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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. 
For places without water, what's wrong with importing a bunch once? Evaporation suppressors exist to help with hotter climates.
You're probably right about the hills. Building a water tower that can hold an entire lake seems inefficient.
How are you importing an entire lake?
Truck? 5G? Just let a tiny faucet run a long time? IDK.
from somewhere import lake
lake.flow()
It's just that simple!
Use a very long hose.