Wire Size based on temperature fluctuations, New metering

[oaknut]

I am using q cell 480w bifacial panels (xl-g1033 / bfg). They have a Voc of 53.39 and Isc of 11.12 (hope I am using the correct numbers for my calculations.) I plan on having 1 string of 12 and one string of 13 both in series which will go to a Fronius 12.5kw inverter. My historical max temp where I live is -35 degrees F and max high of 110 degrees F. The panels have a temperature coefficient of -.27%/k Voc or -.34 %/k Pmpp (not sure which to use)

Using those numbers I think I should only be worried about the cold sunny day which could give me a max voltage of around 811.4V for the 13 panels in series or 749.95V for the 12 panels. I am not sure if I need to worry about the hot days or cloudy days? I can find lots of information about voltage but not much on amperage. I know if one goes up, so will the other but I don't know how much. (probably some simple formula I am overlooking) If I use 811V and 11.12A, I can use 12G wire but the 11.12A should be higher but I don't know how much higher. Were can I go to find the correct math unless someone wants to lay it out for me? I am sure the math works for when the sun starts to drop as well. If I have a lower voltage and only get 600V but still have the 11.12A, I would need 10 Gauge wire. I need help with the correlation between volts and amps.

For the inverter wire size do I just use the Max continuous Amperage at 240V to determine the wire gauge (about 20 feet away)

Once I find the wire size question I know I will be looing info temperature of the wire which will then lead me to conduit size. I plan on having 2 strings of 12 and 2 string of 13 for for two 12.5 kw inviters. The array will be about 250' from the inverter. If anyone knows good resources for finding how to determine wire temperature and size of conduit for the 8 wires that will save me some time. I am learning this one step at a time but don't want to make a rookie mistake if I can avoid it. My plan is I want to get everything in order and then have it checked over by an electrician (hard to find solar people around me) or just ask the inspector before I begin the design.



Thanks for your help.

 

[pollenface]

Theoretically yes, cold morning are worrysome. Cloudy days, no.

Strangely I've observed VOC to be lower than theoretical calculations on really cold mornings and higher on slightly warmer mornings, I guess it depends how early the MPPT's start loading the panels as well (using Victron historical data).

As for wire size, I just refer to an app on my phone to calculate it for me

Voltage Drop Calculator - Apps on Google Play

Comprehensive Voltage Drop Calculator.

play.google.com

 

[zanydroid]

You can hire out solar plans online. I can’t really picture the typical US electrician being better equipped to do solar code calculations compared to an online designer. Think about it — in many US states solar designs are done by solar contractors.

Going over 600V I don’t believe is allowed in US residential. And then there’s the matter of finding equipment that can even go that high.

You need to scale up Isc at STC by 1.25*1.25=1.56

One of the 1.25 safety margins is for continuous load derate the other 1.25 is to account for environmental based increases in Isc.

 

[oaknut]

Most inverters companies have software that you can can input your data into that will give you the data you need based on high and low temperatures as well as angles and directions of the panels.