Harnessing Solar Power
Perhaps you’ve purchased a portable solar charger and got to wondering how the darn thing works. Well, one of the ways we’ve learned to harness solar power is through the use of photovoltaic (PV) cells. These little workhorses are made of semiconductor materials such as silicon, which is sandwiched under a pane of glass. When sunlight passes through the glass and hits the semiconductor, it is absorbed in a narrow range of frequencies called the band gap. This excites the silicon’s electrons like you wouldn’t believe, so much so that they actually escape from the silicon!
Now, if you’ve got all these free electrons running around, the logical thing to do is to channel them into a flow of electricity, which after all is nothing but a stream of electrons. You channel them by having two types of silicon, P and N, which have a positive or negative charge, respectively. This creates a voltage potential, but how are the P and N created? Actually, it’s kind of neat. To give silicon a negative charge, you dose it with a little phosphorus. These two elements form a negatively charged crystal, but what’s cool is that although the silicon absorbs the solar energy, it’s the phosphorus that provides all those free electrons.
OK, so you put the P and N types close to each other, creating an electromagnetic field. All those free electrons that the phosphorus gave up in the N type are attracted to the positively charged P type, and before you can say watt, you’ve got a current. However, that current would be very short lived, because the electrons would quickly neutralize the P layer. Here’s where the sun helps: it forces the built up electrons to cross from the negative side to the positive side, and you get a sustained current. This current flows into metal leads and then wire, completing the circuit. The electric field provides the voltage, and when you mix current with voltage, you get power – solar power.
Things have gotten more refined over the years. There are different types of silicon (amorphous, mono- or poly-crystalline), plus fancy materials such as cadmium telluride and copper indium gallium selenide. The current from a solar charger is usually used to charge a battery, though you could actually directly power a small gadget (after converting the current from DC to AC, but that’s another story). Well, that’s the story in a nutshell.