How Hydropower Works
hydropower projects use a dam and a reservoir to retain water from a
river. When the stored water is released, it passes through and rotates
turbines, which spin generators to produce electricity. Water stored in a
reservoir can be accessed quickly for use during times when the demand for
electricity is high.
Dammed hydropower projects can also be built as power storage
facilities. During periods of peak electricity demand, these facilities
operate much like a traditional hydropower plant — water released from
the upper reservoir passes through turbines, which spins generators to
produce electricity. However, during periods of low electricity use,
electricity from the grid is used to spin the turbines backward, which
causes the turbines to pump water from a river or lower reservoir to an
upper reservoir, where the water can be stored until the demand for
electricity is high again.
A third type of hydropower project, called "run of the
river", does not require large impoundment dams (although it may
require a small, less obtrusive dam). Instead, a portion of a river's
water is diverted into a canal or pipe to spin turbines.
How Hydropower is Used
Hydropower is currently the largest and least expensive source of
renewable electricity produced in the United States.
Large and small-scale hydropower projects are most commonly used by
clean power generators to produce electricity. The Buying
Clean Electricity section provides information on buying electricity
generated from hydro and other renewable resources in your state.
Many large-scale dam projects have been criticized for altering
wildlife habitats, impeding fish migration, and affecting water quality
and flow patterns. As a result of increased environmental regulation, the
National Hydropower Association forecasts a decline in large-scale
hydropower use through 2020. Research and development efforts have
succeeded in reducing many of these environmental impacts through the use
of fish ladders (to aid fish migration), fish screens, new turbine
designs, and reservoir aeration. Although funding has been limited,
current research focuses on the development of a "next generation
turbine, which is expected to further increase fish survival rates and
improve environmental conditions.
A very small hydropower (called microhydro) project can also be
installed to meet the electricity needs of a single home or small
business, and is especially useful for those in remote areas. Our Making
Your Own Clean Electricity section provides more information on issues
involved with producing your own electricity.
Where Hydropower is Used
Hydropower is used throughout the United States, although it is more
common in West Coast (especially Northwest) states.
To find out about the hydropower resources (both developed and
undeveloped) in your state, visit the Hydropower
Resource Assessment page of the Idaho National Engineering &