Even in California it's legal to install non-grid-tied rooftop solar. It requires permitting but does not require an interconnect agreement from the grid electrical utility. We're "remodeling" our house in San Jose currently and the resulting property (includes new ADU) will have 1) old panels (NEM2) grid tied for main house, 2) new panels battery tied for main house & EV charging, 3) new panels (NEM3) grid tied for AGU. PG&E does not care about the second item, provided they are installed per code.