There are approx. 530,000 potentially feasible pumped hydro energy storage sites worldwide, with a total storage potential of about 22 million GWh.

These stupendous numbers have been published in a report recently released by Professor Andrew Blakers and colleagues with Australian National University’s RE100 Group. Today pumped hydro already constitutes 97 percent of electricity storage worldwide due to its low cost, ANU says, and the proportion of wind and solar photovoltaics in the electrical grid is extending considerably. This means “additional long-distance high voltage transmission, demand management and local storage is required for stability.” ANU researchers identified the potential sites and their potential using geographic information system (GIS) analysis. The massive storage potential of about 22 million GWh “is about one hundred times greater than required to support a 100 percent global renewable electricity system,” ANU says. An approximate guide to storage requirements for 100 percent renewable electricity, based on analysis for Australia, is 1 GW of power per million people with 20 hours of storage, which amounts to 20 GWh per million people.  The identified sites are outside national parks and are mostly closed-loop (not river-based).
[source: Smart Energy International]