Hydroelectric Power

Flowing water creates energy that can be captured and turned into electricity. Actually, hydroelectric and coal-fired power plants produce electricity in a similar way. In both cases a power source is used to turn a propeller-like piece called a turbine, which then turns a metal shaft in an electric generator, which is the motor that produces electricity. A coal-fired power plant uses steam to turn the turbine blades; whereas a hydroelectric plant uses falling water to turn the turbine. The results are the same.

Photo by: U.S. Bureau of Reclamation
Hoover Dam
The most common type of hydropower plant uses a dam on a river to store water in a reservoir. Water released from the reservoir flows through a turbine - spinning it, which in turn, activates a generator to produce electricity. But hydropower doesn't necessarily require a large dam. Some hydropower plants can use a small canal to channel the water through a turbine.

As an example, the entire flow of the Colorado River passes through the turbines at Hoover Dam. The 17 generators onsite have a maximum power output of an astounding 2.08 Gigawatts.

Another type of hydropower plant called a pumped storage plant can even store power. The power is sent from a power grid into the electric generators. The generators then spin the turbines backward, which causes the turbines to pump water from the river or lower reservoir to an upper reservoir, where the water is stored. When power is needed, the water is released from the upper reservoir back down into the river or lower reservoir, which spins the turbines forward, activating the generators to produce electricity.

Advantages and Disadvantages of Using Hydropower

The principal advantages of using hydropower are its large renewable domestic resource base, the absence of polluting emissions during operation, its capability in some cases to respond quickly to utility load demands, and its very low operating costs. Disadvantages can include high initial capital cost and potential site-specific and cumulative environmental impacts. Potential environmental impacts of hydropower projects include altered flow regimes below storage reservoirs or within diverted stream reaches, water quality degradation, mortality of fish that pass through hydroelectric turbines, blockage of upstream fish migration, and flooding of terrestrial ecosystems by new impoundments. However, in many cases, proper design and operation of hydropower projects can mitigate these impacts. Hydroelectric projects also include beneficial effects such as recreation in reservoirs or in tailwaters below dams.

Applications and Uses of the Technology

The major application for hydropower energy is in the bulk power market, where it accounts for about 77,000 MW conventional capacity and 18,000 MW of pumped storage capacity, or about 10% of the electric generating capacity in the United States. Plants are owned by Federal and state agencies, cities, metropolitan water districts, irrigation companies, as well as public and independent utilities. Individual persons also own small plants at remote sites for their own energy needs and for sale back to the utilities under the Public Regulatory Policies Act (PURPA).

Hydropower is an essential contributor in the national power grid because of its ability to respond in seconds to large and rapidly varying loads, which other base load plants with steam systems powered by combustion or nuclear processes cannot accommodate.

Potential sites for all types of hydropower exist that would double the U.S. hydroelectric production if they could be developed. However, a variety of restraints exist on this development, some natural and some imposed by our society. The natural restraints include such things as occasional unfavorable terrain for dams. Other restraints include disagreements about who should develop the resource or the resulting changes in environmental conditions. Often, other developments already exist at sites otherwise suitable for hydropower generation. Finding solutions to the problems imposed by natural restraints demands extensive engineering efforts. Sometimes no solution is possible, or is so expensive that the entire project becomes impractical. Solutions to the societal issues are frequently much more difficult to resolve and the costs are far greater than those imposed by nature. Developing the full potential of hydropower will require consideration an coordination of many varied factors.

Additional Resources
  • FERC issues licenses for the construction of a new project, or the continuance of an existing project (relicensing); and provides oversight of all ongoing project operations, including dam safety inspections and environmental monitoring.
  • National Inventory of Dams is a collection of information about dams in the United States and its territories, produced by the U.S. Army Corps of Engineers.