Here (bay area), the power prices are so obscene that I almost makes sense to install batteries first.
Those with homes with solar are going to end up saturating the grid (duck curve) to the point where renters can buy batteries and "coast", through the peaks of power cost.
Are spot electricity contracts available, so that you can do it like that? Makes sense then. And of course the installation cost of battery is way smaller than for a PV plant as no roof work is required.
AFAIK, there is no residential spot market with PG&E. Just different seasonal and hour-by-hour rate schedules with published rates.
There is an "electric home" rate plan that has three periods per day: off-peak, partial-peak, and peak with three rates. This can apply to a home with batteries, where you can shift your load to different periods. The spread can be up to $0.22 per kWh in summer and up to $0.04 per kWh in winter.
There is another rate plan with two periods per day: off-peak and peak. The spread here can be up to $0.09 per kWh in summer and up to $0.03 per kWh in winter. This is a typical plan for homes without solar nor batteries and with moderate consumption. This plan has two pricing tiers. A lower rate for consumption up to a "baseline allowance" and then a higher price after that. This allowance is summed over a whole billing period, in contrast to the time of use variations each day.
The above discussion do not include any net-metering, so you never sell power back to the grid. You just optimize your load during different hours of the day. With a currently available net-metering plan, PG&E will pay for excess power only around $0.02 to $0.04 per kWh.
Also, it seems PG&E distinguishes a "paired storage" net metering system, and requires special metering to track the solar generation that goes into the battery versus recharging from the grid. They will only credit solar production delivered back to the grid, and not off-peak grid energy reflected back during peak hours. So, I'm not sure why some posters seem to be talking about this arbitrage scenario.
For context, the actual per kWh rates are around $0.36 to $0.65 in the different seasons and rate plans. So these peak price differences may range around 5% to 25%. There isn't any of the wild fluctuation or negative numbers we've heard from other energy markets.
Those with homes with solar are going to end up saturating the grid (duck curve) to the point where renters can buy batteries and "coast", through the peaks of power cost.