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Unit 12: Alternative Energy Page 18 of 31
get as high as 35%.) A solar cell's solar cells are structured is such a
efficiency is a measure of how way as to keep the electricity
much sunlight the cell converts into flowing only in one direction. The
electrical energy. electron flow created is DC current
(more on this in Unit 10).
The big leap in technology came in
the 1950s when semiconductors The solar cells you can buy from
were experimented with at Bell stores require huge amounts of
Labs. energy in creating the solar cell,
which is the primary downside. You
Today, engineers design space need high temperatures, big
satellites armed with solar panel vacuum pumps, and lots of people
arrays which continually rotate to to make a set of solar cells.
track the position of the sun. Solar However, if we focus just on the
panels on homes, however, are physics of the solar cell, then we
stationary and reply on the earth’s can easily create our own solar
rotation to guide their path. battery and other solar cell
projects using household items.
While these cells won't look as
How does a spiffy as the ones from the store,
solar cell work? they still produce electricity from
sunlight.
Solar cells are usually
made of silicon. Sunlight is made But how does the silicon
of packets of energy called photons do that?
(covered in Unit 9). When photons
hit the silicon, one of three things Semiconductors are the secret to
can happen: the photons can pass making solar cells. A
straight through the silicon if they semiconductor is a material that is
have a low enough energy; they part conductor, part insulator,
can get reflected off the surface; or meaning that electricity can flow
(and this is the fun part) they get freely and not, depending on how
absorbed and the electrons in the you structure it. There are lots of
silicon get knocked out of their different kinds of semiconductors,
shell. including copper and silicon.
Once knocked out of orbit, the free In semiconductors, there's a gap
electrons start flowing through the (called the bandgap) that's like a
silicon to create electricity. The
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