Abstract: Electrical energy storage (EES) is a key to break the bottleneck of penetration of renewable generation, and an essential component of smart grids. At the initial stage of commercialization of EES technologies, a systematic analysis and comparison of different technologies is important, which could help technology selection. This paper presents an overview of various EES technologies including mechanical (pumped hydro, compressed air, flywheel) electrochemical (secondary battery, flow battery) and chemical (hydrogen, synthetic natural gas). Finally, future developments of these technologies are summarized.

Key words: renewable power generation, smart grids, electrical energy storage (EES) technologies, mechanical storage, electrochemical storage, chemical storage