The idea of the fictitious grid as a battery is ridiculous.
At least in the beginning, California had surplus generation capacity at night. Nuclear and hydro. During they day they were skating on thin ice. One day in the 1990's, a fire near the Canadian border took out a transmission line. Over the next three days the grid collapsed from Vancouver to Ensenada.
Population and consumption has grown since then. Baseline utility production hasn't kept up.
I think a lot of peaker plants were built after that. California intentionally screwed up the market, keeping retail rates fixed while making wholesale generation "competitive", which meant we paid $0.10/kWh to run A/C on a hot day and PG&E had to pay $1.00/kWh to buy power.
With lots of PV on line, while there of course isn't a grid-scale battery (except one pumped hydro plant), PV generated power during hot days routes through a few wires to neighbor's A/C. Less loss (and infrastructure cost) than traveling further through transmission lines. Then at night when there is surplus we get power using the credits. The "battery" is accounting, much cheaper and more efficient than storing power.
That only works with surplus baseload generation capacity. And PV that isn't excessive to the point of destabilizing the grid.
Moving forward to greater PV penetration, two things are needed.
1) Control of PV production so total output and ramp rate doesn't topple the grid.
2) Control of loads to utilize surplus PV and avoid use of fossil fuel. Also curtailing loads to avoid toppling the grid.
At some point we might have PV capacity 2x what is needed, dynamically adjusting its output to match loads and able to fill in for up to 50% reduction in sunlight across the state.
When utility can't supply all demand, the grid collapses and everyone loses power.
A system of signaling to shed some/all but critical loads would be preferable to the grid going down. That is almost trivial to implement.
PV can be part of the solution rather than part of the problem.
Utility scale PV costs a fraction what rooftop PV does.
Rates and net metering need to keep utility company viable/profitable.
Some reasonable charges and credits for rooftop PV customers can be part of the system.