Solar Panel String Question

[DyslexicDancer]

I'm going to be setting up an off grid power system and had a few questions on panel string size at low temperatures

I'm using 12 Sunpower E20-330-COM-MLSD panels with the following specs
330W
Power Temp Coef. −0.35% / C
Impp 6.04A
Isc 6.52A
Current Temp Coef. 2.6 mA / C
Vmpp 54.7V
Voc 64.9V
Voltage Temp Coef. −176.6 mV / C

I'm using a SPF 3000TL LVM-48P Inverter which has a maximum Voc of 145V

If I wire two panels in series I should have a Voc of 129.8V @ 25C

The all time low temp record in my area is somewhere around -25C

I found an online calculator (https://footprinthero.com/solar-panel-voltage-calculator) to figure out my maximum Voc and it is showing 138.8V with the panel specs given above and that would keep me under the 145V limit of the inverter

Just wanting to make sure I'm understanding this correctly and that the online calculator is correct, because if I run the math myself I come up with a Voc of 147.46V, but then I was never great at math, maybe the calculator is factoring in voltage line loss which I have not done?

Any help would be appreciated

 

[sunshine_eggo]

I come up with about the same as the calculator:

-50°C (from 25° to -25°) * -.1766V/°C = +8.83V

129.8V + 8.8V = 138.6V

 

[DyslexicDancer]

I come up with about the same as the calculator:

-50°C (from 25° to -25°) * -.1766V/°C = +8.83V

129.8V + 8.8V = 138.6V

Wouldn't the -50°C (from 25° to -25°) * -.1766V/°C = +8.83V be added to each panel?

So if I only had one panel it's voltage would be 64.9V + the 8.83V for a total of 73.73V

Then if 2 panels in series take that voltage of one panel, 73.73V, and times it by 2, ending up with 147.46V for two panels in series?

This may be where I'm going wrong, but it only makes sense to me that each panel would have it's voltage increased and that these voltages would all add up since they are in series

 

[sunshine_eggo]

Dagnabbit. I'm used to temp coefficients expressed as -%/°C, and that calculator does the same.

YOU are correct.

 

[DyslexicDancer]

Dagnabbit. I'm used to temp coefficients expressed as -%/°C, and that calculator does the same.

YOU are correct.

Appreciate the help, Looks like I'll need to use charge controllers instead of the built in MPPT charger of the inverter.

I think I'll just order 2 Victron 150/45 Smart Solar charger controllers, my Max Voc at a very rare extreme cold event should never get to 150V, but could surpass the 145 V limit of the Inverter MPPT controller

 

[sunshine_eggo]

.

 

[400bird]

If you are already looking at purchasing a new charge controller, I'd look at one with a higher voltage limit.

With a 150 volt limit, your running a 6 to 1 combiner.

If you run a 450 volt SSC, you could do two 6s strings, no need for fuses or combiner (depending on the SSC). Or a simpler 2s combiner. Also, you'd save in wiring as the current would be lower.

 

[sunshine_eggo]

There are other 3000W/48V with 450V MPPT limits.