"Across the country, power companies are increasingly using giant batteries the size of shipping containers to address renewable energy’s biggest weakness..."

"... the fact that the wind and sun aren’t always available.... When power companies first began connecting batteries to the grid in the 2010s, they mainly used them to smooth out small disruptions in the flow of electricity.... But power companies also use batteries to engage in a type of trading: charging up when electricity is plentiful and cheap and then selling power to the grid when electricity supplies are tighter and more expensive. In California power prices often crash around midday, when the state produces more solar power than it needs.... Prices then soar in the evening when solar disappears...."

From "Giant Batteries Are Transforming the Way the U.S. Uses Electricity/They’re delivering solar power after dark in California and helping to stabilize grids in other states. And the technology is expanding rapidly" (NYT).