Hi this is Amy from the altE Store.
You might have seen the videos 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 39, 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 video 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 39.4V. 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.
According to Trojan Battery, their flooded batteries, they want to be charged anywhere
from 29.4 - 30.96V for their flooded batteries.
And their sealed AGMs are somewhere around 28.8V.
Now different charge controllers, some of them let you set what voltages to use, and
some are just fixed based on what type you tell it that you are charging.
So for the Morningstar ProStar that we are going to be using, their flooded setting is
28.8V, and can equalize up to 30.2V. And AGM is anywhere from 28.3 to 28.7V.
So that is right around, a little low, but right around what Trojan says they want their
battery to be charged at.
So let's take a look, we're going to keep those numbers up, because they are the numbers
that we are striving for.
So I am first going to plug in the 24V solar panel to the charge controller to the 24V
battery bank, and we'll see what kind of numbers we get out of that.
Alright, so now we've got our 24V solar panel plugged in, and if we look at our meters,
we are getting 31.9V connected from the solar panel to the charge controller, and then out
to the battery, I'm seeing 27.7V.
So I'm seeing about 5.9A. So this is really actively charging this battery.
So now let's turn that off and pop over to my 60 cell panel, and see what we get.
OK, so I've got my 60 cell, 20V solar panel plugged into this 24V charge controller, to
the 24V battery bank.
Now I'm seeing 29.1V going into the charge controller, about 27.7V to the battery, and
5.19A. So it is in fact charging, and that 29V, that is slightly above, by maybe a volt
what the rating was, what the ideal rating was.
So what this shows is great, if I've got really good sun, I'm going to be able to charge.
So, , this is a tough one, because yes, it kind of works, and in the winter, I bet it'll work
great, maybe in the winter we'll do this exact same thing on a nice cold day.
But if you are trying to get the best output, the best charge for your battery bank for
the healthiest battery bank, you really do want to use either a 72 cell, or two 36 cell,
12V panels in series, to get that 24V.
There's a reason they picked these size solar panels to charge batteries.
The 36 cell for 12V and the 72 cell for 24V.
These are the really good voltages to charge a 24V battery.
A 60 cell panel, the reason you see so many of them out there, these were designed for
grid-tie, so they don't really care about if they have a high enough voltage to charge
a battery, they're not.
They are not going to be charging a battery, they are made for connecting directly to a
grid tie inverter and powering your house through the grid tie inverter.
Not through the battery bank.
So, I think that this shows you that, yah, it kind of works, but not as well as it could
if you did a 72 cell solar panel.
OK?
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