WEBVTT - How Solar Panels Work 0:00:00.280 --> 0:00:02.840 Brought to you by the reinvented two thousand twelve camera. 0:00:03.160 --> 0:00:06.880 It's ready. Are you hey there, Text Stuff listeners, This 0:00:06.920 --> 0:00:09.200 is Jonathan Strickland and I have got a request for 0:00:09.240 --> 0:00:11.440 all of you. Now, Chris and I have decided that 0:00:11.440 --> 0:00:13.720 we're going to try and experiment. We're doing our first 0:00:13.920 --> 0:00:17.400 crowd sourced episode of tech Stuff and we want to 0:00:17.400 --> 0:00:21.480 know what your pick is for the worst video game 0:00:21.720 --> 0:00:25.600 of all time. Now, nominations you can. You can make 0:00:25.680 --> 0:00:28.479 one nomination. You nominate one game, and you need to 0:00:28.480 --> 0:00:30.639 tell us the name of the game and the platform 0:00:30.760 --> 0:00:32.839 it was on. And it could be any platform. It 0:00:32.840 --> 0:00:37.000 could be an arcade game, it could be a PC, Mac, Xbox, 0:00:37.040 --> 0:00:41.360 PS three, Nintendo handheld console. It can be web based 0:00:41.840 --> 0:00:43.839 if you like. But just you let us know what 0:00:43.840 --> 0:00:45.560 the platform is so we can make sure we count 0:00:45.600 --> 0:00:49.440 that as the votes. So you can nominate your game 0:00:49.600 --> 0:00:53.920 either through email, which is tech Stuff at how stuff 0:00:53.920 --> 0:00:58.320 works dot com, or you can nominate through Twitter or Facebook. 0:00:58.720 --> 0:01:01.560 And we're gonna put a cut off date on this. 0:01:01.680 --> 0:01:03.640 I want to have the episode go up by the 0:01:03.720 --> 0:01:07.720 end of September of eleven. So let's say you need 0:01:07.800 --> 0:01:12.960 to get your nominations in by September eleven, So if 0:01:12.959 --> 0:01:15.880 you get those nominations into us, we will make sure 0:01:15.920 --> 0:01:19.240 we include those in the process and we will have 0:01:19.280 --> 0:01:22.640 an episode where we give you the worst video games 0:01:22.800 --> 0:01:25.800 of all time based upon the votes of our listeners. 0:01:26.040 --> 0:01:30.840 Thanks a lot. Can't wait to hear from you. Get 0:01:30.840 --> 0:01:34.039 in touch with technology with tech Stuff from how stuff 0:01:34.040 --> 0:01:42.640 works dot com. Hello, everyone, Welcome to tech Stuff. My 0:01:42.720 --> 0:01:44.560 name is Chris Poet and I am an editor at 0:01:44.560 --> 0:01:47.760 how stuff works dot com. Sitting across from me as 0:01:47.800 --> 0:01:51.520 always and for some reason twisting up a rubber dinosaur 0:01:51.800 --> 0:01:55.960 is senior writer Jonathan Strickland, Little Darlin, the smiles returning 0:01:56.000 --> 0:01:59.280 to the faces, Little Darling, it seems like years since 0:01:59.320 --> 0:02:02.960 it's been here. H. That was a nice choice for 0:02:03.040 --> 0:02:07.320 today's topic, which is I think something that everyone will 0:02:07.360 --> 0:02:09.840 find electrifying. Yeah, and in fact, this comes to us 0:02:09.840 --> 0:02:20.480 courtesy of a Google Plus suggestion. This comes from Adam, 0:02:20.520 --> 0:02:22.600 who says this may be a bit simple, but have 0:02:22.680 --> 0:02:25.080 you guys ever done an overview of solar technology and 0:02:25.160 --> 0:02:28.239 solar tech history? Just re listened to your battery podcast 0:02:28.280 --> 0:02:33.200 and it made me wonder more about alternative energy sources. Adam, um, 0:02:33.240 --> 0:02:36.120 your definition of simple and my definition of simple are 0:02:36.240 --> 0:02:40.240 too very different things. But but yeah, we're gonna talk 0:02:40.240 --> 0:02:45.040 about solar power, solar cells also known as photo voltaic cells, 0:02:45.639 --> 0:02:49.520 and uh kind of where it came from. M Yeah, 0:02:49.560 --> 0:02:52.400 they're not they're certainly not new. UM. We have an 0:02:52.480 --> 0:02:56.200 article about how solar cells work on the website UM 0:02:56.280 --> 0:02:59.000 which discusses how they were used in the nineteen fifties 0:02:59.400 --> 0:03:02.840 in space uh space technology. Yeah. In fact, the well, 0:03:03.280 --> 0:03:06.960 to go back even further, the photoelectric effect, which of 0:03:07.000 --> 0:03:11.720 course is the basis of photovoltaic fells, that was first 0:03:12.160 --> 0:03:16.800 discovered by a or at least first observed by a 0:03:16.840 --> 0:03:23.320 French physicist named Edmund Beckerel. It's an eighteen thirty nine. Wow, 0:03:23.360 --> 0:03:26.840 that was some time ago. Yeah. Now, granted he observed 0:03:26.880 --> 0:03:32.200 that certain materials, if if exposed to sunlight, would produce 0:03:32.240 --> 0:03:35.360 a certain amount of electric current, but there wasn't really 0:03:35.400 --> 0:03:38.240 any way of putting that to any use at the time. 0:03:38.280 --> 0:03:41.720 It was just it was an interesting scientific observation and 0:03:41.800 --> 0:03:46.360 that was the the limit of it. Einstein himself began 0:03:46.480 --> 0:03:49.400 to ruminate on this, decided about, you know, to kind 0:03:49.400 --> 0:03:52.080 of think about what is the nature of light, how 0:03:52.120 --> 0:03:54.720 does it interact with the nature of electricity, what's the 0:03:54.760 --> 0:03:58.760 relationship there? Um? And then he actually won a Nobel 0:03:58.840 --> 0:04:04.560 Prize based on his observations. Now, the first module photo 0:04:04.640 --> 0:04:07.280 vote vol take module, because a module is a collection 0:04:07.440 --> 0:04:10.880 of photo voltaic cells. In fact, we can get this 0:04:10.920 --> 0:04:13.080 out of the way and really early on, if you 0:04:13.120 --> 0:04:15.520 want to talk about like the a sense of scale, 0:04:16.080 --> 0:04:21.560 an individual photo voltaic cell, when grouped together with other 0:04:21.680 --> 0:04:24.719 photo voltaic cells, makes a module, and groups of modules 0:04:24.760 --> 0:04:28.640 together make an array. So it's just it's just as 0:04:28.839 --> 0:04:31.120 a question of scale. So array isn't a group of 0:04:31.120 --> 0:04:34.000 modules and modules a group of photo photo voltaic cells. 0:04:34.120 --> 0:04:36.680 I'm gonna stumble over that over and over in this episode, 0:04:36.720 --> 0:04:38.919 so I hope you guys are listening at twice speed 0:04:38.960 --> 0:04:40.760 so that the chipmunk is messing up over and over 0:04:40.760 --> 0:04:43.200 and not me. Anyway. The first module was built by 0:04:43.240 --> 0:04:47.720 Bell Laboratories, and that was in nineteen fifty four. And uh, 0:04:47.960 --> 0:04:50.640 at that point they were thinking of it kind of 0:04:50.760 --> 0:04:53.520 they think they called it a solar battery. They didn't 0:04:53.560 --> 0:04:55.920 even call it a solar cell at that point, and 0:04:56.360 --> 0:04:59.360 it was kind of considered to be an interesting idea 0:04:59.480 --> 0:05:03.360 but not at all practical. I think they determined that 0:05:03.640 --> 0:05:06.719 based upon the amount of work and uh it took 0:05:06.760 --> 0:05:11.240 to develop and manufacture that first module. They were getting 0:05:11.279 --> 0:05:15.039 about a watt for every I think it's two fifty 0:05:15.040 --> 0:05:19.720 bucks per what, which is not efficient doesn't even compare 0:05:19.800 --> 0:05:24.960 to other materials at all. Right, So not something that 0:05:24.960 --> 0:05:27.640 they could implement immediately in order to to try and 0:05:27.680 --> 0:05:31.240 generate electricity. And and then later on the fifties and 0:05:31.240 --> 0:05:34.600 then into the sixties, really primarily in the sixties, that's 0:05:34.640 --> 0:05:37.840 when the space industry began to use these solar cells 0:05:37.880 --> 0:05:42.640 in order to get power for vehicles that be traveling 0:05:42.680 --> 0:05:47.159 through space and also satellites that would be placed in 0:05:47.320 --> 0:05:48.919 orbit around the Earth. You know, you have to have 0:05:49.040 --> 0:05:55.039 power going to these satellites somehow, and you know, batteries 0:05:55.080 --> 0:05:58.360 can provide power, but power batteries will die out and 0:05:58.400 --> 0:06:01.599 there's no way of recharging easily when you can't tether 0:06:01.760 --> 0:06:08.159 the device to the Earth. Okay, spot Nick, enough of that. Um. So, 0:06:08.160 --> 0:06:11.320 solar cells were a way to be first for satellites 0:06:11.320 --> 0:06:15.640 to gather power and remain in orbit functioning properly for longer. 0:06:16.240 --> 0:06:20.320 Um Now, why are we even talking about solar power 0:06:20.320 --> 0:06:25.000 in the first place. Well, mainly because it's abundant, and 0:06:25.720 --> 0:06:29.960 one would imagine inexpensive. I mean, you've got about a 0:06:30.000 --> 0:06:33.719 thousand watts of energy per square meter of the planet's surface. Yeah, 0:06:33.760 --> 0:06:37.279 that's a lot of energy. Uh. You know, the Sun 0:06:37.520 --> 0:06:40.480 shoots out lots of lots of energy towards the Earth. 0:06:40.520 --> 0:06:43.159 I mean, really, the Sun shoots out lots of energy everywhere, 0:06:43.240 --> 0:06:46.080 but we on Earth are happy to receive quite a 0:06:46.080 --> 0:06:49.880 bit of it. Uh and we some of it gets 0:06:49.880 --> 0:06:52.720 absorbed in the atmosphere, some of it gets absorbed by 0:06:52.720 --> 0:06:55.799 the surface of the Earth, some of it is converted 0:06:55.880 --> 0:07:01.200 into energy via photosynthesis by the agitation, and then the 0:07:01.240 --> 0:07:03.960 rest of it just kind of gets reflected back off 0:07:04.000 --> 0:07:07.880 into space. So there's all this energy that is not 0:07:07.960 --> 0:07:11.160 being used in any meaningful way at all, and it's 0:07:11.240 --> 0:07:15.480 just it's going away. And uh So the thought is 0:07:15.680 --> 0:07:18.840 using solar cell technology, we could perhaps harness some of 0:07:18.840 --> 0:07:22.280 this energy that otherwise we would just lose um. And 0:07:23.320 --> 0:07:29.000 that's the basis behind the the push for solar energy. Now, 0:07:29.440 --> 0:07:32.800 the engineering challenges that face us as we try to 0:07:33.200 --> 0:07:36.400 actually harness that power are what kind of keep us 0:07:36.440 --> 0:07:39.920 from just adopting it wholesale. That and also, I mean 0:07:39.920 --> 0:07:43.440 there's some practical problems besides the engineering issues. Right, Like, 0:07:44.240 --> 0:07:46.560 if you live in a place where there's not a 0:07:46.600 --> 0:07:49.400 lot of you don't get a lot of sun, then 0:07:49.560 --> 0:07:51.680 solar energy doesn't make a whole lot of sense. It 0:07:51.680 --> 0:07:54.920 would be a lot it would be a heavy investment 0:07:55.280 --> 0:07:57.720 for very little payoff. Um. Now, if you live in 0:07:57.720 --> 0:08:00.240 a place that tends to get sun most of the error, 0:08:00.680 --> 0:08:05.840 than solar cells make a lot more sense. Yeah. The 0:08:05.880 --> 0:08:10.320 basics involve something that we've talked about many times in 0:08:10.320 --> 0:08:14.440 the show. Semiconductors, which is a material that allows some 0:08:14.520 --> 0:08:18.720 electrons to flow, but not all the available electrons to flow, 0:08:19.360 --> 0:08:23.640 permits some flow of electricity, but not there's some control, right. 0:08:23.680 --> 0:08:26.640 It acts somewhat like a conductor and somewhat like an insulator. 0:08:27.440 --> 0:08:31.200 And uh and and it's the relationship between the semiconductor 0:08:31.280 --> 0:08:35.840 and photons, which are the particles that we can you know, 0:08:36.400 --> 0:08:39.680 units of light energy really because you talk about how 0:08:39.800 --> 0:08:41.440 light can be both a wave and a particle, but 0:08:41.520 --> 0:08:44.559 really talk about a photon having a certain amount of 0:08:44.640 --> 0:08:49.600 energy um. And the energy has to be enough to 0:08:49.679 --> 0:08:52.600 cause the semiconductor to conduct electricity. And I guess we 0:08:52.600 --> 0:08:56.600 can get into how that works and the basis behind that, 0:08:57.120 --> 0:08:59.960 and uh really comes down to things like a selah 0:09:00.040 --> 0:09:05.200 common crystals. Yeah, yeah, well it's possible. I should say 0:09:05.360 --> 0:09:10.080 upfront that it's not always silicon. That's true, silicon being 0:09:10.200 --> 0:09:14.679 the predominant material it's used. I think for the purposes 0:09:14.720 --> 0:09:17.559 of of this early part of the discussion, I think 0:09:17.559 --> 0:09:20.400 we should think of the solar cells that you see 0:09:21.040 --> 0:09:24.280 mounted on roofs and different places, because those are the 0:09:24.280 --> 0:09:26.560 ones with which most of us are familiar. So, yeah, 0:09:26.760 --> 0:09:30.280 the dominant semiconductor used in that as silicon. Right, So 0:09:30.480 --> 0:09:33.080 in order to understand how the solar cells work, we're 0:09:33.080 --> 0:09:35.320 gon we're gonna have to take a little a little 0:09:35.400 --> 0:09:39.439 chemistry lesson here and learn more about silicon itself. So, 0:09:39.600 --> 0:09:43.880 silicon is an atom that has fourteen electrons. Yea. There 0:09:43.880 --> 0:09:47.600 are three different shells um and the first two are 0:09:47.760 --> 0:09:51.360 are full. There are two and eight electrons, but uh 0:09:51.480 --> 0:09:55.480 the outer shell has room for eight, but generally only 0:09:55.480 --> 0:10:00.560 has four. So, uh, you know the shells case you 0:10:00.679 --> 0:10:04.640 don't remember, the shells are essentially they represent a general 0:10:04.760 --> 0:10:09.040 space around the nucleus of the atom where electrons are 0:10:09.480 --> 0:10:13.640 capable of existing. And because electrons are negatively charged and 0:10:13.640 --> 0:10:22.079 and like charge, Uh, what's the word thank you? It 0:10:22.280 --> 0:10:26.160 just escaped repulse to repelled? Yes, that those those sometimes 0:10:26.160 --> 0:10:28.840 they away from thank you. Yeah. I was like, I 0:10:28.880 --> 0:10:31.240 think they don't like each other. And I was like, 0:10:31.400 --> 0:10:34.840 that's probably not quite as sophisticated as our listeners expect, 0:10:34.920 --> 0:10:40.200 well they expected from me. You're so so like like 0:10:40.360 --> 0:10:44.640 charges repel one another, Thank you, Mr Palette. Without you, 0:10:44.760 --> 0:10:47.400 I would have just been sitting here quiet and Matt 0:10:47.400 --> 0:10:50.360 would have been snickering in the other room. Space is 0:10:50.400 --> 0:10:52.480 getting really read. It was really entertining, you know, it 0:10:52.600 --> 0:10:56.040 happens sometimes my brain just gives out on me. So, yes, 0:10:56.160 --> 0:11:00.600 light getting back to it like charge repels like so, so, 0:11:00.960 --> 0:11:04.199 these electron shells represent a space where electrons are capable 0:11:04.200 --> 0:11:07.200 of existing, and you can't have more electrons in that 0:11:07.280 --> 0:11:11.840 space because the negative charges would push push the electrons out. 0:11:12.400 --> 0:11:14.840 So then the second shell, that's the one where you 0:11:14.840 --> 0:11:17.560 can have up to eight electrons there, and then the 0:11:17.600 --> 0:11:20.040 third shell, up to eight can exist there, but only 0:11:20.160 --> 0:11:23.480 four are there in a in a silicon atom, So 0:11:24.080 --> 0:11:27.960 if you you know, there's room for more electrons there. 0:11:28.200 --> 0:11:31.440 In a way, I hesitate to use the word want 0:11:31.679 --> 0:11:35.360 because it's just sentience. But it's it's these atoms are not, 0:11:35.440 --> 0:11:38.080 as far as we know, sentient in any way, tend 0:11:38.200 --> 0:11:44.040 to Yeah, they there is a a there's a tendency 0:11:44.160 --> 0:11:47.640 for these atoms to require more electrons in that final 0:11:47.679 --> 0:11:51.360 shell to have a full outer shell. Right, that's that's 0:11:51.400 --> 0:11:54.560 the goal of these atoms, as if there were like 0:11:54.600 --> 0:11:57.880 some sort of conscious goal. So, so when you get 0:11:57.920 --> 0:12:01.440 a whole lot of silicon atoms together, they tend to 0:12:01.840 --> 0:12:06.959 bond together, um because they begin to share electrons in 0:12:07.000 --> 0:12:09.280 their outer shells, and so they get really really tight. 0:12:09.679 --> 0:12:12.640 So a silicon atom will bond with four other silicon 0:12:12.760 --> 0:12:15.360 atoms to fill up that outer shell. And each of 0:12:15.360 --> 0:12:18.000 those silicon atoms are bonding to up with up to 0:12:18.120 --> 0:12:20.320 four other silicon itoms to fill up their outer shell, 0:12:20.320 --> 0:12:23.000 and this creates a crystalline structure, and they bond with 0:12:23.040 --> 0:12:26.679 four friends and so on and so on. So, yeah, 0:12:26.760 --> 0:12:29.480 you get this crystalline structure. Now, once you have this, 0:12:30.559 --> 0:12:34.640 we're talking right now about a pure silicon crystalline structure, right, 0:12:34.760 --> 0:12:37.680 So when you get all these these outer shells full 0:12:37.679 --> 0:12:40.880 of electrons, there's a problem and that it doesn't really 0:12:41.600 --> 0:12:44.920 conduct electricity at that point because you don't have any 0:12:44.960 --> 0:12:49.160 free electrons, free raining electrons to uh to move through 0:12:49.200 --> 0:12:53.320 that material. So if you introduce electricity, it's hard. It 0:12:53.360 --> 0:12:56.280 takes a lot more energy to break the electrons out 0:12:56.280 --> 0:12:59.760 of those bonds so that they will flow through. If 0:12:59.760 --> 0:13:01.040 you you can do it, but you have to put 0:13:01.080 --> 0:13:03.360 a lot of energy into the system. Yeah. What you're 0:13:03.360 --> 0:13:06.120 looking for here is free carriers, the electrons that are 0:13:06.120 --> 0:13:10.160 wandering around. Um. That will allow you to conduct electricity. 0:13:10.480 --> 0:13:13.080 You know, if there are a lot of them. Um. 0:13:13.160 --> 0:13:16.800 So what you have to do next is really dope. Yeah, yeah, 0:13:17.040 --> 0:13:19.360 you have to dope the silicon. Now that means that 0:13:19.400 --> 0:13:24.520 you are introducing impurities or other elder ingredients if you will, 0:13:24.600 --> 0:13:27.320 into the silicon crystal. So you know when you think 0:13:27.320 --> 0:13:30.160 about impurities and usually that has a negative connotation to it, 0:13:30.200 --> 0:13:32.760 but in this case, it's something that's really necessary you 0:13:32.800 --> 0:13:36.600 can put there. Now, there are two different routes to go, right. 0:13:36.679 --> 0:13:39.240 You can put in atoms into You can introduce atoms 0:13:39.280 --> 0:13:43.120 into this mixture that have more electrons in their elder 0:13:43.200 --> 0:13:47.840 shell than silicon does. Now, that's going to introduce extra 0:13:47.920 --> 0:13:51.679 electrons into this crystall instructures. Some electrons that are not 0:13:51.880 --> 0:13:54.679 bonded with other atoms. So that's where you've got these 0:13:54.679 --> 0:13:57.720 free carriers, and then it doesn't take as much energy 0:13:57.880 --> 0:14:00.439 when you introduce energy into the system to break those 0:14:00.440 --> 0:14:05.680 electrons free from the structure. UM, it's still requires energy 0:14:05.720 --> 0:14:09.840 because they're the those electrons are still attracted to the um, 0:14:09.880 --> 0:14:14.319 the positively charged nucleus, but it doesn't take as much 0:14:14.360 --> 0:14:17.720 as if all the atoms were bonded to one another 0:14:18.160 --> 0:14:22.240 with no free electrons. Yeah, if you used, for example, 0:14:22.280 --> 0:14:26.680 phosphorus and uh introduced that to pure silicon, first of all, 0:14:26.840 --> 0:14:29.400 they would really hit it off at the party. Yes. 0:14:30.880 --> 0:14:32.880 Oh wait, I'm thinking of introducing in a totally different 0:14:32.880 --> 0:14:37.840 way anyway. So if you dope some pure silicon with 0:14:38.360 --> 0:14:42.920 with phosphorus um, you would add you would essentially be 0:14:43.000 --> 0:14:46.160 adding free electrons or source of free electrons, let's say that, 0:14:46.480 --> 0:14:50.800 and that would create an end type uh semiconductor and 0:14:51.040 --> 0:14:53.960 meaning negative because again, electrons have a negative charge, so 0:14:54.040 --> 0:14:56.640 you've actually got more of a negative charge than a 0:14:56.720 --> 0:15:00.120 positive charge because you have these extra electrons. Uh. Now, now, 0:15:00.240 --> 0:15:03.400 if you were to introduce a material that had fewer 0:15:03.920 --> 0:15:06.680 electrons in its outer shell than silicon, you would end 0:15:06.800 --> 0:15:12.280 up with spaces for electrons where no electrons exist. That 0:15:12.320 --> 0:15:15.720 would be a P type of silicon, yes, because you 0:15:15.720 --> 0:15:18.640 would have a space for electrons, but there would be 0:15:18.680 --> 0:15:21.400 no electron to fill that space. Now, if you were 0:15:21.440 --> 0:15:24.400 to take these two types of silicon, the N type 0:15:24.400 --> 0:15:27.360 and the P type and put them together, then the 0:15:27.720 --> 0:15:30.760 like the extra electrons from the N type want to 0:15:30.920 --> 0:15:33.960 go and again want being just they tend to go 0:15:34.200 --> 0:15:37.640 to the P type because there's a positive hole there 0:15:38.160 --> 0:15:40.800 and you have the negative charged electrons in the N type. 0:15:41.040 --> 0:15:46.000 So there's this immedia desire to transfer or tendency to transfer. 0:15:46.200 --> 0:15:51.320 Chris is just laughing because I'm adding anthropomorphiz sizing electrons. Look, 0:15:51.760 --> 0:15:56.040 some of my best friends are free carriers. Okay, hey, 0:15:56.120 --> 0:16:00.880 let's go to the P type. Oh, man, is too early. 0:16:01.600 --> 0:16:03.280 I didn't want to see the animated version of this. 0:16:03.560 --> 0:16:06.040 Little know, the electrons with little faces drawn on a 0:16:06.120 --> 0:16:09.680 big smile. Hey, so you got a hole there? I 0:16:09.680 --> 0:16:13.560 can feel that. So the uh yeah, there's this tendency 0:16:13.640 --> 0:16:16.120 for the electrons to move across. Well, this creates this 0:16:16.160 --> 0:16:19.000 actually can create a barrier that acts like a diode. 0:16:19.280 --> 0:16:22.080 And if you've listened to our Basic Electronics podcast, you 0:16:22.120 --> 0:16:26.320 know that a diode is this channel that allows electricity 0:16:26.320 --> 0:16:28.880 to flow one way but not back in the other 0:16:28.920 --> 0:16:34.560 directions one way street exactly. And in this case, interestingly enough, 0:16:35.000 --> 0:16:38.360 it will allow electrons to transfer from the PA side 0:16:38.400 --> 0:16:43.000 to the inside, but not the other way around. Oh yeah, 0:16:43.160 --> 0:16:45.960 so because that's not what they normally want to do, right. 0:16:46.560 --> 0:16:50.880 So now this is where we finally get into introducing 0:16:50.920 --> 0:16:54.360 photons into this system. All right, So you've got this, 0:16:54.440 --> 0:16:57.080 You've got the system here where you've got this barrier 0:16:57.160 --> 0:16:59.920 between the N type selicon and the B type cell 0:17:00.080 --> 0:17:03.920 con and you've got the potential for electrons to move 0:17:04.000 --> 0:17:08.560 across this barrier if you introduce energy into the system, 0:17:08.600 --> 0:17:12.560 and the photons are that energy. So when a photon 0:17:13.280 --> 0:17:16.800 of a proper amount of energy strikes the silicon, UH, 0:17:16.920 --> 0:17:20.400 it can create enough energy for the electrons to transfer 0:17:20.440 --> 0:17:23.639 across this barrier. Now, once the electrons cross cross that 0:17:23.680 --> 0:17:26.280 barrier from the P type to the ND type UH, 0:17:26.320 --> 0:17:29.800 they are now in a negatively charged environment, so that 0:17:29.960 --> 0:17:32.760 the tendency is for these electrons to try and get 0:17:32.800 --> 0:17:35.560 back to the positively charged environment, but they can't pass 0:17:35.640 --> 0:17:40.280 that barrier. So if you were to create a pathway 0:17:40.320 --> 0:17:43.240 from the negative side to the positive side. The electrons 0:17:43.280 --> 0:17:46.439 would follow that pathway and do whatever it was you 0:17:46.480 --> 0:17:48.560 wanted them to do if it meant they could get 0:17:48.600 --> 0:17:51.160 to the positive side on the other end. So it's other. 0:17:51.200 --> 0:17:53.439 In other words, it's like a really exclusive party and 0:17:53.440 --> 0:17:55.040 you're like, Okay, you can come into the party, but 0:17:55.119 --> 0:17:59.320 you gotta carry my stuff into the room with you. 0:17:59.600 --> 0:18:02.280 And people want to get the party, You're like that totally. 0:18:02.359 --> 0:18:04.479 The party is worth it. I will carry your stuff. 0:18:04.920 --> 0:18:07.360 That's kind of the the analogy I'm going with here. 0:18:07.440 --> 0:18:09.560 There's a party I want to go to tonight. Did 0:18:09.560 --> 0:18:13.320 I mention that anyway? So, so do you do you 0:18:13.359 --> 0:18:17.120 have to power somebody's computer to do it? No? Fortunately not. 0:18:17.359 --> 0:18:21.080 So the electrons will do work along this pathway. And 0:18:21.080 --> 0:18:23.880 that's just a basic circuit, right, it's a and it's 0:18:23.920 --> 0:18:27.160 it allows current to flow. So photon hits the silicon 0:18:27.600 --> 0:18:29.480 uh and as long as the photon has enough energy 0:18:29.520 --> 0:18:32.680 to break that bond, the electron goes across the barrier, 0:18:33.080 --> 0:18:34.720 wants to get back to the pea side, will go 0:18:34.840 --> 0:18:37.600 through this pathway to get back to the peace side, 0:18:37.600 --> 0:18:39.600 and along the way will do work. So that work 0:18:39.680 --> 0:18:43.280 might be lighting a light bulb. That's the basic example 0:18:43.320 --> 0:18:48.600 that you see in most uh sure drawings. So that's 0:18:48.680 --> 0:18:52.040 that's the basic principle. Now we gotta address a couple 0:18:52.080 --> 0:18:55.600 of other minor points to actually play a big role 0:18:55.680 --> 0:18:58.639 in in y solar cells work and why they aren't 0:18:58.680 --> 0:19:02.359 as um why we don't see them everywhere right now, Yeah, 0:19:02.520 --> 0:19:05.520 you mean, like, um, the fact that, well there are 0:19:05.560 --> 0:19:10.440 other components to the solar cells to sure how light 0:19:10.520 --> 0:19:14.320 bounces off stuff like silicon. Right, Silicon tends to be 0:19:14.400 --> 0:19:16.720 very shiny, which means that some photons when they strike 0:19:16.800 --> 0:19:18.760 the surface are just going to reflect off and not 0:19:18.800 --> 0:19:21.560 get absorbed at all, which is a problem. If you're 0:19:21.560 --> 0:19:25.120 not absorbing the energy, then you cannot, um, you don't 0:19:25.119 --> 0:19:27.320 have enough energy for the electrons to break free by 0:19:27.320 --> 0:19:30.080 the way, that that we call that the band gap energy, 0:19:30.200 --> 0:19:33.720 to to break free of that that final electron shell. 0:19:34.119 --> 0:19:37.240 So one problem is that not all photons have the 0:19:37.280 --> 0:19:40.760 same amount of energy because light comes in a variety 0:19:40.920 --> 0:19:45.080 of forms. You know, we talked about the spectrum of light. 0:19:45.160 --> 0:19:47.000 So you know, you can see light like visible light 0:19:47.119 --> 0:19:50.080 and has a pretty wide spectrum, but even beyond that 0:19:50.320 --> 0:19:54.879 is an even wider spectrum infrared light, ultraviolet light, and 0:19:54.880 --> 0:19:56.800 then you know of course all the different colors. Well, 0:19:56.840 --> 0:20:01.399 each of those types of of light have a different 0:20:01.400 --> 0:20:04.600 amount of energy, and if the energy is not sufficient 0:20:05.040 --> 0:20:08.840 to UH to overcome the band gap energy, the electron 0:20:08.880 --> 0:20:12.840 is not going anywhere. So if the energy is more 0:20:13.200 --> 0:20:16.480 than what the band gap needs, that electron will move, 0:20:16.520 --> 0:20:20.000 but some of that energy is wasted. Like for example, 0:20:20.040 --> 0:20:21.840 if I need if I can lift a hundred and 0:20:21.880 --> 0:20:25.800 ten pounds and there's a weight in front of me 0:20:25.840 --> 0:20:28.000 that's a hundred pounds, I can lift that up. But 0:20:28.040 --> 0:20:30.000 if there are two weights that are a hundred pounds, 0:20:30.080 --> 0:20:31.879 I'm still only gonna be able to lift one up. 0:20:31.880 --> 0:20:34.399 Even though I'm capable of lifting over a hundred pounds, 0:20:34.440 --> 0:20:38.440 I'm not capable of lifting two hundred pounds. So if 0:20:38.480 --> 0:20:41.320 you get a photon that actually has say twice as 0:20:41.400 --> 0:20:43.680 much energy as the band gap energy, then you could 0:20:43.720 --> 0:20:50.520 actually move to electrons per photon UM. So that's another problem. 0:20:50.600 --> 0:20:53.800 So how do we get past the reflective problem? Well, 0:20:54.040 --> 0:20:56.880 usually they get around it by putting on some kind 0:20:56.880 --> 0:21:00.959 of material that is an anti reflective property, um, just 0:21:01.000 --> 0:21:05.640 to keep the photons from bouncing away UM. And that 0:21:05.640 --> 0:21:07.199 that's one thing they have to do. They also have 0:21:07.280 --> 0:21:10.080 to put a cover plate on it, you know, glass, 0:21:10.200 --> 0:21:14.840 essentially to keep the solar cell from being damaged. Because 0:21:15.040 --> 0:21:17.520 again we were talking about the solar cells that you 0:21:17.560 --> 0:21:21.600 see the arrays that you see in on rooftops and 0:21:21.960 --> 0:21:24.639 um and for in some instances on the side of 0:21:24.640 --> 0:21:26.000 the I see a lot of them on the side 0:21:26.000 --> 0:21:30.560 of the road where they have some kind of equipment there, um, 0:21:30.600 --> 0:21:32.560 you know, a sign or something that they want to 0:21:32.680 --> 0:21:36.680 use to uh, you know, to provide messages to people 0:21:36.680 --> 0:21:38.919 who are traveling on the roadway. They'll have a giant 0:21:39.119 --> 0:21:41.159 or not a giant, but a large solar panel out 0:21:41.200 --> 0:21:43.720 there to help power the sign. Um. You know, that's 0:21:43.720 --> 0:21:46.040 sitting out there all the time, so you know, you 0:21:46.040 --> 0:21:48.240 don't want it to be damaged by the rain or 0:21:48.760 --> 0:21:51.560 or anything. Um, So you know, you have to have 0:21:51.600 --> 0:21:54.560 these other things that are they're going on. But unfortunately, 0:21:55.440 --> 0:21:59.360 these uh, these solar cells are not particularly efficient. Yeah, 0:21:59.400 --> 0:22:02.919 there's actually there's several reasons why efficiency is a problem. 0:22:03.000 --> 0:22:04.840 One of those is, you know, I mentioned the whole 0:22:04.880 --> 0:22:10.200 band gap energy problem. Whereas one temptation would be to 0:22:10.240 --> 0:22:12.639 build a solar cell that be able to gather as 0:22:12.640 --> 0:22:15.119 many photons as possible. In other words, aim for the 0:22:15.160 --> 0:22:18.760 lowest common denominator, like create material that's going to have 0:22:18.880 --> 0:22:24.000 the lowest band gap energy, so that even weak photons 0:22:24.880 --> 0:22:28.080 would be able to make electrons flow. Well, here's the 0:22:28.119 --> 0:22:32.400 problem with that. Current is that would be the number 0:22:32.400 --> 0:22:35.520 of electrons that move through a system. Right, But there's 0:22:35.520 --> 0:22:39.520 another element called voltage, and and voltage is more like 0:22:40.040 --> 0:22:41.760 if you want to think of it in terms of plumbing, 0:22:41.800 --> 0:22:44.800 voltage would be the pressure and current would be the 0:22:44.800 --> 0:22:50.280 amount of water um. So voltage and current together, When 0:22:50.320 --> 0:22:52.760 you combine the two together, you get power. That's the 0:22:52.800 --> 0:22:56.280 product of current and voltage. So you mustapply the two 0:22:56.280 --> 0:22:59.200 and you get power. So the power from any system 0:22:59.240 --> 0:23:01.200 is going to be dependent upon the current and the voltage. 0:23:01.240 --> 0:23:05.040 If you use material that has a low band gap energy, 0:23:05.800 --> 0:23:09.440 you get a lower voltage in that system, so you've 0:23:09.480 --> 0:23:12.320 actually decreased the voltage. So the current increases, but the 0:23:12.359 --> 0:23:17.359 voltage decreases, so the product does not necessarily become enough 0:23:17.400 --> 0:23:20.400 for it to be a good return on investment. So, 0:23:20.720 --> 0:23:23.360 in other words, you could create something that creates has 0:23:23.400 --> 0:23:26.320 more current but a lower voltage, the power is less. 0:23:26.560 --> 0:23:28.640 It does it doesn't do as much work as say, 0:23:28.880 --> 0:23:31.520 materials that have a higher band gap energy, even though 0:23:31.600 --> 0:23:34.600 you've even though you are discounting more photons in that 0:23:34.720 --> 0:23:37.359 in that other system, the photons that are hitting are 0:23:37.400 --> 0:23:42.080