Hi this is amy from the alte store. You might have seen the tutorials that we’ve done showing the difference between a 60 cell and a 72 cell solar panel, a 20V and a 24V solar panel. So what I wanted to do was show you some real world usage of it, of trying to use either of them to charge a 24V battery bank. Now a lot of people will call up and say I’ve got a 60 cell solar panel, and I want to charge.
A 24v battery bank with it. Can I? Because when I measure it, I’m getting say ‘, 38V out of it, open circuit voltage, so shouldn’t that be plenty to charge a 24V battery bank? The problem is, as you might have seen in another tutorial we did, with heat. When it gets hot out, the voltage output of solar panels drop pretty dramatically.
So it’s about 88 degrees out right now, which for a northern girl like me, it is really hot! I know this is probably a lovely day for you guys down south, but any way. So I did measure the voltage of these panels, and the temperature. So I’m going to show you after measuring the open circuit voltage. The temperature of the panels was about 140 degrees Fahrenheit.
Now when solar panels are rated, they are rated at 77 degrees fahrenheit or 25 degrees Celsius. So these panels are almost twice the temperature that you would have at standard test conditions. I also measured the intensity of the sun, and it’s right at 1000W/m2, so we’ve got perfect sunshine, I’ve got the panels at a nice angle so it’s facing the sun, really the only thing that is different from the standard test conditions is the temperature.
It’s hot. So let’s take a look at the panels behind me. They look a little bit different, but really they are practically the same. This one over here is a Canadian Solar 280W 72 cell panel. So you’ll see it’s got 6 cells down and 12 cells across. Now this panel over here is a SolarWorld 275W panel.
It’s a 60 cell, so it’s got 6 cells down, and 10 cells across. So the 24V panel is 2 rows longer than the 60 cell panel. The reason that they look a bit different from each other color wise, is this one is in fact a mono crystalline, so we see it’s a little darker, and it’s got the rounded corners that create those diamonds in the middle. And this is a poly crystalline, so they are made out of blocks.
So it does look a little bit different, but the ratings of them are very similar, so i think they are really very close and so should be able to give you a good demo here. So let’s measure the Canadian Solar 72 cell panel, the 24V panel. The open circuit voltage is measured at 44.6V. And again, it’s hot out. I’m just going to measure right across, and I’m measuring 38.5V. Again, Voc was 44.6V, so that’s nothing against the panel, that’s just the way solar panels behaves when it’s.
Hot out. So now let’s go over and measure the 60 cell panel. I’m tucked back here so I’m not shading it, now this is a 275W 60 cell panel, its open circuit voltage is ‘.4V. I’m measuring 34.1V. So again, it’s a little lower than the Voc was, because it’s hot. So different types of batteries like to be charged at slightly different voltages.
How to Size Your Solar System
I’m going to talk about how to truly properly size your solar system how much power batteries can really store and the way of solar system really works because it’s pretty amazing how many people that have solar systems don’t truly understand how much power they have and it’s important to know because if you end up with a situation where your modules break your solar panels aren’t functioning.
For a period of time or you have a series of cloudy days it’s good to understand exactly how many kilowatt hours you can actually pull out your battery safely so how many days and how you can ration your power and also that really helps you sighs your system properly without with what appliances you’re using so I’m.
Going to start by explaining how the batteries are set up that first one to say the caps are off the batteries right now because I’m equalizing explain that in another tutorial but hydrogen gas is escaping right now and you don’t want these caps on while that’s happening so right here I have eight Deka LT16 batteries now these are 350 amp hours batteries.
I’m going to explain as part of what i can explain today what that means but before I do that these are set up in two strings parallel together so we have four batteries a group of four batteries that are in series which means that they’re wired from the positive to the negative positive to the negative positive to the negative and then positive to the positive and negative to the negative.
Over to the next string when you wire for batteries in series every time you do that the amperage stays the same but the volts double so each of these batteries is 6 volts so when I put 4 in series i end up with essentially one bigger 24 volt battery the amps are still the same though so what i have here are two 24 volt batteries and then they’re parallel together negative 2 negative and positive to positive and when you parallel.
Two batteries together you double the amprage so i have sized my battery system to make this 24 volts with double the amperage of a single battery so each of these batteries is 350 amp hours ok so first i want to clarify that when your solar panels on the roof the electricity that they generate you’re not using that electricity directly.
You’re never using that electricity directly any time you pull power from solar system you’re always pulling from the batteries the solar panels send electricity to the charge controller and the charge controller reads what the voltage of the battery system is and maybe even a couple other metrics and it determines how it should charge these batteries so if you’re using power during the day the pleading power from these batteries when.
The sun’s out that electricity from the panels is actually directed into the batteries to charge them but it’s not actually but the the power that you’re using your pulling power from the batteries and the solar modules through the charge controller are charging the batteries back up that’s the best way to look at this so that being said you only have as much power to use as what’s stored in the batteries.