Solar Industry, May 2014, by Michael Puttre.
http://www.solarindustrymag.com/issues/SI1405/FEAT_03_Mandates-Unleash-Power-Of-Large-Battery-Storage.html

"California has essentially jump-started the renewable energy storage market in North America with its requirement that the big three public utilities in the state deploy a total of 1.325 GW of grid storage capacity by 2024." Article also discusses various battery storage technologies.