Reclamation and Hydropower

Hydropower Generation Basics

The process of generating electrical power involves converting one form of energy to another. Energy can never be created or destroyed but it can change form. Hydroelectric power production converts moving water into electrical power. Kinetic, or moving energy, is created by water in motion such as a waterfall or river. The amount of kinetic energy created depends on the speed of the moving water which varies depending on factors such as streamflow and change in elevation (head).

To generate hydroelectricity, water from a river or reservoir is directed into a large pipe called a penstock. Water flows from the penstock through the turbine, causing the turbine to rotate at a fast speed. The turbine is connected to a rotor by a shaft so the rotor rotates at the same speed as the turbine. The outside edge of the rotor is comprised of very strong electromagnets connected in a way to provide alternating polarity around the rotor. 

Another generator component is called a stator. The stator encompasses the rotor, is made of steel with many coils of small copper wire inside, and is placed close to the rotor. The energy produced by the water pressure turning the turbine and rotor, combined with the strong electromagnets, creates voltage across the stator coils which are connected in patterns that allow the voltage to be controlled. By changing the strength of the magnets on the rotor and the amount of the water flowing in the penstock, the amount of electricity being generated can be regulated.

Once generated, the electricity is conveyed to transformers via large copper bars called buses, where it is converted to a very high voltage for long-distance transmission to power customers.

drawing: hydroelectric power generation process
Above:  Hydroelectric power generation process
Right:  Water flow through penstock, scroll case, turbine, and draft tube
drawing: water flow throug penstock, scroll case, turbine, and draft tube

Benefits of Hydropower

There are numerous benefits provided by hydropower over other energy sources. These include:

  • Clean - Because hydropower utilizes water to generate electricity, it doesn’t produce air pollution or create toxic by-products like powerplants that burn fossil fuels such as coal or natural gas.
  • Renewable - Hydropower is renewable because it relies on the hydrological (water) cycle driven by the sun which provides a renewable supply of water. Hydropower facilities harness the natural energy of flowing and falling water to generate electricity. About 96 percent of the United States' renewable energy comes from hydropower.1
  • Reliable - Hydropower can meet changing demands because it can go from zero power to maximum output rapidly and predictably.2
  • photo: generators at Glen Canyon Powerplant
    Generators at Glen Canyon Powerplant
  • Efficient - Today's hydropower turbines are capable of converting more than 90 percent of available energy into electricity which is more efficient than any other form of generation (the best fossil fuel powerplant is only about 50 percent efficient).3
  • Flexible -  Hydropower output can be changed quickly in response to changes in electrical demand because of the ability to control the flow of water. This ability is considered essential to electric transmission grid stability.4
  • Domestic and Secure - Hydropower is a secure source of energy because it comes from water in domestic rivers and is not subject to disruptions from foreign suppliers, cost fluctuations, and transportation issues that are associated with other fuel sources.5
  • Cost-Effective - Hydropower generation has low operating costs and a long powerplant life compared with other large scale power-generating options. Once the initial investment is made, powerplant life can be extended economically and remain in service for many years. Typically a hydropower plant in service for 40-50 years can have its operating life doubled.6
  • Stored Energy Source - Because hydropower is most often generated by water stored in a reservoir behind a dam, a vast amount of potential energy exists in the reservoir which is available over a long period of time.
  • Black Start Capability - Hydropower facilities have the ability to start generation without an outside source of power. This service allows system operators to provide auxiliary power to more complex generation sources that could take hours or even days to start.7
  • Growth and Development - Hydropower has played in important role in the growth and development of the Western United States and in the Nation's electric power industry. Both large and small hydroelectric power developments were instrumental in the early expansion of the electric power industry.
  • The Future - Hydroelectric power is important to the United States. Growing populations and modern technologies require vast amounts of electricity for creating, building, and expanding. Hydropower currently supplies about 10 percent of the electrical generating capacity of the US.8

1,4,8  Bureau of Reclamation, Power Resources Office, Hydroelectric Power, (July 2005)
2,3,5  National Association of Hydropower (
6,7  International Hydropower Association, Hydropower and the Worlds Energy Future, (November 2000)

Hydropower Program

The Bureau of Reclamation has a long and successful history providing renewable, clean, reliable, and affordable hydropower to its customers. As the operating environment has evolved over the past century, Reclamation has adapted, leveraging new technologies and partnerships to meet the nation’s water and energy needs. For more information, visit Reclamation's Hydropower Program site.

Last Updated: 3/21/17