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PV Panel Calculations

Jsbgraphics

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Jul 3, 2022
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I am trying to understand the minimum number of panels I need to get a 48-volt system up and running. While I'm sure a "minimum" is far from ideal, I can add on to the PV array and also add batteries as I can.

The inverter I am looking at shows the below specs for the PV array Using a reference panel of 330 watts. The panels I would like to use are 240 watts simply because I already have 3 of them but can get more. Here are the specs of the inverter:

1658517907942.png

My panel specs are:

  • Rated Power: 240W
  • Open circuit voltage (VOC): 37.2 V
  • Max power voltage (VMP): 30.4 V
  • Short circuit current (ISC): 8.37 A
  • Max power current: 7.89 A
  • Power Tolerance 0/+3%

By my calculations, I should be able to use 5 of these panels in one input to start with. That would give me:

1200 watts
PV array voltage = 152
PV array VOC = 186

Am I thinking about this in the right way or am I missing something? The plan is to start with a single 48-volt battery and build from there.
 

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Five of those panels in series does give the values you stated. And that arrangement is within all of the specs for the charge controller. You are under the 250V max (even in extreme cold). You are above the 80Voc startup and you are within the 90V~230V voltage range. It all seems good to me.
 
Five of those panels in series does give the values you stated. And that arrangement is within all of the specs for the charge controller. You are under the 250V max (even in extreme cold). You are above the 80Voc startup and you are within the 90V~230V voltage range. It all seems good to me.
Thanks rmaddy,

The only other thing I want to make sure of is the amperage. The unit says it has a max 120A MPPT charge controller, but since it has two PV inputs, I assume that means 60A max per input. however further down in the manual it has this:
1658522306979.png

Now, based on the other screenshot above they say they are using 3 panels in series for a single input, but I don't see how they can do that using the reference panel numbers they show and keep the max input current to 18A. Maybe I am misunderstanding something about calculating the amperage.
 

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Thanks rmaddy,

The only other thing I want to make sure of is the amperage. The unit says it has a max 120A MPPT charge controller, but since it has two PV inputs, I assume that means 60A max per input. however further down in the manual it has this:
View attachment 103686

Now, based on the other screenshot above they say they are using 3 panels in series for a single input, but I don't see how they can do that using the reference panel numbers they show and keep the max input current to 18A. Maybe I am misunderstanding something about calculating the amperage.
OK I had a moment.

I realize now in series; the amperage doesn't change. man, a lot to wrap your mind around!!
 
3 of the 330w reference panels in series has an Isc of 10.4A which is obviously well below the 18A maximum. Your 240W panels will have an Isc of only 8.37A. You could put 10 panels in 5S2P and still be under the 18A. Don't forget - in series you add voltage and keep amperage the same. In parallel you add amperage and keep voltage the same.

Edit: OK, you just realized that.

I do believe the 120A is a total for both since 120A x 56.8V = 6816W. If it were 120A each then the controller could support almost 14kW but it only supports 8kW (really 6.8kW).
 
3 of the 330w reference panels in series has an Isc of 10.4A which is obviously well below the 18A maximum. Your 240W panels will have an Isc of only 8.37A. You could put 10 panels in 5S2P and still be under the 18A. Don't forget - in series you add voltage and keep amperage the same. In parallel you add amperage and keep voltage the same.

Edit: OK, you just realized that.

I do believe the 120A is a total for both since 120A x 56.8V = 6816W. If it were 120A each then the controller could support almost 14kW but it only supports 8kW (really 6.8kW).
Yes, I realized my mistake and posted I think at the same time you were replying. Thank you for your help.
 
6 in series seems to be more optimal.
6x37.2Voc = 223.2 V < 250Vdc

and you can later have 2 strings of 6 PV in parallel on each input since 2xIsc = 16.43 A < 18Amax.

Try to get at least 2 backup panels, for each mppt channel, in case you need replacement alter.
 
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