is almost impossible to calculate exactly how
much gas you can produce from any given “recipe.” There are, however, rules of thumb that offer
enough guidance to point us in a generally useful
Rule of thumb for biogas production: A
well-managed generator may produce approximately its own volume of biogas each day. To put
this in terms of energy production, a bit of math
is required:
• A 55-gallon drum has a volume of about 7.35
cubic feet.
• One cubic foot of methane contains 1,000
Btus of energy.
• Biogas containing 60 percent methane offers
600 Btus of energy for each cubic foot.
• 7.35 cubic feet x 600 Btus per cubic foot =
4,410 Btus.
A typical gas cook stove burner might burn through
15,000 Btus of fuel per hour on maximum heat.
At this rate, a 55-gallon methane generator can
potentially produce enough gas in a day to supply the burner for about 18 minutes, allowing
you to boil about 2 gallons of water (assuming a
60-percent transfer efficiency between the energy
in the flame and the water in your pot).
This might be enough in some cases, but in a
practical sense, a small family with modest daily
cooking needs will require the output of a warm,
well-fed, 200-gallon (27-cubic-foot) methane generator at a minimum. This much biogas represents about 16,000 Btus and offers about one
hour of cooking time, or enough energy to boil
around 8 gallons of water.
Lots of Variables
The quantity and quality of methane you make
depends on the nutrient value of the feedstock
and how well the microbes convert the available
nutrients into methane. For practical purposes,
biogas production and quality are functions of
your specific recipe and generator management.
Important things to understand about making biogas are:
• Recipe development and the carbon-tonitrogen ratio of ingredients
• Solids, liquids, and digestible quality
• Temperature
• Feeding rate
• Retention time
• pH
• Mixing
We’ll cover all of these topics, but as you can
see, any estimate of methane yield for each unit
of digestible material has quite a few variables.
That means any lists you come across indicating specific values for any of the variables are
only estimates. Your actual production will vary. I
encourage you to not get lost in the numbers or
details, and simply experiment. You can learn at
least as much by doing as by studying!
Recipe for
Making Gas
of organic
materials can be digested, including vegetables,
food scraps, grass clippings, animal manure,
meat, slaughterhouse waste, and fats — almost
anything as long as it contains carbon and/or
nitrogen. Avoid using too many woody products,
A l m o s t a n y c o m b i n at i o n
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like wood chips and straw, which contain large
amounts of lignin (which is resistant to microbial
breakdown and tends to clog up the digestion
process). Also avoid material that may be
contaminated with heavy metals or other toxins,
and materials with large amounts of ammonia or
The ideal ingredients are those materials you
have a plentiful, convenient, and consistent supply of, so you can make consistent and useful
quantities of biogas. If you have experience with
mixing compost, you already have a good idea of
what the recipe needs to be: If you can compost
it, you can digest it.
The Right Ratio
Organic material can be classified by how much
carbon and nitrogen are in its makeup, and the
ratio between those two elements. This ratio
is expressed as C:N. Carbon is a source of
energy for microbes; nitrogen is needed for protein and used to build cell structure. A C:N ratio
of between 20:1 and 30:1 is suitable, with the
higher C:N range being ideal. Too much carbon
slows the decomposition, while too little means
organisms don’t grow. Too much nitrogen produces ammonia, but with too little you don’t get
enough of the right kind of microorganism growth.
Don’t worry too much about getting the C:N
ratio perfect at first, since a wide range of C:N will
produce something you can use. Experiment and
find a recipe that works well with ingredients you
have available, then perfect the recipe for maximum gas production.
Brown vs. Green
In general, things that are brown are high in
carbon. This includes cardboard, wood chips,
cornstalks, dry leaves, pine needles, and straw.
Green things are generally higher in nitrogen,
including food and garden wastes, grasses, seaweed, and manure (an obvious exception to the
general color rule). The chart, Evaluating Raw
Materials, on pages 238 and 239, lists approximate C:N ratios, moisture content, weight, and
estimated volatile solids content of common
organic materials. Any combination of these can
be mixed to yield the ideal ratio.
Keep in mind that the C:N ratio describes the
chemistry of the material — it does not mean
that you need 30 times more brown material
than green material. The actual amounts of
carbon and nitrogen in any material will vary
depending upon the specific makeup and age
of that material, and the data should be taken
as a general approximation of C:N ratios. Note:
The terms “TS,” “VS,” and “FS” are discussed
on page 237.
Calculating C:N Ratio
You can determine the C:N ratio of any combination of ingredients — and the relative quantity
of each ingredient required in your mix — if you
know the C:N ratio and the approximate moisture content of the material. Note that C:N ratios
are given in dry weight, not wet weight. This is
because moisture content varies greatly, even
with quantities of the same material.
Factoring in moisture content requires an extra
step in the calculation, but it’s a fairly simple step
when weighing ingredients to add to your recipe.
You can get away with using volume measurements only if the water content of the ingredients
is similar.
Using the C:N ratios and moisture content
data from the Evaluating Raw Materials chart,
here’s how to calculate the C:N ratio of your
entire recipe:
1. Make a list of each of the ingredients you
wish to add, along with their carbon values (the C
side of their C:N ratios).
2. Weigh
the total amount of each ingredient.
(You can use any weight unit you want — pounds,
kilograms, ounces — just be consistent.)
3. Find
the moisture content percentage of
each ingredient in the chart.
4. Figure the dry weight of each ingredient using this formula:
Wet weight x (1 – moisture content percentage)
= dry weight.
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5. Multiply the carbon value of the ingredient by
Entering the numbers for each item onto a list
or chart, you can easily add up all the dry weights
and carbon units to complete the calculation:
its dry weight to find the carbon units.
6. Add up all of the dry weights (step 4) of the
45 (total carbon units) ÷
1.6 (total dry weight unit) = 28
7. Add up all of the carbon units (step 5) of the
8. Divide the total carbon units by the total dry
weight. The number you get is the carbon value
(C) of the ratio, where the nitrogen value (N) is 1.
Here’s an example using ingredients you might
have around your homestead (see chart below).
The quantities are relative and can be scaled up
or down as needed. We want to develop a recipe
using chicken droppings, grass clippings, kitchen
scraps, and paper. Chicken manure has a C:N
ratio of 6:1, and you have 2 pounds (wet) to add
to your recipe.
Chicken manure has a 70-percent moisture
content, so to figure the dry weight:
2 x (1 – 0.70) = 0.6
Round off any decimal places (let’s not
worry about precision as it is not obtainable, or
required, outside of a lab).
Next, multiply the carbon value and dry weight
to find the carbon units:
Your C:N ratio for this recipe is approximately
Consider this example a place to start and
not the final word on the available carbon and
nitrogen in any given recipe. Experiment to find
out what works best for you using your specific ingredients. Notice the very small amount
of newspaper required, due to its high carbon
content. Small changes in the addition of woody
material will make large differences in the C:N
Solids, Liquids,
and Volatile
some amount
of water, and many contain lots of water. Water is
an aid to digestion, but it cannot be digested. If
you evaporate all the water from a material, you’re
left with only the solid portion. Organic materials
M o s t ma t e r i a l s c o n t a i n
6 x 0.6 = 3.6
Re c i p e e va l u at i o n — C : N Rat i o i n Yo u r Re c i p e
Carbon units
(carbon value x dry weight)
Chicken manure
Grass clippings
Kitchen scraps
Total dry weight
Total carbon units
C:N ratio of recipe
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3Smaller pieces of
5Breaking down organics:
biomass will break
down more quickly
and completely.
Food scraps = 25% total solids and 75% water
Total solids = 90% volatile solids and 10% fixed solids
might be 75 percent water by weight, more or
less, leaving 25 percent total solids.
Not all solid material is susceptible to the bacterial breakdown required for anaerobic digestion.
The portion of the total solids (TS) available for
AD are called volatile solids (VS), which might be
80 or 90 percent of TS, more or less. The rest
of the solids are known as fixed solids (FS), and
these are unavailable as food for the digesting
If you evaporated all the water from a material
and then burned the solids, only the volatile solids would burn up, and you’d be left with a pile of
ash (the fixed solids). Chemically speaking, this
approach is a bit rough in determining exactly how
much of which part of the material gets digested,
but it’s the best we can do at this point.
VS and Gas Production
Knowing the VS is important for determining how
much gas can be produced for any given material.
One pound of volatile solids can theoretically
yield a maximum of 30.5 cubic feet of biogas. In
reality, anywhere from 10 to 60 percent of the VS
will be converted in the digesting process, so the
practical result is that you can expect anywhere
between about 3 and 18 cubic feet of biogas production per pound of volatile solids. The gas will
likely be somewhere between 55 and 80 percent
methane, so the methane yield for each pound
of VS consumed in the generator can range from
1.7 to 14 cubic feet.
Studies of biogas yields from various feed
stocks are generally represented in terms of
cubic feet of methane produced for each pound
of VS converted under the specific conditions of
that test. Expect that your results will be different from anything you see published. The specific
composition of VS within organic wastes, along
with the environment within the digester and how
you manage the whole process will all affect gas
iBallparking Wateri
The commonly accepted range of total solids in the mix for optimal biogas generation is between
2 and 10 percent, meaning that 90 to 98 percent of the material inside your generator, including the
moisture in the material itself, can be water. Other considerations in determining how much water
to add are material handling and digester volume.
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E va l u at i n g Raw M at e r i a l s
Refer to this chart as you read through this chapter and work through the examples. It compiles all of the
useful information you’ll need about typical ingredients that might be available to you. Look up the material
you’re considering for your recipe, then read across the chart to get an idea of its value to your mix. For
example, manure from laying hens has a nitrogen content range from 4 to 10 percent by weight, with an
average of 8 percent. It has an average C:N ratio of 6 to 1, average moisture content of 69 percent, and
weighs about 1,479 pounds per cubic yard. The important value of volatile solids (VS) will vary within the
range of most animal manures, lying somewhere between 70 and 85 percent of total solids (TS).
C h a r a c t e r i s t i c s o f r aw mat e r i a l s
Type of value
(dry weight)
C:N ratio
(weight to
content %
(wet weight)
Bulk density
(pounds per
cubic yard)
Average %
VS of TS
Crop Residues and Fruit/Vegetable-processing Wastes
60–73 a
Fruit wastes
Vegetable wastes
Broiler litter
12–15 a
14 a
Dairy tie stall
Dairy free stall
Horse, general
Horse, race track
Laying hens
Turkey litter
16 a
Estimated average between 70 and 85% VS for most manures
Animal Manures
2 3 8 B I OGAS
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Bulk density
(pounds per
cubic yard)
content %
(wet weight)
Type of value
(dry weight)
C:N ratio
(weight to
(food waste)
Night soil
Paper from domestic
Refuse (mixed food,
paper, and so on)
Sewage sludge
Corn silage
38–43 a
Hay, general
Hay, legume
Hay, non-legume
Straw, general
Straw, oat
Straw, wheat
Average %
VS of TS
Domestic Wastes
most grass products average 90-95% VS
Agricultural Products
Note: Data was compiled from many references. Where several values are available, the range and average of the values found in the
literature are listed. These should not be considered as the actual ranges or averages, but rather as representative values.
Table Credit: NRAES and the Cornell Waste Management Institute grants permission to reprint “Characteristics of Raw Materials” (see
Resources for website), taken from the On-Farm Composting Handbook, NRAES-54. Estimated VS content added by the author.
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S e t t i n g Up a W a s t e M a n a g e m e n t Sy s t e m
Having a system for processing
your organic waste material will
save time, minimize mess, and
generally make an easy task of
the whole process. When things
are easy, they get done!
We set up a fairly simple
system in a corner of our garden
hoop house, using an old sink
and a 3/4-horsepower under-
sink food grinder. A heavy-duty
extension cord brings power to
the disposal, a 5-gallon bucket
catches the ground-up food
and grass cuttings, and a water
hose flushes material through
the grinder. With some rubber
gloves at the ready, we’ve got a
relatively easy way to manage
digester feeding.
What once went straight to
the compost pile now takes a
detour through the food grinder
and biogas generator. The effluent from the generator spills
over into a 5-gallon bucket
as fresh material is added, and
finally makes its way to the
compost pile.
3Sequence of
preparing food
1. compostable raw material placed in sink
3. slurry poured into digester
2. waste disposal under sink drains slurry into a bucket
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Feeding Your Biogas
Now that you’ve developed a recipe, you can begin
to feed the generator. Solid material should be
chopped or shredded into 1" or smaller bits. Having more surface area available to the microbes
promotes better digestion of organic material,
yielding more efficient production of biogas.
Add enough water to make a pourable slurry,
then mix it all up and pour the slurry into the
digester. The general rule of thumb is to add the
same amount of water as solid material, but this
ratio will vary according to how much water is
already in the organic material in your recipe, as
well as how much fiber is in the organic matter.
More fiber requires more water to break it down,
but less water means more room for digestible
solids, and thus more gas.
A power drill with a paint mixer attachment
works well for mixing a manure slurry, but for food
and plant scraps, you may find that a blender,
garbage disposer (see Setting Up a Waste Management System, facing page), or a yard waste
chipper/mulcher is a convenient way to chop up
material before adding water. Fibrous material
may digest more readily if it has been allowed
to age (allowing fungi to begin breaking down
the fiber) for a few days before putting it into the
generator. Just don’t age it for too long or energy
will be lost.
When you first load the digester, you will need
to inoculate it with a culture of methane-producing organisms (methanogens). These microbes
exist naturally in animal dung, so if you’re using
manure you don’t need to worry about adding
them. But if you want to digest only food scraps
or grass clippings, you’ll need to inoculate it initially to get the biological processes going.
A good culture can come from farm animal
manure (ideally cow or pig manure), slurry from
another operating digester, pond muck, or a
shovel­ful from the bottom of a compost pile that
has not been turned in a long time. Once added
to the slurry at the digester’s initial startup, the
methanogens will reproduce on their own so you
don’t need to continue to feed manure or other
source of methanogens.
Depending upon your location, finding a good
source of inoculating manure or pond muck may
be the toughest ingredient to find. With proper
management, though, you may need to do this only
one time, even with a batch digester that is periodically emptied and refilled. Much like keeping sourdough bread culture alive, some of the last batch
is added to the next batch, inoculating the fresh
material with the bacteria generated from the previous batch. Try not to expose the inoculant to air
for too long, as oxygen will kill the methanogens.
The Process
Fill the digester about 80 percent full with slurry.
More air space is okay if you’re starting with just
a small batch of material, but it will take a bit
longer for your gas quality to improve so that it
will burn. At first the generator will produce a
large amount of CO2, as the available oxygen
is consumed and the methane producers catch
up to the acid producers. This means that the
first batch of gas will be mostly CO2 and will not
burn. Once the oxygen in the generator is used
up, the process stabilizes and shifts from aerobic
(microbial breakdown with oxygen) to anaerobic
the most
critical detail in the generation of biogas. Different
groups of methanogens have been identified that
respond to different temperature regimes.
You must choose which regime you wish to
work with, and design your system accordingly:
Tem p e r a t u r e i s p r o b a b l y
• Psychrophilic methanogens survive at cooler
temperatures, above 32°F (0°C).
• Mesophilic methanogens are active at
temperatures between 70 and 105°F
• Thermophilic methanogens will dominate
at temperatures between 105 and 140°F
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Not much information is available about digestion in the psychrophilic range, but the gas production rate will be quite low. Mesophilic methanogens are much more tolerant to changes
in their environment than thermophilic and are
faster producers than psychrophilic. Mesophilic
methanogens may produce gas at 70°F, but the
rate at this temperature will be very slow.
One advantage to the thermophilic methane
producers is that they are much faster at digesting, requiring only about half the material retention
time to achieve similar gas production compared
to the mesophilic range, thus requiring a smallervolume digesting vessel. However, to achieve this
efficiency you will pay a penalty in energy consumed to provide the required heat. For our purposes, we’ll focus on the safer and more easily
managed mesophilic temperature range.
The mesophilic conditions you are trying to mimic
within the digester are similar to those inside an
animal’s gut — that is to say, oxygen-free and a
temperature of around 98°F (37°C), plus or minus
a few degrees, for maximum gas production. Biological activity within the digester will produce
some heat, but depending on your climate you
may need to supply heat to your digester.
To reduce the amount of external heat
required, place the generator in the sun or inside
a greenhouse. An insulated wrap can be made
with thin, flexible foam insulation, or even bubble
wrap, covered with black, UV-resistant, 6-mil polyethylene plastic.
Cold Climates
To produce gas during the winter in cold climates
you’ll need to provide an additional source of
heat. A larger generator may produce enough
gas for some of it to heat water, which can be
circulated via closed piping acting as a heat
exchanger inside the digester. Or, you can wrap
the outside of the barrel with flexible tubing (covered with insulation) and pump hot water through
it (a good use for the solar batch collector project
in Chapter 6). Another option is a submersible,
thermostatically controlled electric water heater
designed for heating plastic animal waterers (see
In any case, you will need to weigh the costs of
providing heat against the benefits of gas production. Alternatively, if you live in a hot climate you
may want to provide some shade so that the temperature inside the digester does not rise much
above 105°F.
Retention Time
and Loading Rate
material you put into a wellmaintained methane generator operating in the
mesophilic range will be fairly well digested in
about a month. You might get more gas from
the same material over a longer period, but the
production rate will fall off over time.
Handling more material for a longer period also
requires a larger generator. Retention time (also
called hydraulic retention time, or HRT) is the
amount of time material stays in the digester vessel, where it is broken down over time. Retention
time is determined by how quickly the material
breaks down, the gas output requirement, and
the volume of the digester vessel. The desired
retention time and the volume of the digester
determine the rate at which you feed the digester
so that material stays in the vessel for the optimum amount of time. Material should stay in
the digester long enough to produce most of the
gas that it can, but not too long because without
enough nutrients the methanogens will die.
For example, if you have a 55-gallon drum
(with a volume of 7.35 cubic feet) and you need a
retention time of 30 days to produce the optimum
amount of gas, you want to add 55 gallons of
material over a period of 30 days, or just under 2
gallons (0.27 cubic feet) per day. Every time you
add 2 gallons of new material, nearly 2 gallons
of digestate will flow out the effluent tube. Over
half of what you add will be water, so your average
daily gas production is limited to the digestible
content (VS) of the added organic matter.
In most cases,
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Optimum retention time will vary with recipe
and temperature, so experiment and find out what
works best in your situation. For maximum efficiency, you want to match retention time with gas
production and the rate at which you feed material, known as the loading rate.
Loading Rate
Loading rate refers to the amount of volatile solids added to the generator with each feeding, as
well as the frequency of those feedings. Loading
rate is generally expressed in terms of pounds
of VS per cubic foot of generator volume and is
managed according to the properties of the material being used. If the material put into a digester
is fairly consistent, you don’t need to go through
the exercise of calculating VS every time. After
a while, you will get a feel for how much and
how often to feed, based on your recipe and the
observed results of gas production.
The rate at which you feed the generator is a
function of how large your digesting vessel is and
how well the methane-forming microbes keep up
with the acid-forming bacteria. The rate will vary
somewhat depending upon the digestibility of the
feedstock you’re using, since not all VS behave
in the same way. Assume that only about onehalf of the VS added will be digested, and expect
that amount to vary for different feedstock — and
even among the same feedstock, depending on
its exact makeup. You will get different amounts
of VS and gas from the same cow at different
times of the year if that cow is on pasture for the
summer and grain and hay for the winter.
Where to Start
As a general rule, start the generator on a small
amount of VS — say, 0.1 pound VS for every
cubic foot of digester capacity. As the methanogens become established, you can add more, perhaps up to 0.25 pounds of VS for each cubic foot
of filled digester capacity. Some sources of VS
will convert to gas at a higher rate and more completely, and you’ll need to adjust the loading rate
for best results. If gas production is fast and efficient, you can decrease retention time and move
material through more quickly by increasing your
loading rate.
Calculating VS and Gas Production
To understand just how much VS is in your recipe,
and therefore how much gas you can expect to
produce, refer to the table Evaluating Raw Materials (pages 238 and 239) and take a look at
the column “Average %VS of TS.” We’ll pull values from that column and expand on the Recipe
Evaluation chart (page 236) to calculate the VS
content in the sample recipe.
Of the 6 pounds of organic material fed to the
generator, only about 1.4 pounds is VS. If you put
all this material into a 55-gallon drum (7.35 cubic
feet of volume) that is 80-percent full (including
5.9 cubic feet of additional water), your loading
rate works out to be:
1.4 pounds ÷ 5.9 cubic feet
= 0.24 pounds per cubic foot
This is a good loading rate for an operational
55-gallon drum digester. Assuming a 50-percent
Re c i p e E va l u at i o n : v o l at i l e s o l i d s
wet weight
Dry weight
% of TS
that are VS
VS weight
Chicken manure
Grass clippings
Kitchen scraps
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conversion of VS to biogas, total production over
time might be:
(1.4 pounds VS) x (30.5 cubic feet of biogas
per pound VS) x (50% conversion rate)
= 21 cubic feet
These are very general estimates, and your
biogas production may be quite a bit less. The
retention time (the amount of time it takes to convert the VS to biogas) will be determined through
direct observation by you. Once your digester is
loaded and operating, keep track of the rate of
gas production by observing the displacement
of the gas collection tank. When the production
rate starts to drop off, it’s time to feed. You may
need to feed every day or once a week, depending on the conditions inside the digester and your
Some material fed to your generator will form a
crusty layer of scum on the surface. This scum
can prevent gas formation, so daily mixing is recommended. You can mix by shaking, stirring, or
otherwise agitating the slurry as long as no air is
introduced into the generator. A barrel-sized generator can simply be rocked back and forth to
mix, but larger vessels often require an internal
mixing system. More agitation means less scum
formation, and better mixing means more efficient
gas production. You can help keep scum to a minimum by avoiding large amounts of lignin and by
chopping ingredients into small pieces.
Types of Methane
T h e r e a r e t w o general approaches to
methane generator construction: batch and
continuous-flow. I’ve also developed a third type
of construction, which is sort of a hybrid of the
two other processes.
Batch Generators
The simplest design is a batch processor where
you fill the digester once, collect the gas until
there isn’t any left, then empty the digester
T w e a k i n g Y o u r G e n e r a t or ’ s D i e t
The methanogenesis (methaneforming) process is the limiting
factor in how much to feed
your generator. If you feed too
much, the acid-forming process
overtakes the relatively slow
methane-forming process. This
leads to a low (acidic) pH level
that inhibits methane-forming
activity, poisons the process,
and ultimately will shut down
gas production. If you’re feeding the generator regularly and
gas flow stops, you can check
for this imbalance by testing the
pH of the slurry. The pH should
normally be right around 7 or
7.5. Perform this simple test by
dipping pH paper into a sample
of liquid digestate. Here’s what
to do with the results:
1.If the pH is below 6.5, the
digester has gone “sour.”
Stop feeding for a few days
so that the methanogens can
catch up, then test the pH
2.If things are really bad and
stay bad for more than a
few days, you may need to
add some baking soda to
help bring the pH back up.
Add only ¼ to ½ cup at a
time for a 55-gallon barrel
generator, wait a day, and
check the pH again.
3.When the pH has returned
to normal, gas should start
bubbling out again. Resume
feeding and adjust your recipe
and/or the rate at which you
feed, while monitoring pH as
you make adjustments.
The ecosystem within the generator evolves to suit the recipe.
If you change recipes in a sudden
and dramatic way, the chemistry
will react and readjust. Think of
how you feel after you try a new
food or travel to a foreign country
and indulge in local cuisine. Make
small, incremental changes to
your generator’s diet to avoid
a belly­ache.
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gas outlet pipe
Batch generator
made with two open-top barrels
inverted barrel
collects gas
slurry level
digester barrel
feeding tube inlet
gas outlet
flow plastic bag generator
effluent out
vessel, compost the digestate, and start all over.
A batch processor is time-intensive and involves
the dirty job (at least once a month) of emptying
the digester and starting a new batch. The advantage is that it’s simple, cheap, and works great
for small, easily managed volumes of material.
You can build a fairly simple batch processor
using an open-top 55-gallon barrel for the digester
vessel, and a second, smaller barrel (also opentop) for gas collection. Drill a hole into the bottom
of the smaller barrel and insert a gas collection
tube. Then, put the smaller barrel into the larger
barrel with the open end down and the gas outlet
tube up. Push the top barrel all the way down into
the slurry, allowing air to escape from the gas outlet. Close the gas outlet to seal the barrel.
As gas is produced, the top barrel will rise up,
and the gas can be drawn out through a pipe to a
burner. This is a good way to get started quickly
and to gauge gas production as the barrel rises.
You can determine the gas quantity by measuring
how much of the barrel rises above the slurry and
calculating the displaced volume.
The simplicity of a batch generator ends when
it comes time to empty and refill the barrel: 55
gallons of effluent is not a pretty sight to behold
and can be difficult to manage. This is not such a
big drawback with a small, 5-gallon-bucket batch
digester like the project on page 253.
As you move beyond experimenting with test
batches of buckets and barrels in your biogas
hobby, you may find that a continuous-flow process
is more practical than a batch setup. Continuousflow is also called plug-flow, because a “plug” of
material is introduced to the generator periodically.
A continuous-flow generator has a feeding
inlet on one end, an effluent outlet on the other
end, and a gas outlet pipe in between. It’s sized
according to the daily input volume and desired
retention time. As you put new material in, it
pushes older material through the generator until
it gets to the effluent outlet, where the digestate
it is removed. You can build a very simple continuous-flow generator with a UV-resistant polyethylene plastic bag (such as those used for bagging
hay) and PVC piping for the inlet, outlet, and gas
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55-gallon hybrid
feeding tube
gas out to burner
bulkhead adapter
inverted barrel
immersed in
water; gas
bubbles up and
fills barrel, making
it rise
effluent overflow
water-filled barrel
heater (power cord goes
up and out feeder tube)
Hybrid Generator
As a compromise between simplicity, practicality, and space constraints, I have settled on
a hybrid generator system for my own use that
takes advantage of the best of both designs
and allows for cleaning, tweaking, and upgrading as needed. The hybrid design requires three
barrels and piping between them. One barrel is
used as the digesting vessel and incorporates
the feeding tube, effluent overflow, and gas outlet
pipe. The other two barrels are used to make an
expandable and isolated gas collection system. I
describe how to build this generator in the project
on page 256.
Using Biogas
used in place of natural gas
or liquid propane gas for space and water heating,
lighting, and cooking, with some modification to
the burner. It can also provide power by fueling an
engine or an absorption cooling system, such as
a gas refrigerator or chiller.
Purified, or “scrubbed,” biogas behaves just
like natural gas, but if you choose not to scrub
the gas, you will need to deal with the CO2 and
water vapor content by modifying burners or other
equipment to ensure good combustion. In other
words, you can either modify the gas or modify
your equipment. Ideal combustion requires a
Biogas can be
W h a t t o Do w i t h t h e E f f l u e n t
Effluent is the digested “waste”
material from your biogas
generator. It’s a low-odor blend
of compostable solids and
nutrient-rich liquid. What you do
with the effluent you produce
depends upon what you put into
the generator, how well the solids are digested, and, perhaps,
where you live. You can apply
effluent directly to your garden
or fields as a soil amendment,
or you can compost it and
further refine it for improving
your soils.
One of the biggest concerns
is the presence of pathogens in
animal wastes. Some pathogens will be destroyed in the
mesophilic temperature range
over a typical retention period,
but some require much hotter
temperatures to be completely
destroyed. High-temperature
composting (greater than
140°F) generally eliminates
most pathogens. The only way
to be sure is to have a sample
tested at a reputable lab.
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Gas storage system
burner that is designed specifically for a particular gas. Modifying burners will involve compromises in efficiency and performance but should
yield a usable flame. But first and foremost:
When working with or around biogas, safety is
your top priority.
using an inverted
barrel inside a
larger barrel filled
with water. Gas
from the digester
displaces the water,
causing the barrel
to rise. If needed, a
guide can be built to
keep the gas barrel
straight as it rises
so that weight can
be placed on top of
the barrel to provide the required
pressure. Adding
bricks for weight is
sometimes called
Handling Biogas Safely
Methane is a highly flammable gas that will burn
when mixed with air at a ratio of between 5 and
15 percent by volume. Biogas has a flammability
range of about 4 to 25 percent concentration in
air, and possibly wider, depending on its purity.
Always take great care when working with biogas. It is quite possible for a biogas generator to
explode, especially if there are leaks in the generator or gas piping, or when the gas pressure at
a burner falls too low. It’s better to have a small
amount of biogas leak to the outdoors (where it
will be quickly diluted) than to have air leaking
into the generator where it’s more likely to reach
the critical range of flammable ratios.
Maintain Positive Pressure
Keeping a positive pressure inside the digester
and gas lines will help to prevent air from leaking
into the generator, as well as prevent the burner
flames from traveling through the gas tube back
to the generator. The processes within the generator will create positive pressure as gases are
produced, but as the gas is consumed, the pressure will drop, possibly allowing flame to burn
back through the pipe (flashback) to the generator. Always turn off the burner flame if the gas
pressure is too low.
Use a Flame Arrestor
To help reduce the chances of a flashback, use
a flame arrestor inside the gas pipe. The idea
behind a flame arrestor is to stop gas flow and/
or reduce the flame temperature to below the ignition point.
There are two relatively simple (though not
foolproof) ways to approach this:
1. Incorporate a water trap into the gas line by
creating U-shaped bend, or trap, in the line that
is filled with a few inches of water. The biogas will
bubble through the water on its way out of the
digester vessel and into the gas storage vessel.
In the event of a flashback, the water in the trap
will cool and extinguish the flame inside the line.
This approach will not work very well on the gas
supply side, as the flame will sputter as each gas
bubble makes it to the burner. Biogas contains
water vapor that will condense in the gas line, so
keep an eye on the water level in the trap.
2. The second approach works well on the gas
supply line: Pack some fine bronze wool (similar
to steel wool) into the gas hose just before the
burner. Add enough to fill 3" or 4" of hose length.
Gas can still move through the bronze wool, but
should it start to flow back through the hose, the
bronze wool will effectively extinguish the flame.
Respect the Hazards
Treat biogas with the same respect you would
treat any other fuel or flammable product. Keep
sparks and flame well away from biogas and biogas generators. Never use biogas indoors or in
enclosed spaces. Ethyl mercaptan is the odorant
added to both natural and bottled gas so that a
leak is readily detectable by smell. When burning
biogas — in a burner or other suitable equipment
— ensure proper ventilation to prevent a buildup
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of explosive, toxic, or even deadly gases and combustion byproducts. Burning biogas produces carbon monoxide, along with CO2, water vapor, and
nitrogen oxides.
Storing Biogas
Once you’ve produced biogas in your generator,
you can pipe it into a simple holding container.
For very small batch generators (of the scienceproject variety) you can use a latex balloon.
Larger amounts of gas can be stored in small
barrels inverted into larger barrels that are filled
with water. The gas storage container should be
airtight, allow for expansion and contraction as
gas flows into and out of it, be able to deliver the
required pressure to the gas appliance, and not
turn into shrapnel in the event of flashback. How
much storage capacity you need depends on how
much gas you make, along with how much and
when you use it.
Compared to natural and propane gas, biogas has less energy per unit due to the dilution by CO2 and, to a much lesser extent, water
vapor. This means that the energy in the flame
of unscrubbed biogas will be lower when used
with conventional natural gas or propane burning
equipment. A good biogas flame requires greater
fuel flow, higher pressure, and less combustion
air than natural or propane gas.
Nozzle size. The burner nozzle size will need
to be larger than what you might use for natural or
propane gas to yield a similarly energetic flame.
How much larger depends on the purity of the
biogas and the fuel gas you are converting from.
The Orifice Diameter Multiplier chart, above right,
indicates how much larger a fuel nozzle orifice
needs to be when converting equipment from natural gas or propane to biogas. If you choose not
to enlarge the orifice, you may still get a flame but
the energy content of the flame will be reduced.
O r i f i c e D i a m e t e r M u lt i p l i e r
for gas burners
% Methane (CH4) Orifice Diameter
in Biogas
Natural Gas
Here’s an example: If your biogas contains
60 percent CH4, and you want to convert a natural gas appliance with an existing orifice diameter of 0.1", you need to enlarge the orifice to:
0.1 X 1.46 = 0.146" diameter. Some gas appliance nozzles can be removed and a different
one installed, but many are pressed in place and
cannot be removed. The nozzle orifice can be
enlarged with a drill press and the appropriate
drill bit.
Airflow. For a good flame, the primary air supply to the burner must be reduced. This is easily
accomplished by closing the air shutter on the
gas appliance’s burner tube until a steady, blue,
cone-shaped flame is produced at the burner.
Gas pressure. Pressure in the biogas system can be regulated by applying external weight
to the top of the container. Increase the weight
until the gas flows to the burner at the required
pressure. A gas pressure regulator is used on all
gas-burning appliances to prevent too much pressure from being delivered to the burner. However,
finding equipment suitable for use with biogas is
A typical propane gas kitchen range might
require a delivery pressure of 11" of water column (wc) pressure. This simply means that where
the gas enters the appliance it exerts the pressure required to lift a column of water in a vertical
tube 11" tall. Expressed another way, 27.71" of
water column is the same pressure as 1 pound
per square inch (psi). Delivering biogas to a conventional cook stove burner may require up to
20" wc.
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Biogas and Enginesi
Some gasoline engines are designed — or can be modified — for use with natural gas, propane gas,
or biogas. Modifications include installing a special carburetor, adjusting the timing, and regapping
the spark plugs. Diesel engines can accept up to 80 percent biogas when the biogas is mixed with the
incoming combustion air.
When burning unscrubbed biogas in engines, the oil must be changed more frequently than when
using purified biogas. Also, since there is less energy in a volume of biogas compared to natural gas,
gasoline, or diesel fuel, the engine will produce less power than its factory rating.
Co w P oop a n d G a s G e n e r a t i o n
I realize that most of us don’t
have a family cow at our disposal, but the following example
will illustrate the process of
planning a methane generator
around available resources and
realistic expectations.
Fresh cow manure is often
used exclusively for on-farm
methane production and is well
suited to this application. But
cow manure has a less-than-optimal C:N of only 15:1 and relatively low gas production by total
volume of raw material. Despite
these apparently unfavorable
conditions, cow manure works
well due to a number of other
properties that make it attractive
for dairy farmers incorporating
anaerobic digestion into their
daily operations. These include:
• Large quantities of cow
manure produced on a
typical farm
• Methanogen-rich quality of
cow manure, making it a
guaranteed gas producer
• High water content, requiring
little additional water
• Co-benefit of capturing
manure before it winds up
as a pollutant in lakes and
• Using the digestate as a
high-quality fertilizer
• Potential for producing large
amounts of gas to generate
electrical power for on-farm
use or to sell power back to
the utility grid
One cow might produce
about 18 gallons (140 pounds)
of manure each day. Given
the amount of water in cow
manure, only about 12 percent
of the total weight is TS, and
somewhere around 85 percent
of TS is the useful VS portion,
which may ultimately generate
about 60 cubic feet of methane (or around 85 cubic feet
of biogas). That amount of gas
represents perhaps 3 hours of
cooking fuel produced each day.
Compare the output of a
dairy cow with the amount of
food scraps or human excrement (0.5 lb per person, per
day) available, and the logistics
of material choice for biogas
production becomes clear.
That’s not to say you can’t make
useful amounts of biogas with
other materials; you just need
more of them. But most importantly, you need to use what’s
available to you.
If you have one cow on your
homestead property and want
to collect all of its manure to
make gas, you would first need
to contain the cow so you could
collect the poop. If you collect
18 gallons of material, and you
add another 18 gallons of water
to make a slurry, you quickly
realize that you’ll need a fairly
large, continuous flow generator
to handle a daily feeding while
allowing for sufficient retention
time to make a useful amount
of gas.
Alternatively, a batch generator made from a 55-gallon
drum loaded with a 50/50 mix
of manure and water will begin
producing gas within a few days,
but the quantity will be limited
by the amount of VS you can
put in the drum.
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To give you an idea of how much weight might
be required in practical terms, when my 170pound body compresses a volume of air under a
12"-diameter barrel, it exerts a pressure of about
20" wc. After enlarging the orifice, my Bunsen
burner works well over a wide pressure range,
and the flame height varies with pressure. A
larger (20,000 Btu) burner delivers a steady, high
flame at 15" to 20" wc.
Purifying Biogas
intended use and quality
of the gas required, you may need to remove
impurities from the gas before burning it. Biogas
contains up to 50 percent carbon dioxide (which
won’t burn) and possibly traces of hydrogen
sulfide (H2S), which will corrode metals and break
down engine oil.
Purifying, or scrubbing, biogas can decrease the
detrimental effects of these ingredients, decrease
gas storage requirements, and increase available
heating energy per unit of gas. Unless you’re converting an engine to operate permanently on biogas, there is really no pressing need to purify it. If
you choose to scrub biogas, it can be done with
costly high-tech purification systems, but our discussion will be limited to simpler methods.
One method for reducing both carbon dioxide
and hydrogen sulfide in biogas is by bubbling the
gas through a solution of calcium hydroxide (or
calcium oxide) and water. Calcium oxide is the
chemical known as lime, commonly used to fertilize soil. You can further reduce amounts of
hydrogen sulfide by passing the gas through iron
oxide, or rust. This setup can be as simple as
a 4"-diameter x 4-foot-long PVC pipe filled with
loosely packed rusty steel wool or coarse iron
shavings. The rust will eventually be consumed
De p e n d i n g o n t h e
and need to be replaced at a rate that is dependent upon the H2S concentration in the biogas.
The pipe will need to have gas-tight fittings and
cleanouts. If you’re making biogas for backyard
cooking or tiki torch lighting, there is no need to
add the complexity of scrubbing.
Environmental Care
Anaerobic digestion is essentially a controlled cow
fart. Both cow farts and biogas generators produce
methane. Methane is a very potent greenhouse
gas and should not be released directly into the
atmosphere. If you are going to make methane, you
must burn it rather than release it into the atmosphere. Burning methane produces carbon dioxide
(also a greenhouse gas but less potent than methane) and water vapor. Carbon dioxide is also produced naturally when organic material decays.
Generator and Storage Materialsi
Given the potentially corrosive nature of biogas with even small amounts of hydrogen sulfide (which
may be produced when some manures are digested), avoid using materials that are susceptible
to corrosion. Plastic barrels and PVC pipes will prove more durable over time than metal barrels and
galvanized pipe.
2 50 B I OGAS
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clo s e - up
Biogas Is More than a Gas
I wrote the book, and then took some time to do other things, including running a medical
device company. But more recently, fate brought me back to this subject of biogas when a dear friend of mine from
Sri Lanka came to visit me. He was in my office, which is packed with books, and he noticed the biogas book. He
asked me about it, and I explained. He got very excited. “We need this in Sri Lanka!”
o m e y ea r s a g o
David House
is the author of The
Complete Biogas Handbook (see Resources).
During my research for
this book, I discovered
a handful of people like
David who represent an
altruistic community of
dedicated clean-energy
researchers and advocates. Their work goes
way beyond the technical and digs deep into
how energy choices
can affect the human
condition. It’s too easy
for those of us with the
convenience of automatic fuel delivery and
programmable thermostats to complain about
the high cost of energy,
while elsewhere the cost
of a hot meal is simply
unreasonable. In this
profile, David comments
on the non-energy benefits of renewable energy
in the developing world.
This set me on a path to researching and
thinking about biogas in the developing
world, in a far more detailed and intensive
manner than I had before. What I learned (or
relearned) was that biogas is associated with
strong improvements in health, education,
financial well-being, gender equality, and
a reduction in deforestation, among other
benefits. When you think about it, that’s an
incredible list for something that for most of
us is pretty obscure — biogas — but each
item on the list has solid reasons for being
• Health. The World Health Organization
says that nearly two million people,
mostly women and children, die every
year as a result of indoor smoke from
wood cooking fires. That’s almost 4,500
people every day, about two a minute.
Biogas burns with a smokeless flame.
• Education. Gathering firewood is very
time-consuming (2 to 6 hours a day),
and it is usually the eldest girl who does
that work, so she has no time for school.
Caring for a biogas digester may take a
half-hour a day, and in the evening the
family can have the benefit of the very
bright light that biogas can provide, with
the right lamp, allowing reading and
• Financial well-being. Improved health
and increased time help the family
— usually the mother — to start a
business, barter work for an animal, or
improve their financial status in other
ways. Finally, the family has a crucial
new increment of time and energy, both
personal and household.
• Gender equality. The improved health
and any improvements in financial
strength contributed by the mother imply
certain changes.
• Deforestation. Less wood is taken
from trees cut down to feed the cooking
fires. Poor countries cannot afford to
replant their forests, and carbon dioxide
(CO2) released into the atmosphere from
trees that are burned and not replanted
has exactly the same effect as CO2
from fossil fuels. Some studies indicate
that as much as 15 percent of the
increase in global CO2 comes from those
disappearing forests.
So naturally one should ask: If biogas is such
a powerful tool to help achieve the United
Nation’s Millennium Development Goals (see
Resources), then why isn’t it used more often?
In fact, it is being used a great deal, but not
nearly as much as it could be used, because
the most commonly built biogas digesters
are expensive: $350 to $700 for a singlefamily digester.
Some digester programs offer a subsidy
to help purchase one, because funders and
governments know what a powerful catalyst for
development this technology is. Unfortunately,
these programs usually leapfrog right over
those who are really poor, because they want
biogas is more t h an a gas 251
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c lo s e - up
Biogas Is More than a Gas
UN Millennium Development
to ensure that these expensive digesters
are used, and the poor do not have animals
to produce manure to feed the digester. So
the subsidies more often go to those who are
already doing fairly well.
To address these barriers to using biogas,
my work is focusing on the development of a
very low-cost biogas digester. The prototypes
cost about $10 in parts purchased retail in
the United States in low quantity, and these
digesters (like all digesters) can be fed grass,
leaves, food waste, and similar materials, so
they can be used by people who do not have
animals. Depending on local costs, a mature
and manufactured version may cost from $6
to $8 to produce, and could be subsidized,
sold at cost, or sold for two to three times the
cost of manufacture. If the carbon market
perks up, these digesters could earn carbon
credits and be profitable even if given away.
Consider that the wealth of the world
is her people, above all. We cannot doubt
that people of enormous talent — nascent
Mozarts, possible Einsteins, potential
geniuses and savants of all stripes and
kinds — have lived and died in the world’s
villages without the benefit of the education
which would have unlocked all that was
imprisoned in their hearts and minds. These
gifts are lost to the whole world.
In addition, poverty begets war, and one
of those wars could easily suck our children
into its mouth. Swine flu started in a poor
village somewhere, where pigs and birds and
humans all lived too close together in very
difficult circumstances. Will the next global
pandemic be born in a mud hut, and travel
the world at the speed of a 747? Addressing
poverty is not merely of benefit to the world’s
poor, then: it will benefit everyone on this
singular green planet.
Imagine! If we are successful at intro­
ducing these very low-cost digesters and
showing that modest profits can be made,
then the idea could march across the
equatorial belt like a breath of hope, helping
lift families and whole villages out of poverty.
To draw attention to this project, I am
building a solar greenhouse on my Oregon
farm which will enclose a 10-cubic-meter
digester made from a silage bag (used by
farmers). I have an agreement with a local
fast-food restaurant to feed it all the food
waste it generates. My present estimate is
that the digester will provide the equivalent
of nearly $4,000 of energy every year.
To learn how you can participate in
bringing low-cost biogas projects to places
and people in need, visit the website for
Bread from Stones (see Resources).
I am building a solar greenhouse on my Oregon farm, which will enclose a 10-cubicmeter digester made from a silage bag (used by farmers). I have an agreement
with a local fast food restaurant to feed it all the food waste it generates. My present
estimate is that the digester will provide the equivalent of nearly $4,000 of energy
every year.
252 B I OGAS
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Make a Biogas Generator
aking biogas usually involves
smelly, messy ingredients. It
will be important to develop
systems that work for you to minimize
handling while maximizing your potential for success.
Two generator designs are presented here. The first is a very simple
“test”-batch processor made from
a 5-gallon bucket — good for trying
out the process without having to get
too involved. The second is a hybrid
configuration featuring both batch
and plug-flow design elements. Using
plastic barrels and common plumbing
supply parts, it is fairly simple and
inexpensive to make and use, but
requires some material processing
and waste management.
B atch v s .
Cont i nuous-F l ow
As discussed earlier, a batch generator breaks down one batch of material
at a time: You load the material and
seal the vessel. Gas is produced after
several days (at a rate and duration
that depends on the recipe and the
internal conditions). After the gas production stops, you empty the generator, compost the effluent, and repeat
the process.
In a continuous-flow generator, mat­­
erial can be loaded at a certain rate and
is constantly pushed through the vessel over a period of time that matches
the retention rate required by the material and conditions. Effluent flows out
the opposite end of the generator from
the intake, and gas is produced in a
fairly continuous process.
A hybrid system allows you to
extend the “batch” into a periodic
“plug” so that you don’t need to empty
the bar­rel quite so often. At some point,
however, you will need to empty out the
barrel and remove all the sludge that
builds up over time.
5 -G all on B atch
For a small-scale test or science project, you can start with this simple
5-gallon bucket batch generator. It’s a
manageable and inexpensive project
that will help you get a feel for the process. It’s also useful for testing your
feedstock recipe before moving on to
something more complex.
M at e r i a l s
5-gallon bucket with gasketed, airtight
One 1/2" NPT threaded bulkhead fitting
One 1/2" NPT male threaded x 1/2" O.D.
(outside diameter) hose barb T-fitting
One 1/2" to 1/4" barb hose adapter
Teflon tape
One 9" length 1/2" I.D. (inside diameter)
flexible plastic tubing
One 4-foot length 1/4" I.D. (inside
diameter) flexible plastic tubing
One PVC ball valve for 1/2" I.D. tubing
Five hose clamps for 1/2" tubing
Two hose clamps for 1/4" tubing
One large “punching bag” balloon
Fine bronze wool pad
One Bunsen burner designed for
“artificial” gas (a burner with an
integral “flame stabilizer” works
1. Prepare the lid.
Make sure the bucket’s lid gasket is in
good condition for an airtight seal. Drill
a hole through the top of the lid, using
a hole saw properly sized to the bulkhead fitting. To ensure a good seal, be
sure the hole is in a flat section of the
lid, without curves or raised lettering.
Fit the threaded male end of the
bulkhead fitting into the hole and secure
it on the underside of the lid with the
Making and using biogas is dangerous — potentially deadly — and can cause fires or explosions. Use common sense
and proper safety equipment. Perform all experiments (including these projects) outdoors with plenty of ventilation and
appropriate personal safety gear. If you’re in doubt about any procedure or have never worked with the materials and
equipment described, please work with an experienced helper.
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fitting’s gasket and nut. Make sure this joint
creates an airtight seal through the hole in the lid.
2. Complete the gas outlet and hose
Wrap the threaded end of the 1/2" T-fitting with
Teflon tape. Screw the taped end into the female
threads in the top of the bulkhead fitting, and
tighten it snugly by hand.
Cut the 9" length of 1/2" I.D. plastic tubing into
one 1" piece and two 4" pieces. These lengths
can be adjusted as needed, depending on your
specific requirements.
Fit one 4" piece of tubing onto one end of the
T-fitting, and secure it with a hose clamp; this is
the gas supply line. Attach the other end of the
same tube to one side of the ball valve and secure
it with a hose clamp. This valve will act as a shutoff between the digester and burner. Attach one
end of the remaining 4" piece of tubing to the
other side of the valve and secure it with a hose
The 1/2" gas supply line must be reduced to
accept a 1/4" hose to connect to the Bunsen burner’s gas inlet. Install the barbed hose adapter in
between the 1/2" and 1/4" hoses and secure each
connection with a hose clamp.
Slip the open end of the balloon through the
1" piece of 1/2" tubing, then stretch the balloon
over the remaining port on the T-fitting. Slide the
tubing down so the end of the balloon is sandwiched between the fitting port and the tube;
secure it with a hose clamp. (The tube merely
protects the more fragile balloon material.) The
balloon serves as a gas storage vessel as well
as a pressurizing system; it can also act as a
safety valve by popping if the pressure inside becomes too great.
3. Connect the burner.
Test the system for airtightness before making
the final gas connection: Hold your hand over
the bottom end of the bulkhead fitting, then blow
through the open end of the gas supply tubing,
and check for leaks. The balloon should inflate
and there should not be any leaks.
Complete the gas line connection by fitting
the 1/4" tubing to the gas inlet on the burner.
Make sure the burner control knob is OFF.
4. Make a simple flashback preventer.
As gas pressure drops, the flame at the burner can
burn back through the gas line and into the bucket
where some gas remains. The best way to prevent
E x p l o d i n g w i t h Imp a t i e n c e
When I made my first biogas, I could not get the
burner to light even after bleeding off the first balloonful. In disgust, I pulled the hose off the burner
and held a match right up to the hose. A flame
popped briefly out of the hose as the balloon
quickly deflated, followed by a groaning noise from
inside the bucket. I ducked, ran, and turned just in
time to see the balloon expand and pop, followed
by a dramatic geyser of partially digested slurry
rise from the gas outlet pipe where the balloon
once was.
The methane was not concentrated enough to
light the burner, but the methane-to-air mixture
inside the bucket was perfect for combustion. Once
the balloon was empty, there was no gas pressure
pushing the gas out of the barrel, and the flame
flashed back through the gas hose. The mixture
inside the bucket ignited, causing a small (but
contained) explosion.
Fortunately, all of this happened outdoors, and
the amount of gas inside a 5-gallon bucket that is
mostly full of noncombustible material does not
contain a lot of energy. Had I not been so impatient to burn the gas, and had I bled off another
balloonload or two of gas, I would not have been
able to relate this cautionary tale — all the better
for you, and I am none the worse for wear! Please
take care when working with flammable and
explosive gases, and do not a
­ ttempt to repeat this
2 54 B I OGAS
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this is to turn off the gas supply before the pressure drops too low. “Too low” means before the
flame starts to sputter. As a secondary precaution,
create a flashback preventer by inserting some
fine bronze wool (similar to steel wool) into the 1/2"
gas hose. Add enough to fill a few inches of hose
length. Gas can still move through the bronze wool,
but should it start to flow back through the hose, it
will be extinguished by the wool.
Note : These prevention techniques are not foolproof, so
take all necessary safety precautions!
5. Make and use the biogas.
Fill the bucket about one-third full with ground-up
or finely diced food scraps. Add about 1/2 gallon
of cow or pig manure (or a gallon of effluent from
another digester) to provide the methanogen
inoculant. Add water to fill the bucket no more
than three-quarters full, and mix up the slurry.
Fit the lid onto the bucket, making sure it seals
completely. Check for leaks again to be sure the
gasket is well seated. Keep the digester warm,
ideally between 80 and 100°F.
3Completed bucket
After a day or two, the balloon will begin to fill
with gas, but this is mostly CO2 and will not burn.
Bleed off this gas by opening the gas valve on the
burner, but do not attempt to light the burner. After
a few more days (perhaps up to one week) and a
balloon (for
gas storage)
1/2" I.D. plastic tube
(gas supply line)
1/2" NPT male
threaded x ½"
O.D. hose barb
bucket lid
Lid and gas
Bunsen burner
tube and nozzle.
The burner tube of
a Bunsen burner
easily screws off,
revealing the nozzle.
The orifice of the
nozzle is easily
drilled to a larger
outlet assembly
(exploded view)
PVC ball
valve for 1/2"
I.D. hose
1/2" I.D.
tube (gas
1/2" to 1/4" barbed
hose adapter
1/4" I.D. plastic tube
(gas supply line)
hole for
fitting nut
teflon tape
(bronze wool
inside hose)
Bunsen burner designed
for “artificial” gas. These
have a larger orifice and allow
for less primary air.
ma k e a b i ogas gener ator 255
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Make a Biogas Generator
few more balloonfuls, the digester should be producing methane that will burn. When the balloon
is full, open the gas valve on the burner and light
the gas. If it sputters and doesn’t light, the gas is
not yet combustible. Bleed off this gas from the
balloon and try again later. Keep an eye on the
balloon, because as it deflates the pressure will
drop. Remember that low pressure in the gas line
can cause the flame to roll back into the bucket.
5 5 - Gal l on H y br i d
G e ne r at or
This project shows you the basics of building a
hybrid generator using a 55-gallon (or larger) plastic, wide-mouth, screw-top barrel for the digesting
vessel, and two additional barrels for gas storage. The essential design elements are to provide an airtight system that lets you put digestible
material in, get gas out, and allow for effluent
overflow. Once you get the hang of operating this
unit, you’ll be able to design your own biogas
generator, scaling it up or down, if desired, and
adapting the system and materials to suit your
specific needs.
If you buy all new parts for this project, you
can build the 55-gallon generator for under $300.
Optional additional equipment includes a $30 electric heater to keep the slurry warm, a camp stove
to burn the biogas, and perhaps a $100 garbage
disposer to facilitate grinding up food scraps for
feedstock (see Setting Up a Waste Management
System on page 240). Most of these parts are
available at plumbing supply houses and hardware stores. You can also find tank and barrel
connectors online at such places as Tank Depot
(see Resources). The thermostatically controlled
submersible heater is sold through livestock
supply stores or online at Jeffers Livestock (see
Resources). Be sure to prepare all materials and
test-fit before permanently fastening.
Tro u b l e s h oo t i n g Y o u r 5 - G a l l o n G e n e r a t or
If you’re making gas but it
won’t light after a week, try the
1.Remove the burner tube
from the Bunsen burner to
expose the gas nozzle. Open
the gas valve and try to
light the flame at the nozzle
orifice. The blue flame will
be very difficult to see in the
2.If the gas burns at the
nozzle but not at the end
of the burner tube, either
the nozzle orifice is too
small or the gas pressure is
either too high or too low.
Be sure there is sufficient
pressure in the balloon. Try
squeezing the balloon to
force the gas out, or closing
the gas valve to reduce the
pressure. Completely close
the burner’s air inlet.
3.A typical inflated balloon
may exert a pressure of about
10" water column (wc), about
what is needed to operate
a typical gas appliance, but
half what you will need with
an unmodified biogas burner.
Try enlarging the gas nozzle
orifice by drilling the hole
progressively larger in small
increments (0.5 mm or 1∕64").
After experimenting with
different burners and pressures,
I’ve found that a 2.5-mm nozzle
orifice with very little primary
air works well with a Bunsen
burner. A larger portable stove,
with a burner rating of 20,000
Btus, requires a 4–6-mm orifice.
Both burners work over a wide
pressure range, with the flame
energy increasing as gas pressure increases. Keep in mind
that my biogas is made primarily
from food scraps, but the gas
you make may be different and
require different burner settings.
If the gas still does not
burn, you may not be producing
methane yet, or there is a leak
in the gas line that is diluting the
gas with air. A leak anywhere in
the system can introduce oxygen
that will kill the methanogens,
causing your digester to go aerobic and produce only CO2.
2 56 B I OGAS
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M at e r i a l s
For Generator
For Gas Storage and Use
One 55-gallon screw-top barrel (for digester vessel)
One PVC toilet flange to fit over 3" PVC pipe
One 4-foot length 3" PVC pipe
Two 1-foot lengths 2" PVC pipe
Two 1/2" NPT bulkhead fittings (one is optional for
One 2" socket bulkhead fitting (for 2" PVC
Two 2" 90-degree PVC street elbows
One 2" PVC cleanout
One 3" PVC cap
PVC primer and solvent glue
Silicone caulk
Four machine bolts with washers and nuts (sized for
toilet flange mounting holes)
One 1/2" NPT male threaded x 1/2" O.D. (outside
diameter) hose barb fitting
One 1,000-watt submersible heater with thermostat
Insulation (see step 4)
One thermowell (optional; sized to match 1/2"
bulkhead fitting)
One dial thermometer with stem (optional; sized to
match thermowell)
Teflon tape
One 10-foot length 1/2" I.D. (inside diameter) flexible
plastic tubing
One PVC ball valve for 1/2" I.D. tubing
Four hose clamps for 1/2" tubing
One 55-gallon open-top, wide-mouth barrel (for gas
One 30-gallon open-top barrel (or other size,
as needed, to fit inside gas collection barrel)
One 1/2" NPT bulkhead fitting
One 1/2" NPT male threaded x 1/2" O.D. hose barb
One 10-foot length 1/2" I.D. flexible plastic tubing
One PVC ball valve for 1/2" I.D. tubing
Five hose clamps for 1/2" tubing
One single-burner propane camp stove
Adapters and hoses as needed to connect gas 1/2"
gas outlet hose to camp stove
Fine bronze wool
barrel lid
toilet flange
1. Install the effluent overflow
Drill a 2" hole through the side of the barrel,
about 6" down from the top. Install the 2" socket
(unthreaded) bulkhead fitting into the hole, making sure the joint is airtight. This fitting makes
the connection between 2" inch PVC pipes on
both the inside and outside of the barrel.
Solvent-glue a 90-degree street elbow to the
inside of the bulkhead fitting, pointing the elbow
3Digester vessel
with feeder
tube assembly
bolts and nuts
seal under flange
with caulk
3" PVC pipe
(feeder tube)
ma k e a b i ogas gener ator 257
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Make a Biogas Generator
Alternate Assemblyi
As an optional feature, you can also install a special thermometer assembly (designed for plumbing
applications) that uses a thermowell, a metal probe that projects into the barrel interior and accepts a
thermometer on its outside end. Install the thermowell using a 1/2" threaded bulkhead fitting, as with
the gas outlet, locating the fitting about one-third of the way up from the bottom of the barrel. Insert
the probe end of the thermometer inside the thermowell to complete the assembly. A long thermowell
will provide a better temperature indication.
toward the bottom of the barrel. Cut a piece of 2"
pipe to extend from the elbow down to about the
middle of the barrel. Glue the pipe to the elbow.
The bottom of this pipe must be above the bottom of the feeding tube. When the digester is
filled, the pipe must be covered by the slurry at
all times to prevent air from entering the barrel.
Glue another 90-degree street elbow to the
outside end of the bulkhead, pointing down. Add
a pipe to this elbow so it extends down to an
effluent collection bucket. Install the cleanout
onto the end of this pipe to help keep odors down.
As you load the barrel, the slurry will rise in the
interior pipe until it reaches the top of the elbows
and flows out, keeping the material inside the
barrel at a constant level.
2. Install the gas outlet.
Drill a hole into the lid to accept the threaded
male end of one of the 1/2" threaded bulkhead
fittings. Install the fitting onto the lid, securing
it on the bottom side of the lid with the provided
Gas outlet assembly 
Optional thermometer assembly4
nut. Make sure this joint creates an airtight seal
with the lid.
Wrap the threaded end of the 1/2" NPT x 1/2"
barb fitting with Teflon tape, and screw the fitting
into the top of the bulkhead fitting. Cut a 12"
piece from the 10-foot length of 1/2" plastic tubing, attach it to the barb fitting and secure with a
hose clamp. Connect the other end of this hose
to a ball valve and secure it with a hose clamp.
This valve can be used to isolate the digester
from the gas storage.
3. Install the feeder tube.
Cut a hole in the center of the barrel lid, sizing it
for a snug fit around the underside of the 3" toilet
flange. Test-fit the flange in the hole to confirm a
good fit. Mark and drill four holes through the lid for
mounting the flange to the lid with machine bolts.
Cut the feeder tube to length from 3" PVC
pipe. The length of the tube depends on how tall
the barrel is: The pipe runs through the toilet
2 58 B I OGAS
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flange and should extend several inches above
the lid at the top end to about 12" from the
bottom of the barrel when the lid assembly is
installed. (It’s important for the bottom of the tube
to be covered by the slurry inside the digester so
that no air gets in.)
Solvent-glue the pipe and flange together, following the glue manufacturer’s directions. Apply
silicone caulk liberally around the hole on the top
side of the lid, then insert the pipe and flange
through the lid. Secure the flange to the lid with
four machine bolts, washers, and nuts. Add more
caulk as needed around this joint to ensure that
it’s airtight. Let the caulk cure completely.
4. Insulate the barrel and add
the heater.
If you use a black barrel for the generator, it will
absorb solar heat, and some heat will be generated by the digesting process. Depending on
your location, there’s a good chance you’ll want
to insulate the barrel and have an additional heat
source to keep the slurry at around 100 to 105°F.
For my system (which lives in New England), I
insulated the barrel with black poly-covered foam
wrap designed for insulating beehives (see
Resources), but you can make your own similar
insulating wrap, if desired.
5Notch detail for submersible
pump cord
Don’t forget to insulate underneath the barrel to keep heat from conducting to the ground.
One approach is to set the barrel on top of a 2"thick piece of rigid foam insulation sandwiched in
between two pieces of plywood.
A submersible, thermostatically controlled
electric stock tank heater will help to ensure the
correct temperature. This setup requires about a
half kilowatt-hour of heat on a cloudy 70°F day,
but on a warm sunny day, the heater does not
come on at all.
To install the heater, simply set the unit on
the bottom of the barrel, and route the power
cord up and out through the feeder pipe. I cut a
little notch in the top edge of the pipe to slip the
cord through so that the cap can still slide over
the top of the 3" feeder pipe.
5. Load the digester.
Start your first batch by adding a 5-gallon bucketful of cow or pig manure (or other source of
anaerobic bacteria; see Feeding Your Biogas
Generator on page 241). Use more if you have
it. To this you can add a mixture of food scraps,
grass clippings, or any combination of organic
material that results in a C:N ratio of somewhere
between 20- and 30-to-1. Be sure the material is
chopped up well for best digestion and minimum
scum formation.
Fill the barrel about one-third to one-half full
with organic material, then cover it with an equal
amount of water so that the barrel is about twothirds to three-quarters full. Don’t worry about
getting this ratio exact. (You would produce a little bit of gas with only 5 gallons of organic material and 30 gallons of water, but this wouldn’t be
an efficient use of space inside the generator.)
For subsequent feedings, mix the chopped
material 50/50 with water and pour the slurry
into the feeder tube through a large funnel. Over
time, you can experiment with the ratio of solid
and liquid material to find the best mix for your
recipe. If necessary, use a stick as a plunger to
push the material all the way down and into the
barrel. When you’re not feeding the generator, fit
ma k e a bi ogas gener ator 259
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Make a Biogas Generator
the 3" PVC cap onto the end of the feeder pipe
to help keep odors in and air out.
6. Prepare the gas collection barrels.
When the gas collection system is in use, the
30-gallon barrel (the gas collection barrel) is
inverted into the larger, 55-gallon barrel (the water barrel) and receives the gas from the digester
by way of the gas outlet hose and a fitting installed on the bottom of the gas collection barrel.
As gas fills the collection barrel, the water in the
larger barrel creates a seal.
Drill a hole in the bottom of the gas collection barrel and install a 1/2" NPT bulkhead adapter
using the same procedure as before. Wrap Teflon
tape around the threaded end of the 1/2" NPT x
hose barb T-fitting and screw it into the bulkhead
adapter, hand-tightening it securely.
Begin filling the 55-gallon barrel with water.
When it’s nearly full, turn the gas collection barrel
upside down and push it down so that all of its
air escapes through the T-fitting.
7. Make the gas line connections.
Pour a few cups of water into the digester gas
outlet hose, and create a dip in the hose so that
the water stays at the bottom of this “trap.” The
water in the hose will act as flashback protection
for your digester should the gas in the gas collection barrel ignite. The tubing also lets you gauge
the gas production rate by observing bubbles
moving through the water.
Connect one end of the hose to the ball valve
on the digester’s gas outlet. Connect the other end
of the hose to one side of the T-fitting on the gas
collection barrel, securing it with a hose clamp.
Attach a 12" length of 1/2" tubing between
the other end of the gas outlet T-fitting, then to a
PVC ball valve. This valve controls gas flow to the
gas burner. Connect the remaining hose to the
other end of the ball valve, and finally to the gas
valve on the gas burner.
Before making the final connection to the
burner, tear off some bronze wool and pack it into
the gas hose to fill 3" to 4" of the hose. Pack it as
5Gas line connections at collection barrel
tightly as you can so as to still allow gas to flow
through it. Secure all hose connections with hose
clamps, keeping in mind that you need a tight seal
because the system will be under pressure.
8. Test the gas for flammability.
Over the next few days to a week, gas should
start to fill the gas barrel, and it will rise up out of
its water bath (be sure the gas inlet valve is open
and the gas outlet valve is closed). The first barrel full of gas produced will be primarily carbon
dioxide and will not burn. Simply open the gas
outlet valve and the weight of the barrel will
release the gas. After the oxygen in the digester
vessel is depleted, combustible gases will be
To safely test for flammability, sink the gas
outlet hose into a bucket of water. Push down
on the gas barrel until bubbles rise in the water.
Have a helper hold a lighter with a long handle
(such as a barbeque lighter with a long shaft)
over these bubbles as they pop: If this produces
a little flare, you know you’re producing biogas.
Give it a try in the burner!
2 6 0 B I OGAS
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Adjusting Gas Pressure
For best results, use a burner with an adjustable
air shutter to help control combustion. Natural and
propane gas burners require a pressure of about
10" of water column (wc), which is equivalent to
about 0.36 pounds per square inch (psi). It will
likely be necessary to increase the gas supply
pressure by bricking the inverted barrel until the
burner is working satisfactorily (see page 247).
feeding tube
gas line out
inverted barrel
immersed in water
gas out to burner
insulated digester
water-filled barrel
water in hose trap for
flashback prevention
Do not hold a flame directly to the outlet of the digester’s gas tube. With the right mixture of oxygen
and gas, a flashback could occur and the generator could explode. You are working with material that
is as flammable, as dangerous, and as useful as natural gas. Use common sense, caution, and the
proper safety gear.
ma k e a b i ogas gener ator 261
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Paul Scheckel’s Website
Chapter 1 —
Getting Ready for
Appropriate Development Solutions
Promoting renewable energy in developing
Database of State Incentives for Renewables &
U.S. Department of Energy
Del City
Cable, connectors, fuses, and wiring supplies
Global Exchange
Home Energy Magazine
Home Power Magazine
The Power of Community — How Cuba Survived
Peak Oil
Arthur Morgan Institute for Community Solutions
Solar Energy International
Tax Incentives Assistance Project
Websites by Chapter
Chapter 2 —
Do Your Own
Energy Audit
Air Conditioning Contractors of America
Air-Conditioning, Heating, and Refrigeration
Allergy Control Products
Allersearch and De-Mite products
BITS Limited
Smart Strip Surge Protector
Building Performance Institute, Inc.
Technical standards and certified contractors
in the Home Performance with ENERGY STAR
G. E. Kerr Companies, Inc.
Carbon monoxide alarms
Efficiency First
P3 International Corporation
Kill A Watt Power Monitors
Residential Energy Services Network
Technical standards and certified contractors in
the ENERGY STAR for New Homes program
BackyardEnergy_Final_Pages.indd 262
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ThinkTank Energy Products Inc.
Watts Up? meters
Additional Resources
Advanced Energy Panels
Windo-Therm, LLC
Removable storm window panels
Battic Door Home Energy Conservation
Chimney balloon draft stopper
Energy Circle, LLC
Energy Federation Incorporated
Gordon's Window Decor, Inc.
Greenhouse Gas Emissions
U. S. Environmental Protection Agency
Information on greenhouse gases
Chapter 3 —
Insulating Your Home
Aspen Aerogels, Inc.
BuildingGreen, Inc.
Publishers of Environmental Building News
Commercial Thermal Solutions, Inc.
Tiger Foam Insulation
Cool Roof Rating Council
Energy Federation Incorporated
EnviroHomes Ltd.
VacuPor Vacuum Insulation Panels
Green Building Advisor
Taunton Press, Inc.
Intergovernmental Panel on Climate Change
Guardian Energy Technologies, Inc.
Foam It Green Spray Foam Insulation Kits
Niagra Conservation
Louisiana-Pacific Corporation
Shelter Analytics LLC
Bret Hamilton and Paul Scheckel
Additional Resources
Building Envelopes Program
Oak Ridge National Laboratory
Handbooks and fact sheets
resources 263
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Provides a Thermal Bypass Checklist Guide
(home insulation and air-sealing training material); enter Thermal Bypass Checklist Guide
into the search bar tool
The Home Energy Diet
Written by Paul Scheckel. New Society Publishers, 2005.
Open Sash
Window retrofits
University of Bath
United Kingdom study of embodied energy in
building materials: Inventory of Carbon & Energy
(ICE) database
U.S. Department of Energy
Various topics on energy and efficiency
Chapter 4 —
Deep Energy Retrofits
National Fenestration Rating Council
New York State Energy Research and
Development Authority
Passive House Institute US
RenewABILITY Energy, Inc.
Power-Pipe, drain water heat recovery system
Swing-Green, LLC
Green Fox, drain water heat recovery system
Tremco Commercial Sealants & Waterproofing
Additional Resources
Building America, Building Technologies
U.S. Department of Energy
Alliance for Low-E Storm Windows
Building Science Corporation
Performs high-level work on high-efficiency buildings; site includes publications for download
Benjamin Obdyke, Inc.
BuildingGreen, Inc.
Publishers of Environmental Building News
Davis Energy Group Inc.
Fine Homebuilding Magazine
Taunton Press
Dow Chemical Company
Perimate insulation
Green Building Advisor
Information on building energy and green building
Efficient Windows Collaborative
Health House
American Lung Association
Grace Construction Products
2 6 4 R ES OU R C ES
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Home Ventilating Institute
Ventilation products, information, and ratings
Navien America, Inc.
On-demand water heaters
Passive House Institute US
Source for new homes; exemplary standards for
efficiency and durability
NRG Systems, Inc.
Data logger
Omega Engineering, Inc.
In-line water meter
Chapter 5 —
Home Energy Monitoring
Onset Computer Corporation
APRS World, Inc.
Microcontroller platform
OutBack Power Technologies, Inc.
BizEE Software Limited
Degree Days
Blue Line Innovations
Power Cost Monitor
Campbell Scientific, Inc.
Efergy Technologies Limited
The Energy Detective
Horizon Fuel Cell Technologies
Hotwatt, Inc.
P3 International Corporation
Plot Watt
Powerhouse Dynamics
PowerWise Systems
RainWise, Inc.
Serious Energy, Inc.
Serious Energy Manager software
Intellergy, Inc.
SmartLabs, Inc.
Pulse-enabled gas meter
ThinkTank Energy Products Inc.
Watts Up? meters
resources 265
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Water Heater Innovations, Inc.
Rheem Manufacturing Company
Marathon water heaters
Solar Rating & Certification Corporation
W.W. Grainger, Inc.
Weather Underground, Inc.
Web Energy Logger
ZigBee Alliance
Wireless communication standard
Chapter 6 —
Solar Hot Water
American Solar Energy Society
Armacell Enterprises GmbH
Community Hydro, LLC
Florida Solar Energy Center
Industrial supply retailer
National Renewable Energy Laboratory
Home of the Renewable Resource Data Center,
as well as analysis tools and maps
Solar Radiation Data Manual for Flat-Plate and
Concentrating Collectors.
Written by William Marion and Stephen Wilcox.
National Renewable Energy Laboratory, 1994.
Solar radiation data
Chapter 7 —
Solar Electric
Array Technologies, Inc.
Solar tracking racks
Dow Chemical Company
Solar shingles
DPW Solar
Preformed Line Products
PV array mounting systems and information
In My Backyard Tool
National Renewable Energy Laboratory
Solar power estimator
National Climate Data Center
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National Geophysical Data Center
National Oceanic and Atmospheric Administration
Geomagnetic map
National Renewable Energy Laboratory
Home of the Renewable Resource Data Center
and the In My Backyard solar and wind power
Shelter Analytics
Energy improvement analysis tool
Solar Pathfinder
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Solmetric, Inc.
Zomeworks Corporation
Solar tracking racks
Additional Resource
Solar Energy International
Classes on solar and wind energy
Chapter 8 —
Wind Electric
American Wind Energy Association
Bergey WindPower Co.
Wind generators
Blow by Blow: Our Best-ever Guide to Home-scale
Wind Turbines
Home Power Magazine
June/July 2010 issue, #137
Cable and Wire Shop
Chance Civil Construction
Anchors and tools
Distributed Wind Site Analysis Tool
The Cadmus Group, Inc.
Hubbell Power Systems
Anchors and design guide resources, LLC
Wind measurement and data loggers
Kestrel Wind Turbines
Kingspan Renewables Ltd.
Proven wind generators
Loos & Company, Inc.
National Climatic Data Center
National Oceanic and Atmospheric Administration
NRG Systems, Inc.
Wind towers, measurement, and data loggers
ROHN Products, LLC
Rohn towers, parts, engineering, and design
Sabre Industries, Inc.
Tower parts
Small Wind Certification Council
Talco Electronics
Tower parts
Wind Energy Resource Atlas of the United States
Written by D. L. Elliott, C. G. Holladay,
W. R. Barchet, H. P. Foote, and W. F. Sandusky,
National Renewable Energy Laboratory
Wind Powering America
U.S. Department of Energy
Ian Woofenden
Home Power Magazine
resources 267
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Additional Resources
Additional Resources
Antenna Systems
Guy wire for towers
Clean Water Act, Section 401 Certification
United States Environmental Protection Agency
Water Quality Certificate
Solar Energy International
Classes on wind energy
Paul Gipe’s wind website
Chapter 9 —
Hydro Electric
Alternative Power & Machine
Hydroelectric systems
Ampair Energy Ltd.
Canyon Hydro
Hydroelectric systems
Energy Systems & Design
Hydroelectric systems
Harris Hydroelectric
Hydroscreen, LLC
Debris screens
Hydroelectric systems
Small Hydropower & Micro Hydropower
Small hydro resource site
Federal Hydro Licensing
Federal Energy Regulatory Commission
U.S. Geological Survey
U.S. Army Corps of Engineers
Water Measurement Manual, revised ed.
United States Department of the Interior, Water
Resources Research Laboratory, 2001.
Chapter 10 —
Renewable Electricity
Del City
National Fire Protection Association
NFPA 70: National Electrical Code
Inverters, chargers, controllers,
and monitors
Apollo Solar, Inc.
Blue Sky Energy, Inc.
Bogart Engineering
Tri-Metric power system monitor
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Fronius International GmbH
MidNite Solar
Morningstar Corporation
OutBack Power Technologies, Inc.
Additional Resources
Delta Lightning Arrestors
Mapawatt Blog
Zephyr Industries, Inc.
Battery box vent
SMA Solar Technology
Solectria Renewables
Specialty Concepts, Inc. (SCI)
Xantrex Technology, Inc.
Kohler Co.
Northern Lights, Inc.
Chapter 11 —
Biodiesel: Do-it-yourself Production Basics
National Sustainable Agriculture Information
Written by Rich Dana. NCAT, rev. ed. 2012.
Biodiesel Fuel Education Program
University of Idaho
Conney Safety Products
Frey Scientific
Jeffers, Inc.
East Penn Manufacturing Company, Inc.
Deka batteries
Journey to Forever
Interstate Battery System of America, Inc.
Kitchen Biodiesel
Biodiesel books, resources, how-to
Rolls Battery Engineering
Surrette Battery Manufacturing
Trojan Battery Company
Biodiesel books, resources, how-to
resources 269
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Pump Solutions Group
Drum mixers
Northern Tool + Equipment Catalog Co.
Oilseed Processing for Small-Scale Producers
National Sustainable Agriculture Information
Written by Matt Rudolf. NCAT, 2008.
United States Plastic Corporation
W. W. Grainger, Inc.
SVO Conversion Kits
Alternative Technology Group GmbH
Frybrid Diesel/Vegetable Oil
Greasecar Vegetable Fuel Systems
Alternative Technology Group GmbH
Five Star Manufacturing
Biodiesel Kits and Supplies
B100 Supply
Biodiesel parts and supplies
Diesel Toys, LLC
Ever Green Recovered Energy Distribution, Inc.
Utah Biodiesel Supply
Additional Resources
Alternative Fuels Data Center
U.S. Department of Energy
ASTM International
Biodiesel Emissions Analyses Program
United States Environmental Protection Agency
Biodiesel Handling and Use Guide, 4th ed.
Prepared by the National Renewable Energy
Laboratory, 2009.
Fuel Economy Guide
U.S. Department of Energy
Learn about auto fuel economy and tax incentives
for all vehicles
National Biodiesel Board
Vehicle Technologies Program
U.S. Department of Energy
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Chapter 12 —
Wood Gas
Low-tech Magazine
All Power Labs
Gasifier Experimenters Kit
Mother Earth News
Aprovecho Research Center
Biochar Activity Kit
Greater Democracy
Biochar information
BioEnergy Discussion Lists
G. E. Kerr Companies, Inc.
Global Alliance for Clean Cook stoves
ProTech Safety
Slower Traffic Keep Right
Spenton LLC
Victory Gasworks
Additional Resources
Biomass Energy Foundation
Chapter 13 —
B and B Honey Farm
Colony Quilt, an insulating beehive wrap
Bread from Stones
Jeffers, Inc.
Thermostatically controlled submersible heater
(product #W-449)
On-Farm Composting Handbook
Cornell Waste Management Institute
Published by NRAES, 1992.
Tank Depot
Tank and barrel connectors
United Nations Development Programme
Biogas Books and Articles
“3-Cubic Meter Biogas Plant: A Construction
Published by Volunteers in Technical Assistance.
Available for download from various sources
Food and Agriculture Organization of the United
“Wood Gas as Engine Fuel,” 1986 ;
enter “woodgas” in the search bar
resources 27 1
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Biogas Books and Articles continued
Additional Resources
A Chinese Biogas Manual
Journey to Forever
Edited by Arian van Buren. Intermediate Technology Publications, 1979.
AgSTAR Program
U.S. Environmental Protection Agency
The Complete Biogas Handbook
Written by David House. Alternative House Information, 2010.
Handbook of Biogas Utilization, 2nd ed.
General Bioenergy
Written by Charles C. Ross and T. J. Drake III.
Environmental Treatment Systems, 1996.
Beginners Guide to Biogas
University of Adelaide
“Methanol Recovery: Dickinson College
Dickinson College
Methanol recovery presentation by Matt Steiman.
"Methane Recovery from Animal Manures: The
Current Opportunities Casebook”
ManureNet, Conservation Ontario
Written by P. Lusk. National Renewable Energy
Laboratory, 1998.
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Conversion Charts
Unless you have finely calibrated measuring equipment, conversions between U.S. and metric
measurements will be somewhat inexact. It’s important to convert the measurements for all of the
ingredients in a recipe to maintain the same proportions as the original.
General Formula for Metric Conversion
Ounces to gramsmultiply ounces by 28.35
Grams to ouncesmultiply grams by 0.035
Pounds to gramsmultiply pounds by 453.5
Pounds to kilograms
multiply pounds by 0.45
Cups to litersmultiply cups by 0.24
Fahrenheit to Celsius
subtract 32 from Fahrenheit temperature, multiply by 5, then divide by 9
Celsius to Fahrenheit
multiply Celsius temperature by 9, divide by 5, then add 32
Approximate Equivalents
by Volume
Approximate Equivalents by Weight
7 grams
14 grams
35 grams
40 grams
2 /2ounces
70 grams
280 grams
4 cups (1 quart)
0.95 liter
425 grams
1 liter
454 grams
1.06 quarts
4 quarts (1 gallon) 3.8 liters
(1 pound)
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italic = illustration bold = chart
American Wind Energy Association, 142
amperes, defined, 35
anaerobic digestion (AD), 231–33, 237, 241, 249–50
anchors for wind towers, 152–53, 153
AC vs. DC, 28, 124, 176
anemometer, recording, 143
hydroelectric power, 160, 171
annual fuel utilization efficiency (AFUE), 49
wind electric generation, 138
anode rod replacement, 47–48, 48
acetogenesis, 233
Apollo Solar, 180
acid rain, 18, 194
acidogenesis, 233
auditing and monitoring electrical use, 38–41,
active solar hot water system, 107, 107–8
air conditioning systems, 25
combustion, 89, 89
air ducts, sealing, 49–50, 50
controlling humidity, 91
power rating, 40
deep energy retrofits, 92–93
replacing older models, 10–11, 20, 45, 48, 55
energy audit, 37, 39, 40, 48–51
standby loads, 24, 41, 55
evaporative coolers, 93
Aprovecho Research Center, 225
ground coupling system, 93
APRS World, 98
peak demand, 130
aquastat, adjusting temperature, 46, 46
refrigerant charge, 57
Arduino microcontroller platform, 99
window leaks, 87–88
Armaflex, 112
air leakage, 48–49
arrays for solar electric generation, 123–24, 127,
129–31, 134, 189
around chimneys, 64, 72–73
common paths for, 73
asthma, 11, 18, 191
how heat moves, 61
ASTM standards, 201
infrared camera detection, 53, 53
insulation, 64–65, 71–73
chimneys, 64
roofs and ice dams, 76
exhaust fans venting to attic, 63
stack effect, 56, 56
hatch panel insulation, 73, 73
thermal envelope, 52–54, 87–88
insulation inspection, 63–64
walls, 82–84
venting, 75
windows, 54–56, 86–87
automobiles. See cars
air-source heating system, 92, 92–93
All Power Labs, 217, 226
Allersearch cold water detergent, 45
Alliance for Low-E Storm Windows, 85
alternating current (AC). See AC vs. DC
American Society for Testing and Materials (ASTM),
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Betz limit, 144
Bicycle-Powered Battery Charger, 29–35
bicycle-powered generator, 25, 28
Bidgely home energy monitoring, 97
B100, 194–95, 204, 270
bin data, 140
B20 mix, 204
biochar, 217–18
backdrafting, 89–91
Biochar Activity Kit, 218
balloon framing, 77
biodiesel, 192–214
Barg, Lori
Homemade Hot Water, 116–18
base load energy use, 37–40
sample of household electricity usage, 39
basic process for making, 200–201
benefits, 194–95
Calamari Cruiser, 193, 200
collecting waste grease, 193, 196, 200
base-catalyzed production method (biodiesel), 194
definition and terms, 194
basements and foundations
drawbacks, 195
cross-section of basement wall, 82
environmental care, 205
drainage, 82
equipment needs, 196–98, 197–98
insulation, 65–66, 65–66
essential ingredients, 195–96
moisture, 80–84
esters, 200, 202
batch generator, biogas, 244–45, 245
filtering, 198
lab ware, 198, 198
12-volt battery charge profile, 187
lye as catalyst, 193–94, 196, 198–99, 203
battery box basics, 188, 188
methanol, 196–200, 204–5
bicycle-powered charger, 28–29, 35
mixing a batch of biodiesel, 213–14
charge profile, 185–87
mixing tank and motor, 197, 197
charging, 180–83, 181
mixing with other fuels, 204
electric car, 16
pumping, 196–97
electrical wiring, 178–79
quality and standards, 201
hydroelectric generation, 160, 171–72
safety, 199, 199–200
My Hot Water Heating Story, 101–3
soy mileage, 194
rating and type, 183–84
storage, 198
safety, 187, 189
test batch with new vegetable oil, 201–2
sizing your battery bank, 184–85
test batch with used vegetable oil, 203
solar electric system, 22, 128–29, 133–36
testing the mix, 202
system backup, 175, 175–76, 189
titration, 198, 200, 203, 210, 213
testing using specific gravity, 187
Veggie Oil Conversion, 206–8
vented battery box, 188
wind electric system, 147, 156, 157
battery chargers, 186–87
12-volt battery charge profile, 187
bicycle-powered, 29–35
washing biodiesel, 204–5
Biodiesel Kit, 209–14
assembling the kit, 211
mixing a batch of biodiesel, 213
biogas, 231–61
inverters, 180, 180
brown vs. green ratios, 235
micro-hydropower systems, 160
burners, 248, 248
off-grid power systems, 182, 182
calculating VS and gas production, 243
wind-electric generation, 137–38
carbon and nitrogen ratios, 235–36
batts and blankets (insulation), 68–69, 69, 72, 77
cow poop and gas generation, 249
Beaufort scale, 143
effluent, 232, 242, 245–26
Bergey wind generators, 149
environmental care, 250
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feeding your generator, 241
flame arrestor, 247
how biodiesel works, 8, 232–33, 232–34
inoculation, 241
loading rate, 243
methane (CH4), 231–34, 237, 248, 249–50, 256
Cable and Wire Shop, 150
Calamari Cruiser, 193, 200
methane generators, types, 244–46, 245–46
Campbell Scientific, 98
orifice diameter multiplier (for gas appliances), 248
carbon dioxide (CO2), 18
purifying, 250
biochar, 218
raw materials, 238–39
biogas, 232–33, 250
recipe evaluation: volatile solids, 243
CO2 emissions of various energy sources, 58
recipe for making gas, 234–36, 236
monitoring, 98
retention and loading, 242–44
ventilation control, 88, 91
safety, 247–48
wood gas generators, 216, 220, 225
slurry, 232, 240, 241, 245, 245, 254–59
carbon dioxide equivalency (CO2e), 18
solids, liquids, and volatile solids, 236–37
carbon equivalency (Ce), 18
storing, 247, 248
carbon footprint, 10–11, 18, 58
temperature, 241–42
carbon monoxide, 49, 57, 89
using, 246–48
biodiesel emissions, 194
variables, 234
wood gas generators, 216, 219–25
waste management, 240
Biogas Generator
cars. See also diesel
carbon footprint of, 58
5-gallon batch generator, 253–56
collecting waste oil, 193, 209
55-gallon batch generator, 256–61
converting from gasoline to electric, 16
adjusting gas pressure, 261
modifying gasoline engines, 249
completed 55-gallon generator, 261
with onboard gasifiers, 215
Biogas Is More than a Gas, 251–52
catalyst/lye (biodiesel), 196
blower door, 52–53, 53, 55–56, 88
cellulose insulation, 68, 68, 70–71, 83
Blue Sky Energy, 180
Chance anchors, 152
bottled gas, 98
charge controller, 101–2, 180–81, 181, 189
Bread from Stones, 252
battery box basics, 188
breaker boxes and service panels, 38, 38
PV system wiring, 128–30
British thermal unit (Btu), 20–21
wind electric generation, 148, 156
calculating Btus for solar hot water, 114–15
chase within walls, 23
defined, 20, 177
chimney effect, 91
fuel energy content, 57
bucket measure, 163
backdrafting, 89–90
Building Performance Institute, 57
heating system, 49–50
building wrap, 73–74, 83
insulation around, 64, 72–73
Building Green, Inc., 68
potential air leakage, 64
burners, biogas, 248, 248
wood stove, 21
circuit-level electrical monitoring, 97, 97
CO Experts, 225
CO2 emissions of various energy sources, 58
coefficient of performance (COP), 94
solar, 20, 22
solar hot water, 101, 107–15
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combiner box, 129–30, 181
basement, 82
combustion process of wood gas, 216, 216
minimum performance levels, 80
combustion water heater, 89–91, 101
overview, 79, 79–80
Community Hydro, 116
team planning, 80–81
concrete forms, insulated (ICF), 66
windows, 84–87
deep-cycle duty, 183, 185
resistance (CR), 86
Degree Days, 100
the effects of, 66
Deka batteries, 184
condensing water heaters, 94
Del City Wire, 178
conduction of heat, 60
Delta lightning protection, 182
continuous-flow generator, biogas, 245, 245
descaling or de-liming water heater, 47
controller for solar hot water, 113, 113
design flow, 163
convection of heat, 60
Dier III, Hilton
and human health, 225
Veggie Oil Conversion, 206–8
gas stove, 90
backup generator, 101
gasifier cook stove, 217, 217, 218, 225
CO2 emissions, 58
simple wood gas cook stove, 229–30, 229–30
dual fuel system for a diesel vehicle, 207
wood stove, 21
fuel replaced by biogas, 249
Cool Roof Rating Council, 61
fuel replaced by SVO, 194–95, 206–8
cow poop and gas generation, 249
fuel replaced by wood gas, 221–22, 226
cross-sectional flow measure, 164
gasifier system to produce gas, 222
crossdraft gasifier, 224, 224
Diesel, Rudolf, 192
crossflow turbines, 170, 170
Diesel-Therm, 197
Cuba’s energy program, 26–27
differential temperature controller, 113, 113
curtain walls, 84, 84
digestate for biogas, 232
cut-in speed, 140
direct current (DC). See DC vs. AC
cyclone separator, 220–21, 221–22
distributed generation, 175
Distributed Wind Site Analysis Tool, 143
diversion or dump load, 181, 181–82
hydroelectric, 159–61, 163, 166
ice dams, 51, 76, 76, 87
Dow Solar Shingles, 134
downdraft gasifier, 224, 224
drain water heat recovery system (DWHR), 94, 94, 101
drainback systems, 108
dual fuel system for a diesel vehicle, 207
ductwork sealing, 50, 50
Dunham, John
Two Men and a Truck, 226
Database of State Incentives for Renewable Energy,
DC vs. AC, 28, 124, 176
hydroelectric power, 160, 171
wind electric generation, 138
De-Mite cold water detergent, 45
debris screen, 166, 188, 212
deep energy retrofit (DER), 78–94
above-grade walls, 82–84
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electrical wiring, 177–79
Efficient Windows Collaborative, 85
effluent, biogas, 232, 242, 245–26
wire size and ampacity chart, 179
wire sizing, 178
electricity. See also renewable electricity management
Farm Innovators, 197
Federal Energy Regulatory Commission, 169
biogas, 232, 234, 243
wood gas, 218
fiberglass insulation, 54, 64, 68, 68–70, 70,
breaker boxes and service panels, 38, 38
energy audit, 38–41
73, 73, 77
grid-tied systems, 22, 128, 147
biodiesel, 194–95, 197–98, 206–8
monitoring home energy, 96–97, 96–97
furnace, 50
sample of household electricity usage, 39
penstock intake, 166
Energy Action in Cuba, 26–27
energy audit, 36–58
wood gas, 216–17, 220–22, 226–28
fixed and tracking racks, comparison, 133
“AAA” approach to savings, 37–38
fixed solids (FS), 237
electricity, 38–41
flame arrestor, biogas, 247
heating and air conditioning, 48–51
flash point, 199
hot water, 42–48
flat plate heat exchanger, 108, 108
prioritizing improvements, 55–57
flat-plate solar collector, 109, 109
thermal envelope, 51–54
flow rates for hot water, 42–44, 43
tools for, 37
flue draft, 89, 89
windows, 54–55
fluid vs. fixed bed (gasifier), 220
energy auditor, 37, 49, 52, 55–57, 63, 65
Energy Detective, The, 96–97, 97
biodiesel fuel tank, 195, 208
Energy Federation Incorporated, 71
hot water heater, 42, 45, 47
energy profit ratio (EPR), 12
Foam It Green spray foam insulation kits, 71
ENERGY STAR appliances, 24, 40
energy view-shed, 18
energy audit questions, 51–52
enthalpy recovery ventilator (ERV), 91–92
deep energy retrofits, 82-83, 88
Environmental Building News, 68
for solar panels, 131-33
environmental impacts of wood gas, 225
for wind towers, 149, 151-52
environmental monitoring, 98–100
Environmental Protection Agency, U. S., 58, 162, 169,
insulation, 62, 65-67, 73, 79
Frey Scientific, 198, 210
friction loss, 167–68, 168
ETI lightning protection, 182
Fronius, 180
evacuated tube solar collector, 109–110, 110
fuel energy content, 57
evaporative coolers, 93
Exeltech, 180
air ducts, sealing, 49–50, 50
exhaust fans, 90–91
electrical usage, 38, 39, 41
attic exhaust, 75
improving efficiency, 50
blower door, 53–54
types of, 92, 92
stack effect, 56, 56
venting to an attic, 63
expansion tank for solar hot water, 112–113
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heating systems, 92
monitoring, 98
habits and readiness tips, 23–25, 41
Hamilton, Bret
When “High Performance” Doesn’t Perform, 77
stove, ventilation, 90
Harris Hydro, 170
water heater, 46
hatch panel insulation, 73, 73
gasifiers. See also wood gas
cook stoves, 217, 217
Hazen-Williams equation, 167–68
friction loss, 168
four stages of gasification, 218–19
heat exchangers, 108, 108
schematic of gasifier truck, 227
heat pumps, 92–93, 94
system to produce gas for an engine, 222
heating degree day (HDD), 99
types of, 224, 224
heating systems
gel point, 195
air ducts, sealing, 49–50, 50
gin poles for wind towers installation, 150–51,
air-source system, 92, 92–93
choosing a system, 92–93
Global Alliance for Clean Cook stoves, 225
combustion analysis, 49
Global Exchange, 27
efficiency and expense, 49
glycerin (in biodiesel), 193–94, 196–97, 200–205
energy audit, 48–51
Grainger industrial supply, 119, 199
flue draft check, 49
Green Building Advisor, 68
furnaces and boilers, 92, 92
greenhouse gases (GHG), 18, 58, 218
heat pumps, 92–93
heating with wood, 21
grid-tied wind generators, 147
off the grid, 19–20, 102, 116, 136, 146, 157–58
short cycling, 48–49
wood-burning, 21
off-grid room, 9, 176
Home Energy magazine, 25
off-grid vs. grid-tied, 130, 137–38, 171–72, 175,
Home Power magazine, 25, 129, 139, 151, 157
179, 182
off-grid wind system, 156
Homemade Hot Water, 116–18
circulation diagram, 118
on- and off-grid solar electric systems, 128
Horizon Technology, 143
smart grid, 95–96
hot water. See also solar hot water
Griggs-Putnam Index of Deformity, 143, 143
adjusting the thermostat, 45–46
grip hoist, 150, 150
anode rod inspections, 47–48, 48
gross head, 162
efficiency, 44–45
ground coupling cooling system, 93
electric water heater element, 45
ground rack for PV panels, 132
energy audit, 42–48
ground source heat pump, 17
Energy Factor (EF), 44
ground-fault circuit interrupter (GFCI), 199, 210, 213
flue draft, 89, 89–90
flushing the water heater, 47
gas water heater, 46
high-efficiency options, 94
in-line mixing valves, 43, 43
low-flow shower head, 42, 42
measuring flow rates, 42–44, 43
oil and indirect-fired, 46
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reducing water used, 45
sealed combustion water heater, 89–91, 101
smart plumbing, 94
used in a shower, 44, 44
Hot Water Heating Story, My, 101–3
HotWatt, 102, 181
House, David
Biogas Is More than a Gas, 251–52
ice dams, 51, 76, 76, 87
improvements, prioritizing, 55
impulse turbines, 170, 170
in-line mixing valves, 43, 43
Hubbell Power Systems, 152
incentives, government, 25
humidity control, 11, 24–25
indirect solar hot water system, 107–8
air conditioning, 49, 93
indirect ICS, 110, 110
basement, 82
schematic, 113
relative humidity (RH), 53
working fluids, 112
space conditioning, 48–49
infrared camera for insulation check, 53, 53
ventilation, 53–54, 88, 91
inoculation (biogas), 241
hybrid generator, biogas, 246, 246
Inspeed wind measurement, 143
hybrid grid-tied PV system, 175
insulated concrete forms (ICF), 66
hydraulic retention time (HRT), 242
insulation, 59–77
hydroelectric generation, 159–73
attic, 63–64
estimating power, 165–66
basements and foundations, 65–66, 65–66
flow calculations, 160, 162–63
batts and blankets, 68–69, 69, 72, 77
friction loss, 168
cellulose, 68, 68, 70–71, 83
head calculations, 160–62, 162
choosing the right product, 67–68
intake site selection, 166, 166
damp-sprayed, 70
location, 160, 160
dense-pack, 70
maintenance checklist, 173
fiberglass, 54, 64, 68, 68–70, 70, 73, 73, 77
measuring flow, 163–65
how heat moves, 60–61
measuring velocity, 165, 165
how much you need, 66–67
micro-hydro systems, 20, 159–61, 167, 169,
insulation contact (IC-rated), 64
penstock (pipeline), 160, 160–62, 166, 166–69,
172, 173
loose-fill, 68–70, 70
measuring value, 62–63
mineral wool, 68, 68, 70
power generators, 171–72
options, 68, 68
power station in Cuba, 27
rigid foam board, 63–65, 65, 71–73, 72–73, 82,
powerhouse design, 172
82–84, 84, 88
reservoir, 159–60, 160, 163, 166
spray foam, 68, 70–71, 77, 82–84
rough power estimation, 165–66
U-factor and R-value, 62, 68
runners, 160, 169–73, 170, 173
upgrading, 67
system efficiency, 172, 173
vapor barrier, 69, 82
turbines, 169–71
walls, above-grade options, 82–84
HydroGap, 83
walls, how to check, 64–65
hydrolysis, 233
where you need it, 62, 62
hydropower system component efficiencies, 173
integrated collector storage (ICS), 110, 110
Intellergy, 98–99, 99
Interstate batteries, 184
bicycle power, 28–30, 34–35
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hydroelectric generation, 160
Living with Solar (and Wind) Power, 135–36
PV systems, 10, 124, 129–30, 131, 175
loading rate, 243
renewable electricity management, 176, 179–80,
Loos & Company, 154
180, 182, 189
wind electric generation, 147, 156
Itron gas meter, 98, 102
loose-fill insulation, 68–70, 70
low-E windows, 61, 86
low-flow shower head, 42, 42
lye as catalyst for biodiesel, 193–94, 196, 198–99
lye quantity table, 203
Jeffers Livestock, 197, 210, 256
make-up air, 56
Kaiser, Chris
Mapping Motivations . . . and Watts, 190
Kestrel turbines, 135, 141, 144–46, 267
map, solar power estimation, 127
Mapping Motivations . . . and Watts, 190–91
Marathon water heaters, 102
material safety data sheet (MSDS), 199
maximum power point tracking (MPPT), 180
McMaster-Carr, 119, 207
mesophilic methanogens, 241
Kill A Watt meters, 40, 96
gas, 98
kilowatt-hours (kWh), 10
monitoring electricity, 96
battery charging, 184–85
bicycle generator, 25
reading, 24, 52
methane (CH4), 58, 219
household electrical usage, 38, 39, 39, 40
biogas basics, 231–34
planning for a PV system, 125–27, 133, 133
biogas production, 237
power equivalents, 26
cow poop and gas production, 249
sizing solar collectors, 114–15
environmental care, 250
solar power generation, 135–36
feeding your biogas generator, 241
Kingspan wind products, 138
generators, 242, 244–46
Kohler, 182
orifice diameter multiplier (for gas appliances), 248
safety, 247
wood gas composition, 220
laundry, 41, 44–45, 157
lead paint, 80–81
light bulbs, 12, 25, 177
replacing with LEDs or flourescent, 40
lightning protection, 134, 156, 178, 181–82
methanogenesis, 233–34, 244
methanogens, 231, 233–34, 241–42, 244, 249
groups by temperature, 241–42
methanol. See also biodiesel
defined, 196
flammability and safety, 197–200
washing biodiesel, 204–5
micro-hydro systems, 20, 159–61, 167, 169–72
components and layout, 169
microwave, 41
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Midnight Solar, 180
mineral wool insulation, 68, 68, 70
mixing valves, in-line, 43
attic, 63
basement, 80–84
effects of condensation, 66
stopping, 72–75
off the grid, 19–20, 102, 116, 136, 146, 157–58
off-grid room, 9, 176
off-grid vs. grid-tied, 130, 137–38, 171–72, 175, 179,
thermal envelope energy audit, 51–54, 57
off-grid wind system, 156
vapor barriers, 69
ohms, defined, 35
ventilation control, 91
Omega Engineering in-line water meter, 98, 102
monitoring, home energy, 95–100
on- and off-grid solar electric systems, 128
electricity, 96–97
on-demand water heaters, 94, 101, 112
environmental, 98–100
On-Farm Composting Handbook, 239
gas, 98
Onset Computer Corporation, 98
heating energy, 99–100
OpenEnergyMonitor, 99
mono alkyl ester, 194
orientation tuning, 86–87, 87
Morningstar, 180
oriented strand board, 83
Mother Earth News, 226
orifice diameter multiplier (for gas appliances), 248
Outback Power charge controller, 101, 180
National Climate Data Center, 125
National Electric Code (NEC), 177
National Fenestration Rating Council, 85
National Fire Protection Association, 177
National Renewable Energy Laboratory, 114, 125, 143
outdoor wood boilers, 21, 21
oxidize, 216
Passive House Institute U. S., 93
passive solar hot water system, 107, 107
Navien on-demand water heaters, 101
payback calculation, 9–10, 42
Neptune Chemical Pump Company, 198
peak sun hours, 125, 130–31, 135
net metering, 175
pellet stoves, 21, 93
New York State Energy Research and Development
pellets for wood gas generators, 216, 220, 229
Authority, 79
penstock (pipeline), 160, 160–62, 173
NightBreeze, 93
hydropower system component efficiencies, 173
Northern Lights, 182
micro-hydro system components and layout, 169
Northern Tool and Equipment, 197, 210
pipe maintenance, 168
NRG Systems, 101, 143, 149
selection/design, 166–67, 166–69
Perimate insulation, 82
pilot lights, 24, 41, 47, 225, 998
planning for renewables, 22
Plot Watt home energy monitoring, 97
plug-in electric meters, 96, 96
hot water heaters, 94
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solar hot water heaters, 112
pole mount for PV panels, 132
PolyDome, 197, 209–10, 212
pool heaters, solar, 111, 111
Power Cost Monitor, 96–97, 97
Power of Community, The — How Cuba Survived Peak
Oil, 27
power strips, 24–25, 38, 41
that monitor electricity, 96
R-value, 62–63
insulation comparisons, 68, 68–70
recommended insulation values, 67
windows, 85–86
radiant barrier, 61, 61
Powerhouse Dynamics eMonitor, 101
radiation of heat, 60–61
pressure relief valve (hot water), 43, 113, 118
Rainwise, 98
Pro-Tech Safety, 225
rated annual energy, 142
raw materials for biogas, 238–39
Biogas Is More than a Gas, 251–52
reaction turbines, 171, 171
Energy Action in Cuba, 26–27
recording anemometer, 143
Homemade Hot Water, 116–18
rectifier, 176
Living with Solar (and Wind) Power, 135–36
relative humidity (RH), 53
Mapping Motivations . . . and Watts, 190–91
remote control electricity monitors, 97
My Hot Water Heating Story, 101–3
renewable electricity management, 174–91
Two Men and a Truck, 226
batteries, charge profile, 185–87
Veggie Oil Conversion, 206–8
batteries, type and size, 183–85
When “High Performance” Doesn’t Perform, 77
battery charger, 182
Wind Wisdom from an Expert, 157–58
charge controller, 180–81, 181, 189
definition of terms, 176–77
Bicycle-Powered Battery Charger, 29–35
diversion or dump load, 181–82, 182
Biodiesel Kit, 209–14
electrical wiring, 177–79
Biogas Generator, 253–260
grid-tie vs. off-grid, 175–76
Simple Wood Gas Cook stove, 229–30
hybrid grid-tied PV system, 175
Solar Hot Water Batch Heater, 119–22
inverters, 176, 179–180, 180, 182, 189
psychrophilic methanogens, 241
lightening arrestor, 181–82, 182
system monitoring, 180–81
biodiesel, 197, 200
heat pumps, 92-94
solar hot water, 107, 107-8, 113, 115
PV systems
testing batteries using specific gravity, 187
wire size and ampacity chart, 179
renewable energy
benefits, 11
arrays, 123–24, 127, 129–31, 134
cost effectiveness, 9
hybrid grid-tied PV system, 175
habits and readiness tips, 23–25, 41
installation options, 132
system efficiency, 12, 12
inverters, 10, 124, 129–30, 131
Residential Energy Services Network, 57
photovoltaic (PV) explained, 123
resistance, defined, 35
photovoltaic cells, 124
respirator, 37, 63, 68, 199, 199, 210, 212–13
safety, 134
rigid foam board insulation, 63–66
series, parallel and combination, 128–30, 129
around concrete foundation, 65
system planning, 125, 125–26
basements and foundations, 65–66, 65–66,
system wiring configurations, 128–30
tracking racks, 131–32, 132, 133
pyrolysis, 218, 219
82, 82
in walls, 71–73, 72–73, 83–84, 84
Rohn towers, 149–50
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Rolls batteries, 184
arrays, 123–24, 127, 129–31, 134
economics and payback, 132–33
air leakage at rafters, 53
fixed and tracking racks, comparison, 133
airflow path, 75, 75
map, solar power estimation, 127
energy audit questions, 51
on- and off-grid systems, 128
ice dams, 51, 76, 76, 87
open circuit voltage, 128
radiant barriers, 61, 61
orientation, 130
unvented roof assemblies, 87
payback calculation, 10
venting, 75
photovoltaic (PV) explained, 123
wall and roof assemblies, 84, 84
photovoltaic cells, 124
roof mount for PV panels, 132
potential power produced, 123
runners (turbines), 160, 169–73, 173
PV panel installation options, 132
runner cups, 170
PV system planning, 125–26
PV system wiring configurations, 128–30
safety, 134
seasonal sun trajectories, 125
semiconductor, 124
series, parallel and combination, 128–30, 129
silicon wafers, 124
single- vs. dual-axis, 131–32, 132
Sabre Industries, 150
site survey, 125–26
Scheckel, Paul
sizing a system, 126–27
Energy Action in Cuba, 26–27
Living with Solar (and Wind) Power, 135–36
My Hot Water Heating Story, 101–3
SCI (Specialty Concepts, Inc.), 180
space requirements, 134
tracking racks, 131–32, 132
Solar Energy International, 27
solar heat gain, 17, 21
sealed combustion water heater, 89–91, 101
roofs, 75
sedimentation, 166
window performance ratings (SHGC), 54, 86
sensible heat fraction (SHF), 93
windows, 54–56, 85
Serious Energy, 97
solar hot water, 22, 106–22
sheathing options, 83, 83
active systems, 107, 107–8
Shelter Analytics, LLC, 77, 133
collectors, 109–111
short cycling, 48–49
heat exchangers, 108, 108
shower head, low-flow, 42, 42
maintenance, 115
passive solar, 107, 107
energy audit questions, 51
pool heaters, 111, 111
Simple Wood Gas Cook stove, 229–30
sizing the system, 114–15
sine wave, 179
storage, 111, 111–12
single- vs. dual-axis tracking racks, 131–32, 132
system components, 112–14
SMA Solar Technology, 180
Solar Hot Water Batch Heater, 119–22
Small Wind Certification Council, 142
Solar Pathfinder, 125–26, 126
smart grid, 95–96
Solar Rating & Certification Corporation, 111
Smart Strip Surge Protector, 41
solar thermal energy. See solar hot water
sodium hydroxide. See lye
Solarex, 176
sodium methoxide, 199–202, 213–14
Solectria, 180
soil classifications, 152
Solmetric SunEye, 126
solar electric generation, 22, 123–36
soy mileage, biodiesel, 194
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space conditioning, 48
EHS cable breaking strength, 149
Spenton LLC, 217
guyed towers, 149, 149–50
spray foam insulation, 68, 70–71, 77, 82–84
installation with gin poles, 150–51, 150–51
stack effect, 56, 56
tilt-up, 149–55
stacking, 179
types of towers, 151
standby loads, 24, 41, 55
tracking racks, 131–32, 132, 133
static head, 162
transesterification, 194, 196
steady state efficiency (SSE), 49
Tri-Metric power system monitor, 181
storage tanks for solar hot water, 111, 111–12
Trojan batteries, 184
sizing, 115
storm windows, 54–55, 80, 85, 85
straight vegetable oil (SVO), 194, 206–8
running on SVO, 206–8
running on wood gas, 226–28, 227
subpanels, 175, 176
true north, 130
SunEye, 126
tube-in-shell heat exchanger, 108, 108
Surrette batteries, 184
turbines, hydroelectric
swamp gas, 231
crossflow turbines, 170, 170
swept area, wind turbines, 139, 139, 139–40
impulse turbines, 170, 170
systems and planning, 22
micro-hydro system components and layout, 169
reaction turbines, 171, 171
turbines, wind
anchors, types of, 152–53, 153
designs, 138, 138
efficiency and power, 144–45
estimating speed, 142–43
HAWT and VAWT defined, 137
tailrace, 160, 169
Living with Solar (and Wind) Power, 135–36
Talco Electronics, 143
noise, 147–48, 154
Tank Depot, 256
power curve and energy curve, 141
Tax Incentives Assistance Project (TIAP), 25
rotors and blades, 147, 147, 154
temperature and pressure relief valve (TPRV), 43, 43
Tessco towers, 150
tower installation, 148–51
Two Men and a Truck, 226
thermal bridge, 63
thermal envelope, 49
blower door, 52–53, 53, 55–56, 88
deep energy retrofit, 79–81
energy audit for, 51–54
prioritizing improvements, 55–56
thermophilic methanogens, 241
thermosiphon, 107, 107
U-factor, 54, 62–63
windows, 85–87
programmable, 50, 251
U.S. Army Corp of Engineers, 169
remote control, 97
U.S. Department of Energy, 142
water heaters, 45–46, 45–46
U.S. Environmental Protection Agency, 58, 162, 169,
Tiger Foam, 71
tilt angle, 109
U.S. Geological Survey StreamStats, 163
titration, 198, 200, 203, 210, 213
U.S. Plastic Corporation, 197
total solids (TS), 237
updraft gasifier, 224, 224
towers, wind, 148–51
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vapor barrier, 69, 82
windows and doors, 54, 54–55, 78
Web Energy Logger, 99, 102–3
Weibull wind speed distribution, 145, 145–46
weir measure, 163, 163–64
weir flow table, 164
vegetable oil for biodiesel, 195
When “High Performance” Doesn’t Perform, 77
veggie oil bag filter, 207
whole-house electrical meters, 96–97, 97
Veggie Oil Conversion, 206–8
wind electric generation, 137–58
ventilation, 88–92
AC systems vs. DC battery chargers, 138
balanced ventilation, 90
air density variations, 140, 140
cooking with gas, 90
anchors, types of, 152–53, 153
enthalpy recovery ventilator (ERV), 91–92
annual energy output, 144
exhaust fans, 91
Beaufort scale, 143
exhaust ventilation, 90
Betz limit, 144
flue draft, 89, 89
cost effectiveness, 146–47
heat recovery ventilator (HRV), 90, 91–92
efficiency and power, 144–46
sealed combustion water heater, 89–91, 101
estimating wind energy, 139–41
venting a roof, 75
finding the best location, 138–39
vermiculite warning, 74
foundation and soil, 152, 152
Victory Gasworks, 217
gathering wind speed data, 142–43
visible transmittance (VT), 86
grid-tied generators, 147
volatile solids (VS), 237
Griggs-Putnam Index of Deformity, 143, 143
voltage drop, 128
HAWT defined, 137, 138
volts, defined, 35
hybrid energy systems, 146
Kestrel turbines, 135, 141, 144–46, 267
loose cable tension gauge, 154, 155
above-grade, retrofit, 82–84
cross section of basement wall, 82
cutaway of framed, insulated wall, 65
exterior curtain walls, 84, 84
how to check insulation, 64–65
wall and roof assemblies, 84, 84
water heater. See hot water
Watt, James, 26
wattmeter, 40, 40
Watts Up? meters, 40, 96
weather monitoring, 98–100, 125
weather-resistant barrier, roof, 84, 84
weatherization, 20, 52, 74
maintenance, 154, 155
monitoring equipment, 144
off-grid wind system, 156
power curve and energy curve, 141
power relative to wind speed, 140, 140, 141, 141
rated annual energy, 142
recording anemometer, 143
rotors and blades, 147, 147, 154
safety precautions, 155
swept area, 139, 139, 139–40
towers, 148–51
turbine designs, 138, 138
turbine noise, 147–48, 154
turbulence, 143, 148
VAWT defined, 137, 138
Weibull wind speed distribution, 145, 145–46
wind speed distribution assessment, 145, 145–46
wiring and grounding, 156
Wind Powering America, 142
Wind Wisdom from an Expert, 157–58
attic hatch panel, 73, 73
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air infiltration, 54
deep energy retrofit, 84–87
energy audit, 51, 54–55
innies v. outies, 85
low-E, 61, 86
Xantrex, 180
orientation tuning, 86–87, 87
performance ratings, 85–86
windwashing, 73
wire size and ampacity chart, 179
Zomeworks, 132
sealed with wall sheathing, 83, 83
storm windows, 54–55, 80, 85, 85
treatments, 55, 61
upgrading, 54
weatherstripping, 54, 54
wood gas, 215–30
Zephyr Industries, 188
ZigBee Alliance, 97
challenges, 217
cleaning and filtering, 220–21
combustion process, 216, 216
composition, 220
environmental impacts, 225
estimating production, 223
four stages of gasification, 218–19, 219
fuel sources, 216–17
gasifier cook stoves, 217, 217
gasifier operation, 219–20
how generators work, 216
improving acceleration, 222
powering diesel vehicles, 222
powering gasoline vehicles, 222
quantifying your needs, 223
safety, 225
sizing, 224
storing gas, 223
system schematics, 221–22
types of gasifiers, 224, 224
wood stoves, 17, 48, 60, 93, 101, 116–18
heating and cooking with wood, 21
outdoor wood boilers, 21, 21
v. wood gas generators, 216
Woofenden, Ian, 151
Wind Wisdom from an Expert, 157–58
World Health Organization, 251
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