I don't think this is true anymore.
California already has over 7000 MW in energy storage on the grid. That number was only 770 MW at the start of 2020.
You can go to the CAISO website and see battery storage in action as it goes into negatives during the day (batteries charging), and then go into positive supply (discharging) as solar begins to drop in the evening:
http://www.caiso.com/TodaysOutlook/Pages/supply.html#section-renewables-trend
They just need to keep adding more storage if they want to get to carbon-free, and there's already quite a bit in the pipeline. Plus there is planning for a massive new offshore wind farm underway as well.
This will truly become an amazing new period in science and technology. Because with all that extra electricity we may see more energy intensive developments occur (hopefully something more useful that Bitcoin mining). Like desalinization for example. Whenever you hear the negatives for desal, it's always "it needs too much energy to work".