Alternative Energy Source

Hydropower is the nation’s most available, reliable, affordable and sustainable energy source. Requiring only the power of moving water – rivers, streams and ocean tides– hydropower is also domestic and sustainable. Free from a dependence on volatile fuel prices, much of the money spent on hydropower stays in America and expanding hydro capacity would create hundreds of thousands of U.S. jobs (National Hydropower Association, 2013).
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Hartwell Dam Spillway Gate Test

HARTWELL, Ga. -- The U.S. Army Corps of Engineers Savannah District tested the spillway gates at the Hartwell Dam, July 10, 2013. The test was part of the Savannah District's Dam Safety Program to ensure the gates can be activated properly in the event of an emergency. Photo by Jenny Vickery, used with permission.

How Does it Work?

The theory is to build a dam on a large river that has a large drop in elevation (there are not many hydroelectric plants in Kansas or Florida). The dam stores lots of water behind it in the reservoir. Near the bottom of the dam wall there is the water intake. Gravity causes it to fall through the penstock inside the dam. At the end of the penstock there is a turbine propeller, which is turned by the moving water. The shaft from the turbine goes up into the generator, which produces the power. Power lines are connected to the generator that carry electricity to your home and mine. The water continues past the propeller through the tailrace into the river past the dam (U.S. Geologic Survey, 2013).

A typical hydro plant is a system with three parts: an electric plant where the electricity is produced; a dam that can be opened or closed to control water flow; and a reservoir where water can be stored. The water behind the dam flows through an intake and pushes against blades in a turbine, causing them to turn. The turbine spins a generator to produce electricity. The amount of electricity that can be generated depends on how far the water drops and how much water moves through the system. The electricity can be transported over long-distance electric lines to homes, factories, and businesses (National Geographic).

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Take a look at the diagram above (courtesy of the Tennessee Valley Authority) of a hydroelectric power plant to see the details in how hydroelectric dams work.

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This diagram (above) of a hydroelectric generator is courtesy of U.S. Army Corps of Engineers.

As to how this generator works, the Corps of Engineers explains it this way:
"A hydraulic turbine converts the energy of flowing water into mechanical energy. A hydroelectric generator converts this mechanical energy into electricity. The operation of a generator is based on the principles discovered by Faraday. He found that when a magnet is moved past a conductor, it causes electricity to flow. In a large generator, electromagnets are made by circulating direct current through loops of wire wound around stacks of magnetic steel laminations. These are called field poles, and are mounted on the perimeter of the rotor. The rotor is attached to the turbine shaft, and rotates at a fixed speed. When the rotor turns, it causes the field poles (the electromagnets) to move past the conductors mounted in the stator. This, in turn, causes electricity to flow and a voltage to develop at the generator output terminals" (U.S. Geologic Survey, 2013).

Where Hydropower is Generated

Over half of World hydroelectric capacity for electricity generation is concentrated in three states in the U.S.: Washington, Oregon, and California. Approximately 29% of the total World hydropower was generated in Washington in 2011, the location of the Nation's largest hydroelectric facility - the Grand Coulee Dam on the Columbia River in northern Washington (U.S. Energy Information Administration). More than 70 percent of the electricity made in Washington State is produced by hydroelectric facilities (National Geographic).

Most hydropower is produced at large facilities built by the federal government, such as the Grand Coulee Dam. The West has most of the largest dams, but there are numerous smaller facilities operating around the country.

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Hydropower is the renewable energy source that produces the most electricity in the United States. It accounted for about 7% of total U.S. electricity generation and 56% of generation from all renewables in 2012.


  • Sustainable: Hydropower is also the nation’s leading source of renewable energy and with new technologies such as marine and hydrokinetics, will continue to provide vast amounts of sustainable energy throughout the country. Learn more about how new technologies are expanding hydropower’s reach.
  • Renewable: Hydroelectric energy is renewable. This means that we cannot use up. However, there’s only a limited number of suitable reservoirs where hydroelectric power plants can be built and even less places where such projects are profitable.

  • Green: Generating electricity with hydro energy is not polluting itself. The only pollution occurs during the construction of these massive power plants.
  • Reliable: Hydroelectricity is very reliable energy. There are very little fluctuations in terms of the electric power that is being by the plants, unless a different output is desired. Countries that have large resources of hydropower use hydroelectricity as a base load energy source. As long as there is water in the magazines electricity can be generated.
  • Flexible: As previously mentioned, adjusting water flow and output of electricity is easy. At times where power consumption is low, water flow is reduced and the magazine levels are being conserved for times when the power consumption is high.
  • Safe: Compared to among others fossil fuels and nuclear energy, hydroelectricity is much safer. There is no fuel involved (other than water that is).


  • Environmental Consequences: The environmental consequences of hydropower are related to interventions in nature due to damming of water, changed water flow and the construction of roads and power lines.
    - Hydroelectric power plants may affect fish is a complex interaction between numerous physical and biological factors. More user interests relate to exploitation of fish species, which helps that this is a field that many have strong opinions on.
    - Fish habitats are shaped by physical factors such as water level, water velocity and shelter opportunities and access to food. Draining would be completely devastating to the fish. Beyond this, the amount of water may have different effects on the fish in a river, depending on the type and stage of the life cycle. Not all unregulated river systems are optimal in terms of fish production, because of large fluctuations in flow.
    - Dams could flood large areas of land that were once forested and/or farmed.
  • Expensive: Building power plants in general is expensive. Hydroelectric power plants are not an exception to this. On the other hand, these plants do not require a lot of workers and maintenance costs are usually low.
- There are many economic costs in protecting the environment in which hydroelectric plants are located.
  • Droughts: Electricity generation and energy prices are directly related to how much water is available. A drought could potentially affect this.
  • Limited Reservoirs: We have already started using up suitable reservoirs for hydroelectric power plants. There are currently about 30 major power plants that are expected to generate more than 2.000 MW under construction. Only one of these projects was started in the last two years.


Maehlum, M. A. (2013, June 1). Hydroelectric energy pros and cons. Retrieved from http://energyinformative.org/hydroelectric-energy-pros-and-cons/

National Geographic. (2010). Hydropower: going with the flow. Retrieved from http://environment.nationalgeographic.com/environment/global-warming/hydropower-profile/

National Hydropower Association (2013). Why hydro?. Retrieved from http://www.hydro.org/why-hydro/

National Hydropower Association (2013). Hydro technology. Retrieved from http://www.hydro.org/tech-and-policy/technology/

Power Young (2012). Renewable hydropower. Retrieved from http://poweryoung.org/energy.cfm@page=hydropower_home-basics

The USGS Water Science School. (2013). Hydroelectric power: how it works. Retrieved from http://ga.water.usgs.gov/edu/hyhowworks.html

U.S. Energy Information Administration. (2012). Renewable hydropower. Retrieved from http://www.eia.gov/kids/energy.cfm?page=hydropower_home-basics