Pumped storage hydropower (PSH) is one of the most-common and well-established types of energy storage technologies and currently accounts for 95% of all utility-scale energy storage capacity in the United States.
Basic idea is water is pumped up to a reservoir when the sun is out or the wind is blowing and the electricity is cheap and abundant. Then when demand requires it, the water is passed through a turbine and ends up in a lower reservoir.
That would have been a good first post to birdguy. Unfortunately we've lost a decent and informative guy. Sorry, had to squeeze that one in. Won't no more. ;-)
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