SOLAR
CELLS
A solar cell is an
electronic device that produces electricity when light falls on it. The light
is absorbed and the cell produces dc voltage and current. The device has a
positive and a negative contact between which the voltage is generated and
through which the current can flow. Solar cells have no moving parts. Effectively
they take light energy and convert it into electrical energy in an electrical
circuit in physical process known as the photovoltaic effect.
The discovery of the
photovoltaic effect is credited to the French physicist, Edmond Becquerel in
1839. He found that by concentrating the sun's light on one side of a battery
the output current of the battery could be increased. This revolutionary
discovery triggered the idea that one could produce energy from light by an
artificial process. In 1883 an American inventor produced a solar cell from a
material called selenium, but it was very inefficient. Selenium became used in
light-exposure meters for cameras, but not for power production.
The efficiency of a solar cell is a measure of the
proportion of the light hitting it that is actually converted into electricity.
If the cell were 100% efficient then it would turn all the incident light into
energy, but sadly this is impossible. Practical solar cells made from silicon wafers
can have an efficiency of 16% or so.
A
solar cell is a PV cell designed to convert sunlight to electricity. The
simplest cells consist of a circular silicon wafer with a pn-junction
sandwiched in the middle, a metallic bottom contact and a transparent top
contact. Solar panels with cells like this have played a vital role in space
technology since the late '50s, powering space satellites. They are expensive
to produce because silicon wafers are expensive to produce but their cost was
unimportant in the space race.
In
recent years there has been a continuous search for cheaper forms of PV cell,
economical enough to be used in applications here on earth. Attempts have been made to use cheaper forms
of silicon, of lower quality than that used in computer chips, despite the
poorer cell efficiencies that result. One possibility has been to replace the
single-crystal wafer by polycrystalline squares. This material has the
advantage of being much more light-absorbing than crystalline silicon. Cell
efficiencies are perhaps only half those in crystalline silicon, but the
amorphous cells potentially cost much less than half for the same surface area.
So they seem to be the most economical choice at the moment.
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