Sodium and Sodium‐Ion Batteries: 50 Years of Research

Pumped-Storage of Water: It is the most efficient; it is developed in very large scale capacity storage facilities which require specific sites; nevertheless, in the future due to its long lifetime it will play a significant role for intermediate time storage of a few hours to several days, and even for intermediate scale capacity energy storage. Electrochemical Energy Storage in Batteries: It is now used locally in some places that are not connected to the electricity network and on the smart grids for frequency regulation or small peak production shifts. Examples include sodium sulfur batteries (NaS) which are used in Japan; redox flow batteries under development, and some large scale lithium–ion batteries (LIBs) that are used in specific places. Storage via Hydrogen: The development of hydrogen as a way of using fuel cells is considered and seems very interesting from the pollution point of view at the local scale. From the technical point of view, most of the problems are almost solved. Nevertheless, hydrogen has to be produced and stored; and in this case, the yield is quite low, similar to that of the internal combustion engine. Electricity storage via hydrogen requires water electrolysis, H2 gas storage, and electricity production in fuel cells, all of which leads to a low efficiency and therefore, significant energy loss during electricity storage.