For systems that only run for a few hours per day (4-6), battery systems are cheaper to build, faster to build, and far easier to site. There are only a few critical hours of peak demand in California, in the late afternoon/early evening.
For example, look at the demand graph here for yesterday (11 July 2019):
Demand goes above 35 gigawatts at 3:30 in the afternoon and is back below that level by 7:00 PM, 3.5 hours later.
Battery systems are useful for shaving off that daily peak. They reduce the need to activate more expensive and more polluting open cycle gas turbines that have typically been used as peakers. It will be a few years more yet before solar plus storage systems can make a significant dent in the use of more efficient combined cycle gas turbine generation.
For example, look at the demand graph here for yesterday (11 July 2019):
http://www.caiso.com/TodaysOutlook/Pages/default.aspx
Demand goes above 35 gigawatts at 3:30 in the afternoon and is back below that level by 7:00 PM, 3.5 hours later.
Battery systems are useful for shaving off that daily peak. They reduce the need to activate more expensive and more polluting open cycle gas turbines that have typically been used as peakers. It will be a few years more yet before solar plus storage systems can make a significant dent in the use of more efficient combined cycle gas turbine generation.