Good point. There is another issue there for PG&E, (and possibly the other two utilities too). That is that PG&E is a decoupled utility: their income comes partly from getting us to reduce demand, and when we make our own power, it does decrease demand (on their – mostly natural gas-fired power) so they benefit.

You are right, our roofs don’t count towards the total renewable power on the grid credited to the utility, (even though California rooftops are providing over 2.5% now of peak power demand!) – only utility-bought-or-contracted for renewables count. Though PG&E manages the CSI rebates, they are actually state rebates.