Pumped hydro is burning energy to pump energy into a (usually artificial) reservoir. Then, later, allowing that filled reservoir to drain through a hydroelectr

Pumped hydro is burning energy to pump energy into a (usually artificial) reservoir. Then, later, allowing that filled reservoir to drain through a hydroelectric plant and generate electricity. This solves 2 major problems, compared to alternatives. 1) The scaling costs (with respect to energy storage capacity / volume) are extremely low. E.g. instead of building twice as much battery, you're just consuming additional empty space behind the dam. 2) There is no time-cost to storing energy in pumped hydro, which affords great flexibility in when it's stored and when it's extracted. E.g. stored on a bright day when the wind is blowing, extracted at night when there's no wind. In essence, it turns spikey supply and demand patterns into more constant ones, which are cheaper and more efficient to service.