How Does Hydroelectricity Work?

Types of Hydropower Facilities

Impoundment Hydropower:

Uses a dam to store water. Water may be released either to meet changing electricity needs or to maintain a constant reservoir level.

Diversion Hydropower:

Channels a portion of the river through a canal or a penstock but may require a dam.

Pumped Storage:

Pumps water from a lower reservoir to an upper reservoir at times when demand for electricity is low. During periods of high electrical demand, the water is released back to the lower reservoir to generate electricity.

The Hydrologic Cycle

Water constantly moves through a vast global cycle, in which it evaporates from lakes and oceans, forms clouds, precipitates as rain or snow, then flows back to the sea. The energy of this water cycle, which is driven by the sun, is tapped most efficiently with hydropower.