How much energy storage would be needed for California to reach 50 percent solar?

If California wants to continue increasing its share of solar power on the grid, it will need greater capacity to store it. The question remains: how much?
A new study from the National Renewable Energy Laboratory attempts to quantify the answer. The authors model several scenarios in which the California grid generates 50 percent of its power from solar by 2030. To do so will require some pretty major changes, including more flexible baseload generation, as well as more deployment of electric vehicles, exports to other states and demand response.
Those can only go so far, though. To meet the 50 percent photovoltaic threshold economically will require energy storage. The state already has 3,100 megawatts of pumped storage, with 1,325 megawatts of additional storage set to be deployed by 2020, per the state mandate. Under the most optimistic flexible grid scenario and with PV prices falling rapidly to 3 cents per kilowatt-hour, California will need another 15 gigawatts of storage by 2030.
That’s more than 11 times the amount mandated currently in California, and 66 times the total megawatts deployed in the U.S. last year. And any delays in the price declines of solar, or the rollout of EVs, or the flexibility of conventional power plants, will raise the bar on the amount of storage required.

That sounds daunting, admitted NREL Principal Energy Analyst Paul Denholm, who co-authored the research with Robert Margolis.
“Storage costs are going to have to come down,” Denholm said. “I don’t want to sugar-coat it: we’re not there yet.”
But the challenge becomes more attainable if you frame it as getting storage to a price point where it can take the place of peaker plants, the most expensive form of thermal generation. California had 22 gigawatts of fossil-fueled peakers as of 2014, including 14 gigawatts that were older than 25 years and will eventually need to retire.

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