Why system power isn't matching micro-inverter power rating?

[themetallurgist]

Hello, I just got a new system system installed and I was curious if it is operating correctly or is my math wrong? I have 27 Aptos 440W panels with the Enphase IQ7A-72-2 micro-inverters. The max output of the micro-inverters is 366W. My system is producing 8.0-8.2kW at peak daylight, divide by 27 and that would be about 300W per panel. So where is the other 66W? I know there's some knockdown like the micro-inverter is 97% efficient, but 50W difference is significant. I should be seeing some clipping since the panels are at 440W (410W most likely). I was quoted a 11.88kW (10.766kW CEC rating) system, but on the drawing it says the system rating is STC=11.88, PTC=9.48, CEC=9.88. All panels are facing south, I live in north Texas, and my roof pitch is maybe 35 degrees from horizontal. Thank you for the help!!

 

[SparkyJJO]

Each microinverter can only output 349W continuous, 366 peak. That's why. Each micro is overpanelled a bit.

My Chilicon micros are rated at 720W continuous (dual input) and I have two 400W panels connected to each of them.

 

[themetallurgist]

Each microinverter can only output 349W continuous, 366 peak. That's why. Each micro is overpanelled a bit.

My Chilicon micros are rated at 720W continuous (dual input) and I have two 400W panels connected to each of them.

hmm, so what happened to the other 50W then?

 

[Supervstech]

Panel heat, shading, angle inefficiency etc.
It all adds up.

 

[SparkyJJO]

Yeah. On a good bright clear cool day I'll get the max out of mine, but normal sunny days I'm not getting 720W from each of my inverters. Usually down by some. Sunday was a beautiful day here, but I only got about 7000W peak that day from my otherwise 7500W array of inverters. Not sure what changed on Monday but I got a peak of a hair over 7500W that day (if only for a few seconds!).

 

[themetallurgist]

Panel heat, shading, angle inefficiency etc.
It all adds up.

There's no shading. Wide open. I will note that it is 90-95 degress F outside! If I'm getting 300W from each panel and inverter combo, then that means the panel is dropping from 440W to 300W? That's a huge drop. I figured with all of the inefficiencies and panel degradation over 25 years, I'd have plenty of panel for the inverters, but from the get go, I'm only at 300W. Do I not have enough panel power or is the inverter not working right? Maybe I will get more production when the sun drops down lower to be perfectly perpendicular with the panels? Thank you all again for your help!

 

[Supervstech]

There's no shading. Wide open. I will note that it is 90-95 degress F outside! If I'm getting 300W from each panel and inverter combo, then that means the panel is dropping from 440W to 300W? That's a huge drop. I figured with all of the inefficiencies and panel degradation over 25 years, I'd have plenty of panel for the inverters, but from the get go, I'm only at 300W. Do I not have enough panel power or is the inverter not working right? Maybe I will get more production when the sun drops down lower to be perfectly perpendicular with the panels? Thank you all again for your help!

Of course there is some shading. There is ALWAYS SOME shading… clouds of some type drift around.

 

[Supervstech]

Yeah, heat is #1 sun angle is #2 and random shading #3… fixed angle panels will never output rated capacity. Especially across a huge roof layout. I think eeblog did a video on his new setup with a 60% overpaneling on his system to get close to rated inverter spec.

 

[ncsolarelectric]

There's no shading. Wide open. I will note that it is 90-95 degress F outside! If I'm getting 300W from each panel and inverter combo, then that means the panel is dropping from 440W to 300W? That's a huge drop. I figured with all of the inefficiencies and panel degradation over 25 years, I'd have plenty of panel for the inverters, but from the get go, I'm only at 300W. Do I not have enough panel power or is the inverter not working right? Maybe I will get more production when the sun drops down lower to be perfectly perpendicular with the panels? Thank you all again for your help!

Hot panels underperform. Panels are rated at their maximum at 25C, and their performance increases when temperatures go down from there. Soiling and degradation of the glass face is the next most important factor if there no shading other than clouds. If your AC output power is clipping in the middle of the day, then your panels are ok. If not, maybe they need a good scrub down. Also check for loose or hot connections, as those are losses and hazardous if it's an older system.