Planning string layout - Enphase IQ8+ micro inverters - 385w panels

[STxFarmer]

Trying to make sure I get the right wiring layout for my system. I have 3 different areas on my roof but can have a maximum of 13 micro inverters on a string with these panels. So my question is do I combine panels on 2 different areas to make up the 13 on a string or do I keep each area separate? If I keep each area separate then I have 4 strings of 10, 11, 11, and 7 panels on strings. Which is the correct way?

(39) JA SOLAR : JAM54S31-385/MR MODULES
(39) ENPHASE ENERGY : IQ8PLUS-72-2-US
Enphase IQ Combiner 4

 

[DIYrich]

For micro inverters, it doesn't matter. Put 13 micros from anywhere on a string. They all produce (optimize to) the same voltage (240v), and they push whatever amps they can (combine onto the string). I could be wrong, but that is what I understand about micro inverters. The amps are combined, so I can't see why it makes a difference.

 

[zanydroid]

You can do it either way as long as you stay under the maximum inverter limit for each 20A circuit and don’t run out of breaker spaces in your combiner. There are pros and cons you will have to evaluate.

Note there is a potential code/listing violation if you do not wire up the string in the same topology as in the manual (which is usually one after another). When you combine from two roof planes often you create a fork in the circuit. This may have some edge case interaction with how the OCPD on the microinverters work, somebody told me it is a potential issue but I was not able to analyze the circuit to a definitive conclusion either way.

 

[wheisenburg]

When you combine from two roof planes often you create a fork in the circuit. This may have some edge case interaction with how the OCPD on the microinverters work, somebody told me it is a potential issue but I was not able to analyze the circuit to a definitive conclusion either way.

Enphase is fine having a fork in the circuit. They even suggest that center tapping a string is good because it limits the number of connectors and the amount of wire the last inverter in the chain must go through. So if your are running 12 inverters on a string and you run the end of the string to the junction box, the furthest out inverter has to go through 12 sets of connectors. If you tap the center of the string, then the furthest out inverter only has to go through six sets of connectors.

Think about getting 12 extension cords and plugging then in one after the other. How much power will you lose?

They suggest this center tap configuration as a way of fighting voltage rise which can trip inverters off line and also wastes energy. The losses are small, but cumulative. They are also larger the more current is flowing through the lines. In an end tapped cable the current from 12 inverters is going though the last connection. 11 are going though the second to last connection and so on. So the further you go out the cable, the more the voltage rises. So where does that extra voltage go on it's way to the junction box? It is lost to heat. Now this might only make your system 1-2% more efficient, but over the life of a system, that can turn into a lot of $$$.