Stuck with 100amp Service from PG&E. HELP!!

[bvk_]

Hi @hs315

Here was by existing setup. 100amp main panel with only space for a 2 pole 100 amp breaker that fed a subpanel that had all of the home loads.
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After A LOT of back and forth to Teslas design team / and electrical team (a whole other conversation about how frustrating that was) and my city's building department, here is what I ended up with. I put in a 150amp rated subpanel between my existing 100amp main panel and the sub panel with all of the home loads. In the NEW subpanel I fed in the Solar PV and I also added an EV charger after the PV was installed and signed off on.
View attachment 446507

@

who177e, Thanks for the information​

 

[Eric33432]

PG&E will have its own restrictions on how much solar you can connect to a 100A service. There are two issues:

1) They probably don't want you to be a net exporter over the course of the year (and it doesn't pay for you to be one, either). So they may limit your PV size based on your historical usage, or if you are getting an EV, based on an estimate of your future usage with EV.

2) If you put too much PV on your service, they will have to upgrade their equipment, and so they might either restrict the amount of PV, or want to charge you for the upgrades.

As a simple example, suppose your 100A service is on its own transformer, not shared with any other customers. A 100A service is nominally good for 24 kVA (24000 volt-amps), but it will not be served by a 25 kVA transformer, it would be, say, a 10 kVA transformer.

That is because NEC load calculations (used to size equipment you own) are very conservative, and prior to the advent of EVs and PV, there were basically no residential continuous loads. So even if your load calculation comes to 100A and you need a 100A service, actual monitoring of that service might show that your average current is only 10A, with very rare excursions above 40A. The 10 kVA transformer can handle intermittent overloading as long as it has time to cool down in between excursions above 40A (40A * 240V = 10 kVA, approximately)

But now if you put 60A of PV on your service, or if you get an EV and want to charge it at 60A, your demand profile has changed and you are actually trying to use your 100A service at 60A continuously for multiple hours. The 10 kVA transformer may no longer handle that, and PG&E would have to upgrade to a 15 kVA or 25 kVA transformer.

If your transformer is actually shared with other residences, then it is likely to have more reserve capacity, as long as you are the only customer on that transformer with an EV or PV.

Cheers, Wayne

That is the best description of how real-world loading of residential electrical service works that I have ever read. And it is why I say that often people overestimate their need to upgrade their service.

This is an old post, but if you add an EV to a 100 amp service you can install a load shed device without having to upgrade your service.

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