Some utilities have a newer style meter they plug in that has a line tap built in for solar, probably worth asking if they know about it. Based on the drawing they gave you I doubt if they're on the cutting edge of technology, but who knows.
PG&E in my area offers line-side tap. I think it is an insert between socket and meter. But limited to 40A
Newbostonconst, thanks for the link, it is very good. I can see now that I had the 120% rule all wrong. I have a 150a main panel, meaning my overhead is 180a. Subtract 60 amps for solar, I would have to downgrade my main breaker to 120a, probably not going to work.
(As 12kW said) Double-check labels inside panel for rating of busbar, vs. rating of main breaker. Sometimes busbar rating is higher.
But if panel has main breaker in middle of busbar rather than one end, limit is 100% not 120%.
150A x 120% = 180A, 30A limit on PV breaker
30A x 80% = 24A max continuous on the circuit
240V x 24A = 5760W max inverter rating.
"120A breaker" may not be an option for your panel.
My QO 225A panels accepts 200A and 150A main breakers, 125A panel accepts 125A, 100A, 70A
Some brand panels (Zinsco) should be replaced regardless because they are a fire hazard.
Had expected "Line" side of meter to go toward utility line, but drawing clearly says PV goes to "Line" side. (question #1)
When summing the ratings of the breakers, shouldn't I use the breaker where the PV energy enters the system? In my case that is 60a. The incoming breaker to the sub panel is 100a. So the busbar rating of the sub panel should be at least (100 + 60) * 1.2 = 192 ? And then the main panel busbar rating should be (150 + 60) * 1.2 = 252 ? Am I understanding this correctly? Are the busbar ratings listed on the panel somewhere? Thanks-Mark
(100 + 60) / 1.2 = 133A minimum busbar rating.
(150 + 100) / 1.2 = 208A minimum busbar rating.
It's not the PV current, it's the breaker rating that's used to calculate required busbar.
If your PV needs 60A breaker, that backfed breaker plus main breaker of the panel it goes to are supposed to be no greater than 120% of panel busbar rating. I say each breaker could be 100% of busbar rating for a total of 200%, so long as located at opposite ends of busbar, and nothing bad would happen. The current from two sources subtracts, doesn't add. But NEC doesn't permit that, out of fear PV breaker will later get relocated next to main breaker so the current then adds.
But now you have a 100A breaker in main panel feeding sub-panel. It is backfed with PV, so it must be at far end of main panel. And guess what?? Sum of main panel main breaker and this 100A backfed breaker is limited to 120% of busbar rating.
A single 15A breaker for PV inverter going to one sub-panel (e.g. condo or industrial unit) could require a cascade of panel upgrades all the way through a 600A main panel connected to utility.
If you put in a Squared D QO 225A main panel with 150A main breaker (or other brand with similar values), 225A x 120% = 270A, 270A - 150A = 120A allowed backfeed. That will meet your needs, and perhaps upgrade of sub-panel (or smaller breaker feeding it) as well.
But what could be convenient is to have utility and main meter go to a 200A breaker or fused disconnect. From there, branch wires to a main panel with 150A or whatever main breaker. Also branch to fused disconnect for PV meter etc.
Once you have separate disconnect & OCP for the utility without a busbar, you can branch with wires to several panels (using Polaris or other suitable multi-tap connector). Current in each wire is limited by main breaker on each panel or by fused disconnects. Only the multi-tap connector might carry sum of currents from two sources (utility, PV) to multiple other loads, but could be 400A rated.
Nice thing about this configuration is you can disconnect power from utility to work on any branch or breaker box.