Learn About Solar Modules
What is a solar cell ?
A solar cell or photovoltaic cell is made of special materials
called semiconductors, the most common semiconductor material
which is used in the manufacture of a solar cell is known as
silicon. When a light source strikes a solar cell, a portion
of it is absorbed by the semiconductor material. The absorbed
light energy knocks electrons loose, allowing them to flow
freely. See illustration
Ordinarily pure silicon
is a poor conductor of electricity so impurities such as
phosphorus and boron are added to create what is known as a
semi-conductor. The addition of these impurities not only
allows the silicon to conduct electricity, but also acts to
force electrons freed by light absorption to flow in a certain
direction. This directional flow of electrons is also referred
to as a current. By placing metal contacts on the top and
bottom of the solar cell, it then becomes possible to draw
that current off to use externally to perform work.
What is a solar electric module ?
A solar electric module consists of an aluminum framed sheet
of highly durable low reflective, tempered glass that has had
individual solar cells adhered to the inner glass surface.
These individual solar cells are wired together in a series
parallel configuration so as to obtain the necessary voltage
Individual cells are
wired in series strings to increase the module's voltage and
the series strings are wired in parallel to increase the
module's current. The back of the module is protected by
another sheet of tempered glass or a long lasting material
such as Tedlar.
The series parallel
connections are passed through the protective backing and then
wired to a weather proof junction box which is permanently
mounted to the back of the module. The junction box is where
the module's output connections are made.
Several solar modules
wired together are known as a solar panel.
What is the difference between monocrystalline and
polycrystalline cells ?
There are two cell technologies that are prevalent in today's
market, they are referred to as polycrystalline and
monocrystalline silicon. Some manufacturers will use one or
the other technologies in the manufacture of their product
some will use use both.
Solar cells that are
created from monocrystalline or (single crystal) technology
are cut from a silicon boule that is grown from a single
crystal, in other words a crystal that has grown in only one
plane or (one direction). Single crystalline are more
expensive to manufacture and typically have a slightly higher
efficiency than do conventional polycrystalline cells
resulting in smaller individual cells and thus typically a
slightly smaller module.
Solar cells that are
created from polycrystalline or (multicrystalline) technology
are cut from a silicon boule that is grown from multifaceted
crystalline material, or a crystal that grows in multiple
directions. Conventional multicrystalline solar cells
typically have a slightly lower efficiency resulting in larger
individual cells and thus typically a slightly larger module.
All of this has changed with the advent of the new silicon
nitride multicrystalline cells which are rated as high or even
higher efficiency than similarly sized monocrystalline cells.
It's important to keep in
mind that a 100 watt module is a 100 watt module whether it
was made from polycrystalline cells or monocrystalline cells.
How many solar modules do I need to power my loads ?
The best method that we've found is to convert both your power
consumption and your power production into WATT HOURS that way
we can compare apples to apples. step one is to determine the
individual wattage rating for each load that you intend to run
off solar. Look on the back of each appliance and try to
locate a label which indicates the wattage used by the
appliance, if it dosen't give you the wattage then it may tell
you the amount of volts and amps that the appliance uses.
Remember volts times amps
equal watts. Once you have written down the wattage rating for
each appliance, you then need to determine the amount of time
each appliance will run during the day. For example let's say
that you have a television that runs for three and a half
hours a day, then write down 3.5 hours, or let's say you have
a computer that runs for two hours and 15 minutes, then write
down 2.25 hours, or a microwave that runs for 45 minutes, then
write down .75 hours.
Next take the wattage rating of each appliance and multiply
that by the amount of time it will run, that will give us the
WATT HOUR rating. For example a television that draws 200
watts and runs for three hours (200 x 3 = 600) will use 600
watt hours, or a toaster that draws 1100 watts and runs for 15
minutes (1100 x .25 = 275) will use a 275 watt hours. Add the
up all of the watt-hour ratings for each appliance and that
will equal your total power consumption for each day.
Let's say that your total power consumption equaled 1200 watt
hours per day, then that's the amount of solar power you need
to produce plus about 10 percent for battery losses. Don't
forget that the power you produce with solar panels is also a
factor of time as well. So for example let's say you had a 200
watt solar panel and that panel sat in full sun for seven
hours, than you would have produced 1400 watt hours (200 watts
x 7 hours = 1400 watt hours)
Let's say for example
that you only had five hours of full sunlight then five hours
times two hundred watts would only be 1000 watt hours so you
would be at a deficit, so you would need to either add another
40 watts of solar panels or reduce your power consumption by
200 watt hours.
There's no secret
formula, what you take out of the batteries you must put back
in plus about ten percent or you'll be in the red which can
damage your batteries over time.
Who makes the best quality solar modules
Basically quality is
pretty much equal across the board when your dealing with
major brands such as Photowatt, BP Solar, Kyocera, Siemens and
Sharp. Chinese made solar modules that are not UL approved are
now being imported into the United States, so be careful,
always ask for the country of origin when buying a module. The
safest thing to do is stick with the major brands.