How Do Solar Panels Work? (Physics of Solar Cells)

have actors that work? Thanks to brilliant.org for sponsoring this episode. Hey, crazies, it’s time for another episode of How the heck does that work? I’m sure many of you have wondered over the years, how does solar power work? Well, today’s your lucky day. To help out with this. I’ve designed a special clone just for this video, solar powered clone 20%. Okay, maybe we’ll come back to him later. First, let’s get some lingo out of the way. When I say solar panel, you’re probably picturing something like this, or maybe even this. But these are called solar arrays, they’re collections of solar panels, a single panel or module looks like this.

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And that panel is made of even smaller parts called solar cells. These cells are where the solar power comes from. Technically speaking, though, power sources don’t actually provide power, they provide energy in the form of voltage. But we’ll get to that later. That reminds me a solar powered cloud, are you doing 30%? Hmm, maybe he could have been designed a little better. Anyway, let’s get into the structure of one of those cells, they might look like one thing. But there are several layers and metal plate on the back two different types of semiconductors, a metal grid on the front in antireflection, coating and a piece of glass.

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Now, that’s a lot of layers. But this is all about turning light energy into electrical energy. So let’s follow the light. The first layer, the light encounters is glass. Glass is an insulator, so it’s not going to conduct any noticeable electricity. It’s also transparent. So most of the light just passes through. The reason it’s there is to keep everything else out. The other layers are kind of fragile, so that the glass protects them. Next is the antireflection layer.

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That’s the layer that makes the solar cell look dark. Doesn’t that mean the light never gets through? Oh, no, it lets the light in. It just doesn’t let it back out. Really? How does that work? This coating is so cool. Let me explain. The semiconductors underneath are a bit too shiny. If they were exposed, over 30% of the light would just reflect away. That simply won’t do. If we want to use something like this on the large scale power grid, we need it to be as efficient as possible, the glass already reflected away about 5% of the light, and we’re going to lose a bunch of it to heating, we can’t really afford to lose much more.

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The antireflection coating helps us hold on to what we’ve got left. And it works like this. You can’t just coat it black. Otherwise, all the light would heat the cell and you wouldn’t get any electricity. This coating has to be transparent, it must let the light pass through. But what happens is you get a reflection off the top and the bottom. If the coating is just the right thickness, the tube will cancel and the reflected light disappears, leaving only the incoming light. All of it.

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Unfortunately, no but most of it, the amount of cancellation is wavelength dependent, but it’s the best we can do. So both the glass and the antireflection coating solve some practical issues. But you’re not here for practical issues, you probably want to hear how a solar cell actually generates electricity. That’s where semiconductors come in. Terry Lee, the best one we’ve got is silicone right in the middle of the chart. Full insulators won’t work. Because the jump to the conduction band is too big conductors won’t work because they’re already conductive. We want the incoming light to make it conductive. Semiconductors need a boost to become conductive, but only a small, a little visible light will be just enough.

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There’s a slight any bitty obstacle for us though, silicon is far from the left on the periodic table 1234. That means each silicon atom only has four electrons in the valence band, all four of which get used up when they bond to each other in the semiconductor. The incoming light might break some of those loose, but it’s not enough. Solar powered clone knows exactly what I mean. 65% Man, I really should have pre energized him first. Anyway, pure silicone isn’t going to be enough. We need to enhance it using a process called doping. Well, yeah, kinda like that. We are technically injecting something that doesn’t belong to enhance performance.

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But unlike sports doping, this is totally legal. Where was I right enhancements, we need extra electrons that aren’t part of a bond. The number of valence electrons is equal to how many columns over we are. So we just need to step over one more column to phosphorus. That’s for electrons for bonding, and one extra for us to move around. We still want this to be mostly silicon. But if we mix in some phosphorus, we get some spare on bonded electrons to work with. The incoming light can excite those electrons up to the conduction level, but that’s not going to do us any good. If we don’t have any work for them to go one step to the left of silicon there are only three valence electrons that gives us a hole or openings that are extra electrons will want to fill.

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Unfortunately, aluminum atoms are a little too big to fit inside the silicon. So we take one step up to boron instead, they’ll fit quite nicely in the silicon and leave us some electron holes to work with. The two of them together are the key to how a solar cell works separate. The two types of silicon are neutral, there’s no net charge on either one. But the moment the phosphorus doped silicon touches the boron doped silicon, there’s a mad rush of electrons from the phosphorus to the boron at the boundary. This creates an imbalance of charge inside the solar cell. Some of the phosphorus are now positively charged, because they’re missing electrons.

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And some of the boron are negatively charged, because they have extras, any imbalance of charge will give us an electric field. Or more importantly, for circuits, it will give us a voltage, which is just an amount of energy per unit charge. When more electrons are ready to move, the voltage tells them which way to go pretty quickly, that initial rush of electrons forms a barrier between the two sides, they reach an equilibrium and stop flowing, they’ll only move again, if we give them the energy to move energy from incoming light. We just need a couple of conductors to connect the silicon to a circuit and bam, you’ve got yourself a solar cell.

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Why is the top one shaped like a grid? Oh, yeah, that makes perfect sense. I promise, the back conductor is a full plate, but the front conductor has to leave some space, not enough space, and the light can’t get through to the silicon, too much space and the electrons have to travel too far along the silicon. The grid pattern is a happy medium between the two, a happy little conductor of such a dork. So the silicon pair separates charge and gives us a voltage but the voltage of an individual solar cell isn’t actually that high. It’s only about half a volt. For comparison, a double A battery provides one and a half volts.

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And a wall socket in the US provides 120 volts give or take. If we want to use solar cells in the power grid, we need a lot of cells and a panel and a lot of panels in an array. Of course, there are other obstacles to consider too. Solar cells only provide DC so we have to convert it to AC. But that’s not really a problem with one of these sunlight can vary from moment to moment or place to place. So we need an adequate storage device.

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But we have those they’re called batteries and capacitors. Why use carbon fuels that mess up our atmosphere and ocean? What do we have a giant nuclear furnace releasing a seemingly endless supply of light energy? It’s 1000 watts of power for every square meter of Earth, we should be taking advantage. So are you ever going to look at solar panels the same way again? Let us know in the comments. Thanks for liking and sharing this video.

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Don’t forget to subscribe if you’d like to keep up with us. And until next time, remember, it’s okay to be a little crazy. Okay, I’m ready. Do it I just finished Oh, are you interested in solar energy? Then check out the solar energy course I’m brilliant.org Brilliant is a problem solving website that teaches you to think like a scientist knowing physics as well as I know it takes more than just watching videos. It takes loads of practice. Brilliant gets you to solidify concepts by giving you fun and challenging problems. They even have hints and solutions to help out along the way. It’s a service you don’t really see anywhere else.

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If you’re interested visit brilliant.org/science Asylum and the first 200 people to sign up will get 20% off an annual premium subscription. It’s a really good offer if you want to strengthen your knowledge. Terrell Patil and George Charney pointed out that my current was going the wrong way. That’s not actually true. Because I wasn’t ever showing the currents. I was showing the direction of electron flow, which is opposite the current. Ben Franklin made everything so complicated. Anyway, I’ll address this in more detail when we get to circuits. Thanks for watching.

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How Do Solar Panels Work? (Physics of Solar Cells)

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