See Duck curve https://en.wikipedia.org/wiki/Duck_curve

Essentially, solar is great from 8am to 4pm, and California has replaced about half of their load during those hours with solar. However, they have negligible renewable capacity during other times of the day, including peak demand from 6-10pm.

There's a more up-to-date version of California's Duck Curve here: https://www.energy.gov/eere/articles/confronting-duck-curve-...