Energy storage: Packing some power — Better ways of storing energy are needed if electricity systems are to become cleaner and more efficient

http://www.economist.com/node/21548495

/ pumped-storage hydropower PSH water gravity turbine Electric Power Research Institute EPRI Green Power Island Advanced Rail Energy Storage ARES off peak electricity height differential efficient efficiency compressed-air energy storage CAES pumped heat electricity storage (PHES) molten salt /