Andrew Merecicky:

The recent droughts across the U.S., specifically in California, have stressed the importance of power generation and storage strategies that use as little fresh water as possible. Energy production by fossil fuels and nuclear use water as a key part of power generation.
 Today approximately 99% of grid-scale energy storage relies on pumped hydropower. Beyond the huge amounts of water required by this process, pumped hydropower is limited geographically to where there is a mountain and a water source.
 But according to Jonathan Howes, a British aeronautical engineer, there soon may be a viable alternative. Howes, with partners James Macnaghten and Mark Wagner, co-founded Isentropic, Ltd., a company that is currently developing a new storage technology called pumped-heat electricity storage (PHES), which stores electricity as heat and cold. PHES, Isentropic claims, is cheaper than pumped hydro, is deployable anywhere in the world, and is comparable—and in some cases superior—to pumped hydro with a round-trip storage efficiency of 72 to 80%.