Pumped storage hydro has been proposed but most often it is shot down by environmentalist objections. Not a lot of people know it, but many technology historians trace the origins of the modern environmentalist movement to a fight over a proposed pumped storage reservoir, that being the Storm King Mountain project in the Hudson Valley. And the opposition was led by stinky, ratty, flea-bitten, pony-tailed wackos like you see today. The original "environmentalists" were extremely wealthy landowners along the Hudson River valley, who objected not so much to the idea of a reservoir as to the visual pollution the transmission lines would bring to their views of the picturesque Hudson Valley. Sounds familiar? Think Teddy Kennedy and the proposed Cape Wind project. So I don't have a lot of hope either for large-scale storage systems being built anytime soon. Its all coming down to NIMBYs and NOPEs and BANANAs.
Ask people today what Storm King Mountain was all about, and 9 out of 10 will say it was a nuclear plant. Little do they know that it is something related to that darling of the environmentalist movement, solar energy. Most solar energy advocates will disavow any knowledge of the issue, but that doesn't stop the NOPEs and NIMTOOs from opposing something like it.
Sorry. Should have said “the opposition was NOT led...”