TITLE 24 OF THE CALIFORNIA CODE OF REGULATIONS
A copy of the regulations can be found here for Architects https://www.dor.ca.gov/Home/Title24
Major Changes to the Title 24 Building Code took effect on Jan 1 2020. Solar is now mandatory for all new homes and ADU construction. The one good thing is that a garage conversion to ADU is exempt from this requirement as it can be ran as an addition, even if the garage is detached from the main residence.