DC Series Math Question

I’m embarrassed to ask as I’m relying on my memory from 10th grade electronics class from 50+ years ago. Following are the specs on the panels I’m buying.

Maximum Power (Pmax) 390 Wp STC
Maximum Power Voltage (Vmp) 41.1 V
Maximum Power Current (Imp) 9.49 A
Maximum System Voltage 1500 VDC

If I string 32 of them together in series, is the output below correct?
Amps 9.49
Volts 1315 (32 x 41.1)
Watts 12,479 (1315 * 9.49)

If I’m correct so far and 3 circuits are combined (parallel) then is the combiner output below correct?
Amps 28.47 (9.49 x 3)
Volts 1315

Thanks in advance for any help you can give.

Yes that is correct…

However the string voltage is over 1000V and most inverters are limited to either 1000V (commercial) or 600V (residential). The strings need to be divided up into suitable sizes so the voltage fits within the inverters MPPT operating voltage range.

If you not a licensed electrical solar installer I would advise against doing any work on LV systems as it can be extremely dangerous.

Sparky - you are right and I am not an electrician. Thank you for your concern!

The reason I was asking is that my installer has proposed 3 of these circuits attached to a 33.3kW inverter and am concerned.

However it is a 277/480 VAC system at my shop:. SE33.3K-USR48NN and maybe that is the difference. However reading the specs for the inverter (below) I thought maybe I wasn;t interpreting it correctly…

Hi Terry

Whats the inverter model?


SolarEdge 33.3kW 277-480V Three Phase Inverter wRSD SE33.3K USR48NNU4


I think I figured it out. I was told the entire string was in series instead of them taking the time to explain that they were combining in parallel 4 series circuits of 8 panels each.
41.1 x 8 = 329v
9.49 x 4 = 38a

1 Like

Ah, that’s good to hear.

There is a helpful universal string sizing tool that can help with these type of calculations. :raising_hand_woman: