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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. 
just heat up some sand instead
What makes sand so great? Water has five times the specific heat capacity.
Edit: OH I see, the sand goes through a phase change. That involves a lot of energy, yeah.