Frequently Asked Questions,
Will solar
work in my
Renewable Energy (RE) may seem puzzling to some
people that are not familiar with it. To help those of you
that are being exposed to solar power for the first time,
we have compiled and answered a dozen of the most
frequently asked questions that we commonly hear at
Kyocera Solar. We hope this FAQ file is helpful to you.
How do solar cells
generate electricity?
Photovoltaics or PV for short can be thought of as a direct
current (DC) generator powered by the sun. When light
photons of sufficient energy strike a solar cell, they knock
electrons free in the silicon crystal structure forcing them
through an external circuit (battery, inverter or direct DC load),
and then returning them to the other side of the solar cell to
start the process all over again. The voltage output from a
single crystalline solar cell is about 0.5V with an amperage
output that is directly proportional to the cell’s surface area
(approximately 7A for a 6 inch square multi-crystalline solar
cell). Typically 30-36 cells are wired in series (+ to -) in each solar
module. This produces a solar module with a 12V nominal
output (~17V at peak power) that can then be wired in series
and/or parallel with other solar modules to form a complete
solar array.
Antireflection Coating
Transparent Adhesive
Cover Glass
Front Contact
+ Hole
n-Type Semiconductor
p-Type Semiconductor
Back Contact
Solar is universal and will
work virtually anywhere,
however some locations are
better than others.
Irradiance is a measure of
the sun’s power available at
the surface of the earth and
it peaks at about 1000 watts
per square meter. With
typical crystalline solar cell efficiencies around 14-16%, that
means we can expect to generate about 140-160W per square
meter of solar cells placed in full sun. Insolation is a measure of
the available energy from the sun and is expressed in terms of
"full sun hours" (i.e. 4 full sun hours = 4 hours of sunlight at an
irradiance level of 1000 watts per square meter). Obviously
different parts of the world receive more sunlight than others,
so they will have more “full sun hours” per day. The solar
insolation zone map will give you a general idea of the full sun
hours per day during the summer for your location.
Solar Insolation Zone Map
How much will solar cost for a
2000 square foot home?
Unfortunately there is no per square foot “average” since the
cost of a system actually depends on your daily energy usage
and how many full sun hours you receive per day; and if you
have other sources of electricity. To accurately size a system to
meet your needs, you need to know how much energy you use
per day. If your home is connected to the utility grid, simply
look at your monthly electric bill. If not, you can fill out the “load
evaluation form” on page 15. Using this information, your
authorized Kyocera Solar Dealer can design a system to meet
your needs.
What components do I need for
an off-grid system?
Solar Irradiance
There are many components that make up a complete solar
system, but the 4 main items on a stand-alone system are: solar
modules, charge controller(s), battery(s) and inverter(s). The solar
modules are physically mounted on a mount structure (see
question 7) and the DC power they produce is wired through a
charge controller before it goes on to the battery bank where it
is stored. For more detailed information on solar modules, turn to
page 20. The two main functions of a charge controller are to
prevent the battery from being overcharged and eliminate any
reverse current flow from the batteries back to the solar modules
at night. Turn to page 38 for more detailed information on
charge controller functions and features. The battery bank stores
the energy produced by the solar array during the day for use at
anytime of the day or night. Batteries come in many sizes and
grades, which you can see starting on page 49. The inverter takes
the DC energy stored in the battery bank and inverts it to 120 or
240 VAC to run your AC appliances. For more detailed
information on different inverter models and features, turn to
page 68.
What components do I need
for a grid-tie system?
AC Loads
DC Loads
Can I use all of my normal
120/240 VAC appliances?
Grid-tie systems are inherently simpler than either grid-tie with
battery back-up or stand-alone solar systems. In fact, other than
safety disconnects, mounting structure and wiring, a grid-tie
system is just solar modules and a grid-tie inverter! Today’s
sophisticated grid-tie inverters incorporate most of the
components needed to convert the direct current from the
modules to alternating current, track the maximum power
point of the modules to operate the system at peak efficiencies
and terminate the grid connection if grid power is interrupted
from the utility.
Maybe. Many older homes were not designed or built with energy efficiency in mind.When you purchase and install a renewable energy system for your home, you become your own power company, so every kWh of energy you use means more equipment (and hence
more money) is required to meet your energy needs. Any appliance that operates at 240 VAC (such as electric water heaters, cookstoves,
furnaces and air conditioners) are expensive loads to run on solar.You should consider using alternatives such as LP or natural gas for
water/space heating or cooking, evaporative cooling instead of compressor based AC units and passive solar design in your new home
construction if possible. Refrigeration and lighting are typically the largest 120 VAC energy consumers in a home (after electric heating
loads) and these two areas should be looked at very carefully in terms of getting the most energy efficient units available. Great strides
have been made in the past 5 years towards improving the efficiency of electric refrigerators/freezers. Compact fluorescent lights use a
quarter to a third of the power of an incandescent light for the same lumen output and they last ten times longer.These fluorescent
lights are now readily available at your local hardware or discount store.The rule of thumb in the renewable energy industry is that for
every dollar you spend replacing your inefficient appliances, you will save three dollars in the cost of a renewable energy system to run
them. So you can see that energy conservation is crucial and can really pay off when considering a renewable energy system.
What type of solar module mounting structure should I use?
There are four basic types of mount structures: roof/ground, top-ofpole, side-of-pole and tracking mounts, each having their own pros
and cons. For example roof mount structures typically keep the wire
run distances between the solar array and battery bank or grid-tie
inverter to a minimum, which is good. But they may also require roof
penetrations in multiple locations, and they require an expensive
ground fault protection device to satisfy article 690-5 of the National
Top of Pole Mount
Roof/Ground Mount
Electrical Code-NEC. On the other hand, ground mounted solar arrays
require fairly precise foundation setup, are more susceptible to
theft/vandalism and excessive snow accumulation at the bottom of
the array. Next are top-of-pole mounts which are relatively easy to
install (you sink a 2-6 inch diameter SCH40 steel pole up to 4-6 feet in
the ground with concrete). Make sure that the pole is plumb and
mount the solar modules and rack on top of the pole.Top-of-pole
mounts reduce the risk of theft/vandalism (as compared to a ground
mount).They are also a better choice for cold climates because snow
slides off easily. Side of pole mounts are easy to install, but are
Side of Pole Mount
typically used for small numbers of solar modules (1-4) for remote
lighting systems where there already is an existing pole to attach them to. Last but not least are the trackers, which increase the daily
number of full sun hours and are usually used for solar water pumping applications.Trackers are extremely effective in the summer time
when water is needed the most. In the northern U.S., typical home energy usage peaks in the winter when a tracker mount makes very
little difference as compared to any type of fixed mount (roof, ground or top-of-pole). In this situation, having more modules on a less
expensive fixed mount will serve you better in the winter than fewer modules on a tracker. However, if you are in the southern U.S. and
your energy usage peaks in the summer, then a tracker may be beneficial to match the time of your highest energy consumption with a
tracking solar array’s maximum energy output.
Should I wire my home for Can I use PV to heat water or
for space heating?
AC or DC loads?
It depends on the size of the system and what type of loads
you want to run. DC appliances are usually more efficient than
AC since you don’t have to worry about the loss through the
inverter, but DC loads are typically more expensive and harder
to find than their AC counterparts. Small cabin and RV systems
are typically wired DC while most home systems are wired
exclusively for AC loads. With improvements in inverter
efficiency and reliability in the last 5 years, AC is the way to go
for a home system. Another advantage AC has over DC is that
the voltage drop for a 120VAC circuit is much less than a 12VDC
circuit carrying the same power, which allows you to use
smaller gauge wire.
No. Photovoltaics converts the sun’s energy into DC electricity
at a relatively low efficiency level (14-16%), so trying to operate
a high power electric heating element from PV would be very
inefficient and expensive. Solar thermal (or passive solar) is the
direct heating of air or water from the heat of the sun and is
much more efficient for heating applications than
Where should I mount the solar modules and what
direction should I face them?
5W 10W 15W
Magnetic Declination Map
Should I set my system’s
battery bank up at 12, 24,
or 48 VDC?
If your site is in the northern
hemisphere you need to aim
your solar modules to true south
20W (the reverse is true for locations
in the southern hemisphere) to
maximize your daily energy
output. For many locations there
is quite a difference between
15W magnetic south and true south,
so please consult the declination
map before you setup your
mount structure. The solar
modules should be tilted up
from horizontal to get a better
angle at the sun and help keep
10W the modules clean by shedding
rain or snow. For best year round
power output with the least
amount of maintenance, you
should set the solar array facing
true south at a tilt angle equal to
your latitude with respect to the
horizontal position. If you plan to
adjust your solar array tilt angle
seasonally, a good rule of thumb is:
- latitude minus 15° in the summer
- latitude in the spring/fall
- latitude plus 15° in the winter
Most mount structures are available with a seasonal adjustment
of the tilt angle from horizontal to 65°. To determine if your
proposed array site will be shaded at any time of the day or
year you should consider using the Solar Pathfinder in the tool
section on page 109.
The PV industry really began with the 12V radio communications market. These systems were typically small (1-2 solar modules)
and had all 12 VDC loads. As the solar industry matured and entered the home market, systems became much larger (16+ solar
modules) and no longer used DC loads exclusively. Most home systems today are 24 or 48 VDC since the higher system voltage
gives you a lot more flexibility as to how far away you can place your solar modules from the battery bank as compared to a 12V
system. For a given power output, a higher system voltage reduces your amperage flow (but not your power) which allows you to
use a smaller and less expensive gauge wire for your solar to battery and battery to inverter wire runs. Of course, if you already
have a lot of 12VDC loads, that may be your deciding factor as to what voltage you set your system up at. Most grid-tie systems
operate at 48 volts or higher.
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