CAISO, which is basically a large bulk electric market for them to SELL their excess renewable generation during the day to other markets (for example, AZ utilities are paid to take their solar over generation during the day), and BUY energy from those same markets when the sun goes down or the wind stops blowing.

While lithium ion battery storage is improving in terms of costs, the scale and capacity (usually only 4 hours of storage) has a LONG way to go in terms of facilitating 100% "renewable."