This article is from 2016 and things have changed even more. The California duck curve that can be seen in the daily load at caiso.com shows how utility scale solar is generating so much power during the day that the rest of the power plants have to generate less and less. Then as the sunlight drops in the afternoon there is a sharp increase in the load and a lot more power generation has to be brought online to make up for the drop in solar. This is called the duck curve. It’s actually two curves; one curve upward from the load and one curve downward from solar.
At the time of the article’s writing there was very little battery storage on California’s grid. There was some hydro and pumped hydro, but the main part of the quick ramp-up in generation was done by gas turbine peaker plants. Today in 2020 there have been several utility scale battery storage systems that have been brought online. These are helping to even out the peaks in the demand.
This article explains why there have been rolling blackouts. California has been relying on gas peaker plants when it should be building more battery storage to do the ‘peak shaving’. The fossil fuels have to be eliminated ASAP.
https://pv-magazine-usa.com/2020/08/17/californias-fossil-fuel-plants-failed-us-not-solar/