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What do hexbears think about pumped hydropower storage?
(hexbear.net)
To make solar power viable, we need a solution for overnight energy storage.
Batteries are complicated.
Do you know what isn't? Water go up. 
Honestly, one of the better ways ecologically to store energy instead of ripping apart the earth to get rare elements for batteries. But I do also like flywheels, lets just store energy in flywheels.