Photovoltaic Systems: A Buyer`s Guide
A Buyer’s Guide
Natural Resources
Ressources naturelles
Photovoltaic Systems: A Buyer’s Guide
This guide is distributed for information purposes only and does not necessarily reflect the
views of the Government of Canada or constitute an endorsement of any commercial product
or person. Neither Canada nor its ministers, officers, employees or agents make any warranty
with respect to this guide or assumes any liability arising from this guide.
© Her Majesty the Queen in Right of Canada, 2002
Cat. No. M92-28/2001E
ISBN 0-662-31120-5
Aussi disponible en français sous le titre :
Les systèmes photovoltaïques : Guide de l’acheteur
Table of Contents
About This Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1. What Is a Solar Electric or Photovoltaic (PV) System? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
What Is PV? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
How Does It Work? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
The Three Types of PV Power Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. What Photovoltaics Can Do for You . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
The Advantages of PV Power Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
The Limitations of PV Power Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Photovoltaics at Work in Canada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Cottages and Residences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Power for Remote Lodges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Mobile and Recreational Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Photovoltaics in Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
A PV System to Suit Your Particular Power Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4. Buying Your Photovoltaic System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Be Prepared . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Where to Find PV Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Choosing a Dealer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Making a Decision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5. Installing and Maintaining Your Photovoltaic System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Mounting the PV Array . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Housing the Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6. Estimating Your Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Step 1. Estimate Your Power and Energy Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Step 2. Make a Rough Evaluation of PV System Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
7. Sizing Worksheet Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Example 1. Summer Cabin Power System – The Smiths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Example 2. Year-Round Remote Residential Power System – The Wongs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
8. Technical Information on Photovoltaic System Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
PV Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
The Electric Characteristics of PV Modules: The Current-Voltage (I-V) Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Other Components in PV Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Appendix A: Worksheet to Evaluate System Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Step 1. Estimate Your Power and Energy Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Step 2. Make a Rough Evaluation of PV System Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Appendix B: Typical Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Typical Power Ratings of Some Common Appliances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Appendix C: Energy-Efficient Lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Comparison of Typical Lighting Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Learn More About Solar Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Reader Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
this Guide
The information in the following
pages is for prospective buyers of
photovoltaic (PV) systems for use
in the following:
remote cottages and
recreational and mobile
agricultural applications;
remote lodges; and
remote lighting applications.
The purpose of this guide is to
help you determine whether a PV
system is a suitable option for you
in providing electrical power for
one or more of the above uses. It
describes typical and innovative
PV systems, provides examples of
successful Canadian installations
and answers some of the questions you should ask yourself
before approaching a PV dealer
(as well as questions a dealer
should be able to answer).
Each section of this guide is
divided into short, easy-to-read
subsections. This format allows
you to browse by topic or read
the guide from cover to cover.
Several forms are included to
help you estimate your power
and energy needs.
Once you have read this guide,
you should know enough about
PV systems to consult dealers and,
with them, evaluate the best PV
configuration to meet your needs
– now and for the future. This
guide provides only estimates and
is not intended to replace the
technical expertise required for
the detailed design and installation of a PV system. Nowhere
should you construe that this
guide recommends or promotes
any specific products.
1. What Is a Solar Electric or Photovoltaic (PV) System?
What Is PV?
The term “photovoltaic,” commonly referred to as PV, is derived
from a combination of “photo,”
the Greek word for light, and
“Volta,” the name of the Italian
physicist, Alessandro Volta, who
invented the chemical battery in
1800. The PV effect is the direct
conversion of solar energy into
electricity. This process does not
generate heat like solar domestic
hot water or solar pool heating
systems do. It also differs from
the process used in solar thermal
power plants, where concentrated
solar energy is used to produce
steam that activates a turbine
connected to an electric generator. PV power systems do not
have any moving parts. They are
reliable, require little maintenance and generate no noise
or pollutants. PV systems are
modular – the building blocks
(modules) come in a wide range
of power capabilities, from a
fraction of a watt (e.g. solar
watches and pocket calculators)
to more that 300 W. Modules
can be connected to achieve
the power that your application
requires. Some demonstration
PV power plants have several
megawatts of power, although
most installed PV systems are
much smaller.
How Does
It Work?
PV cells are normally fabricated
using special semiconductor
materials that allow electrons,
which are energized when the
material is exposed to sunlight,
to be freed from their atoms.
Once freed, they can move
through the material and carry an
electric current. The current flows
in one direction (like a battery),
and thus the electricity generated
is termed direct current (DC).
▲ A PV module converts sunlight directly into electricity.
▲ For applications that require electricity during overcast periods, batteries ensure
that the PV system is autonomous.
The energy generated by PV
modules can be used immediately
or stored in batteries for later
use. Normally, the excess energy
generated in autonomous PV
systems during sunny periods is
stored in batteries. The batteries
then provide electricity at night
or when there is not enough solar
radiation. For these applications,
the number of watts in the array
and the capacity of the batteries
are carefully sized to give optimum performance.
Some autonomous applications,
such as water pumping, often
have no need for batteries. Water
is pumped when the sun shines
and is stored directly in a reservoir or a tank that is installed
at a higher level for later use
by gravity feed.
Other PV systems convert the
electricity into alternating current
(AC), feed excess electricity into
the grid and draw out electricity
at night or when the solar radiation is low. These systems are
referred to as grid-connected,
grid-tied or net-metered.
The Three Types
of PV Power
The three typical configurations of
PV power systems are autonomous,
hybrid and grid-connected.
Autonomous and hybrid power
systems are used in stand-alone
applications. They are not connected to the main utility grid
and are often used in remote areas.
or in periods of low solar radiation. Alternatively, they may
power the application entirely,
with no need for batteries
(e.g. water pumping). In general,
autonomous PV systems are the
most cost-effective source of
electrical power. You may,
however, decide to choose a
hybrid PV system because of
the environment in which it
will operate or because you
need a system that operates
independently and reliably.
Autonomous systems rely exclusively on solar energy to meet a
need for electricity. As mentioned
in the preceding, they may
incorporate batteries – which
store energy from the PV modules
during the day – for use at night
Autonomous PV Systems
Hybrid PV System
▲ Autonomous
PV system
without batteries.
▲ Autonomous
PV system
with batteries.
▲ Hybrid PV system.
Hybrid systems, also used in
stand-alone systems, consist of PV
modules and a wind and/or fuelfired generator. A hybrid system is
a good option for larger systems
that need a steady power supply,
when there is not enough sun at
certain times of the year, or if you
want to lower your capital investment in PV modules and storage
Grid-connected PV power systems
are part of the movement toward
a decentralized electrical network.
Power is generated closer to
where it is needed – not solely by
central power stations and major
hydro stations. Over time, such
systems will reduce the need to
increase the capacity of transportation and distribution lines.
A “grid-connected” system generates its own electricity and feeds
its excess power into the utility
grid for later use. This does away
with buying and maintaining a
battery bank. You can still use
battery banks to provide backup
power when the grid goes down,
but they are not required.
Smaller systems have a box –
a small grid synchronous inverter
– mounted on the back of each
panel. Larger systems have one
large inverter, which can handle
many panels (as in a stand-alone
system). Both types convert DC
power output into AC power. Then
they synchronize this output with
the grid to slow down the electrical meter. They can even turn the
meter backward. If the PV output
is less than the load consumption,
the meter slows down.
▲ Water oxygenation compressors
and water pumps are examples
of PV systems that function without batteries. Photo courtesy of
Environergie Québec Inc.
If PV output exceeds the load
consumption, the meter turns
backward, and a credit is accumulated. This credit can be drawn
out of the utility when the sun is
not shining. In essence, the grid
▲ Remote residences or cottages can
have access to electricity without
extending the grid. Photo courtesy
of Solener Inc.
acts like a limitless battery bank.
In most parts of Canada, permission from the local utility is
required in order to back feed
power into the grid.
Grid-Connected PV Systems
▲ Centralized and distributed grid-connected PV systems.
A large portion of the cost of
a grid-connected PV system is
manufacturing the PV modules
themselves. Significant decreases
in manufacturing costs have
occurred in recent years, with
further decreases expected in the
future. This kind of PV system is
thus becoming more affordable.
In some urban areas in warm climates, the cost per kilowatt-hour
of electricity from grid-connected
PV systems is competitive with
that of other electricity-generating
systems. In areas with less solar
radiation, the cost-effectiveness
of this type of PV system is still
marginal. But there is a potential
for peak power savings in areas
where air conditioning causes a
power peak in the summer. There
are also system savings where
the PV modules can replace the
traditional roofing materials for
buildings or the cladding material
that is normally used in building
façades. These material savings
are making the costs per kilowatthour from grid-connected PV
systems increasingly competitive.
Decentralized small home systems
also hold some potential for
grid-connected PV systems, but
the costs will have to be reduced
further in order to compete with
the low electricity rates now available in most parts of Canada.
Note, however, that PV electricity
is “green” energy and, as such, is
worth a premium. Even though
this value is subjective, it should
be expressed in numbers by the
PV system’s designer. For example, how much is the avoided
pollution of conventional sources
worth and how much is the
avoided distribution cost worth?
▲ This house in Edmonton, Alberta, is equipped with a 2.3-kW system that is
connected to the local power utility. About 2500 kWh are produced each year.
The investment cost in 1995 was $28,000.
To install a PV system, you must
pay the capital cost of the system
and amortize this cost over time.
In contrast, where there is a utility
grid, you pay for the electricity
used and not a lump sum for the
generating facility. The costs of
the PV system may appear to be
a burden because the electricity
that the system generates may cost
more per kilowatt-hour than what
a utility charges. But using a PV
system may also be considered a
lifestyle choice, similar to choosing between a fuel-efficient car or
a gas-guzzling sport utility vehicle.
2. What Photovoltaics Can Do for You
Perhaps you need reliable
power in a location that is
not connected to an electrical
grid. In this case, photovoltaics
may be the best and most
cost-effective solution. Many
locations in Canada that have a
dry continental climate have the
same number of daylight hours
as some Mediterranean countries.
A photovoltaic (PV) system used
during the summer in Canada
can take advantage of substantial
daily amounts of solar energy.
Contrary to what many people
think, PV systems convert
sunlight into electricity more
efficiently at lower temperatures.
However, the winter months in
Canada provide half the hours
of sunlight as in summer. Much
of Canada experiences high
winds in the winter, which can
make a wind generator a logical
addition to the system. Fuelfired generators are then used
only for backup.
Among other things, you can use
PV energy to:
supply power for lights,
radios, televisions, pumps and
other appliances in cottages
and residences;
power electric fences, water
pumps and other devices in
agricultural operations;
run water-pumping and circulation systems in game fishing
and aquaculture facilities;
provide reliable electric power
for wilderness lodges and
hunting and fishing camps;
recharge or maintain charge
of batteries for recreational
applications such as recreational vehicles and sailboats;
power portable devices
such as laptop computers;
power exterior lighting;
provide reliable power
for many commercial
applications; and
lower your monthly
utility bills.
The Advantages
of PV Power
Users of PV power systems
appreciate their quiet, lowmaintenance, pollution-free, safe
and reliable operation, as well as
the degree of independence they
provide. Why else should you
consider buying a PV system?
If you are some distance from an
electrical grid, it may be cheaper
to generate your own power
rather than pay to extend
transmission lines from the
grid. Diesel, gasoline or propane
generators are the conventional
alternatives, but many people
find them noisy, polluting and
costly to run and maintain. It
also makes little sense to turn on
a 5-kW generator to power a few
100-W light bulbs. PV systems
reduce the negative aspects of
generators by using them only
as a backup.
When capital cost is an issue, or
when photovoltaics alone are
not enough to replace an existing
generator, you can use a wind
generator as part of a hybrid PV
system, thus reducing the use of
the generator. Such an intermittent charge system is more efficient
than a generator running continuously at low load. In addition to
saving fuel and lowering maintenance costs, you will increase the
generator’s life span. Also, since
the PV panels and battery banks
are modular, you can expand the
PV system gradually as your
budget or needs increase.
The Limitations
of PV Power
It is important to realize that PV
power systems are capital intensive from the buyer’s perspective
and are expensive when compared with the low price of utility
power in Canada. You should
therefore reserve the electric
power produced by PV modules,
an inverter and a storage system
for your most energy-efficient
appliances, tools, lights, etc.
generally more cost-effective and
convenient to use a stove that
operates on propane or natural
gas rather than solar electricity.
Autonomous PV-powered homes
and cottages often rely on wood
cookstoves for cooking and space
heating. Refrigerators are becoming more energy efficient, so the
cost of operating them with PV
power is now feasible. Extremely
energy-efficient refrigerators and
freezers are, unfortunately, still
expensive, however, they can be
had through PV dealers.
Although it is technically possible, heating with photovoltaics is
generally not recommended. You
can easily and more efficiently
collect heat with a solar thermal
system. A solar water heater generates more hot water with less
initial cost than any PV-powered
heater.1 Also, for cooking, it is
From an economic point of view,
first consider investing in energyefficient electric appliances, and
then size your PV system based
on actual consumption. For
example, using compact fluorescent lights will reduce your
electrical consumption for
lighting by 80 percent.
For more information, obtain a free copy of Solar Water Heating Systems: A Buyer’s Guide from Natural Resources Canada.
Call 1 800 387-2000 toll-free, or visit the Web site at
3. Photovoltaics
The use of photovoltaic (PV)
technology is increasing rapidly
in developed and developing
countries. Although the Canadian
PV industry has also expanded
significantly over the past decade,
the use of photovoltaics in
Canada is still relatively limited.
This is partly because of Canada’s
low utility rates, but the following
commonly held myths are also
Myth: “There is not
enough sunlight
in Canada.”
Myth: “Solar electric
technology is not
efficient in a
cold climate.”
Example 1. A Typical
Autonomous PV Application
for a Remote Cottage
at Work in Canada
Myth: “Photovoltaics
is not a proven
Myth: “PV systems are
too expensive.”
Thousands of PV systems in
myriad applications throughout
Canada and millions throughout
the world today have debunked
these myths. Although conditions
in Canada pose a special challenge to the use of photovoltaics,
an appropriately designed PV
system can give you reliable
power to most remote sites. In
the following pages, examples
of actual, cost-effective PV
installations across the country
will demonstrate what photovoltaics can do for you.
A cottage, located away from the
power grid, uses photovoltaics to
power several fluorescent direct
current (DC) lights, some halogen
lights and a DC water pump,
which supplies water to the residents. A stove and a refrigerator
run on propane fuel. No inverter is
needed, but one can be included
any time if alternating current (AC)
loads are added.
The cottage is equipped with
a PV system that consists of
the following:
• two 75-W solar modules
(150 W of photovoltaics);
▲ Photo courtesy of Cimat enr.
• a 20-A (ampere) regulator;
Cottages and
Increasingly, Canadian homeowners are using PV systems to power
lights and appliances in remote
cottages and residences that are
not connected to a utility grid.
Like these homeowners, you’ll
appreciate the quiet, low-maintenance, safe and pollution-free
operation of a PV system, as well
as its versatility and reliability.
In general, PV systems are costcompetitive for cottages and
residences that are more than
several hundred metres from the
electricity grid. But they are not
yet a cost-competitive alternative
in locations that have direct access
to power from the grid.
• a bank of batteries; and
• a second PV system that
powers a small, exterior DC
light with an 8-W panel and
an independent battery.
The cottage is used primarily on
weekends and during vacations,
which explains the large battery
capacity compared with the total
area of PV modules. This allows
more energy to be available
during two days of occupancy,
and the PV modules recharge the
batteries over the remaining five
days of the week. This system
has been functioning maintenancefree since 1997.
• a load/fuse panel;
Example 2. An Autonomous
PV System Powers a Summer
Residence on an Island on
the St. Lawrence River near
Montréal, Quebec
Major power-line damages in
Quebec have occurred twice in five
years, the most recent being the
severe ice storm of 1998. For one
of its customers that has an island
summer cottage, Hydro-Québec
decided to provide a stand-alone
PV system instead of maintaining
a 200-m power line between the
island and the mainland.
to Canadian Coast Guard regulations, the new overhead line would
have to be at least 10–15 m higher
than the one previously installed.
And it would have been expensive
for Hydro-Québec to install a
submerged cable, given the high
levels of polychlorinated biphenyls
(PCBs) in sediments of the
St. Lawrence River. In November
1997, Hydro-Québec decided to
evaluate alternative options. A PV
stand-alone system was preferred
to a wind generator, due to the
potential for low winds in the
Montréal region in the summer.
Finally, a solar-only PV system
was chosen because the electricity
needs in the winter were about
a quarter of those in the summer.
This would avoid the trouble of
maintaining a fuel-fired generator.
The solar-only PV system consists
of the following:
The average amount of electricity
needed to run this cottage is
5.5 kWh/d (very low by Canadian
standards), mainly during the summer. The load consists of lights,
household appliances, power tools,
water and pool pumps, an alarm
system, etc. This load is expected
to be 75 percent less during the
winter, when only exterior lighting
and the alarm system are active.
• twelve 90-W PV modules, with a
total capacity of just over 1 kW in
12 VDC (volt direct current);
Three possible solutions were
analysed: the replacement of the
overhead power line, a submerged
cable and renewable energy. Due
• a 2.5-kW, 120-VAC (volt alternating current) pure sine-wave
inverter with a surge capacity
of 8 kW; and
• the existing Hydro-Québec pole
used for the support structure;
• a separate, ventilated outbuilding
provided by the owner for the
batteries and system components
(not always necessary);
• a 40-A solar controller;
• a 1595-Ah (ampere-hour),
12-VDC battery bank.
The batteries offer seven-day
autonomy when the sun is not
shining, based on the expected
daily load. However, the homeowner knows about the need to
monitor the use of electricity when
overcast or rainy conditions are
forecast. Therefore, a meter was
installed to provide instant information on the reserve capacity
remaining in the battery bank
(based on current load consumption) and on the charge rate from
the PV array.
Hydro-Québec financed the installation of the PV system, even
though the cost of solar electricity
produced was more than 10 times
the regular cost charged by the
utility (about 60¢ per kWh versus
6¢ per kWh). The savings on
electric-line maintenance justify
the cost. Hydro-Québec also
planned funds for replacing system
components after their lifetime
(e.g. 25 years for the PV modules).
After two seasons of use, both
Hydro-Québec and the homeowner are satisfied with the
performance of the PV system.
It can handle the heavy use of
a washing machine, a toaster,
lights, pumps, etc., during weekends when all five bedrooms are
filled by up to all 16 members
of the family.
Power for
Remote Lodges
Owners of remote fishing lodges
may find that a properly designed
PV hybrid system is economically
attractive, be it PV-diesel, PV-wind
or a combination of the two. The
Example 3. A Solar-Diesel
Hybrid System at Tarryall
Resort, Catherine Lake
(Near Keewatin), Ontario
high cost of diesel generation at
remote sites often prompts the
owners to look for alternatives,
namely, renewable energy technologies. In many instances, a
PV-diesel hybrid system proves
attractive because it is cost-
effective, simple and reliable.
During periods of little sunshine,
the use of the diesel generator can
be reduced by drawing power from
a bank of batteries and by running
the generator only when the
batteries are low.
pump, installed timers on the exterior lights and moved their freezer
outdoors in the winter. Using more
efficient lights, in particular, has
had a significant impact on daily
energy consumption.
the end of the charging cycle,
thereby extending battery life and
increasing the system’s efficiency.
Because the diesel generator is
used more efficiently in the hybrid
system configuration than it would
be on its own, it needs fewer oil
changes and less frequent major
overhauls and repairs. Also, the life
span of the generator is extended.
During its first year alone, savings
in fuel and maintenance charges
totalled about $7,000.
The resort’s electrical generating
system consisted of two diesel
generators (a 7.5-kW main generator running 24 hours a day and
a 3.0-kW backup generator). The
high cost of diesel prompted the
owners to investigate a solar-diesel
hybrid system.
Tarryall Resort operates from April
to October. The resort consists of
seven cottages and a main house
that can accommodate up to a
dozen people. The cottages are
equipped with propane-powered
appliances and lighting. Electricity
is used year-round in the main
lodge to power a full range of
appliances, including a clothes
washer, a large freezer, a water
pump, televisions, lights and
power tools.
The resort is located six kilometres
from the electrical grid. In 1980
the owners considered connecting
to the utility grid, but the cost was
estimated at more than $80,000.
The owners instead decided to
improve the resort’s energy efficiency. They switched to more
efficient 12-V fluorescent lights,
put a smaller motor in the water
In 1986 the owners installed a
hybrid system that included the
• a 564-W PV array;
• a bank of 24 two-volt,
deep-cycle batteries; and
• the existing 7.5-kW diesel
The resort’s diesel consumption
has been considerably reduced
since the PV-diesel hybrid system
was installed. The generator is
used once every three or four days
for about 10 hours to recharge the
batteries. Previously, it had consumed fuel continuously, while
supplying only about one quarter
of its nominal capacity. The PV
panels contribute about 15 percent
of the lodge’s energy requirements. They also permit a gentle
trickle charge of the batteries at
Despite the high up-front cost
($36,000 in 1986), the hybrid
system paid for itself within
six years. Tarryall’s owners are
pleased with their PV system and
particularly enjoy the quiet, clean
operation – a major improvement
over the constant noise of a diesel
generator. They have since added
four PV modules, increasing the
capacity to 752 W. This further
reduced the need for dieselgenerated electricity. The original
lead-acid batteries were still being
used in 2000, after 14 years of
service. Tarryall’s owners were
so satisfied with photovoltaics
that they also equipped each
of the seven cottages with an
autonomous PV lighting kit
(one module with one deepcycle battery).
Example 4. A Hybrid PV
System at the Warden Station
on Huxley Island, Gwaii
Haanas Marine Conservation
Area National Park Reserve
Located in the Moresby Island
archipelago in British Columbia,
Huxley Island serves as a registration office for visitors to Gwaii
Haanas Marine Conservation Area
National Park Reserve. These
include scientists visiting the area,
which is dedicated to environmental conservation. The camp has a
75-m2 building with a full kitchen,
bunks for four people and an office
equipped with a satellite telephone, VHF radios and computers.
To meet these electricity needs,
park administrators chose a hybrid
stand-alone PV system. Its advantages over a continuously operated
generator include less engine
maintenance, a lower need for
refuelling and reduced noise.
A power system installed in 1996
consists of the following:
• a 600-W solar array using eight
75-W modules;
• a 4.0-kW sine-wave inverter;
▲ Photo courtesy of Soltek Solar Energy Ltd.
• a 38-kWh lead-acid
battery bank; and
• a 5.0-kW gasoline
To make installation easier, all
electrical components were
pre-assembled and wired on a
1.3-m2 board before shipment.
The distributor also provided a
waterproof aluminum outdoor
cabinet for the batteries and
power equipment. It was installed
directly behind the living quarters.
A state-of-charge battery display
and a remote control for the
inverter and generator were
installed on an interior wall of the
building for the convenience of
park staff.
The integrated power system is
completely automated. The system
provides the bulk of the power
to the loads, with the generator
available for backup. In the event
of poor weather or excessive loads,
the generator is programmed
to start when the battery bank
reaches 50 percent of its nominal
capacity. This way, the batteries
are charged before a potentially
damaging low-battery condition
is reached.
Mobile and
People working in the field with
portable computers appreciate
the autonomy that PV offers.
Photo courtesy of Midnight Sun
Energy Ltd.
Chances are that you are already
relying on PV technology to help
you keep track of time, balance
your budget or enliven your leisure
hours. Many products such as
watches, calculators and toys have
been PV-powered in an inexpensive, reliable and convenient way
for many years. Equipped with
tiny PV cells that produce power
even in dim lighting, these
consumer products eliminate
the need for costly batteries that
need to be frequently replaced.
Nowadays, versatile PV power
packs are also used to power
larger consumer products. They
are available in a range of sizes,
from fractions of a watt to over
100 W. Power packs can also be
hooked up in series or parallel
connections to serve various
power needs. They can be used
as either a direct power source
or as a battery recharger. These
convenient PV systems power
everything from radios, cassette
recorders and cameras to lawn
ornaments, walkway lights and
batteries for sailboats and gliders.
The clean and noiseless operation of PV systems for many
recreational applications is a
significant benefit.
Many owners of recreational vehicles are already using PV technology.
Photo courtesy of Rozon Batteries Inc.
In recreational vehicles and
electric-powered boats, PV panels
can help recharge batteries. The
main advantage of a PV system is
that it will, at the least, maintain
the state of charge of batteries on
board – even during extended
periods of time when you are
not using the equipment.
Example 5. Photovoltaics for a South Pole Expedition
Explorers Bernard Voyer and Thierry Petry were the first North Americans
to reach the South Pole by ski unassisted. Each had to pull a 170-kg pulka
(a toboggan-like sled) over an uneven surface of stratified ice swells. Sunlight
was available 24 hours a day during their expedition; however, the usable
sunlight hours per day was between two and nine hours (or 5.5 hours per
day on average).
Electricity Need
The explorers used a PV system to power a satellite telephone under the
extreme climatic conditions. This system also served as a backup for the
lithium batteries for a video camera. The PV system was designed to power
the following equipment:
▲ Photo courtesy of Bernard Voyer
Explorateur Inc.
Converted to Wh per day
• satellite telephone:
60 W (8 min/d)
60 W x 8/60
8 Wh/d
• portable computer:
42 W (15 min/d)
42 W x 15/60
10.5 Wh/d
• positioning system:
0.5 W (24 h/d)
0.5 W x 24
12 Wh/d
• video camera:
20 W (12 min/d)
20 W x 12/60
4 Wh/d
Average total daily demand: 34.5 Wh/d
As mentioned above, sunshine was usable for 5.5 hours a day on average,
so the team needed 6.3-W worth of PV modules (34.5 Wh/d ÷ 5.5 h/d) daily.
The Power System
As 5.5-W panels are common,
the team needed at least two
panels, which provided extra
power to compensate for bad
weather or additional loads. The
PV system had the following
• installed PV power:
• storage capacity:
Main Advantages of the PV System
Primary lithium batteries are
generally used for this kind of
expedition. An estimated twenty
10-Ah lithium batteries would have
been needed, for a total cost of
$6,000 and a weight of 12.5 kg.
This alternative was rejected due
to its cost and weight.
Another alternative would have
been to carry a small gasoline
generator. The smallest, lightest
generator available was a 300-W
generator that weighed 18 kg.
Apart from its weight, fuel would
have had to be carried and handled. Also, fumes and noise from
the generator would be unpleasant, and starting the engine in
• total weight:
2 x 5.5 W
Lead-acid 12 V, 9 Ah
Nickel-cadmium 12 V, 5 Ah
5 kg
The conditions of operation were as follows:
• average temperature:
-15°C to -33°C (December/January)
The system cost $600.
a cold environment would be
difficult. The team rejected this
alternative as impractical.
PV energy represented the most
economical, reliable, practical
and environmentally friendly way
to generate electricity for such an
expedition – not to mention
the lightest.
in Agriculture
PV systems are particularly well
suited where a small amount of
energy in remote locations is
needed for agricultural applications, such as electric fencing,
water pumping for irrigation or
stock watering, pond aeration, etc.
Electric Fencing
PV-powered electric fencing is
popular in Canada’s western
provinces, chiefly in northern
pastures where land is open for
cattle. Several cattle ranchers
in northern Alberta and British
Columbia have installed PV modules to charge the batteries of
standard electric fencing. These
batteries will never run down.
PV-powered electric fencing not
only eliminates the cost and
inconvenience of regular visits to
check batteries, but also costs less
than barbed wire fencing, which
is the other alternative to conventionally powered electric
fencing. More and more
ranchers and
weather is hot and dry, precisely
when the most solar energy is
available. Simple non-storage
types of PV systems are ideal
for many irrigation applications
where crops can do without water
when the sun is not shining.
In situations where irrigation is
needed independent of weather,
power stored in the form of
pumped water, rather than in
costly storage batteries, makes
PV-powered irrigation systems
economically attractive.
▲ PV-powered electric fencing saves
both time and money for ranchers
and farmers. Photo courtesy of
the Agricultural Technology Centre
(formerly the Alberta Farm
Machinery Research Centre).
farmers in Canada are finding
that PV systems, which can run
all summer with no need for servicing, are a practical alternative
for their remote fencing needs.
Water Pumping for Stock
Watering and Irrigation
Water pumping is one of the
most attractive uses for PV systems. In agriculture, the demand
for water is greatest when the
Today, several million hectares
of remote grazing land in Canada
are not being used because the
costs of pumping water for stock
watering by conventional methods outweigh the grazing benefits.
For many Canadian ranchers and
farmers, PV-powered pumping
systems offer a cost-effective
▲ Stock watering using a PV-powered water
pumping system from a pond to prevent
contamination of the source. Photo courtesy
of Sunmotor International.
A PV System
to Suit Your
Particular Power
Standardized PV systems are
becoming more and more common. However, many PV systems
in Canada are custom-designed to
take into account the particular
needs of the user and the characteristics of the site. Therefore, you
should not necessarily expect to
buy such a system “off the shelf”
as you would a diesel or gasoline
generator. Rather, you will
probably have to consult PV
equipment suppliers for a system
that is right for your needs.
The telecommunications industry
and the Canadian Coast Guard
used PV power systems early
on for remote telecommunications repeater stations, beacons
and navigational aid systems.
Their expectations for reliability
helped the PV industry develop
quality products and improve
design tools.
▲ This PV-powered aquaculture facility is
on an island off Canada’s west coast.
▲ A small PV module is used to
power a trail indicator at night at
Mont-Tremblant, Quebec. Photo
courtesy of TN conseil inc.
Early Uses for PV in Commercial Applications
Small PV lighting packages
are available from dealers. For
ski hills, lighthouses, isolated
stretches of highway and off-grid
communities and businesses,
PV-powered lighting provides
a practical, affordable solution
to remote lighting problems.
▲ The limited power
▲ Due to the remoteness
▲ The Canadian Coast
Guard has been using
thousands of PVpowered buoys along
coasts for many years.
of repeater stations,
has been one of the
first – and remains
one of the most popular – applications
for PV systems.
Photo courtesy of
Northwestel Inc.
needs of remote
monitoring systems
are easily met by
small PV systems.
This example
shows a gas
4. Buying Your Photovoltaic System
Be Prepared
Before approaching a dealer,
you should consider your power
requirements and the type of
photovoltaic (PV) system that will
suit your needs and your budget.
The following are typical
questions that you should ask
yourself. Be prepared to supply
the following information as
precisely and clearly as possible:
What is the application?
What needs to be powered?
Are my loads as efficient as
How much power (wattage)
and/or energy (watt-hours
per day) is required?
What is the energy-usage
pattern (e.g. hour per day,
days per week, seasonal use)?
Do I need battery storage?
Do I want an autonomous,
hybrid or grid-connected
Do I want to start small and
add modules in the future?
A first step in any design or cost
evaluation is to assess your load:
i.e. what do you expect the PV
system to power? Section 6,
“Estimating Your Needs” (page
24) is intended to help you evaluate the options. A worksheet is
provided in Appendix A (page 40)
to help you estimate and choose
a suitable PV system. This worksheet is intended to guide you in
estimating your power and energy
needs, evaluating the PV array
size and estimating the battery
capacity that you require.
Note that this exercise is optional.
However, you should at least
prepare a list of all appliances
and other electrical equipment
that the PV system might power
and estimate their time of use
(see Step 1 in the worksheet
provided in Appendix A). The
more detailed and accurate
the list, the easier the sizing
of your PV system will be for
you or your dealer.
Where to Find
PV Systems
Apart from some specific consumer products or special sales,
PV power systems are just beginning to be widely available in
hardware or department store
chains. Dealers of recreational
vehicles, boats and electric
fences may sometimes offer PV
solutions adapted to their products. However, for most custom
applications, you will need to
find a PV dealer. Generally, this
gives you the advantage of better
service, since such dealers should
have a good understanding of
the technology and can help you
select, size and design the system
that best suits your needs. There
are many distributors and dealers
of PV systems in Canada, and
the industry network is growing.
Some of these companies specialize in different types of systems,
e.g. communications, home
energy systems, consumer
products, agricultural and
unique design.
To find PV distributors or dealers,
contact the Canadian Solar
Industries Association, Natural
Resources Canada (see “Learn
More About Solar Energy” on
page 46) or consult the Yellow
Pages™. You may also wish to
obtain a referral from a satisfied
a Dealer
A PV system should be designed
for the best efficiency and costeffectiveness. It is wise to consult
a professional at the design stage.
Most dealers offer design and
consultation services as well as PV
modules and “balance of system”
components such as batteries
and inverters. Some companies
concentrate on industrial applications; others specialize in
residential and commercial systems. Make certain that the dealer
you select has proven experience
in designing and installing the
type of system you want. Ask
to see some systems that have
already been installed, or talk
to someone who has bought a
system that is similar to what
you want.
A responsible dealer will ask
you questions about your power
consumption, lifestyle and needs
before designing your PV system.
If you cannot afford as many PV
modules as you would like but
intend to add to the system later,
make sure that the system
designer knows this.
The PV dealer should offer a
warranty on parts and labour.
The warranty for PV modules
can now be as much as 25 years,
depending on the type of modules and manufacturers’ policies.
Most modules will perform
reliably for a longer period.
Check which warranties the
dealer offers on the other components (electrical and mechanical)
and on the labour. Moreover,
check on follow-up service available from the dealer. In general,
take the same sort of precautions
when buying a PV system that
you would when buying a new
Following is a list of items to
consider in evaluating a dealer’s
product and service. Use it when
choosing a dealer.
design/sales experience
knowledge of energy
area of expertise
product quality
product warranty
installation service
follow-up service
Making a
Of course, cost is always important in any purchase decision.
The economics of PV systems
are often quite site-specific. In
general, conventional energy
sources tend to have low initial
capital costs but have high operating and maintenance costs. In
comparison, PV systems have
higher initial capital costs but
have lower maintenance and
operating costs. Thus, to evaluate
the economics of a PV system,
you must consider the total
costs of competing alternatives –
including capital costs, fuel costs
and maintenance and operating
costs over the life of the system.
For off-grid commercial operations that have labour and
maintenance costs, PV systems
can often be economical. For
individual homeowners, who
usually do not count their
own labour for operation and
maintenance as a cost of running
a generator, the initial cost of a
PV system may appear to be
high. However, for many home
and cottage owners, the noneconomic benefits of PV systems –
in particular, their reliability and
quiet, non-polluting operation –
far outweigh the extra costs.
Especially in summer, owners of
PV systems appreciate that they
can enjoy the sounds and smells
of nature without interference
from their power system.
Of course, the cost of a PV system
depends on what it includes. A
simple autonomous system for a
cottage or cabin, suitable for powering a few lights, a water pump
and radios (e.g. 40–100 W) can
cost from $700 to $2,000. Larger,
hybrid systems that are suitable
for year-round residences or
lodges (200–1500 W) can cost
from $5,000 to $30,000.
In considering the economics of
PV systems, it is important to
realize that the costs of these systems are steadily declining. The
PV industry, like the computer
industry, is continually evolving.
Improvements in PV cells, batteries and other system components
and in system design are resulting
in lower prices for PV systems.
One of the most attractive features of PV systems is that they
come in modules. The PV component of a hybrid system can be
sized to suit your budget: as prices
decline and/or your savings
increase, you can add more PV
panels and decrease your reliance
on the backup generator. If you
do not already have a generator
and are considering a solar-only
system for a cottage or sailboat,
you can start with a small system
to power a few essential appliances
and upgrade it as your finances
allow. Because PV systems last
25 years or more, they represent a
solid investment. By the way, the
price for used panels is not much
less than that for new panels
because they remain in perfect
condition for years.
The following form will help
you compare the advantages and
disadvantages of an autonomous
or hybrid PV system with conventional diesel, gasoline or propane
PV System – Purchase Decision Factors
Decision Factors
Option A: Autonomous
PV System
Option B: Hybrid PV
Option C:
Conventional System
(diesel, gasoline or
propane generator)
Capital Costs
Operating Costs
Maintenance Costs
Other Factors
(e.g. noise, pollution,
reliability, flexibility for
expansion, refuelling
needs, your time)
5. Installing and Maintaining Your Photovoltaic System
One major advantage of photovoltaic (PV) systems is that they
are relatively simple to install and
maintain. For large or complex
systems, PV companies usually
help with installation and
Your supplier should give you
any relevant system documents.
Carefully read all of the manufacturer’s recommendations. As with
any electrical system, safety is
important. You must obtain any
necessary building and electrical
permits and ensure that the system is installed according to code.
Qualified people should install
the system. If you have a gridconnected system, installation
will involve the local utility.
Wiring must be properly installed
to avoid shocks, fires and other
hazards. The main consideration
is the type and size of wire. For
example, the array wiring must
be suited for outdoor use and be
sized properly in order to carry
the peak current. As a result, you
will normally need larger wires
for low-voltage systems (12 V
compared with 120 V) to prevent
overheating and voltage loss in
the wires. Consult a professional
designer or installer to select the
proper wires. You will also need
the services of a professional
installer to:
properly fuse the system
for protection against short
circuits in the wiring or
ensure that the system is
properly grounded and protected against lightning; and
include switches between all
components of the system
that need to be isolated for
any reason.
Mounting the
PV Array
PV modules are designed to be
installed outdoors without additional protection. A mounting
structure must be constructed to
support the modules in all weather
conditions. Many manufacturers
sell support frames designed to
hold their modules; you may
decide to build your own.
Factors to be considered in mounting the array include orientation,
safety, structural integrity and
local codes. The PV array should
be mounted so as to take full
advantage of the sunlight. In the
northern hemisphere, it should
face south; true south is best, but
a deviation of 15 degrees east or
west will not affect performance
very much. Very large installations
can be mounted to track the sun
either automatically or manually
(see “Technical Information on
Photovoltaic System Components”
on page 35). In most cases, the
mounting is fixed at one angle
(a right angle to the sun at noon),
but can be adjusted according to
the season.
and Fall
▲ Array orientations showing
suggested tilt angles for summer,
spring and fall and winter use
in southern Canada.
Select a site where the array
will not be shaded at any point
during the day. A shadow on the
array can substantially cut power
output. If possible, ask your neighbours if they plan to add trees or
buildings adjacent to your property. Easements and restrictive
covenants (for definitions, see
the glossary on page 44) are
two types of legal instruments.
When used for solar applications,
they provide certain guarantees
to property owners about their
access to sunlight. If access to
sunlight concerns you, such
a written agreement may be
Depending on the array size and
the particulars of the site, the PV
array can be mounted on a roof,
a pole or the ground. In general,
the large surface areas of the modules create high wind loads on
the mounting structure, so the
structure must be designed
accordingly. Due to these high
wind loads, ground-mounted
installations require proper
foundations. For small, groundmounted installations,
▲ Ensure that your PV array will not
be shaded by neighbouring trees or
other sources of shade.
foundations can be posts sunk
into the ground to anchor the
array support frame. The support
frame itself may be made of metal
or wood. Modules are mounted
so that the bottom of the array is
above the highest depth of snow
likely to fall. Make sure that there
is no bottom lip on the array so
that snow can slide off freely.
You can use pole mounting for
small systems (one to 12 modules)
to ensure proper orientation or to
lift them above potential sources
of shade, such as buildings or
trees. The main advantages are no
snow buildup to shade the array
and the potential to track the sun.
For many residences and cottages,
roof mounting is an attractive
option, particularly if the building
is under construction. The modules should be mounted a short
distance above the pitched roof
and tilted to the optimum angle.
Since PV modules work better
when the ambient air temperature is lower, the free circulation
of air around them will improve
their performance. Elevating the
array will also prevent the
buildup of moisture and debris
behind the modules. This buildup
could rot the roof and deteriorate
the electrical connections. For
residences and cottages with a
chimney, the array should be
mounted in such a way that shading from the smoke is avoided.
Wherever you choose to mount
the array, unless shading is a concern, try to locate it as close as
possible to the battery bank or to
the load (if there are no batteries).
This will lower wiring distances
and resultant power losses.
▲ Ground- and roof-mounted PV arrays.
Is Magnetic South Truly South?
Using a compass to help you orient your PV array so that it faces
south means that you will be relying on magnetic south instead of
true south. It is better to use true south. In some parts of Canada, the
deviation of true south from magnetic south can be large enough to
affect the performance of your PV array. If your array is fixed (i.e. it
will not be tracking the sun) and you are unfamiliar with the deviation of the compass needle from true south at your location, ask an
experienced local dealer or installer for assistance.
Housing the
Your choice of battery location
should comply with the Canadian
Electrical Code, whether you
install the batteries inside or outside. The location should also be
designed to keep the batteries
warm (25°C is best), because their
capacity decreases at temperatures
below 25°C. This means that if
you choose to locate your batteries in an unheated space, you will
need to insulate the area properly.
You will also need greater battery
capacity to compensate for the
losses at lower temperatures.
Make sure that your supplier
knows about the planned location
of your batteries.
The batteries and other equipment should be accessible for
maintenance and inspection, but
safety must also be considered.
Batteries may give off hydrogen
gas during charging and can be
a source of electric shock, so the
room or area where they are
housed should be properly vented
to the outside and kept locked.
In addition, other electrical
components, which can also be a
source of spark, should be kept
separately from the battery housing. Do not locate batteries near
sources of heat or possible sources
of open flame or spark. Finally,
read all of the manufacturer’s
recommendations and warnings
about the safe and proper use
and handling of batteries.
Inside Locations
Batteries located inside the living
space should be properly vented
to the outside. For small cottage
systems with, for example, two
12-VDC (volt direct current) batteries, you need a vent that is at
least 2.5 cm (1 in.) in diameter.
Keep batteries separate from the
living space by housing them in
special battery cases (with ventilation to the outside). For summer
▲ Battery housed in a shed.
cottages, keep batteries full of
charge to prevent freezing in
the off-season.
Outside Locations
Batteries located outside of the
living space should be housed in
a box or shed. In a very cold location, you can house the batteries
in a buried container for better
temperature control. In all cases,
batteries should be well protected
from the elements and be well
vented to the outside.
An important advantage of PV
systems is that they require little
maintenance. The arrays themselves are durable and reliable and
need little attention. The following summarizes the principal
maintenance that your system
will need, but you may wish to
ask your dealer for a maintenance
schedule that is adapted to your
particular system and location.
▲ Battery maintenance varies with
the type used. Basic maintenance
includes visually checking the electrolyte levels and regularly verifying
the specific gravity of your batteries
with a hydrometer. Add distilled
water as necessary, and clean and
tighten battery posts (only the latter
are required for maintenance-free
batteries). Also, check for any leaks
or physical damage to batteries.
Follow battery and charge regulator
instructions for annual equalization
charges that help cure the batteries
from plate fouling due to corrosion.
▲ Keep track of any maintenance or
modification made to the system
(date and action). This will help
you remember when your last
maintenance routine was carried
out and may ease troubleshooting
should a problem occur.
▲ Unless you live in an extremely
dusty area or have severe problems
with ice storms, you need to inspect
the wiring and general panel appearance only occasionally. If your
system has an adjustable mounting,
you can carry out this routine maintenance check at the same time as
you adjust the tilt angle of the array.
When you adjust the angle of the
array for winter operation, snow
loading is not a problem because
the array is tilted steeply. If the
array becomes dusty, clean it with
a mild soap or plain water and a
soft cloth. Do not use solvents or
strong detergents.
▲ Generator maintenance for hybrid
systems is simpler and easier than
using a generator to produce all
your power. Change the oil as
recommended (which will be less
frequently than for a continuously
operating generator).
6. Estimating Your Needs
To further investigate which kind
of system will meet your power
needs, this section will help you
estimate your energy requirements and then estimate the
system size that your application
will require (a blank worksheet is
provided in Appendix A, page 40).
Two examples have also been
worked out in the next section.
Once you have followed this
process, you should be more
comfortable discussing different
options with a dealer.
If you are involved in the design
of power systems, a more detailed
sizing and design guide called
Photovoltaic Systems Design Manual
is available from Natural Resources
Canada (see “Learn More About
Solar Energy” on page 46).
Step 1. Estimate
Your Power and
Energy Needs
To work out how much power and
energy you need, you must know
what loads you want to power,
how much power they use (including stand-by consumption) and
how often they are used. For single-purpose applications, such as
powering a water pump, this is
fairly simple to calculate. However,
if you want a system that will run
several appliances in your home
or business, you must estimate the
usage pattern of each load.
The more energy you need, the
larger and more expensive the
system – especially if you want
an autonomous one. Therefore,
decrease your energy requirements as much as possible. This
includes using energy-efficient
appliances and using electricity
only for appliances that really
require it. For example, it is not
practical to use a PV system to
power an electric range or heating
system. Rather, meet your heating
and cooking needs with a more
fitting energy source, such as
wood or propane. A solar water
heater may also meet your hot
water needs (contact Natural
Resources Canada for Solar Water
Heating Systems: A Buyer’s Guide2).
To estimate your power needs,
first list all the loads you want
to power, note whether they are
AC or DC, and obtain their rated
wattage and the number of hours
per day they will be used (see
Step 1 of the worksheet in
Appendix A).
About Efficient Lighting
Next, for each load, multiply
the power rating (using actual
or typical values) by the number
of hours of estimated daily usage
to obtain the total watt-hours
of power needed per day. If consumption is already given in
watt-hours per day (or kilowatthours per year, as on EnerGuide
labels), you can skip columns A
and B in Step 1 of the worksheet
and simply fill in column C using
the watt-hours per day.
For lighting, consider AC
or DC compact fluorescent
lights instead of incandescent
bulbs. They give four times
more light per watt of electricity and last 10 times
longer. Consult a specialized
supplier for information on
high-efficiency lighting for
outdoor applications.
60W ➜ 15W
If available, use the rating
indicated on the label of the
appliance or tool you need to
power. Also use the typical values
given in Appendices B (page 42)
and C (page 43) for common
appliances and lighting.
10 1000h = 10 000h
▲ Fluorescent lights use one quarter the energy of incandescent bulbs and last 10
times longer.
For your copy of Solar Water Heating Systems: A Buyer’s Guide, call Natural Resources Canada at 1 800 387-2000 toll-free, or visit the Web site
EnerGuide Labels
If there is an EnerGuide label on
your appliance, you can use the
electrical consumption rating (in
kilowatt-hours per year) given on
the label for your worksheet. Note
that the EnerGuide ratings for
clothes washers and dishwashers
include the electricity consumed
in heating the water used in those
appliances. These ratings are less
useful to you if, as we recommend, you heat your water with
solar water heaters, propane or
wood (instead of PV-generated
If you use the value on an
EnerGuide label, convert the kilowatt-hours per year (kWh/a) into
watt-hours per day (Wh/d) for
inclusion in column C of the
worksheet in Appendix A. To
make this conversion, multiply
by 1000 and then divide by 365.
Finally, fill in the subtotal(s),
calculate the adjusted AC loads
(for inverter losses) using 0.90 as
your initial conversion efficiency,
and fill in the “total daily load”
value at the bottom of the first
side of the worksheet.
Smaller, efficient appliances
will require less PV equipment.
Some PV dealers also carry
high-efficiency appliances
and lighting.
▲ EnerGuide labels provide energy consumption
Always keep in mind that your
energy requirement has a direct
impact on the following:
the area of PV modules
needed to power the load
or recharge the batteries;
the capacity of the batteries
required to meet your needs
without running a generator
at night or on cloudy days;
the amount of fuel used by
a generator or the size of a
wind generator.
Watch Out For
“Phantom” Loads!
A growing number of electronic appliances draw power
even when they are turned
off. Examples are a TV or
VCR that maintains program
memory, runs its clock and
keeps the remote-control
receiver active. The stand-by
power required can appear to
be negligible, and it is often
not even mentioned in appliance owner’s manuals. But it
may represent a substantial
amount of energy because
power is drawn 24 hours a
day. For example, the stand-by
power for a remote-controlled
portable TV may be as low as
5 W, but it will still require
120 Wh/d (5 W x 24 h). This
represents the same amount
of energy as using this TV
(60 W) for two hours a day
(120 Wh/d)!
ratings (in kilowatt-hours per year) for major
home appliances.
Power or Energy?
The following two terms are used to characterize electricity usage:
• the power or “instantaneous power required”; and
• the energy or “energy consumption over a period of time.”
The power you need (the wattage) is the instantaneous intensity of
electricity that is required to power the appliances you use. The
more appliances used at the same time, the more power required.
Power is expressed in watts (W). A watt is a convenient SI unit in
electricity because it is simply the product of the current – in
amperes (A) – and the voltage – in volts (V).
This simple formula indicates, for example, that a 12-W compact
fluorescent light will require 1 A when connected to a 12-VDC (volt
direct current) power source.
Energy depends not only on the power required by your appliances,
but also on how long and how often you use them. Energy is
expressed in watt-hours (Wh) for a given period of time (per day,
month or year). It is defined as the power times the number of
hours the equipment is used over this time.
1 Wh = 1 W 1 h
For example, using a 1650-W hair
dryer for eight minutes draws the
same amount of energy as using
five efficient lights (11 W each)
for four hours: about the amount
that one 50-W PV module produces in an average day.
Hair dryer:
1650 W x 8/60 = 220 Wh
Fluorescent lights:
5 x 11 W x 4 = 220 Wh
Step 2. Make a
Rough Evaluation
of PV System Size
2.1 Evaluate Which
Stand-Alone System
Is More Suitable:
Autonomous or
Stand-alone PV systems can be
either autonomous (with or without storage batteries), relying only
on solar energy, or hybrid. Hybrid
systems combine PV with one or
more other electrical generating
sources and normally include
storage batteries. Factors that
influence the type of system
include the following: total and
peak power requirements; when
power is needed; required power
reliability; whether the application is seasonal or year-round;
and whether the system will be
easily accessible or installed in
a remote location.
Autonomous Systems
As the name suggests, autonomous
systems are self-sufficient and not
backed up by another generating
source. They normally include
battery storage. Some applications, such as irrigation, pumping
or greenhouse ventilation, require
power only when the sun is shining. Therefore, an autonomous
system without storage would be
suitable in such cases. In most
cases, however, power is needed
whether the sun is shining or
not, so the system includes
battery storage.
▲ The autonomous PV system in Yoho National Park, British Columbia, supplies
electricity for the amphitheatre projector and recharges the batteries of a golf cart
that the staff uses to collect camping fees. Photo courtesy of Sovran Energy Inc.
200 400 600
▲ Average daily number of peak sunlight hours in September (use for seasonal
summer autonomous systems). Source: Environment Canada.
Autonomous systems are also
appropriate for summer vacation
properties, sailboats and other
applications where the period of
use corresponds to the period of
greatest available sunlight. If you
consider power a luxury instead
of a necessity and can tolerate the
odd occasion when the system
cannot meet your loads, an
autonomous system may be
suitable at a reasonable price.
However, if you want guaranteed
power on a year-round basis and
can easily access the site, some
sort of hybrid system will likely
be more affordable.
2 .2
In Canada, about twice as much
sunlight is available in summer
than in winter. To guarantee
power year-round using a solaronly system, a significantly larger
(and hence more costly) array and
battery system is needed. Such
systems are practical for applications in remote, unattended sites,
which are difficult and expensive
to visit, and where the capital
costs are rapidly offset by avoiding costs for maintenance and
fuelling visits. Thus, solar-only
systems with storage are used for
electric fencing in remote areas,
and in communications, marking
and warning signs, monitoring
sites and other situations where
reliability and low maintenance
are critical.
200 400 600
2 .2
▲ Average daily number of peak sunlight hours in December (use for yearround-operated autonomous systems). Source: Environment Canada.
Hybrid Systems
Hybrid systems use a combination
of PV and other power sources.
Usually, hybrid systems use a
wind generator with a diesel,
propane or gasoline generator as
backup. Hybrid systems may be
suited for applications such as
residences and commercial buildings that are not connected to
the grid. If you need more than
2.5 kWh of energy per day
year-round and already have
a generator, or if you live in an
area that has poor sunlight for
long periods, a hybrid system is
probably a good choice.
December map, and insert this
value under Step 2 of the worksheet in Appendix A.
In the summer, September has
the fewest hours of peak sunlight.
Overall, December has the fewest
hours of peak sunlight. To estimate the available sunlight design
value for a seasonal (summer)
autonomous system, use the
values from the September map.
To estimate the available sunlight
design value for a year-round
autonomous system, use the
values from the December map.
2.2 Estimate the
Available Sunlight
Knowing the solar resources
available is key to the design
of an efficient and affordable
PV system. The maps on page 27
show the average daily values
of peak sunlight hours that strike
south-facing, fixed PV arrays
in various parts of Canada in
September and December.
These values assume that the
arrays are tilted at right angles
to the sun at noon. Alternatively,
you can get weather and solar
radiation values for selected sites
from Environment Canada’s
Meteorological Service of Canada
or from RETScreen® International
software (see “Learn More About
Solar Energy” on page 46).
Choose a value for your location
from either the September or
For a PV-diesel hybrid system,
you may choose December
values or average the two values
(September and December). This
is described in the case study
on pages 33 and 34.
Hybrid systems generally include
battery storage; the load draws
power from the batteries. When
there is enough sunshine, the PV
array keeps the batteries charged.
If a wind generator is incorporated, it charges the batteries
during windy periods, which are
often when it is overcast or at
night. For this reason, wind and
solar equipment are a perfect
complement to one another.
The diesel or gasoline generator
is needed only once in a while
to charge the batteries during
extended overcast and calm
periods. The generator operates
at nearly full capacity, and this
results in a better generator duty
cycle, more efficient fuel use,
lower maintenance costs and
longer generator life. Applications
that involve both solar and wind
equipment often do not need
a gas or diesel generator.
Parks Canada’s remote camp located
in the far north on Ellesmere Island,
Nunavut, is powered by a PV array
(on a tracker) combined with a wind
generator and a gasoline generator.
Technical Note: Definition of Units Used to Describe a PV System and
Some Orders of Magnitude
Full (peak) sunlight:
1000 W/m2 of energy density (about the intensity of the sun at noon on a bright
sunny day)
1 hour of peak sunlight: 1000 Wh/m2, the equivalent of 1000 W/m2 during one hour (e.g. 2 h at 500 W/m2 or
1 h at 600 W/m2 and 2 h at 200 W/m2)
100-W PV module:
Power capacity of a PV module able to produce 100 W of electricity when maintained
at 25°C and exposed to full peak sunlight (1000 W/m2)
100 W (PV) exposed to 1 h of peak sunlight = 100 Wh of electricity
Rule of thumb:
Typical annual radiation in Canada is 1500 h of peak sunlight (range of 1100–1700 h).
100 W installed = potential of 150 kWh/a.
Due to system losses and other causes of inefficiency, the energy production of
PV systems is often estimated as follows:
100 W installed ≈ 100 kWh/a
2.3 Estimate
the Required
PV Array Size
The next step is to size the PV
array. This takes into account
power losses in battery charging
(Effbat of 75 to 90 percent) and
regulator efficiency (Effreg of 80
to 90 percent), especially if the
controller does not include a
maximum power point tracker
(MPPT) (see the glossary on page
44). Typically, an MPPT is used
only for medium to large systems
when benefits related to energy
gains are greater than the cost of
this feature. Additional losses due
to dust or snow accumulation on
modules are likely, but they are
relatively low.
After you determine the array
size (in watts), estimate the number of modules required. To do
this, divide the array size by the
power rating of the module you
intend to use in your installation
(normally 20 W to 100 W).
Power, Voltage and Current Ratings of Typical PV Modules
Rated Power (W)
Nominal Voltage (V)
Nominal Current (A)
Kyocera KC 120
Siemens SM100
Solarex SX-85
BP Solar BP-275
Photowatt PWX500
Note: The above modules are examples of those available on the market. Each manufacturer provides a complete line of modules
that have different sizes and power ratings. This list is not an endorsement of these products.
2.4 Estimate Battery
Capacity for
Autonomous Systems
The size of battery you need
depends on whether you require
uninterrupted power and how
much you are prepared to pay
for that privilege. For a weekend
cabin or cottage, you may not
really mind if the power fails
occasionally during an extended
overcast period. On the other
hand, uninterrupted power
may be a necessity for some
For most applications, a good rule
of thumb is to provide enough
battery storage to supply power
during three to five overcast
days. (Battery capacity for hybrid
systems is usually enough for
only one or two days). A battery
should not be completely discharged, so as not to shorten its
life. Thus the available capacity
of a battery is less than the nameplate rating. A “maximum depth
of discharge” factor is already
included in the equation in the
worksheet (see Step 2 in Appendix
A on page 41). It ensures that
the battery charge never drops
below 50 percent of full charge.
This value depends on the type
of battery you select. Consult
your dealer.
Technical Note: Battery Capacity Rating
Watts may be expressed in Wh (volts x amps). Likewise, energy may be
expressed in Ah (amperes x hours) at a given voltage. This is often used
in the battery industry to express battery capacity. For example, a battery
with 960 Wh of capacity is generally referred to as a 12-V, 80-Ah battery
(12V x 80 Ah = 960 Wh).
Wh = V Ah
Use the blank worksheet to help
size your stand-alone PV system.
Now that you have estimated
the size of the PV array and the
amount of battery storage you
require, you are in a position to
approach a dealer. Discuss costs
and make decisions on what is
best for your particular situation.
7. Sizing Worksheet Examples
In the following examples, two hypothetical case
studies show how the worksheets can be used. The
Smiths, for example, are interested in PV power for a
remote vacation cabin. The Wongs, meanwhile, want
a system that will provide reliable power year-round
for their home and business. Both families are interested in renewable energy and want to know if a PV
system would be appropriate for them.
pollution of the city, and they would prefer a quiet,
non-polluting power source. They are particularly
interested in a PV system because it is durable and
requires low maintenance.
The Smiths’ main priority is to keep costs at a minimum, and they are willing to sacrifice power availability
to do this. After all, they do not have power now, and
the thought of the odd blackout does not bother them.
They have a propane-powered refrigerator, and they
are willing to switch to fluorescent lighting and make
do with a minimum of appliances to keep their power
needs low. For their needs, a system that is small, solaronly and is stand-alone appears to be a good solution.
Example 1. Summer Cabin
Power System – The Smiths
The Smiths own a small vacation cabin where they
spend most summer weekends and holidays, as well
as the occasional weekend in the winter. The cabin has
no electricity or running water and is far from the grid.
After several years of filling oil lamps and hauling water,
the Smiths would like to enjoy the benefits of electricity.
However, the cabin is their escape from the noise and
Working through the worksheet, the Smiths find that
roughly a 120-W (watt) system and about 211 Ah
(ampere-hours) of batteries could meet their needs
at a price they can afford.
Worksheet: The Smiths (Summer Cabin)
Step 1. Estimate Your Power and Energy Needs (watt-hours per day)
AC or DC
(A) Rated Wattage
(B) Hours
(check one)
(actual or
Appliance Load
typical values)
Per Day
(C) Watt-Hours Per Day
(A) x (B)
Kitchen lights (2)
✓ (12 V)
1 h (x 2) = 2
Bedroom lights (2)
Living-room lights (2)
✓ (12 V)
✓ (12 V)
1 h (x 2) = 2
4 h (x 2) = 8
Water pump
✓ (12 V)
✓ (12 V)
TV (black and white)
✓ (12 V)
DC: 354 Wh/d
DC to AC inverter efficiency (Effdc ac) ranges from 80 to 95 percent (0.80 to 0.95). To help you with your first
calculation, 0.90 has been inserted in italics. Adjust the efficiency figure, if necessary, once you have chosen the
inverter for your system and have read the manufacturer’s ratings.
The Smiths do not need an inverter because all their loads are 12 VDC (volt direct current). They can add one at
any time.
Adjust AC loads for inverter losses:
AC load = 0
Effdc ac
Total daily load: DC loads + adjusted AC loads = 354 Wh/d
Worksheet: The Smiths (Summer Cabin)
Step 2. Make a Rough Evaluation of PV-System Size
2.1. Evaluate Which Stand-Alone System Is More Suitable: Autonomous or Hybrid
This summer cottage will be equipped with an autonomous PV system.
■ Hybrid
• seasonal use (summer mainly)
• year-round operation and
energy requirements > 2.5 kWh/d
higher latitudes
• year-round operation with
low energy requirements (< 1 kWh/d)
low requirements for power availability
• limited/expensive access to the site
• already have a generator
• very high requirements for power availability
• maintenance is an issue
2.2. Estimate the Available Sunlight
Sunlight: 3.9 h/d (Consult maps on page 27 or
see “Learn More About Solar Energy” on page 46.)
2.3. Estimate the Required PV Array Size (W)
Array size (W)
= Total daily load (Wh/d)
Peak sunlight hours x 0.77*
354 Wh/d
3.9 h/d x 0.77
= 118 W**
* The factor 0.77 assumes a 90-percent battery charge
regulator efficiency and an 85-percent battery efficiency.
** Based on rated power output of PV modules if an MPPT
controller is used (see the glossary on page 44). If an MPPT
controller is not used, further losses should be accounted
for, resulting in an increased power capacity of
15–25 percent. Consult your dealer.
2.4. Estimate the Required Battery Capacity
Nominal voltage of battery:
(typically 12, 24 or 48 volts)
Number of days of battery
storage needed (a good rule of
thumb is three days for an
autonomous system):
(Vbat): 12 VDC
Battery capacity (Ah):
Total daily load (Wh/d) x days of storage
Battery voltage (Vbat) x 0.42***
= 354 Wh/d x 3 d
12 V x 0.42
= 211 Ah at 12 V
*** The factor 0.42 assumes an 85-percent battery efficiency
and a 50-percent maximum depth of discharge. If the
battery is used at temperatures lower than 25°C, its
capacity (ampere-hours) will decrease. Consult your
PV system supplier.
Example 2. Year-Round
Remote Residential
Power System –
The Wongs
stove run on propane. (Running large loads on propane
greatly reduces the up-front cost of a PV system.)
The Wongs are a young couple who have been living
beside a small lake for several years, away from the
electric grid. They run a small handicrafts business,
manufacturing woven goods. The Wongs use a
propane generator to provide power for their home
and studio. But they have grown tired of constant noise
and pollution, increasingly high fuel bills and frequent
maintenance requirements. Their electrical consumption is low despite many loads because the fridge and
After filling out the worksheet, the Wongs find that
meeting their needs with an autonomous system would
be too expensive. They figure that they can currently
afford only a small fraction of the PV panels required,
but they may be able to add more panels in a few
years. In the meantime, they decide to combine their
existing propane generator with PV panels to make a
hybrid PV system that offers the potential to reduce
the aggravation and costs linked with using a generator. Based on their current resources, this appears to
be their best option. Knowing this, they are now in a
better position to talk to a PV dealer about the type
of system they want.
Worksheet: The Wongs (Year-Round Residence)
Step 1. Estimate Your Power and Energy Needs (watt-hours per day)
AC or DC
(A) Rated Wattage
(B) Hours
(check one)
(actual or
Appliance Load
typical values)
Per Day
Kitchen lights (2)
Living-room lights (2)
Bedroom lights (2)
Basement, bathroom
and hall lights (4)
Freezer (very efficient)
Water pump
Outdoor lights (2)
Clothes washer (front load)
Furnace fan
Workshop lights (4)
Radio (in workshop)
Colour TV (no remote control)
Vacuum cleaner
Intermittent loads
(C) Watt-Hours Per Day
(A) x (B)
3h x 2 lights
5 (x 2)
2 (x 2)
1 (x 4)
1000 (estimate)
8 (x 2)
1 (1 load)
7 (x 4)
✓ (12 V)
✓ (12 V)
(e.g. coffee-maker, iron, small
power tools, block heater, etc.)
AC: 3999 Wh/d
DC: 360 Wh/d
DC to AC inverter efficiency (Effdc ac) ranges from 80 to 95 percent (0.80 to 0.95). To help you with your first
calculation, 0.90 has been inserted in italics. Adjust the efficiency figure, if necessary, once you have chosen the
inverter for your system and have read the manufacturer’s ratings.
Adjust AC loads for inverter losses:
AC load = 3999
Effdc ac
Total daily load: DC loads + adjusted AC loads = 4803 Wh/d
Worksheet: The Wongs (Year-Round Residence)
Step 2. Make a Rough Evaluation of PV-System Size
2.1. Evaluate Which Stand-Alone System Is More Suitable: Autonomous or Hybrid
This summer cottage will be equipped with a hybrid PV system.
■ Autonomous
• seasonal use (summer mainly)
• year-round operation and
energy requirements > 2.5 kWh/d
higher latitudes
• year-round operation with
low energy requirements (< 1 kWh/d)
low requirements for power availability
• limited/expensive access to the site
• already have a generator
• very high requirements for power availability
• maintenance is an issue
2.2. Estimate the Available Sunlight
Sunlight: 3.4 h/d (consult the maps on page 27 or
see “Learn More About Solar Energy” on page 46.)
2.3. Estimate the Required PV Array Size (W)
Array size (W)
Total daily load (Wh/d)
Peak sunlight hours x 0.77*
4803 Wh/d
3.4 h/d x 0.77
= 1835 W**
* The factor 0.77 assumes a 90-percent battery charge
regulator efficiency and an 85-percent battery efficiency.
** Based on rated power output of PV modules if an MPPT
controller is used (see the glossary on page 44). If an MPPT
controller is not used, further losses should be accounted
for, resulting in a required power capacity increase of
15–25 percent. Consult your dealer.
2.4. Estimate the Required Battery Capacity
Nominal voltage of battery:
(typically 12, 24 or 48 volts)
Number of days of battery
storage needed (a good rule of
thumb is two days for a
hybrid system):
(Vbat): 24 VDC
Battery capacity (Ah):
Total daily load (Wh/d) x days of storage
Battery voltage (Vbat) x 0.42***
= 4803 Wh/d x 2 d
24 V x 0.42
= 953 Ah at 24 V
*** The factor 0.42 assumes an 85-percent battery efficiency
and a 50-percent maximum depth of discharge. If the
battery is used at temperatures lower than 25°C, its
capacity (ampere-hours) will decrease. Consult your
PV system supplier.
8. Technical Information on Photovoltaic System Components
PV Technology
The most common photovoltaic
(PV) cell material is silicon. It
is one of the most abundant
elements on earth: sand from
the beach is an oxide of silicon.
The first commercial PV cells
were monocrystalline silicon.
Other manufacturing techniques
resulted in polycrystalline
silicon cells. A monocrystalline
cell is made of a single crystal;
a polycrystalline cell contains
many crystals. Commercial
polycrystalline cells are only
slightly less efficient than
monocrystalline cells and are,
therefore, widely used because
their cost-performance ratio
is similar.
production techniques led to the
manufacture of “multi-junction”
amorphous cells, which contain
two or three layers of semiconductor. Because of the lower
efficiency, modules that are
physically larger are needed in
order to generate a given amount
of power.
Other thin-film technologies
have been developed – such as
cadmium telluride and copper
indium diselenide – and are
beginning to appear on the market.
The development of thin-film
technologies reduces costs further
by decreasing the amount of
material needed to make a cell.
Amorphous silicon modules
require only a thin layer of silicon
and can be mass produced. New
▲ Monocrystalline, polycrystalline
and flexible amorphous silicon cells.
Photos courtesy of Siemens Solar
Industries, Photowatt International
S.A. and United Solar Systems
Corp., respectively.
The Electric
of PV Modules:
The CurrentVoltage
(I-V) Curve
The PV module can be operated
at any combination of current
and voltage found on its “I-V
curve.” But in reality it operates
at only one combination at a
given time. This favoured combination is chosen not by the
modules, but rather by the electric characteristics of the circuit
that is connected to the modules.
The voltage that occurs when
current is zero is known as the
open-circuit voltage (Voc). On
the other hand, the current when
the voltage is zero is referred to
as the short-circuit current (Isc).
While current and voltage are at
their highest under short-circuit
and open-circuit conditions,
respectively, the power at these
points is zero. In practice, a
system operates at a combination
of current and voltage at which
a reasonable amount of power is
produced. The best point is the
maximum power point (MPP).
Corresponding voltage and
current are called Vp (nominal
voltage) and Ip (nominal
current), respectively. This point
of operation (MPP) is used to
define the nominal rating and
efficiency of a module.
Maximum Power
Point Pmax = Ip x Vp
I = Isc
▲ Important points that characterize a PV module.
Serial number
Manufacturer XYZ
Made in WZC
Performance at 1999 W/m2 solar irradiance and 25°C cell temperature
Max. power
Short circuit current
48 Wp
Max. syst. open circuit voltage
3.35 A
Open circuit voltage
600 V
Fire rating
19.8 V
Series fuse
Class C
▲ Typical information found on a PV module label.
You should find all of these
electric characteristics (Voc, Isc,
MPP, Vp, Ip) on the label of a
good-quality PV module (note
that the Vp and Ip values are also
called nominal or rated voltage
and current). Do not expect to
get the rated power from your
installed system – it is impossible
for a fixed system to operate at
the highest power point at all
times. Temperature variations
alone will change the amount
of power your system generates.
Rated current
3.02 A
Rated voltage
15.9 V
Field wiring
copper only, 14 A WG min.
insulated for 75°C min.
in PV Systems
Most off-grid PV systems use
batteries to store power for use
during periods of low or no
sunlight. Certain specialized
applications (e.g. some pumping
and ventilation systems and calculators) do not require storage
because power is needed only
during periods of light. Some
pumping applications use
pumped water as the storage
medium rather than electricity.
However, most PV systems in
Canada use batteries.
Your choice of battery size and
type is an important design
consideration, particularly for
systems that have no backup
power source. The batteries alone
can represent 25 to 50 percent of
total system cost, so it is essential
to select the right type. You can
use different types of rechargeable
batteries, depending on the system’s requirements. Batteries with
a long expected life have higher
initial costs but should cost less
in the long run. Several batteries
on the market are designed for
use with renewable energy systems, such as PV and wind
systems. Deep-discharge marine,
golf cart or recreational vehicle
(RV) batteries may also be suitable
and are generally more affordable
up front. An experienced PV
dealer can advise on what type
of battery is best for your needs.
Most PV systems use lead-acid
batteries such as deep-discharge
lead-calcium or lead-antimony
batteries. Do not use car batteries
as they are not designed for
repeated deep discharges. Nickelcadmium (Ni-Cd) batteries are
rarely used in residential applications. Although they can be
deeply discharged many times
without harm and are less
affected by temperature changes
than lead-acid batteries, Ni-Cd
batteries are more expensive and
very expensive to recycle. As a
result, their use is primarily
restricted to applications where
their increased reliability and
low maintenance are worth the
premium price.
Battery storage capacity is generally rated in ampere-hours (Ah).
This is the amount of current that
a battery will deliver over a given
number of hours at its normal
voltage and at a temperature of
25°C. The rated capacity of any
battery drops with temperature.
The size of battery you require is
determined by the total anticipated drain on the battery. You
can calculate this if you know the
following information: the voltage of the battery, the wattage of
the load, the length of time the
load is operated and the ambient
temperature of the batteries.
For example, to run a 25-W bulb
for eight hours from a 12-V battery
that is maintained at 25°C, you
would need a battery with a capacity of at least 16.7 Ah (200 Wh
at 12 V). If the battery must
operate at temperatures as low as
Technical Note:
Selecting Batteries for
PV Systems – Points
to Consider
• voltage and current
• storage capacity is quoted at
a certain discharge rate. If
the discharge rate (the rate at
which power is being drawn
out) is less than what the
manufacturer quotes, the
battery’s capacity is greater.
The opposite is also true;
• maximum depth of
discharge (different for
each type of battery);
• operating temperature range
and how temperature affects
• battery lifetime: the number
of times the battery can be
charged and discharged
before it has to be replaced.
This number depends on the
depth of discharge of cycle.
The less discharged the battery is at each cycle, the
more cycles it can sustain;
• maintenance requirements:
some batteries are almost
• energy density: the amount
of usable energy a battery
can produce over a given
time relative to its weight
and volume;
• cost; and
• warranty.
Percent of 25°C Discharge Capacity Delivered
Discharge Temperature (°C)
▲ Operating batteries at temperatures
below 25°C implies that you will
need more nominal capacity. (This
will vary, according to the type of
batteries and rate of discharge
0°C, then at least a 20-Ah battery
would be required for the same
load. But in practice, to protect
the battery against accelerated
aging, a larger capacity is used to
avoid a complete discharge. For
deep discharge batteries, do not
use more than 80 percent of
their nominal capacity. Also, car
batteries start to be damaged if
discharged more than 20 percent
of their nominal capacity; therefore, they are not well suited for
this type of application.
In the sizing worksheet examples
in Section 7 (Step 2.4), an average
value of 50 percent was chosen
for the depths of discharge (the
portion of battery nominal
capacity used) so that the recommended sizes for the examples
above would be 40 to 50 Ah,
depending on the temperature
at which the battery is operated.
PV battery systems are usually
designed to provide several days
of storage in the absence of
sunlight. In cases where longer
overcast periods are anticipated,
such as in the Far North, it is usually wiser to use a hybrid system
rather than trying to provide
enough battery storage. In this
and many other cases, your most
practical approach may be to use
a combination of backup power
and batteries.
(100–1000 W) are suitable for
small systems (e.g. power for
lights). They are available with
12- or 24-volt direct current
(VDC) input voltages and
120-volt alternating current
(VAC) output. Larger inverters
(1000–4000 W) are available,
mainly with 12, 24 and 48 VDC
input and 120 or 240 VAC output.
For high-start power surges
(e.g. from large electric motors),
heavy-duty inverters are needed.
Low-cost inverters produce a
modified square wave, which
is not as good as utility power.
Roughly a dozen electrical loads
do not run well on this type of
inverter. Your dealer can help
you overcome most of these load
problems by choosing proper
appliances, tools, etc. Sine-wave
inverters generally produce power
that is similar to the quality of
utility power.
Power-conditioning equipment
modifies the power from the PV
array to make it more usable.
Two power-conditioning devices –
inverters and battery charge
regulators – are described in
the following.
PV cells generate direct current
(DC), and batteries store electricity as DC, but most common
appliances require alternating
current (AC). In cases where you
need AC power, an inverter is
used to change low-voltage DC
(12, 24, 32, 36, 48, 96, 120) to
higher voltage AC (120 or 240).
Some power is lost in the conversion as inverters are, on average,
about 80- to 95-percent efficient.
AC wiring, components and
appliances are more available and
generally less expensive than similar DC products. Consequently,
inverters are convenient for
many systems.
Inverters cover a wide range of
power capacity, and the type
needed depends on the application. Light-duty inverters
Some PV modules even come
with built-in inverters. Such modules are called AC modules. You
can build up a complete AC system, AC module by AC module,
increasing the capacity with each
addition. (These inverters are used
only for grid-connected systems.)
Many of today’s inverters also
come equipped with the following features:
1) Metering: a display to
provide volts input/output,
frequency output, voltage
and frequency of a fuel-fired
2) Fuel-fired generator start
capability: Extra relays are
provided to auto-start a generator if the batteries reach a
programmed state of low
capacity. Some can even be
programmed to keep the generator from starting during
the night (to avoid the noise),
unless the batteries reach a
second programmed low, in
which case the generator will
start regardless.
3) Grid-connected capability:
The inverter can convert
the DC output from the
array to AC power that can
be synchronized with the
grid (utility). This feature
makes it possible to reduce
or even eliminate monthly
utility bills.
4) Charging capability:
Inverters can draw power
from either the grid or a
fuel-fired generator to charge
the battery bank while, at
the same time, continuing to
pass that power through to
the electrical loads in your
house. Some inverters vary
the charge rate and voltage to
certain types of batteries and
their current temperature.
5) Stacking: Some inverters can
be linked together, either to
produce twice the output or
to produce power that is out
of phase from inverter to
inverter in order to produce
240-VAC power.
Battery Charge Regulators
Battery charge regulators control
the amount of current entering
the battery and protect it from
overcharging and from completely discharging. They can also
measure battery voltage to detect
the state of charge. Regulators
range from 2 to 300 A for voltages
from 12 to 48 volts DC.
Different types of controllers
exist: the on-off and the pulsewidth modulation controls are
the most common types. More
sophisticated controllers are
more efficient, but you and your
dealer should evaluate whether
their performance justifies the
investment. For example, some
controllers include a maximum
power point tracker (MPPT)
feature. It allows a PV module
or array to work at its highest
power point depending on solar
intensity, even if the battery is
recharged at a constant voltage.
This feature provides about
10 percent more power in the
summer and roughly 30 percent
more in the winter. These gains
are generally higher for panels
with high voltage peak (Vp) values.
pros and cons of manual and
automatic trackers that are
currently on the market.
When considering the use of a
tracker, remember that it will not
significantly increase the performance of the PV system during
the winter in Canada. The use of
a tracker is more cost-effective for
applications operating from the
spring to the fall, especially those
located at higher-latitude sites.
Because automatic trackers make
the system more complex, they
are rarely used for applications
where no one is present for
extended periods of time, such
as telecommunications.
PV Trackers
The sun “tracks” across the sky
every day. To get maximum output from your PV array, a tracker
can be a cost-effective feature.
The main issue is economics.
Does the increased output from a
reduced number of tracked panels
outweigh the cost of the extra
panels bought for a fixed array?
Generally speaking, the larger the
array, the more cost-effective the
tracker. Remember, a fixed array
must be mounted on a structure,
so the true cost of a tracker is the
difference between its cost and
the cost of a fixed array mounting
Trackers are usually mounted
3 m (10 ft.) off the ground,
avoiding the need to drill through
a roof. Less snow and ice accumulates out in the open and off the
ground, compared with a roof.
Ask your dealer to explain the
Appendix A: Worksheet to Evaluate System Size
This worksheet will help you get a
rough estimate of the size of your
PV system. For this level of
design, you need only choose a
nominal battery voltage and collect the information on the
available hours of peak sunlight
in your area. The results that you
will obtain below are only estimates and do not replace the
technical design and expertise
required for a proper system. If
you wish to undertake such a
technical design, consider ordering Photovoltaic Systems Design
Manual from Natural Resources
Canada (for contact information,
see “Learn More About Solar
Energy” on page 46).
Note: Figures in the equations
below must be expressed as
fractions, not percentages.
For example, an efficiency
of 90 percent should be written
as 0.90 in your calculations.
Step 1. Estimate Your Power and Energy Needs (watt-hours per day)
AC or DC
(A) Rated Wattage
(B) Hours
(check one)
(actual or
Appliance Load
typical values)
Per Day
(C) Watt-Hours Per Day
(A) x (B)
DC to AC inverter efficiency (Effdc ac) ranges from 80 to 95 percent (0.80 to 0.95). To help you with your first
calculation, 0.90 has been inserted in italics. Adjust the efficiency value, if necessary, once you have chosen the
inverter for your system and have read the manufacturer’s ratings.
Adjust AC loads for inverter losses:
AC load =
Effdc ac
Total daily load: DC loads + adjusted AC loads = ________ Wh/d
Step 2. Make a Rough Evaluation of PV System Size
2.1. Evaluate Which Stand-Alone System Is More Suitable: Autonomous or Hybrid
■ Autonomous
■ Hybrid
• seasonal use (summer mainly)
• year-round operation and
energy requirements > 2.5 kWh/d
higher latitudes
• year-round operation with
low energy requirements (< 1 kWh/d)
low requirements for power availability
• limited/expensive access to the site
• already have a generator
• very high requirements for power availability
• maintenance is an issue
2.2. Estimate the Available Sunlight
h/d (consult the maps on page 27 or
see “Learn More About Solar Energy” on page 46.)
2.3. Estimate the Required PV Array Size (W)
Array size (W)
Total daily load (Wh/d)
Peak sunlight hours x 0.77*
h/d x 0.77
* The factor 0.77 assumes a 90-percent battery charge
regulator efficiency and an 85-percent battery efficiency.
** Based on rated power output of PV modules if an MPPT
controller is used (see the glossary on page 44). If an MPPT
controller is not used, further losses should be accounted
for, resulting in a required power capacity increase of
15–25 percent. Consult your dealer.
2.4. Estimate the Required Battery Capacity
Nominal voltage of battery:
(typically 12, 24 or 48 volts)
Number of days of battery
storage needed (a good rule
of thumb is two days for
a hybrid system and three days
for an autonomous system):
(Vbat): ____ VDC
_____ days
Battery capacity (Ah):
Total daily load (Wh/d) x days of storage
Battery voltage (Vbat) x 0.42***
Wh/d x
____ V x 0.42
= _______ Ah
*** The factor 0.42 assumes an 85-percent battery efficiency
and a 50-percent maximum depth of discharge. If the
battery is used at temperatures lower than 25°C, its
capacity (ampere-hours) will decrease. Consult your
PV system supplier.
Appendix B: Typical Loads
Typical Power Ratings of Some Common Appliances
Power Rating (watt)
12-V DC loads
Auto stereo
CB radio:
Digital clock (LED)
Drill (3/8 inch)
Compact fluorescent
Four-foot type (double-ended)
Portable TV:
Black and white
Vent fan (15-cm blade)
Water pump
Hair dryer
120-V AC loads
About Electric Motors
Power is often expressed in horsepower (hp) for
motors. This refers to the mechanical power output
of the motor. If you have information on current
and voltage, always use this information rather
than converting hp into watts. A watt (W) is the
SI unit for power (1 hp ≈ 746 W). However, this may
differ from the actual electric power requirements,
due to the power factor of a motor in AC or other
sources of inefficiency found in any motor. If
you intend to power a standard AC motor with
a PV system, you can use the following formula
to estimate your electric power requirement:
1 hp (mechanical output) ≈ 1 kW (electrical input).
Power Rating (watt)
Block heater
Clothes washer, excluding hot water
Front-loading washer
Dishwasher, excluding hot water
Drill (3/8 inch)
Fan, portable
Furnace fan motor (varies greatly)
Hair dryer
Curling iron
Compact fluorescent
Four-foot type (double-ended)
Microwave oven
Personal computer:
Desk model
Laser printer (while printing/standby)
Laptop in use
Laptop charger
100 (max.)
Radio-telephone (transmitting/idle)
Single-side band radio (idle)
TV (19 inches):
Black and white (in use)
Colour (in use/standby with
remote control)
Remote control (standby)
Vacuum cleaner
VCR (on/standby)
Water pump ( 1/2-hp jet)
Note: These are typical values only. For exact numbers, consult
product literature or supplier.
Appendix C:
Energy-Efficient Lighting
Comparison of Typical Lighting Systems
Incandescent Bulbs
Lights (CFLs) with
Magnetic Ballast
CFLs with
Electronic Ballast
▲ Source: Energy-Efficient Lighting Products for Your Home
(Natural Resources Canada’s pulication)
Ampere-hour (Ah)
Kilowatt (kW)
Photovoltaic (PV) array
A current of one ampere running
for one hour.
One thousand watts.
Autonomous system
One kilowatt acting over
one hour.
An interconnected system of PV
modules that function as a single
electricity-producing unit. The
modules are assembled as a
discrete structure with a common
support or mounting. In smaller
systems, an array can consist
of two modules plus a support
structure or mounting.
A stand-alone photovoltaic (PV)
system that has no backup generating source and relies only on
solar energy to meet the needs of
the load. May or may not include
storage batteries.
Balance of system
The parts of a PV system other
than the PV array and batteries.
This may include switches, controls, meters, power-conditioning
equipment, trackers and a supporting structure for the PV array.
An oral or written legal agreement
defining an interest in exclusive,
common or bipartisan use of private property or air/space above
that property. A common form of
easement is the concept of “right
of way,” as when an electric utility has the right of way to extend
electrical transmission lines
across private property. See also
“Restrictive covenant.”
Horsepower (hp)
An imperial system unit of power
equivalent to 746 W.
Hybrid PV system
A PV system that includes other
sources of electricity generation,
such as a wind or diesel generator.
Kilowatt-hour (kWh)
Anything in an electrical circuit
which, when the circuit is turned
on, draws power from that
circuit (lights, appliances, tools,
pumps, etc.).
A metric measurement of the
rate at which light is emitted
from a source.
Maximum power point
tracker (MPPT)
Charge controller that continuously tracks the maximum power
point (MPP) of a PV module or
array, thus increasing its efficiency. The MPP is the point
on a current-voltage (I-V) curve
where a PV device produces
maximum power.
Open-circuit voltage
The voltage across a PV cell in
full sunlight when there is no
current flowing; the highest
possible voltage.
Parallel connection
A method of interconnecting two
or more devices that generate or
use electricity, such that the voltage produced, or required, is not
increased, but the current is the
sum of the two. Opposite of
“series connection” (see entry).
Photovoltaic (PV) cell
A device that converts light
directly into electricity. The
building block of a PV module.
Photovoltaic (PV) module
A number of PV cells electrically
interconnected (in either series or
parallel) and mounted together,
usually in a sealed unit of convenient size to make shipping,
handling and assembly into
arrays easier.
Photovoltaic (PV) system
A complete set of components for
converting sunlight into electricity by the PV process, including
the array and balance of system
Electrical equipment used to convert power from a PV array into a
form suitable for subsequent use.
A collective term for inverter,
converter, battery charge regulator and blocking diode.
Restrictive covenant
Stand-off mounting
A specialized type of easement
that can be used to protect access
to sunlight or wind flow for solar
or wind energy applications. See
also “Easement.”
Technique for mounting a
PV array on a sloped roof that
involves mounting the modules
a short distance above the pitched
roof and tilting them to the
best angle.
Series connection
A method of interconnecting
devices that generate or use electricity so that the voltage, but
not the current, is additive.
Opposite of “parallel connection”
(see entry).
Short circuit current
Watt-hour (Wh)
The current flowing freely from
a PV cell through an external
circuit that has no load or
resistance; the highest current
A quantity of energy. One watthour of electricity is consumed
when one watt of power is
used for one hour.
The remote measurement of
any physical quantity using
instruments that convert the
measurement into a transmittable signal.
Stand-alone (PV system)
A photovoltaic system not connected to a main electric grid.
May be solar-only or hybrid. May
or may not have storage batteries,
but most stand-alone systems
require batteries or some other
form of storage (e.g. water
reservoir for pumping).
Learn More About Solar Energy
Natural Resources Canada
Renewable and Electrical
Energy Division
Energy Resources Branch
580 Booth Street, 17th Floor
Ottawa ON K1A 0E4
Fax: (613) 995-0087
Web site:
Natural Resources Canada
CANMET Energy Diversification
Research Laboratory
1615 Lionel Boulet Boulevard
PO Box 4800
Varennes QC J3X 1S6
Fax: (450) 652-5177
Web site:
Canadian Solar Industries
Association (CanSIA)
2415 Holly Lane, Suite 250
Ottawa ON K1V 7P2
Tel.: (613) 736-9077
Fax: (613) 736-8938
Web site:
Énergie Solaire Québec
460, rue Sainte-Catherine Ouest,
Bureau 701
Montréal QC H3B 1A7
Tel.: (514) 392-0095
Fax: (514) 392-0952
Web site:
To order more copies of this publication or others on renewable
energy and energy efficiency, call
1 800 387-2000 toll-free. You can
also obtain a copy of this publication by visiting Natural Resources
Canada’s (NRCan’s) Canadian
Renewable Energy Network
(CanREN) Web site at
Free Software to Help
You in Your Decision
About Medium and
Large Projects
Renewable energy technologies –
such as photovoltaic systems,
wind farms, solar ventilation
air- heating or solar water-heating
systems – can be a smart investment. RETScreen® International
just made it easier. RETScreen®
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renewable energy project analysis
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help you determine whether a
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uses Microsoft® Excel spreadsheets
and comes with a comprehensive
user’s manual and supporting
databases to help your evaluation.
You can download the software
and user manual free of
charge from the Web site at, or call
NRCan at (450) 652-4621 or fax
your request to (450) 652-5177.
Weather and Solar
Radiation Data
Monthly climate data and
1961–1990 normals are available
on CD-ROM. To order your
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Some data is available
directly on-line at
You can also find some of
that data in the RETScreen®
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previously mentioned.
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