The California Independent System Operator, the nonprofit company that runs the grid, estimates that by 2020 the state will need to double its reserve capacity. California currently maintains a margin of 7 percent to 8 percent above projected daily demand, in case a nuclear power plant goes offline or outages occur. But when 33 percent of the state's power comes from renewables, that margin will have to rise to 15 percent, said Stephen Berberich, the firm's chief executive.
Nobody knows whether Berberich's estimate is right or how much the added capacity will cost. The California Energy Commission, which has responsibility for licensing new power plants and forecasting future power demand, said it doesn't have the analytical tools necessary to know how much reserve power will be needed.
“It is frankly in the development stage,” said Mike Jaske, the commission's senior policy analyst for electricity supply.
The independent system operator is warning that by 2017 the state will be short by about 3,100 megawatts of flexible power that it can dedicate to meeting reserve needs — about what three nuclear reactors produce. The company is pushing the state Public Utility Commission to require that capacity. The commission has been noncommittal so far.
Solar and wind advocates reject those concerns. They say renewables can provide their own reserve cushion because solar and wind generators will be spread across vast areas of the state. If wind power is down in one region, it might be up in another. If wind power is down statewide, desert sunshine might boost solar.
On the day last month when wind energy provided just 33 megawatts of power statewide, a brilliant sun spiked solar plant output.
The independent system operator “likes to show these frightening graphs for shock value,” said Nancy Rader, executive director of the California Wind Energy Association.
Edward Randolph, director of the Public Utility Commission's energy division, said the independent system operator understandably wants more reserves because its primary focus is on the reliability of the system. The PUC is focused on cost. If there is an immediate problem with reserves, the PUC can order utilities to make more available. And in three to five years, batteries, flywheels or other new technology can provide storage that would make reserves much less necessary, he said.