Which Chart for Calculating Required mppt/inverter

[FredVenture]

I have solar panels with these specs, there are 2 sets of specs (red and green in image below), which should be used for my calculations?



Also, shouldn't there be a maximum instead of minimum?

 

[sunshine_eggo]

Plan for STC when sizing components.

Keep NMOT in mind when you're grumpy about the system not performing to spec.

Best to use STC and do a detailed analysis of your available solar with PVWatts. You can actually simulate an array for your location and download HOURLY performance data. It also takes average daily weather into consideration.

 

[FredVenture]

Thanks for the reply.

 

[chrisski]

What I do for wire size, is I use the lower voltage VMP, and highest amperage to determine wire size. In your case 38.79 VMP and 10.69 ISC. When used on a wire size calculator, that will get you the thicker wires. Not taking into account temp losses, this should get you less of a loss than calculated.

I also use the higher ISC to the ampacity chart to make sure it does not exceed amps. For the charts I use, ampacity is 30 amps for 10 AWG and a MC4 spec is 30 amps. So I could parallel two strings of panels and remain under specs for both 10 AWG and MC4, but three or more than that is slightly high. For the ampacity chart, using the lower of the two numbers would have meant Paralleling three is fine With 10 AWG and MC4.

 

[pollenface]

In the red I would look at Power at MPP and Open Circuit Voltage

 

[Browneye]

Wire sizing choice isn't just ampacity, but voltage drop for length as well. So STC for voltage drop as that's what your system will be trying to send over your wiring, and you'll want to shoot for less than a 3% drop. This also aids in system planning for number panels and what gets wired parallel and what gets wired series. You choose your controller to accommodate, or panels to suit controller capacities.

Length is round trip distance - the length of both + and - wires combined - that was a new one on me.

Higher voltage and lower amperage has less voltage drop per length of wire. You probably already knew that.