This is Hacker Public Radio episode 3772 for Tuesday the 17th of January 2023. Today's show is entitled, Adventures with a small solar panel. It is hosted by Andrew Conway and is about 28 minutes long. It carries a clean flag. The summary is I have a look at a cheap solar panel and learn a bit about how it works and doesn't work. Hello and welcome to another episode of Hacker Public Radio with me, McNally, also known as Andrew. And in this episode I'm going to tell you a little bit about my adventures with solar panels. Not all about them because I can probably go on for a long time. It's actually literally about how I've discovered that solar panels work. And most of this you can read by Googling around web searching, should I say around in the internet. But I found that two things, which is quite usual when I'm trying to learn something. The first is there's a lot of rubbish in the internet, a lot of stuff that's plain wrong in misleading. Probably more than there used to be. But secondly, something you just learned best by doing. So this is all pretty much the first hand knowledge from me. Okay. So my first balance with solar panels was a small little low voltage, almost a toy type solar panel. It was, I guess, this is about the size of an A4 sheet of paper, you know, a side of a normal notebook. And it could claim, it could generate, I think, six to seven watts. And maybe it could, if I took it inside the Earth's orbit, perhaps, the distance of Mercury, Venus from the Sun, maybe then it could. But here in the Earth, I couldn't get much more than five watts out of it. And that was in a very good day with the panel pointed straight to direct sunlight. So my first thing was, it don't believe what's written on the label. Now actually, subsequently, with more professional panels that are designed for generating serious amounts of electricity for putting in your roof, for example, the specifications are done according to much tighter standards. But these smaller solar panels, not so much. So don't necessarily believe the, you're going to get the power that you think you will out of them. The other thing I discovered about solar panels very quickly was that they don't behave at all like any power source that I've dealt with before. Now the most common type of power source that I deal with, and I imagine most people deal with, is means voltage electricity. And you have a socket, three pin here in the UK, maybe other countries have more usually two pins, I don't know. But generally, the point of this is that you plug your device into the wall, an outcome of electricity, and if you plug in a electric toothbrush, or if you plug in a 30 kilowatt oven, or some kind of space heater, there's many kilowatts, you'll get the power, lamps will be delivered, and the voltage will hold up. So in this country, I expect where I am at 230 to 240 volt pretty constantly, and when I plug something in the voltage that doesn't drop appreciably, in fact, if it did drop by many volts, it would be time to investigate what the problem was. So in other words, what I'm trying to say is you get the power within reason, the current draw the power from your constant voltage source, and your voltage doesn't drop when you put a load on it, or the drop is negligible. So moving on to the next, most common source of electricity, which is batteries, now batteries are a little bit more delicate to deal with, because when you draw anything but the small current from a battery, you will notice quite a sizeable drop in the voltage, and of course, other different sort of batteries, of course, is that they are DC, direct current, so there's no in main voltages oscillating here, in the UK, it's 50 times per second, 50 Hertz, but a battery just delivers a straight constant voltage, or a straight constant current, with no variation unless the load is asking for a varying amount of current. So the key thing here is that when you draw even fairly modest amounts of current from a small battery is voltage will drop, now the device, most devices are designed to expect that, in fact, they're designed to handle the fact that the battery's voltage will drop, so when you buy a AA battery, or a AAA battery, it's rated at 1.5 volts when you get it, but it time it goes flat in inverted commons, and I'll tell you why I say inverted commons, it may be done to say 1.2 volts, and the devices are designed to work down there, and then make give you a warning, or in the case of a small torch, or flashlight, the device may just quit working completely, and with no warning. Now the reason I said flat in inverted commons is because just because it's a 1.2 volts doesn't mean it's got no energy left, in fact, it could have depending on the type of battery as much as 50% of its energy left, but it just can deliver a voltage that's useful for the purpose that you bought it for, so you discard it and you don't think much of the fact that you've just thrown away some potentially useful energy. There is a way to get energy out of such low voltage batteries, it's called a dual-feet, and maybe I'll do another HPR episode about that at some future point. Anyway, I digress, the point is that a battery will not give you a constant voltage, they won't give you the voltage, it's written on it, you're running it down over time, or because you placed a high current load in the battery. So that means that you have to design your circuits with that in mind. Now, the big surprise with solar panels, I didn't really know much about them, is that there are an extreme version of what happens with batteries, so I could hook up this little plastic solar panel that I bought. The brand name was Sunny Solar, good luck if you try and look that one up. It's almost certainly some meaningless brand name that's been pasted on from some generic product that's been turned out in a Chinese factory somewhere. I'm sure there's many other identical products with different names, but this particular solar panel, as I see, was rated at, I think it's a claimed it could do six volts at a deliver one amp, I think that's was the origin of why it claimed it could do six watts. Now, when I plugged it in and and fill sunlight, I could for a time get about six volts, or even a shade more. I noticed that the two things, first full of voltage would drop, not rapidly, but slowly and then come to a stable value, 5.9 or 5.8 something. Now, I'll be the first thing I noticed. The second thing, and this is the really dramatic thing, is that, oh, I've got, oh, I've got just about six, six volts, the play with here. Okay, that's plenty for my application. Maybe a bit too high for some of my devices, but here we go. But the interesting, you plug in a device to it, nothing happens, or maybe you see a pretty flash of an LED or something, and then it just dies, I think, oh, what's going on here. And when I connected an ammeter, the first thing that I noticed was, well, if actually in direct sunlight, it blew up the fuse in my ammeter, because I had it in the low current range, so, so, another lesson for you is, always go for the, if you've got one of these multimeter, I'm saying that ammeter, but it's a multimeter, especially the cheap ones, make sure, make sure, you put it on the 10 amp range, not the low range for looking at milliamps and microamps, because if you don't, then you'll blow a fuse which has maybe only rated to a few hundred milliamps. That was the first thing I learned. But when I realized what was wrong with my multimeter, and connected up in the 10 amp range, so I was nice and safe, I saw that maybe very briefly I would get the high current, like, I don't know, many hundreds of milliamps, maybe if it was full sunlight, but it would quickly vanish, and the voltage would collapse, and I would be left with nothing. I thought, okay, what's going on here then, and you have to really understand how a solar panel works. So, there are two key panel parameters on the specifications to the solar panel. Well, there's three. The one that most people describe as solar panel with is the power rating. So, in this case, it was, it claimed to be sex watts, I think. We'd be actually even seven, depending on the sales brochure you happen to look at. Anyway, let's say it's sex watts. But that actually isn't very interesting. More interesting is the numbers that lie behind it. So, it's said, voltage six volts and current one amp. Okay, now, I think what that really meant is that the open circuit voltage of the panel in full sunlight, so that's a sunny day of the panel, sun fairly high in the sky in the, and the panel pointed directly at the sun. So, it's absorbing as much sunlight as you can get on the panel. What it was saying is, at that point, the open circuit voltage of the panel should be sex volts, indeed it was. I measured sex volts. And the reason the voltage, I noticed dropped slightly as because as a solar panel heats up, it becomes less efficient. And, in fact, a cold solar panel is more efficient at producing electricity. Not hugely more efficient, maybe a one or two percentage points more efficient, depending how exactly how cool to get. So, I was observing is as the panel, which is dark in color and place it in the sun, it'll heat up quite rapidly to temperatures above 50 degrees C, maybe it's all predicting temperature could be as high as 70 degrees C, in fact. And so, there's quite a sizable change in efficiency because of this. And that's why I saw this voltage drop. Anyway, it's still roughly, give a take a few hundred millivolts, it's still your total torquey about six volts, in about plus and minus hundred millivolts, six, six volts. But that's the open circuit voltage. And that means that I have not completed a circuit that was effective to let infinite resistance between the positive and negative leads of the solar panel. That's what that parameter means, the open circuit voltage. So, you'll quite often see in solar panel specs, the subscript or C voltage in the open circuit. And that isn't the voltage you're getting because the moment that you connect a circuit to it, the voltage will drop. How far it drops depends on how much current you try to draw. So, if I tried to draw the one amp, it said in the label, it could do one amp. If I tried to draw one amp, I would not still have six volts. In fact, I have something very close to zero volts and I wouldn't have one amp either because the voltage wasn't there. And at this point, it's probably a good idea to fall back on the analogy of voltage and current being the pressure and flow of water. So, let's forget electricity for a moment. You have a hose pipe and you connect one into a tap or faucet, I guess, for my colleagues on the side of the Atlantic. And, of course, you open and close the nozzle at this point, if you haven't opened the tap and nothing happened. So, that's like the analogy there. The solar panel is in the dark and nothing is happening. There's no voltage, no pressure, no current is nothing. Then, you open up the tap. So, this is a bit like taking a solar panel out and placing it in strong sunlight. When you open up the tap, water pours in to the pipe and it's up hissing sound for a brief time and then it stops. And then all you're left with is a pipe full of water that's at pressure. And it's the means, in the case of the water pipe, it's whatever your means pressure of your water system is connected to the tap. But that's the key thing, you've got a nice high pressure. Now, when you open this, so I should say this at this point, this is a bit like taking a solar panel and leaving it in sunlight. And you'll see this high voltage, in the case of my solar panel, a six volt across the plus and minus leads. There's lots of voltage there. Just as there's a lot of separation in the pipe, but nothing else is happening. Water is not flowing out, electricity is not flowing out. So, all crazy static. That's useless. The moment you try to do something with the water, what happens is some of the pressure that was built up in the pipe is dissipated as the water flows out in a jet out of the nozzle. And that pressure is turning itself into the flow of water. So the pressure inside the pipe will drop slightly, but not to nothing, otherwise the water wouldn't flow the pipe. And the amount of water that's flowing out the pipe per second, let's say we measure it in liters per second. That is analogous to the current flow in the solar panel. Now, at this point, the analogy isn't so good because the main water is a bit like means electricity. It will supply within reason. You know, whatever pressure you need for the nozzle of your pipe. Now, if you close the nozzle at the end of your hose and then you went and close the tap, then there'll be water inside the hose and it will be held at quite high pressure because it can't go out through the closed tap or the closed nozzle. So this is like analogy of a solar panel in low sunlight. There's some charge stored there. There's next to nothing coming in. Or maybe you open the taps, like very slightly electrical water in, but they're just really not enough pressure to sustain it. So the moment that you open up the nozzle or at the end of the hose, water won't splort out and it kind of, yeah, come on the splort and then it will die down to trickle almost immediately. Because it's just no pressure at the end. Even if you have the tap open slightly to let some water in, there's very little pressure from that. So it will take too long for the hose pipe to fill up again. But if you did close the nozzle, the hose pipe would fill up again and you'd end up with a pressure ice pipe again. That's a bit like the idea of taking a solar panel, putting it in not very sunny conditions, but sunlight. Holding it to open the circuit voltage and then suddenly connecting something, the voltage will collapse. You'll get a sudden burst of current which may require accumulator as I discovered, but it can't sustain that current for any length of time and you'll just end up with a low voltage and an extremely low trickle of electricity, a low current. So that's how you should think of a solar panel. Now the more sunlight that you have, the greater the voltage it can sustain and the greater the current that you can draw off it without that voltage, completely collapsing, anything. So the game really is, is how much current can you pull out of a solar panel in the amount of sunlight that you've got? And that is a quite tricky problem really. But the answer is that you can sort of, you can tell from the voltage, roughly what level of sunlight that you've got. It will vary slightly in sunlight, but actually it's much better to look at the, what's the other parameter that we printed in a solar panel, and that will be, not the open circuit, but the short circuit current. So if you connect the plus and the minus leads to the panel, which you ordinarily never do with mean electricity or even a battery, because a solar panel is a small solar panel, low wattage solar panel, isn't going to damage anything and block the wires, you can do this quite safely. You can connect plus and minus leads together, and if you do so through an ammeter, a multimeter, I said to measure current, then you can measure what current is present when the resistance is negligible that we've got a short circuit. What you will find then is the amount of current, and that situation will be proportional to the amount of solar power falling on the solar panel. So if the sunlight goes from say, I don't know what to say, 100 watts per square meter, which is quite dim, really, there's a very coldy stormy day to 200 watts per square meter. So after a thunderstorm and things are brightening up again, you might see that, you will see maybe the current jump from pulling numbers out of thin air here, but let 100 milliamps to 200 milliamps, not my rubbish that'll solar panel, but a bigger one. So you'll see there's a proportionality between the short circuit current and the amount of power from sunlight falling on your solar panel. And that's, so that is a way that you can start to understand how the solar panels parameters do relate to the sunlight. You can do it with voltage, but I think it's quite a week and non-linear relationships. But it still hasn't really answered the question that I was getting to how much power can you draw from that solar panel and given light conditions? Well, it doesn't answer, I haven't got to that answering that question, but before I do, it makes sense of the stats that are printed in my solar panel. It's said six volts, that was the open circuit voltage. So that's where I'm not drawing any load whatsoever from the panel, useless. I can in theory draw one amp from the panel by providing zero resistance by connecting the plus and minus leads together. Again, yes, I get the current, but there's no power associated with that, because it's nearly at zero volts when I do that. So in both cases, there's a negligible amount of power. Somewhere between those two extremes is where we want to be. So we want to find a value of current draw from the solar panel. We're equivalently a voltage that we want to keep the solar panel at that maximizes the amount of power. Now, it turns out that for any given level of sunlight, there is such a point, it's called the maximum power point, and I can't really describe a graph, I'm not going to try and describe a graph, but if you look at maximum, such up in maximum power points, solar panels, you'll see these graphs of current versus voltage, where the current is plotted in the vertical axis and voltage on the horizontal axis, and there's a constant current up to some voltage, and then the voltage just disappears. When you try to draw current, and sorry, sorry, the other way around, the current disappears when you try to hold that panel at a high voltage. And yeah, I said I wouldn't try and describe the graphs, and I have gone and tried to describe the graphs, and now if I confuse myself and probably use so I apologize for that. Anyway, forget that I confusing the description of the graph. The point is, there's a current and a voltage for any given set of the sunlight where you want to be at to maximize the power draw. And if you're at full sunlight, then in theory you should get the wattage rating of the solar panel. That's a full sunlight with the panel perpendicular to the sun's rays. Now, for a big professional panel, which I do have some of, that those specifications are trustworthy and an information is regulated. The solar panel companies are played by the rules by and large. For a cheaper one, you get from hobbyists, stores online, the lower wattage ones a few, a few watts up to maybe it doesn't, a couple doesn't watts. Yeah, watch out, you probably will get misleading specifications. So what this panel should have said to me is that six volts was the open circuit of voltage, and one amp was the short circuit current, and it should never have quoted a power rating of six watts or whatever. That's just raw. And a good day, I can maybe cook for what, maybe a little bit more than four, maybe four and a half watts out of it, if I'm really on the ball. And what does really on the ball mean? Well, it's finding one way you can do it is just connect different values of resistors between the plus and minus leads until you find the one that gives you the maximum power rating. You have to be a bit careful because most common resistors are rated at a quarter of a watt, and you will literally see even with a small solar panel, it does five watt. You will literally see the resistor disappearing the puff of smoke, if you managed to try and pass several watts through it, you can buy bigger resistors. But actually, much better idea is to rapidly, using pulse width modulation, open and close the circuit to try and regulate the voltage in the current draw. And those devices are called pulse width modulation, so a charge controllers. And if you want to get a bit more juice and make sure you're finding that maximum power point, then you can use these so-called MPPT solar charge controllers. They also use pulse width modulation, but then rather and more intelligently will hunt down that maximum power point that I was talking about. And they will adapt to, as a level of sunlight changes, they'll adjust the current draw to keep the maximum power flowing out. Now, of course this has a problem. If you've got electronics, let's say, for example, like an ESP32 micro controller, it really only wants 3.3 volts, and it's tolerance, it's not going to like it if you give it five volts because the sun's come out. So the solar charge controllers, other job, is not just to find the maximum power point, but it's to output a reliable level of voltage. Generally, they will output 5 volts for these hobbyist ones. For larger ones, for charging battery storage and households, you'll typically see the output voltage of the solar charge controllers at something that will charge either a 12 volt, a 24 volt, or even a 48 volt battery. So my house, this is for a future HPR episode, I've got a 24 volt system, that put together myself, but that uses a rather chunkier and more expensive charge controller. But for the one for the small solar panel, I got this, I think I bought it from Pymaroney or Pi Hut, I can't remember which we are bought exactly, but it was called, the brand name was DF Robot, and it was just ideal for taking the power delivery by the small solar panel and outputting it at 5 volts, literally through USB, and it also allowed me to charge a connected battery if I really had to connect a battery for it to work properly. And you could plug in USB from another source and charge the battery with all solar power so you can do both. So it's quite a clever little device. The thing is that if you only had solar power, you couldn't, and the sun went behind the cloud, then the five volts output will collapse. So you really need a battery and the solar panel together, in order to smooth out the tremendous variation in power delivery, the solar panel is going to give you, you know, because of a cloud going from the sun or suddenly walking in front of the sun, or the sun moving behind the tree, or all these kind of things. So the other lesson I learned was really solar panels by themselves are not that great. You need to have another power source to work with them. Either they offset what you're drawing from the grid in some way, or unless it's been my preference, is that you have a battery in the battery stores the power when the sun is shining, you're charging up the battery and powering the load. And when the sun isn't shining, then the battery takes over and can deliver charge. And so in this way, you can run pretty much indefinitely low power electronics. With a small solar panel, you could probably, and not probably, you can definitely run an ESP32 night and day pretty much indefinitely, even through a Scottish winter. I've discovered it's quite possible. If your battery can take in enough charge when it is sunny, probably a small five watts solar panel is going to do the job and keep your device topped up and powered through long nights here in Scotland. So yeah, that's really all I've got to say about solar panels. I might do future episodes. If people are interested, and I'm interested, which I probably will be to be honest, on my larger solar panels, I've got two sets on the go one from my house, and one observatory that I've been involved in building with Astronomical Society of Glasgow. And so that's a different game. You're dealing with mains voltage coming out of inverter, you're dealing with solar panels that can output kilowatt and that will arc and spark. And DC circuit breakers that can burst into flames in all kinds of exciting things. And you can electrocute yourself and blow up multimeter and oh yes, it's a whole level of new fun to be hand with those. So I'll just end that with the warning as it's very safe to play around the these little voltage solar panels. So if you want to play play with them, be very careful playing with the big boys and girls. The high, when you're dealing with hundreds of watts, kilowatt solar panels are a and inverters, which help it means electricity. You have to be much more careful and also you're dealing with DC. So that's again, as I say, different from dealing with AC. So if you do go up, if you do want to play with bigger solar panels, I do advise some caution as they can be surprisingly fun. Should we say any, I'll leave it there. If I've got anything wrong or could it explain better, please do leave comments and or do a show of your own. If you've got solar panels, I'd love to hear your experiences. I've got certainly plenty more to learn myself. So I'd love to hear other views on how people have got on with their solar panels out there in the Hacker Public Radio Land. Okay, thanks very much, listening. Bye bye. You have been listening to Hacker Public Radio at Hacker Public Radio.org. Today's show was contributed by a HPR listening like yourself. If you ever thought of recording podcast, click on our own tribute link to find out how easy it means. Posting for HPR has been kindly provided by an onsto.com, the internet archive and our sing.net. On the satellite stages, today's show is released on our creative comments, attribution for going to international license.