"California is pushing hard for rooftop solar power, which is a great idea, and I hate to be a wet blanket, but 31.5 GW of peak demand will never ever be met by rooftop solar. During the summer peak demand in California can be more like 75 GW."

Because usage peaked at 31.5GW on a particular day, doesn't address what the AVERAGE peak usage is throughout the year. Solar PV is not a sprint, it is a marathon. If every home in the State had at least 4 to 6KW peak solar PV on their roofs, it would make a monolithic affect on the amount of power the State requires. The fact that 31.5GW was required does not mean that homeowners, business owners,apartment complexes, large box stores, warehouses and factories shouldn't install solar PV. If at least a majority of homes and businesses made some of their power requirements daily, you wouldn't need 31.5GW of power to keep the State running.