The first installment of the “How Solar Power Works” series got some great responses, but one of the questions we got was so good I felt like we had to write up the answer. So, before we get on to part 2, I’d like to answer Tim’s excellent question, “Why doesn’t the silicon in PV modules run out of electrons? There seems to be an endless supply of electrons that are freed up when sunlight hits the panels.”
So good, right?
The question focuses on the photoelectric effect, which I ham-fistedly described as follows:
That “photovoltaic” or “photoelectric effect” happens on an atomic level. That means that when a super-tiny photon hits an atom in just the right way, the atom absorbs a photon and releases (or, “sheds”) an electron. The movement of electrons is— you guessed it!— electricity.
What Tim caught makes sense. If there are a limited amount of electrons “orbiting” an atom— which we all learned in Ms. Wentworth’s 8th grade physical science class, right?— wouldn’t the PV cell eventually run out of electrons to shed?
The short answer is: no.
The longer answer can be answered two ways. The first way is to explain that there are “free electrons” roaming around out there, which aren’t tethered to an atomic nucleus. When an atom sheds an electron, which is negatively charged, the electron-less atom is left with a positive charge. And, because “opposites attract” is a very real thing, that positively charged atom (called a “cation”) will then attract a free electron in order to return to its most stable state: electrical neutrality.
Now, “because: free electrons” might be an acceptable answer for most people— and, don’t get me wrong, it’s a real answer— it’s not the best answer to that question.
The best answer has to do with circuits. Specifically, closed circuits.
“So,” you might be asking, “what’s a circuit?”
In simple terms, a circuit is a complete path around which electricity can flow. It must include a source of electricity (ex.: a battery or, as in our case, a PV cell), and conducting material (a “conductor”) that will allow electricity to pass through them easily. The conductor is then attached to the positive and negative ends of the power supply (terminals) and electrons can begin to flow. Every electrical circuit you’ve ever seen (that works) is built just like this: as a loop.
Here’s two examples of a simple from the Encyclopedia Brittanica (Who knew that was still a thing!?).
When the loop is “open” (light switch off), there’s no electricity flowing. When the loop is “closed” (light switch on), electricity flows. Lightbulbs light. Speakers speak. Automobiles automobilate (?). Etc.
Keep all that in mind as I apply it next to the concept of solar …….
Source: https://cleantechnica.com/2022/05/25/how-solar-power-works-can-pv-cells-run-out-of-electrons/