Did I calculate this correctly?

cdevidal

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Please confirm something. Did I calculate this correctly? The maximum solar charge current on the Growatt SPF 5000ES is listed as 100A @ 48V, 97% at maximum efficiency. The maximum AC charge current is 80A @ 48V. If I have two strings of nine 230W panels (9s2p) = 4,140W of panels with a maximum power voltage (Vmp) of 29.8V and a maximum power current (Imp) of 7.78A each, that would mean the most solar charge current going into the MPPT I could ever expect to see would be 15.56A, and the output charge current would be 42.16A @ 48V at most.

Did I do my math correctly? This affects my battery and BMS choices so I want to get this right.
 
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Bud Martin

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4140W of PV power to the SCC (smart Buck Converter), it is then down converted to charge the 48V batteries, so max charging current = 4140/48VDC = 86.25A x 0.97 = 84A of batteries charging current.

29.8 Vmp x 7.78 Imp =231W
1 string of 9 panel in series = 29.8VMP x 9 = 268.2 Vmp at 7.78A = 2086W
So two strings in parallel you will have Vmp of 268.2 Vmp feeding the SCC and SCC can pull the current up to 7.78 Imp x 2 =15.56 Imp. so total PV power is 2086W x 2 = 4172W.
I do not know how you come up with 42.16A of charging current.
The question is what is the VOC of the panel and what is the max PV input Voltage of the SCC, you want to make sure the VOC willl not exceed the max PV input spec of the SCC, the VOC of the panel also goes up in cold weather so you need to factor that into also to not damage the SCC.
 
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cdevidal

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I do not know how you come up with 42.16A of charging current.
The question is what is the VOC of the panel and what is the max PV input Voltage of the SCC, you want to make sure the VOC willl not exceed the max PV input spec of the SCC, the VOC of the panel also goes up in cold weather so you need to factor that into also to not damage the SCC.
See that's why I asked first. I only calculated one string and got 42.16A and must have also miscalculated the 97%. So 84A it is.

Voc = 37.0V
Max PV input voltage = 450VDC, I derated that by 25% for cold weather = 337.5V
So nine panels = 333V, just under the mark.
 

rmaddy

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I derated that by 25% for cold weather
That's a bit much. It's probably closer to 20% if the panels get down to about -20ºF. But you can get the exact value by looking at the specs for your panels and finding the voltage temperature coefficient and determining the coldest temperature you will ever encounter.
 

cdevidal

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That's a bit much. It's probably closer to 20% if the panels get down to about -20ºF. But you can get the exact value by looking at the specs for your panels and finding the voltage temperature coefficient and determining the coldest temperature you will ever encounter.
They're used panels and the mfg labels were removed, but honestly 4,140W is plenty for my load for now and 333V per string is a nice balance. If I wanted more load I'd need to add nine additional panels (right?) and charge current would go to over the 100A max, if I understand all this correctly.
 

cdevidal

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Well no, I could do 7s3p for 4,830W and battery charge current would be right at the 100A. But I think I don't need to be greedy and I certainly don't need to push the equipment to the max all the time.
 

Bud Martin

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The SCC will only pull current from the panel up the limit of the charger, so when you do over panel it will still produce max 100A of charging current (it will not go over 100A because the charger circuit is limited to 100A) even though your panels can provide more, when over panel it helps when you have cloudy days to compensate for the production loss.
You can learn about over paneling:
 
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