Question about how solar panels work

This question was asked on Reddit:

The answers seemed to indicate that solar panels cause electrons to flow in a kind of closed loop, eg:

If solar panels simply cause a fixed supply of electrons to loop over and over in a closed circuit, then I don’t understand how this can give an endless supply of energy. Eg, lets say I attach a lightbulb in to this circuit. Won’t this cause a loss of electrons as they get converted in to light energy?

Electrons don’t get converted into light energy. It is the flow of electrons that cause work to be done.

Remember that all matter is made up of atoms with electrons zipping around them. All of these electrons are moving around constantly, but because their motion is essentially random, the net flow of all of them is zero. Electric current causes those electrons – which are already there – to all flow in one direction like water through a pipe. When that flow does work (such as lighting up a light bulb) a resistance is added, like friction inside the pipe. The more load attached to the circuit, the more friction there is, and the harder it is to push the electrons through.

Solar panels don’t really create electrons, they already have them. When sunlight (photons) hit the photovoltaic material, they add energy to electrons in the semiconductor which allows them to flow more freely. Those electrons start flowing through the circuit, but are immediately replaced by electrons (with less energy) returning from the circuit. Then more photons hit those electrons, which causes them to jump up to a higher energy level again, and so on.

That’s pretty much what electrical current is. You could spend years in college learning all the details, but making electrons flow is what it’s all about.

OK, picture a hydraulic system, like the one the mechanic uses to lift up your car. You’ve got a compressor at one end, and a big piston at the other. Where does the compressor get the oil from? And why doesn’t the piston use up oil? There’s your answer: The electrons in an electrical system behave very much like the oil in a hydraulic system.

It’s already been mentioned, but I think it bears repeating. Your first step should be understanding electricity, not worrying about solar panels. In no electric circuit are electrons consumed and converted into something else. Read the other replies here for more detail.

When I studied EE (5 years at Rensseltute) they tried to convince us that electric current is the flow of “holes”, not electrons. Powered by a battery, that’s from the positive terminal to the negative terminal. Baloney. Try explaining how a CRT works. Or a vacuum tube, if you want to go way back.

Another vote to stop thinking in terms of solar power.

Look at any current source: batteries, DC or AC generators, etc. None of them run out of electrons. It’s all about pushing a current around.

There are a lot of odd theoretical constructs due to the weird quantum nature of electrons, but at the macro level, and usually for people actually building electrical circuits, thinking in terms of “power source pushes electrons through the tube from negative side to positive side” is perfectly adequate, if not one hundred percent accurate.

I just want to add that perhaps it is true that “the power source pushes electrons…from the negative side to the positive side”, it can cause a lot of confusion when designing electrical circuits (at least it was for me).

Current flows from positive to negative.

While it is true that the electrons actually are moving in the opposite direction of the current, the direction of the electron movement is not really important, but the direction of current flow is.

The way it was explained to me (by a EE professor), the electrons themselves are so small and, individually, carry so little charge that you don’t really need to concern yourself with them when analyzing a circuit. Just remember that current flows from positive to negative and you can keep things straight.

Photovoltaics can cause more confusion, since to understand the physics behind how the PV work means you have to consider the actual movement of the electrons and the electron holes, but you really don’t have to understand exactly how the PV works to design a working PV circuit and keeping with the convention that current flows from positive to negative helps.

Direction of current flow isn’t important, either. Oh, you’ll get yourself confused if your circuit contains diodes or the like, and you’re thinking of current going the opposite way from the way the diode-makers did, but in the end, it’s just an arbitrary sign convention.

And it’s extremely difficult to prove that it’s the negative particles moving, not positive ones. You need to use the Hall effect. And even then, it turns out that in some semiconductors, it really is the positive holes that are moving.