In 2013, the CPUC mandated installing about 1.3GWhr of grid energy storage by 2020. Installation of de facto additional capacity appears to be underway. Brief summary: [1] Absent base load or other dispatchable, non-renewable generation, energy storage is the only way to deal with the duck curve.
[1] https://www.utilitydive.com/news/california-puc-finalizes-ne...