There are three types of hydropower
facilities: impoundment, diversion, and pumped storage. Some hydropower plants
use dams and some do not. The images below show both types of hydropower
plants.
Many dams were built for other purposes and
hydropower was added later. In the United States, there are about 80,000 dams
of which only 2,400 produce power. The other dams are for recreation,
stock/farm ponds, flood control, water supply, and irrigation.
Hydropower plants range in size from small systems for a home or
village to large projects producing electricity for utilities. The sizes of hydropower plants are described below.
IMPOUNDMENT
The most common type of hydroelectric power
plant is an impoundment facility. An impoundment facility, typically a large
hydropower system, uses a dam to store river water in a reservoir. Water
released from the reservoir flows through a turbine, spinning it, which in turn
activates a generator to produce electricity. The water may be released either
to meet changing electricity needs or to maintain a constant reservoir level.
Diversion
A
diversion, sometimes called run-of-river, facility channels a portion of a
river through a canal or penstock. It may not require the use of a dam.
Pumped Storage
When
the demand for electricity is low, a pumped storage facility stores energy by
pumping water from a lower reservoir to an upper reservoir. During periods of
high electrical demand, the water is released back to the lower reservoir to
generate electricity.
SIZES OF
HYDROELECTRIC POWER PLANTS
Facilities
range in size from large power plants that supply many consumers with
electricity to small and micro plants that individuals operate for their own
energy needs or to sell power to utilities.
Large
Hydropower
Although
definitions vary, DOE defines large hydropower as facilities that have a
capacity of more than 30 megawatts.
Small
Hydropower
Although
definitions vary, DOE defines small hydropower as facilities that have a
capacity of 100 kilowatts to 30 megawatts.
Micro
Hydropower
A
micro hydropower plant has a capacity of up to 100 kilowatts. A small or
micro-hydroelectric power system can produce enough electricity for a home,
farm, ranch, or village.
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