Rocky Mountain Institute, Winter 2014, by Amory B. Lovins.
http://www.rmi.org/winter_2014_esj_ramping_up_renewable_electricity

"Many people in the electricity industry long thought that the two renewable sources of electricity that vary widely over time—windpower and solar photovoltaics (PVs) —could provide only a few percent of total generation without endangering reliability. Those who still believe this now face increasingly severe reality tests.

As we’ll see, Germany and other countries are successfully powering their grids with astonishingly high fractions of renewable generation by combining five techniques: a) leveraging diverse generation sources across interconnected regional and national grids, b) improving renewables’ forecasting and predictability, c) integrating dispatchable renewables, d) adding distributed storage, and e) leveraging demand response."