I would think that everything on the customer side of the point of common coupling would be governed by the NEC and a consistent set of rules within it.
Everything looked fine until I looked up at the pole transformer......10kva transformer. That unit is going to get warm on a bright sunny day.
Luckily the POCO swapped out for a 25kva without charge to the homeowner.
Good example of of what ggunn is talking about.
ggunn- Thanks for the real world example there, I just narrowly avoided the problem by accident, strangely enough.
Carultch- Yes on the first part and yes on the other comments about the consistent-ness! Combined with Dan's quote, *now* I understand a POCO "guideline"- there's a "simplified process" for systems under 10kWAC.
Simple is either under 10kW single phase and under 25kW 3ph...
The common "providing 10kVA xfmrs for residential services" thing is the reason for that- 10kVA is only 83.3A @ 120V.
edit: Which is kind of cool- 90% of 83.3 is 75A @ 120v- which is exactly the max output of the 9kW inverter! Nice.
Dan- So how could you tell by just looking? Because of the size? I'm looking at one- it does look a little smaller than a nearby 25kVA...but it's also quite a bit newer. Hmm.
Another real world example, regarding the simplified process.
Inverters =<10kWAC/10kVA (or =<25kWAC/kVA 3ph) are the simplified.
However, one particular brand of inverter says the inverter(s) have to be =<90% the size of the interconnection xfmr.
So you could not technically use a 10kW inverter of that brand on a house that has a 10kVA xfmr.
I was comparing 8,9 and 10kW models (with 10kwDC of panels on each) and decided on 9kW *before* I saw this thread. They all ended up with pretty similar outputs, there was a little too much clipping with the 8kW, and the 10kW put out such a small amount more it didn't seem worth it. (Yes, the 10kW put out more than the 9kW inverter, with 9.977kWDC of panels on each, which I don't think it would everywhere- something about the weather I suppose)
Depending on which type of panels and differences in amps @lsc, the 10kW was a option- but now I know it isn't really a possibility with a 10kVA service xfmr.
Thanks, people!