Help a new guy with his math?

[killakitty]

I've searched and read here and on reddit and I think I understand, but before I order panels, I want to be sure I understand. I have a pair of Ecoflow Delta Pros. I know they can take 1600 watts of solar with a limit of 150 volts. I think it's ok if I'm over on the watts, but I can never go over on the volts without cooking the Delta Pros. If I were to get 3, as an example, 445 watt panels in series (for each Delta Pro so 6 total), and they are rated at open circuit voltage of 46.1 volts, that would give me 1335 watts max and 138.3 volts max? I really only have room for about 6 panels total, so I'm trying to maximize solar charging without melting my Delta Pros.

Thanks!

 

[BentleyJ]

Your math is accurate on the Voc or 138.3, there is one other consideration. In cold weather PV Voc goes up. The datasheet Voc is at 25 deg. C.
What is the coldest temps you will experience in your region? Does the datasheet list the temp/voltage coefficient? Will be a negative value something like -0.3%/ deg. C.

 

[killakitty]

Your math is accurate on the Voc or 138.3, there is one other consideration. In cold weather PV Voc goes up. The datasheet Voc is at 25 deg. C.
What is the coldest temps you will experience in your region? Does the datasheet list the temp/voltage coefficient? Will be a negative value something like -0.3%/ deg. C.

Thanks for the quick reply.

I guess I have 2 concerns to think about. First, the temperature coeficient:
Temperature Coefficient (Pmax) -0.35 % / °C Temperature Coefficient (Voc) -0.27 % / °C Temperature Coefficient (Isc) 0.05 % / °C

Around here in winter, we might get a few 0 degrees F days.

Also, if they're bifacial, at 30% gain they can hit 48.9V, 15.0A which is still under the rating. Is that cutting it too close between the risk of it being super cold and super sunny one day in winter and melting my Delta Pro?
These are the Canadian Solar CS3W-445MB-AG at Solar Steals although I'm not married to that particular panel. These will be mounted in a way that could benefit from bifacial but I wonder if it's not worth the risk of boosting the V on a cold sunny day.

Thanks!

 

[DIYrich]

they are rated at open circuit voltage of 46.1 volts,
Also, if they're bifacial, at 30% gain they can hit 48.9V,

Doesn't the OC Voltage include both sides? Shouldn't the OC Voltage be greater than max voltage at 30% gain (at STC).

According to the spec sheet: At STC, Operating Voltage is 40.3, with OC Voltage of 48.5v, regardless of the gain.

https://d2fp8gxcp7iq0s.cloudfront.net/documents/JiQnTgy4a7t3jJ99bhYkzqFEtXO5xzIqvxSg7IX4.pdf

 

[BentleyJ]

48.9V x 3 = 146.7V

At 0 deg C there is a 25 deg temp differential from STC Voc value. -0.27% x 25 = 6.75%

146.7 + ( 6.75% x 146.7) = 146.7V + 9.9V = 156.6V

 

[BentleyJ]

Doesn't the OC Voltage include both sides? Shouldn't the OC Voltage be greater than max voltage at 30% gain (at STC).

Even if the lower Voc is used in the calculation it comes up to 147.6V at 0 deg C. That's dangerously close to the limit.

 

[killakitty]

Maybe better to look at the JA Solar 440. 3 in series gives me:

• Max power output: 1320.52W
• Max power voltage (Vmp): 134.61V
• Max power current (Imp): 10.44 A
• Loss: 0%

Cheaper anyway.