"The California Public Utilities Commission has called on utilities and private companies to install about $5 billion worth of batteries and other forms of energy storage to help the state power grid cope with the erratic power supplied by wind and solar energy."

"The need to store energy has become urgent because the state is planning to get a third of its electricity from renewable sources by the end of the decade. And the shift in strategy could open up some big opportunities for small startups, including one called .

Stem is housed in an abandoned showroom in Millbrae, Calif., just across the highway from San Francisco International Airport. And the company is not just aiming to help the state's power grid."

Richard Harris reports for NPR's Morning Edition December 23, 2013. [2]