A photovoltaic (PV) cell directly converts light energy into
electrical energy. It is light from the sun—not heat—that
is used; crystalline photovoltaic cells are actually more
effective when cool.
Each cell develops about half a volt of DC electrical
potential. The maximum amperage of the cell is proportional
to its surface area. While series strings of about 36 cells put
together to charge a 12-volt system were the norm, series
strings of 60 cells (or more) are now common. We call these
organized strings of cells “modules.”
The PV effect was first discovered in the 1800s, when
scientists noticed that light shining on crystalline selenium
produced an electrical current. Later, researchers found
that silicon was more effective as a base material. In our
present-day PV modules, the silicon is doped with boron,
phosphorous, gallium, arsenic, or other materials. This creates
loosely bound electrons, easily liberated by incoming photons
(energized light particles). It also forms the “p-n junction,”
a region that naturally pushes those freed electrons one
direction through an electrical circuit to do useful work.
The PV cell is overlaid with a grid of conductive wires
that are connected together. When the photons bump the
electrons, they are free to follow the rest of the circuit set up
by the wires. Renewable energy expert Hugh Piggott says PV
technology is “the energy shortcut—from the source to the
ultimate goal in one conversion.” There are no moving parts
in this system. Only the photons and electrons move, and
there are plenty of them to go around.
One of my favorite demonstrations of this technology
is the pump in the bucket. Connect a small PV module to
a bilge pump that’s in the bottom of a bucket filled with
water. Put the PV modules in the sun and watch the pump
run. I’ve enjoyed seeing young children, scientific folk, and
even my local backhoe operator become excited about solar
electricity’s potential after seeing this simple demonstration.
One closing note on the word: While we in the industry are
very comfortable saying “photovoltaic” and “PV,” the terms
seem mysterious to many people. I think it’s often better to say
“solar-electric” when speaking to the uninitiated. When we
say “solar panels,” lots of people think of solar thermal panels,
an entirely different technology that gathers the sun’s energy
in the form of heat. “Solar-electric” is a much easier phrase
for most people to understand, and it clearly distinguishes
the two different technologies.
The magic of PV: Children learn about
the energy of the sun when they see this
solar-electric module powering a pump,
which stops when the module is shaded.