The dominant technology for the large-scale storage and retrieval of electricity is pumped hydro – electrical energy. In this approach, electricity is converted to gravitational potential energy by moving water uphill and is then retrieved by allowing the water to flow downhill through a turbine. However, a new concept in gravity storage eliminates the need for hills and simply uses water pumps to hydraulically lift massive rocks in an underground shaft. The acquired potential energy is reclaimed as electricity by discharging the water under pressure though a turbine.
See full article at Advanced Science News.