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Hydroelectric is one of the oldest electrical storage systems there is -- you can store more electricity as gravitational energy by pumping the water back uphil

• jacobush 9y ago
  ... that reason being that dams are used to collect the water from rainfall.
• snowwrestler 9y ago
  Very few dams have the capacity to pump water back uphill. And they don't need it, because power-generating dams are generally only built in places that provide lots of downstream flow naturally, like the U.S. Pacific Northwest, or in places where a reservoir is already desired for other reasons (typically drinking water, navigation, and/or flood control). Dams have the capacity to route downstream flow around some turbines to lower their generating capacity. It's not really accurate to think of that routed water as "wasted capacity," because that water would flow naturally even if the dam wasn't there.