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Water up mountains' has been a preferred energy store for a long time, and very effective it is too.
Viz. the Dinorwic pumped storage scheme, with which I was intimately and rather dangerously associated - as a one time photogrammetrist I was 'volunteered' to go into the old mineshafts around the planned tunnel with a pair of calibrated survey cameras on a sledge and photograph long abandoned shafts that were deemed too dangerous to send a surveyor down, and subsequently pull the plates up on a stereo-comparator to see if there were any side shafts.
The this was in the mid seventies, and the Dinorwic scheme is still working successfully today.