Hydroelectric Dam
A structure that impounds water in a reservoir, releasing it through turbines to generate electricity. The energy comes from the gravitational potential of water stored at elevation.
Why It Matters
Hydropower is America's oldest and largest source of renewable electricity (~6%). Existing dams provide cheap, reliable, dispatchable clean power — a unique combination among renewables.
Related Topics
Related Terms
Pumped Storage Hydropower
A grid-scale energy storage system using two reservoirs at different elevations. Excess electricity pumps water uphill; when power is needed, water flows downhill through turbines. About 22 GW of capacity exists in the U.S.
Penstock
A pipe or channel that carries water from a dam's reservoir to the turbines below. The penstock converts the water's potential energy (from height) to kinetic energy (from velocity) as it descends.
Run-of-River
A type of hydroelectric facility that generates power from the natural flow and elevation drop of a river, without creating a significant reservoir. Output varies with river conditions.