How Solar Panels Work

one nomination. You nominate one game, and you need to tell us the name of the game and the platform it was on. And it could be any platform. It could be an arcade game, it could be a PC, Mac, Xbox, PS three, Nintendo handheld console. It can be web based if you like. But just you let us know what the platform is so we can make sure we count

that as the votes. So you can nominate your game either through email, which is tech Stuff at how stuff works dot com, or you can nominate through Twitter or Facebook. And we're gonna put a cut off date on this. I want to have the episode go up by the

end of September of eleven. So let's say you need to get your nominations in by September eleven, So if you get those nominations into us, we will make sure we include those in the process and we will have an episode where we give you the worst video games of all time based upon the votes of our listeners. Thanks a lot. Can't wait to hear from you. Get in touch with technology with tech Stuff from how stuff

works dot com. Hello, everyone, Welcome to tech Stuff. My name is Chris Poet and I am an editor at how stuff works dot com. Sitting across from me as always and for some reason twisting up a rubber dinosaur is senior writer Jonathan Strickland, Little Darlin, the smiles returning to the faces, Little Darling, it seems like years since it's been here. H. That was a nice choice for today's topic, which is I think something that everyone will find electrifying. Yeah, and in fact, this comes to us

courtesy of a Google Plus suggestion. This comes from Adam, who says this may be a bit simple, but have you guys ever done an overview of solar technology and solar tech history? Just re listened to your battery podcast and it made me wonder more about alternative energy sources. Adam, um, your definition of simple and my definition of simple are too very different things. But but yeah, we're gonna talk about solar power, solar cells also known as photo voltaic cells,

and uh kind of where it came from. M Yeah, they're not they're certainly not new. UM. We have an article about how solar cells work on the website UM which discusses how they were used in the nineteen fifties in space uh space technology. Yeah. In fact, the well, to go back even further, the photoelectric effect, which of course is the basis of photovoltaic fells, that was first discovered by a or at least first observed by a

French physicist named Edmund Beckerel. It's an eighteen thirty nine. Wow, that was some time ago. Yeah. Now, granted he observed that certain materials, if if exposed to sunlight, would produce a certain amount of electric current, but there wasn't really any way of putting that to any use at the time. It was just it was an interesting scientific observation and

that was the the limit of it. Einstein himself began to ruminate on this, decided about, you know, to kind of think about what is the nature of light, how does it interact with the nature of electricity, what's the relationship there? Um? And then he actually won a Nobel Prize based on his observations. Now, the first module photo vote vol take module, because a module is a collection

of photo voltaic cells. In fact, we can get this out of the way and really early on, if you want to talk about like the a sense of scale, an individual photo voltaic cell, when grouped together with other photo voltaic cells, makes a module, and groups of modules together make an array. So it's just it's just as a question of scale. So array isn't a group of modules and modules a group of photo photo voltaic cells.

I'm gonna stumble over that over and over in this episode, so I hope you guys are listening at twice speed so that the chipmunk is messing up over and over and not me. Anyway. The first module was built by Bell Laboratories, and that was in nineteen fifty four. And uh, at that point they were thinking of it kind of they think they called it a solar battery. They didn't even call it a solar cell at that point, and it was kind of considered to be an interesting idea

but not at all practical. I think they determined that based upon the amount of work and uh it took to develop and manufacture that first module. They were getting about a watt for every I think it's two fifty bucks per what, which is not efficient doesn't even compare to other materials at all. Right, So not something that they could implement immediately in order to to try and

generate electricity. And and then later on the fifties and then into the sixties, really primarily in the sixties, that's when the space industry began to use these solar cells in order to get power for vehicles that be traveling through space and also satellites that would be placed in

orbit around the Earth. You know, you have to have power going to these satellites somehow, and you know, batteries can provide power, but power batteries will die out and there's no way of recharging easily when you can't tether the device to the Earth. Okay, spot Nick, enough of that. Um. So, solar cells were a way to be first for satellites to gather power and remain in orbit functioning properly for longer. Um Now, why are we even talking about solar power

in the first place. Well, mainly because it's abundant, and one would imagine inexpensive. I mean, you've got about a thousand watts of energy per square meter of the planet's surface. Yeah, that's a lot of energy. Uh. You know, the Sun shoots out lots of lots of energy towards the Earth. I mean, really, the Sun shoots out lots of energy everywhere, but we on Earth are happy to receive quite a

bit of it. Uh and we some of it gets absorbed in the atmosphere, some of it gets absorbed by the surface of the Earth, some of it is converted into energy via photosynthesis by the agitation, and then the rest of it just kind of gets reflected back off into space. So there's all this energy that is not being used in any meaningful way at all, and it's just it's going away. And uh So the thought is using solar cell technology, we could perhaps harness some of

this energy that otherwise we would just lose um. And that's the basis behind the the push for solar energy. Now, the engineering challenges that face us as we try to actually harness that power are what kind of keep us from just adopting it wholesale. That and also, I mean there's some practical problems besides the engineering issues. Right, Like, if you live in a place where there's not a lot of you don't get a lot of sun, then

solar energy doesn't make a whole lot of sense. It would be a lot it would be a heavy investment for very little payoff. Um. Now, if you live in a place that tends to get sun most of the error, than solar cells make a lot more sense. Yeah. The basics involve something that we've talked about many times in

the show. Semiconductors, which is a material that allows some electrons to flow, but not all the available electrons to flow, permits some flow of electricity, but not there's some control, right. It acts somewhat like a conductor and somewhat like an insulator.

And uh and and it's the relationship between the semiconductor and photons, which are the particles that we can you know, units of light energy really because you talk about how light can be both a wave and a particle, but really talk about a photon having a certain amount of energy um. And the energy has to be enough to cause the semiconductor to conduct electricity. And I guess we can get into how that works and the basis behind that, and uh really comes down to things like a selah

common crystals. Yeah, yeah, well it's possible. I should say upfront that it's not always silicon. That's true, silicon being the predominant material it's used. I think for the purposes of of this early part of the discussion, I think we should think of the solar cells that you see mounted on roofs and different places, because those are the ones with which most of us are familiar. So, yeah,

the dominant semiconductor used in that as silicon. Right, So in order to understand how the solar cells work, we're gon we're gonna have to take a little a little chemistry lesson here and learn more about silicon itself. So, silicon is an atom that has fourteen electrons. Yea. There are three different shells um and the first two are are full. There are two and eight electrons, but uh the outer shell has room for eight, but generally only

has four. So, uh, you know the shells case you don't remember, the shells are essentially they represent a general space around the nucleus of the atom where electrons are capable of existing. And because electrons are negatively charged and and like charge, Uh, what's the word thank you? It just escaped repulse to repelled? Yes, that those those sometimes they away from thank you. Yeah. I was like, I

think they don't like each other. And I was like, that's probably not quite as sophisticated as our listeners expect, well they expected from me. You're so so like like charges repel one another, Thank you, Mr Palette. Without you, I would have just been sitting here quiet and Matt would have been snickering in the other room. Space is getting really read. It was really entertining, you know, it

happens sometimes my brain just gives out on me. So, yes, light getting back to it like charge repels like so, so, these electron shells represent a space where electrons are capable of existing, and you can't have more electrons in that space because the negative charges would push push the electrons out.

So then the second shell, that's the one where you can have up to eight electrons there, and then the third shell, up to eight can exist there, but only four are there in a in a silicon atom, So if you you know, there's room for more electrons there. In a way, I hesitate to use the word want

because it's just sentience. But it's it's these atoms are not, as far as we know, sentient in any way, tend to Yeah, they there is a a there's a tendency for these atoms to require more electrons in that final shell to have a full outer shell. Right, that's that's the goal of these atoms, as if there were like

some sort of conscious goal. So, so when you get a whole lot of silicon atoms together, they tend to bond together, um because they begin to share electrons in their outer shells, and so they get really really tight. So a silicon atom will bond with four other silicon atoms to fill up that outer shell. And each of those silicon atoms are bonding to up with up to four other silicon itoms to fill up their outer shell, and this creates a crystalline structure, and they bond with

four friends and so on and so on. So, yeah, you get this crystalline structure. Now, once you have this, we're talking right now about a pure silicon crystalline structure, right, So when you get all these these outer shells full of electrons, there's a problem and that it doesn't really conduct electricity at that point because you don't have any free electrons, free raining electrons to uh to move through

that material. So if you introduce electricity, it's hard. It takes a lot more energy to break the electrons out of those bonds so that they will flow through. If you you can do it, but you have to put a lot of energy into the system. Yeah. What you're looking for here is free carriers, the electrons that are wandering around. Um. That will allow you to conduct electricity. You know, if there are a lot of them. Um. So what you have to do next is really dope. Yeah, yeah,

you have to dope the silicon. Now that means that you are introducing impurities or other elder ingredients if you will, into the silicon crystal. So you know when you think about impurities and usually that has a negative connotation to it, but in this case, it's something that's really necessary you can put there. Now, there are two different routes to go, right. You can put in atoms into You can introduce atoms into this mixture that have more electrons in their elder

shell than silicon does. Now, that's going to introduce extra electrons into this crystall instructures. Some electrons that are not bonded with other atoms. So that's where you've got these free carriers, and then it doesn't take as much energy when you introduce energy into the system to break those

electrons free from the structure. UM, it's still requires energy because they're the those electrons are still attracted to the um, the positively charged nucleus, but it doesn't take as much as if all the atoms were bonded to one another with no free electrons. Yeah, if you used, for example, phosphorus and uh introduced that to pure silicon, first of all, they would really hit it off at the party. Yes. Oh wait, I'm thinking of introducing in a totally different

way anyway. So if you dope some pure silicon with with phosphorus um, you would add you would essentially be adding free electrons or source of free electrons, let's say that, and that would create an end type uh semiconductor and meaning negative because again, electrons have a negative charge, so you've actually got more of a negative charge than a

positive charge because you have these extra electrons. Uh. Now, now, if you were to introduce a material that had fewer electrons in its outer shell than silicon, you would end up with spaces for electrons where no electrons exist. That would be a P type of silicon, yes, because you would have a space for electrons, but there would be

no electron to fill that space. Now, if you were to take these two types of silicon, the N type and the P type and put them together, then the like the extra electrons from the N type want to go and again want being just they tend to go to the P type because there's a positive hole there and you have the negative charged electrons in the N type. So there's this immedia desire to transfer or tendency to transfer. Chris is just laughing because I'm adding anthropomorphiz sizing electrons. Look,

some of my best friends are free carriers. Okay, hey, let's go to the P type. Oh, man, is too early. I didn't want to see the animated version of this. Little know, the electrons with little faces drawn on a big smile. Hey, so you got a hole there? I can feel that. So the uh yeah, there's this tendency for the electrons to move across. Well, this creates this actually can create a barrier that acts like a diode.

And if you've listened to our Basic Electronics podcast, you know that a diode is this channel that allows electricity to flow one way but not back in the other directions one way street exactly. And in this case, interestingly enough, it will allow electrons to transfer from the PA side to the inside, but not the other way around. Oh yeah, so because that's not what they normally want to do, right. So now this is where we finally get into introducing

photons into this system. All right, So you've got this, You've got the system here where you've got this barrier between the N type selicon and the B type cell con and you've got the potential for electrons to move across this barrier if you introduce energy into the system, and the photons are that energy. So when a photon of a proper amount of energy strikes the silicon, UH, it can create enough energy for the electrons to transfer

across this barrier. Now, once the electrons cross cross that barrier from the P type to the ND type UH, they are now in a negatively charged environment, so that the tendency is for these electrons to try and get back to the positively charged environment, but they can't pass that barrier. So if you were to create a pathway from the negative side to the positive side. The electrons would follow that pathway and do whatever it was you wanted them to do if it meant they could get

to the positive side on the other end. So it's other. In other words, it's like a really exclusive party and you're like, Okay, you can come into the party, but you gotta carry my stuff into the room with you. And people want to get the party, You're like that totally. The party is worth it. I will carry your stuff. That's kind of the the analogy I'm going with here. There's a party I want to go to tonight. Did I mention that anyway? So, so do you do you

have to power somebody's computer to do it? No? Fortunately not. So the electrons will do work along this pathway. And that's just a basic circuit, right, it's a and it's it allows current to flow. So photon hits the silicon uh and as long as the photon has enough energy to break that bond, the electron goes across the barrier, wants to get back to the pea side, will go through this pathway to get back to the peace side, and along the way will do work. So that work

might be lighting a light bulb. That's the basic example that you see in most uh sure drawings. So that's that's the basic principle. Now we gotta address a couple of other minor points to actually play a big role in in y solar cells work and why they aren't as um why we don't see them everywhere right now, Yeah, you mean, like, um, the fact that, well there are other components to the solar cells to sure how light

bounces off stuff like silicon. Right, Silicon tends to be very shiny, which means that some photons when they strike the surface are just going to reflect off and not get absorbed at all, which is a problem. If you're not absorbing the energy, then you cannot, um, you don't have enough energy for the electrons to break free by the way, that that we call that the band gap energy, to to break free of that that final electron shell.

So one problem is that not all photons have the same amount of energy because light comes in a variety of forms. You know, we talked about the spectrum of light. So you know, you can see light like visible light and has a pretty wide spectrum, but even beyond that is an even wider spectrum infrared light, ultraviolet light, and

then you know of course all the different colors. Well, each of those types of of light have a different amount of energy, and if the energy is not sufficient to UH to overcome the band gap energy, the electron is not going anywhere. So if the energy is more than what the band gap needs, that electron will move, but some of that energy is wasted. Like for example, if I need if I can lift a hundred and ten pounds and there's a weight in front of me

that's a hundred pounds, I can lift that up. But if there are two weights that are a hundred pounds, I'm still only gonna be able to lift one up. Even though I'm capable of lifting over a hundred pounds, I'm not capable of lifting two hundred pounds. So if you get a photon that actually has say twice as much energy as the band gap energy, then you could actually move to electrons per photon UM. So that's another problem.

So how do we get past the reflective problem? Well, usually they get around it by putting on some kind of material that is an anti reflective property, um, just to keep the photons from bouncing away UM. And that that's one thing they have to do. They also have to put a cover plate on it, you know, glass,

essentially to keep the solar cell from being damaged. Because again we were talking about the solar cells that you see the arrays that you see in on rooftops and um and for in some instances on the side of the I see a lot of them on the side of the road where they have some kind of equipment there, um, you know, a sign or something that they want to use to uh, you know, to provide messages to people

who are traveling on the roadway. They'll have a giant or not a giant, but a large solar panel out there to help power the sign. Um. You know, that's sitting out there all the time, so you know, you don't want it to be damaged by the rain or or anything. Um, So you know, you have to have these other things that are they're going on. But unfortunately, these uh, these solar cells are not particularly efficient. Yeah, there's actually there's several reasons why efficiency is a problem.

One of those is, you know, I mentioned the whole band gap energy problem. Whereas one temptation would be to build a solar cell that be able to gather as many photons as possible. In other words, aim for the lowest common denominator, like create material that's going to have the lowest band gap energy, so that even weak photons would be able to make electrons flow. Well, here's the problem with that. Current is that would be the number

of electrons that move through a system. Right, But there's another element called voltage, and and voltage is more like if you want to think of it in terms of plumbing, voltage would be the pressure and current would be the amount of water um. So voltage and current together, When you combine the two together, you get power. That's the product of current and voltage. So you mustapply the two

and you get power. So the power from any system is going to be dependent upon the current and the voltage. If you use material that has a low band gap energy, you get a lower voltage in that system, so you've actually decreased the voltage. So the current increases, but the voltage decreases, so the product does not necessarily become enough

for it to be a good return on investment. So, in other words, you could create something that creates has more current but a lower voltage, the power is less. It does it doesn't do as much work as say, materials that have a higher band gap energy, even though you've even though you are discounting more photons in that in that other system, the photons that are hitting are producing more energy. UM. So that's one issue. Although you can kind of work around that in a way. You

can create a multi junction cell. And a multijunction cell is uh. You can think of that as layers of cells on top of one another, and one layer has a certain band gap energy, and then the next one has a different band gap energy, and the next one has yet another band gap energy. In order to capture as many of these photons as possible, and that will help a little bit. So that's one way you can do it. It's a very expensive thing to do, but

NASA has been doing it for years. That's that's what NASA solar cells tend to be, our multi junction cells because you know, you want to you want the satellites to last a really long time so um, and you want them to be very efficient. But that's one problem with efficiency. Another is just the design of the solar cells themselves. In order for these electrons to hit a pathway a circuit, you know, they have to they have, you have to create that pathway for them, and that

raises some challenges. Where do you put how do you create this pathway the top of the solar cell. It's hard to make a conductive layer, right, because I mean usually we tend to use metal. Metal is a good conductor. Most metals are good conductors. Yeah, and the series resistance of silicon is so high that it causes a lot of loss. Mean, if you're using something like copper, right, it would do great. Yeah, but copper doesn't have that

photovoltaic quality. There's the problem. So if you're using metal to conduct the electricity, to act as the circuit, to act as the pathway for these electrons, um, the question is, well, you can't really, you can't encase it in metal because if you did, then no photons would get through. There has to be at least one side open. You know, you can create some conductive material that is, uh, you can,

you can weave through the glass. But there's also a concern that you know, photons are these tiny, tiny, tiny particles, and even the thinnest metal material that might make up a grid in a solar module, for example, will block some electron photons. Rather which means that you're losing efficiency

that way. So that's that's one of the reasons why solar panels can have problems with efficiency is that just based on the design itself, in order to conduct those electrons and provide electricity, you're blocking off some of the photons. So you're never going to get a hundred percent efficiency because just based on the technology itself, it's blocking its

own source of power. That's frustrating. Photons just shake. Yeah, So they've been working on trying other types of materials, uh, stuff like a morphous silicon, cadmium tell your ide and copper iridium, gallium decelenide. Had some of that the other day. It was delish, But yeah, I mean these are using these materials, uh, you know, they've they've been trying to

find some advantages. One of those is that with some of those materials you can create a thinner material, a thinner panel or thinnel thinner cell, and they call them thin film solar cells. And basically, yeah, these are very neat because, um, a lot of the again the arrays that we had in our initial example are pretty solid. They don't they don't bend, and the thin film solar cells. Yes,

they do break, but um. Actually a couple of companies have found ways to print thin film solar cells by spraying and and ink made with these materials onto foil UM, which is really cool because uh, it enables it to be somewhat flexible, and you can use it in places, uh, these types of solar cells in ways that you wouldn't

be able to otherwise. UM. Really you could see something like this on a handheld calculator because those solar cells, you know, the little itty bitty ones um, are thinner than the ones that you see on on rooftops and in different places like that. UM. The thing is they they're about fifty efficient at maximum UM, which is more likely to be more like fifty efficient UM, which is of course also south of the efficiency that they strive for with the uh, the silicon based wafer cells, the

hard cells. So you know, it's it's they're getting to be more of a reality. This is something that's been in development for several years now, UM, and they're you're seeing them in more places. But they also have their drawbacks, you know, and you know there are other drawbacks with solar panels as well. The efficiency is a big one, because the less efficient a solar array is, the more cells you're going to need in order to generate the electricity you want. Right you and in general big areas

to get a lot of sun. That's that's your prime target for any sort of solar power facility. Um, you know, it's it's one thing to put solar cells over the roof of your house, is very difficult to generate enough power to actually uh be completely subsist just on on

solar power. For one thing, if you're if it's if you're using the power as soon as it's generated, then you're only going to be able to use power during the day and on a sunny day at that, right, So you're gonna have to have batteries, some sort of storage medium in order to h to store power and use it later. And just frankly, I don't think there are that many houses that are have enough efficient solar

panels to just rely on solar energy and battery backup. Now, there are some and in fact, I've I've heard stories about people who are still connected to the electricity grid who are using solar power predominantly in their houses and um, and in some cases if they generate more electricity than they are consuming, they can actually feed energy back into the grid and their power company will compensate them for

that much. Is a nice benefit, especially because these solar arrays can be very expensive to install, right And usually that only I mean, if you are in the right area and you've got the right kind of solar cells, then you may actually make enough where you're making money from the power company. But more often it's a reduction in your power bill. Like, first of all, your power bill is not gonna be that high anyway, because you're mostly relying on the solar cells and the power company

is providing whatever amount left over you require. But then occasionally you produce more than what you need, uh, so your bill will just be lower at the end. Yeah, it's not like your you can recoup your investment overnight or over sunny day, right especially. Yeah, and if you happen to have a stretch of time where it's just overcast day after day after day, then that those are

days when you're not really gonna be producing that much power. Um. Not to say that it isn't worthwhile, no, but it you know, don't expect you know, to make it back up immediately. And another difficulty is that some depending on the materials that are going into those solar panels, they may or may not be either rare earth metals, which there there's a whole host of problems. We if you've heard O our podcast on rare earth materials, then you know you know that that has its own host of

issues as well. Uh. There's also the possibility of depending on again on the material in the solar cell, there may be very toxic material in there, or material that may not it'sself be toxic, but the manufacturing process of that material itself produces toxic toxic materials. So there is the potential for solar power to do environmental harm indirectly. You know, the actual production of electricity isn't environmentally destructive, but the process of building those solar panels itself maybe.

So you have to look at the big picture and the full impact of the system. You can't just look at Hey, you know, I'm getting energy from the sun. I'm not burning any fossil fuels. Uh, this is clean energy. Everything's hunky dorry. You have to look beyond that in order to really consider the impact of the system. Yeah, which you know that mean eventually get to a point where you're looking at it from such a big picture

that you're thinking there's no solutions out there. Goodnight kids. Well, I think, uh, well, we've sort of talked about it another podcast to like the bloom Box and other other things. But yeah, I mean it's it's one of those things where in the long run, I think it's a it's gonna end up being a combination of solutions, you know, to get off of fossil fuels, rather than just a single, uh, you know, single one. I think it will probably involve

jackostile terriers on a treadmill. It might, and it might very well, because as far as I can tell, they have an inexhaustible supply of energy. Yeah, especially if you if you, you know, have a treat at the end of the the little conveyor belt, they'll just run, run, run, anyway, that's neither here nor there. Well, that was a great

discussion about solar panel technology. I hope that answered your question, Adam. Uh, it was a fun things topic to cover and uh, well, if you guys have suggestions for topics that you would like us to talk about, feel free to let us know. You can contact us on Twitter or Facebook. Our handle at both of those is text Stuff hs W. Or you can send us an email and that address is text Stuff at how stuff Works dot com and Chris

and I will talk to you again really soon. Be sure to check out our new video podcast, Stuff from the Future. Join how Stuff Work staff as we explore the most promising and perplexing possibilities of tomorrow. The How Stuff Works iPhone app has arrived. Download it today on iTunes, brought to you by the reinvented two thousand twelve camera. It's ready, are you