Seasonal challenges for a California renewable- energy-driven grid

Currently, the most difficult time of year for California to supply the demanded electricity is around sunset on very hot summer days. As California uses more renewable electricity, that challenge may shift to any time of the year depending on the supply of electricity more than on the demand. We study various scenarios for applying a 100% renewable energy grid using six years (2015-2020) of historical demand and scaled-up solar and wind generation to investigate the main function of the storage in affording adequate electricity supply at all times of the year. We identify the times of year that may be most challenging. We detect that, for a solar dominant generation profile, the ultimate challenge shifts from summer to winter. Furthermore, the critical time of the year may be shifted by one or two months depending on the amount and the mix of the renewable generation that will be built.