California solar plateaus at 10-12GW during the day, a bit less than total coal generation capacity in Australia (per ElectricityMap.org). California needs more solar, wind, and batteries, full stop (and CAISO is working on it if you review their interconnect queue). At least they decided to hold on to Diablo Canyon. You refer to Australia’s desert; 75% of California’s natural gas generation could be replaced with solar sited over existing irrigation canals, and there is a large Nevada desert to the east of the state.

Large AC needs after the sun goes down will need to be served by time shifting chillers, batteries, wind, hydro, and the last nuclear plant standing in the state.