I'll be honest, I dont remember CA ever having this credit.   I did find this in the Instructions for Form FTB 3540
Credit Carryover Summary

Code 180 – Solar Energy Credit Carryover
You may claim a credit carryover for the costs of installing solar
energy systems under former R&TC Sections 17052.5 and 23601, only
if a carryover is available from tax years 1985 through 1988.

If its from back in 1985-1988, thats probably why I dont remember it.