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.