Electricity
from Light: How?
Light striking certain substances causes the surface of the material
to emit electrons. It is as if light somehow kicks electrons right out
of atoms. Light striking other substances causes the material to accept
electrons. It is the combination of these two substances that can be
made use of to cause electrons to flow through a conductor.
This is the so called photo-electric effect. Photovoltaic means sunlight
converted into a flow of electrons (electricity). Photovoltaic devices,
or solar cells, are like generators that work in sunlight. They make
electricity without waste, noise or pollution. They produce electricity
without combustion. A solar cell is a solid state device in which there
are no moving parts (except for photons and electrons) so nothing wears
out.
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The fuel is "photons". These can be thought of as "packets
of sunlight" that carry a phenomenal amount of energy to earth
at a prodigious rate. The Solar Panels of today make use of this abundant
energy by using silicon crystals with small amounts of impurity added.
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This process of adding minute amounts of different elements into an
otherwise pure crystal is called "doping". By having two thin
layers of doped material bonded against one another, an electric current
can be induced when exposed to light.
Energy Content of Sunlight Sunlight has an energy content of 1 kW (1,000
watts) per square metre. The typical Solar Panel today achieves between
10% and 15% conversion. The theoretical maximum efficiency of a silicon
cell is about 21%. Using a more costly technology 31% conversion has
been achieved.
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