An oft cited deficiency of solar energy is its intermittency. However, in the Southwest solar is surprisingly reliable. The graph above is typical and notice that it is auto-scaled so the lowest point on the graph is still well above zero at 900 kwhrs. The overcast days can be forecast so that other sources can be dispatched with some degree of planning. Also, since less air conditioning is required when it is overcast, this does not lead to a situation where peak demand is starved from source.
The graph above is often referred to as the Duck Curve due to it appearing like a duck in profile.
Some suggest that the “duck curve” is a problem. However, CA has wind that reliably kicks in about the time solar is winding down. See CAISO figure below. Hydo power is a great compliment to renewable energy due to its dispatchability. There are a whole host of Transmission projects that are being added in CA to make their grid more flexible. Type “CA transmission line upgrades” into google and a large list pops up.
Here is a link to the CAISO site where you can access historical graphs like the one above.