For what it's worth, that's actually correct, as far as the 2017 NEC, in force in California. It is only with 2020 NEC and its recognition of Power Control Systems that you wouldn't have to consider the Powerwall inverters.
But usually it's moot, as the the main disconnect is just a 200A feeder (any other breakers are removed), so the 120% ruled doesn't apply there. And the feeder topology is arranged so that there are no panels subject to the 120% rule. Are you sure it wasn't just that PG&E was misunderstanding the alternatives to the 120% rule?
Yeah that day I posted the 120 percent NEC rule, I had been stuck on the stupidest planning meeting. Sunrun forbids customers from talking to engineers and designers (just like in Office Space). So the one Sunrun rep on the call was franticly trying to text me so I could respond to PG&E. Sunrun wouldn't even send me the flippin' line diagram. I had to go off of what was being explained to me. Talk about the blind leading the stupid on this.
Luckily you were here to give me insight on like a real time basis. So you helped this blind man see enough to lead PG&E and Sunrun someplace.
The gist of what I understood during that terrible exchange with Sunrun was that the PG&E planner was telling the Sunrun engineer:
1) Assume the house has a 200A main service panel
2) Assume 3x Powerwalls could each export (15 kW total AC)
3) Assume 23 Enphase IQ7+ (6.7 kW AC)
They calculated the max potential export is 100A. For the 120 percent rule to be followed, the house loads had to be de-rated to 125A.
100A + 125A <= 200A x 1.20
Thus the TEG2 needed a 125A breaker and the sum of the home loads in total could not exceed 125A. This meant getting rid of an air conditioner.
I kept trying to tell Sunrun that the Powerwalls were not able to be grid exporting. I kept saying the only thing they should include in the 120 percent rule was the 35A coming from solar. But PG&E kept pushing back saying Powerwalls (when paired with solar) could in fact grid export. They kept accusing me of trying to bypass their NEM rules.
Ultimately we agreed (I can't tell if it was an agreement or just being massively frustrated) to put the following language in the actual permitted design.
NOTE: PRODUCERS STORAGE DEVICE(S) WILL
NOT CAUSE THE HOST LOAD TO EXCEED ITS
NORMAL PEAK DEMAND. NORMAL PEAK
DEMAND IS DEFINED AS THE HIGHEST
AMOUNT OF POWER REQUIRED FROM THE
DISTRIBUTION SYSTEM BY PRODUCERS
COMPLETE FACILITIES WITHOUT THE
INFLUENCE OR USE OF THE ENERGY
THE INSTALLED BATTERY IS NOT CHARGING
FROM THE GRID.
THE BATTERY IS EXPORTING TO THE GRID
UNDER NEM AND TOU.