Wiring Panels to All-in-One Inverter with MPPT limits

[Wilde]

Choosing between the Sol-Ark 15k and EG4 18Kpv. When wiring the panels to the inverter (to the MPPT inputs), each input has voltage and amperage limits. The Sol-Ark also has a limit of 6.5kw per MPPT. I'm trying to see if they will work with my 42 panel, 17.64kw pv array.

After doing some research I ran into an issue. When looking at the panel specs, it has the "Short Circuit" current/amperage and the "Open Circuit" voltage as well as the "Nominal" voltage and amperage. My understanding is that I need to use the short and open circuit volts and amps when calculating how to wire the MPPT strings. So, my 420w panel, when using the short and open circuit volts and amps becomes a 530w panel. That means that my 17.64kw system turns into a 22.26kw system when I start figuring out how to wire it to the inverter. Is that the case?

 

[Solar Guppy]

ISC is near zero watts as it is a dead short across the +/- of the string.

Voc is no load again near zero watts and must be checked for your coldest temperature as Voc increases as the ambient temperature decrease from standard test conditions of 25C.

The rated STC power is usually good enough for maximum power allowed, if you are in a cold climate ( your not in from your sig ) then you would have to do the calculations with the low temperature as vmp will increase.

 

[Shimmy]

It's even more complicated than that.

First, check for voltage, corrected for record low temperature. That tells you how many panels can be in series on any input. If you are inland, your low might be 0ºC (25ºC below the rated temperature), so you take your temperature coefficient ( (Vtc) x 25ºC +1) x Voc - should be around 53V. For the EG4 you have 600V/53V = 11 panels maximum in series. Then check the Vmp x number of panels in series and make sure that is in-range for the MPPT operation. Should be around 440V, so it is ok on the EG4.

Then you check current. One string is going to be around 10A MP and 12Asc. The EG4 has three MPPTs, rated for 25A/15A/15A. That means you can have two strings in parallel on the 25A and one each on the others, for a maximum of 44 panels. The short-circuit ratings are 31A and 19A, so those should be good as well. If you want 42 panels then I would do 2 parallel strings of 10 on the first input and 11 each on the second and third. You have enough buffer that temperature derating shouldn't be an issue, but it is always good to check.

Last thing you do is check the maximum PV power. You are well under the maximum input of 21kW so that should not be an issue.