Solar panels convert sunlight into electricity.
They are made of semiconductors, most commonly
the semiconductor silicon
Some solar panel materials are:
- Single crystal silicon
- Multicrystalline silicon
- Amorphous silicon
- Gallium Arsenide
- Silicon Nitride
- Copper Indium Diselenide
- Cadmium Telluride
- Titanium Dioxide and Dye
We will discuss
solar cells work
in another section, and in this
section we will discuss how the panels are made and used.
Solar cells individually only produce small voltages,
typiocally 0.7 volts for a silicon cell. To raise the
voltage, cells are linked up in series, so the voltages
add up. In a typical silicon solar panel, 36 cells are
linked in series to produce about 25 volts (36 times 0.7).
Solar panels producing 25 volts can then be linked
in parallel to provide more current, or in series to
further raise the voltage. No matter how the panels
are linked, the total watts are the same, since watts
are the product of voltage and current.
If you run a lot of current through a wire, it will
heat up. This heat is lost energy. If you raise the
voltage, and at the same time lower the current, the
watts delivered will be the same, but the losses will
be less. For this reason, some systems are configured
with the panels mostly in series, delivering as much
as 400 or 600 volts.
In other systems, the panels are connected to 24 or
48 volt batteries through short cables, so loss through
the short cables is not a problem. In these systems
it can be more convenient to have the voltage match the
batteries, so the panels are connected in parallel.
Gallium Arsenide solar panels are very expensive, and are
used mostly in spacecraft, where the high power, low weight,
and resistance to radiation are important.
Titanium dioxide and dye panels are a relatively new
technology, and their lower costs are offset by their
lower efficiency, so a larger area is needed. Space
is often at a premium on residential roofs, so these
cells are used as architectural accents (they are
translucent, so they can be used as windows that provide
power and still let some of the light through).
The most common solar cell types used in solar panels are
the silicon forms. Single crystal silicon is the most
expensive, but is also the most efficient, so less area is
needed. Single crystal cells work better in hot weather
and low light conditions than multicrystalline or amorphous
cells. Because they can sometimes be smaller for the
they can reduce the wind and gravity load on systems that
track the sun (as opposed to systems that are fixed in
Multicrystalline panels, while having lower efficiencies
than single crystal panels, can nonetheless have the same
wattage per square foot as some single crystal panels,
because the cells can be rectangular, filling all of the
available surface without the gaps left by round or
octagonal cells used in some single crystal panels.
An Astropower (GE) single crystal 120 watt panel (16.9 volts, 7.1 amps)
has 10.5 square feet of surface area
(11.42 watts per square foot), and weighs 26.1 pounds.
A Kyocera multicrystalline 120 watt panel (16.9 volts, 7.1 amps)
has 10.0 square feet of surface area
(11.99 watts per square foot), and weighs 26.3 pounds.
A Sharp multicrystalline 123 watt panel (17.2 volts, 7.16 amps)
has 10.7 square feet of surface area
(11.51 watts per square foot).
Other manufacturers include Shell Solar, Seimens, Evergreen,
and BP Solar.