Fortnightly's Power Profit, Feb. 26, 2014, by Scott M. Gawlicki, Public Utilities Fortnightly.
 http://powerprofit.fortnightly.com/fortnightly/storage-steps

"Duke Energy Renewables’ 153-MW Notrees (Texas) Wind Power Project includes a 36-MW advanced lead acid battery – the largest capacity battery facility in North America. Duke says developing expertise in this advanced technology will help expand the use of renewable energy, better integrate it into the power grid, and make the company more efficient at serving customers. Could batteries and other storage technologies affect the way power producers evaluate and operate their generating assets – in particular fossil fired generating assets they currently rely on to supply ancillary services?"