Charge Controller Design

Solargrow

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Dec 12, 2021
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Hello all,
I recently acquired twenty 240w 36v panels. I'm splitting them into two runs and I'm trying to calculate which charge controller I should use. I know I'll need two controllers so I'm just focusing on half of the panels for now. I heard that it's simply dividing your total watts by the battery voltage but that seems so excessive to me. 10 panels would be 2400 watts and I'm using a 24 volt battery so that means I'll need two 100 amp controllers for my system?
I mean, most controllers only handle 100 - 150 volts so I plan on running the 10 panels for each side in 5 parallel pairs giving me 72 volts and 40 amps (8 amps per panel). Couldn't I use a 50 amp controller per side or do I need to bite the bullet and get a couple of 100 amps?
Thank you
 

Rocketman

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Sep 27, 2020
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What are all the spec's on the solar panels? Voc Imp, etc...

That way we can really help you.
 

sunshine_eggo

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Hello all,
I recently acquired twenty 240w 36v panels. I'm splitting them into two runs and I'm trying to calculate which charge controller I should use. I know I'll need two controllers so I'm just focusing on half of the panels for now. I heard that it's simply dividing your total watts by the battery voltage but that seems so excessive to me. 10 panels would be 2400 watts and I'm using a 24 volt battery so that means I'll need two 100 amp controllers for my system?

Yes.

I mean, most controllers only handle 100 - 150 volts so I plan on running the 10 panels for each side in 5 parallel pairs giving me 72 volts and 40 amps (8 amps per panel). Couldn't I use a 50 amp controller per side

No. The 50A is output, not input. If you only have 50A output, you only get 50*24= 1200W from your 2400W panels.

or do I need to bite the bullet and get a couple of 100 amps?

If you want to get 4800W out of a 4800W array, yes.
 

Rocketman

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Do you want two controllers for your half array or one?

Instead of one 150/100 or 250/100 you could put in two 150/60’s - or two 100/50’s (probably not) Will you have one large array? Or do you want several smaller ones?

A 3s2p or 2s3p on a 150/60, may fit your space better than a 5s2p on a 250/100 or a 2s5p on a 150/100.

Be sure and design your array - before buying the SCC.

Also, are you stuck on 24v - a 48v battery would mean half the SCC’s…
 

Solargrow

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Dec 12, 2021
Messages
40
Do you want two controllers for your half array or one?

Instead of one 150/100 or 250/100 you could put in two 150/60’s - or two 100/50’s (probably not) Will you have one large array? Or do you want several smaller ones?

A 3s2p or 2s3p on a 150/60, may fit your space better than a 5s2p on a 250/100 or a 2s5p on a 150/100.

Be sure and design your array - before buying the SCC.

Also, are you stuck on 24v - a 48v battery would mean half the SCC’s…
Thank you for your feedback. I'm still working all these out.
I've been under the impression that I want maximum amps so I've been thinking the 2s5p would give the most power (40a). Am I mistaken here? Or does the charge controller use 72v 40a the same way it would use 180v 16a?
I'm not stuck on the 24v either, but I'm trying to figure out the power difference of a 48v. It's almost the same question as above. So with my 24v pack I have 560 amps. If I combine it and go to 48 I'll have 280 amps. Does this mean I'll have half as much power to pull from?
Thanks again.
 

Solargrow

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Dec 12, 2021
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Yes.



No. The 50A is output, not input. If you only have 50A output, you only get 50*24= 1200W from your 2400W panels.



If you want to get 4800W out of a 4800W array, yes.
Thank you for your response. So then how does my panel design impact my system? How will 2s5p (180v 16a) impact different than 5s2p (72v 40a)?
 

Rocketman

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Mistaken there…
Volts*amps = watts (watts are power).
A 5s2p array on a 250/100 into 24v battery will basically equal a 2s5p array into 150/100 in a 24v battery. (There will be slight differences - but not much).

You could put a 5s4p array (all your panels) into a 48v battery with one 250/100.

The mppt will convert all the power it can - it doesn’t care if it is 5s2p (180v 16a) or 2s5p (72v 40a) it will convert both to 24v 100a. I understand there is some slight efficiency with higher voltage- because of lower voltage drop, but it will be small (a percent or so - depending on wire lengths).
 

Rocketman

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A 100Ah 48v battery will provide the same power as two 100Ah 24v batteries. (There can be slight efficient gains in the designs of higher voltage inverters - or not). The big difference is your wires will be much smaller in a 48v system and your can use smaller SCC’s in a 48v system or twice as many panels on the same SCC at 48v compared to 24v.
 

Solargrow

New Member
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Dec 12, 2021
Messages
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Mistaken there…
Volts*amps = watts (watts are power).
A 5s2p array on a 250/100 into 24v battery will basically equal a 2s5p array into 150/100 in a 24v battery. (There will be slight differences - but not much).

You could put a 5s4p array (all your panels) into a 48v battery with one 250/100.

The mppt will convert all the power it can - it doesn’t care if it is 5s2p (180v 16a) or 2s5p (72v 40a) it will convert both to 24v 100a. I understand there is some slight efficiency with higher voltage- because of lower voltage drop, but it will be small (a percent or so - depending on wire lengths).
Hell yeah thanks a million. That really helps!
A 100Ah 48v battery will provide the same power as two 100Ah 24v batteries. (There can be slight efficient gains in the designs of higher voltage inverters - or not). The big difference is your wires will be much smaller in a 48v system and your can use smaller SCC’s in a 48v system or twice as many panels on the same SCC at 48v compared to 24v.
Okay this is great! So then with a 48v battery pack the math on the entire system is 4800÷48=100amp controller. And I could configure my panels any way that keeos it under the voltage requirements? Or I could use two 50a controllers as long as they work with a 48v system?
One last question. Does my inverter size change depending on my battery bank? I know I have to get an inverter rated for my battery voltage but I was planning on getting a 5000w inverter because that's the system wattage. Does that change with a 48v battery? Would it be better to do two 2500w inverters?
Thanks again Rocketman. You're filling in a lot of gaps for me.
 

Rocketman

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720
Inverters… that’s a whole other can of worms…

Will a 5000w inverter run your loads? Do you have any motors that have LRA - locked rotor amps. Large motors like A/C’s, well pumps, compressors, etc. (assuming you are all ok there).

A single 5000w inverter will pull slightly more than 100amps from your batteries. Can your batteries handle that? Can the bms?

You are probably better with one 5000 inverter than two 2500’s. But that can depend on how the inverter is made.

Make sure you do an energy audit before buying stuff and plan it all out in detail - then post those details and let everyone hash on it.
 

MichaelK

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Mar 21, 2020
Messages
2,132
I have to say whoa, and you need to slow down a bit and start planning first in a different direction. The way you are going about this is really like putting the cart before the horse.

What you should be doing first, is making list of what it is you want to power, and then come up with a plan on how you'll supply that power. With that many panels, I'd say you are already in 48V territory. We really do need specifications if you want meaningful advice, so start out with what the panel specs are? With 240W panels I'd guess you are talking at 36Voc, is that correct?

I could give you some general directions to head in....
48V system. This is too much power for a 24V system
Wire your panels 4S5P and use a 200V controller. You can position some arrays SE, some South, and some SW, or other appropriate orientations.
Get a large low-frequency 48V inverter like a Radian or XW
You will need a large battery bank in the range of 300-600Ah to store this much power.
 
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