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Hydroelectric Power Plants

The project describes how electricity is generated from water, the types of hydroelectric
plants, and the costs and benefits associated with hydropower.

Since the time of ancient Egypt, people have used the energy in flowing water to operate
machinery and grind grain and corn. However, hydropower had a greater influence on
people's lives during the 20th century than at any other time in history. Hydropower
played a major role in making the wonders of electricity a part of everyday life and
helped spur industrial development. Hydropower continues to produce 24 percent of the
world's electricity and supply more than 1 billion people with power.

Evolution of Hydropower
The first hydroelectric power plant was built in 1882 in Appleton, Wisconsin to provide
12.5 kilowatts of electricity to light two paper mills and a home. Today's
hydropower plants generally produce several hundred kilowatts to several
hundred megawatts of electricity, but a few mammoth plants have capacities up to
10,000 megawatts. These hydroelectric power plants can supply electricity to
millions of people.
Worldwide, hydropower plants have a combined capacity of 675,000 megawatts and
annually produce over 2.3 trillion kilowatt-hours of electricity, the energy equivalent of
3.6 billion barrels of oil.

How Hydropower Works

Hydropower converts the energy in flowing water into electricity. The quantity of
electricity generated is determined by the volume of water flow and the amount of "head"
(the height from turbines in the power plant to the water surface) created by the dam. The
greater the flow and head, the more electricity produced.
A typical hydropower plant includes a dam, reservoir, penstocks (pipes), a powerhouse
and an electrical power substation. The dam stores water and creates the head; penstocks
carry water from the reservoir to turbines inside the powerhouse; the water rotates the
turbines, which drive generators that produce electricity. The electricity is then
transmitted to a substation where transformers increase voltage to allow transmission to
homes, businesses and factories.
Types of Hydropower Plants
Most hydropower plants are conventional in design, meaning they use one-way water
flow to generate electricity. There are two categories of conventional plants, run-of-river
and storage plants.
Run-of-river plants—These plants use little, if any, stored water to provide water flow
through the turbines. Although some plants store a day or week's worth of water, weather
changes—especially seasonal changes—cause run-of-river plants to experience
significant fluctuations in power output.
Storage plants—These plants have enough storage capacity to off-set seasonal
fluctuations in water flow and provide a constant supply of electricity throughout the
year. Large dams can store several years worth of water.
Pumped Storage
In contrast to conventional hydropower plants, pumped storage plants reuse water. After
water initially produces electricity, it flows from the turbines into a lower reservoir
located below the dam. During off-peak hours (periods of low energy demand), some of
the water is pumped into an upper reservoir and reused during periods of peak-demand.

Building Hydropower Plants

Most hydropower plants are built through federal or local agencies as part of a
multipurpose project. In addition to generating electricity, dams and reservoirs provide
birds. Private utilities also build hydropower plants, although not as many as government
Hydropower is a clean, domestic and renewable source of energy. Hydropower plants
provide inexpensive electricity and produce no pollution. And, unlike other energy
sources such as fossil fuels, water is not destroyed during the production of electricity—it
can be reused for other purposes.

Hydropower plants can significantly impact the surrounding area—reservoirs can cover
towns, scenic locations and farmland, as well as affect fish and wildlife habitat. To
mitigate impact on migration patterns and wildlife habitats, dams maintain a steady
stream flow and can be designed or retrofitted with fish ladders and fishways to help fish
migrate upstream to spawn. However, there are still other risks with the introduction of
dams into the river systems. By introducing new water conditions such as a reservoir or a
dam, a well-oxygenated river can turn into an anoxic lake (being devoid of oxygen).

Also, the water stored behind dams tends to accumulate sediment and silt. This
accumulation can hinder the water flow and cause harm to the turbines and pumps. As an
example, after only four years of operation, the Sanmen George Dam on the Yellow
River, China lost 41% of its water storage capacity and 75% of its maximum power
capacity due to sedimentation.