Community Energy Opportunity Finder : Renewable Energy Information

	Hydroelectric Power: Resources and Economics

	Hydroelectric Power: How Do I Get It in My Community?

	Hydroelectric Power: Information and Resources

What is Hydroelectric Power?
Flowing water creates energy that can be captured and turned into electricity. Hydropower makes up about half of renewable energy generation.

Hydropower facilities can range in size from large plants that provide electricity to many consumers to small and micro projects that provide electricity to a few households or individuals. The Department of Energy defines large hydropower as facilities that have a capacity of more than 30 megawatts; small hydropower as between 0.1 and 30 megawatts, and microhydropower as up to 100 kilowatts (0.1 megawatts). These distinctions are important when discussing the environmental impacts of hydropower projects.

Large Hydroelectric Power
Renewable Energy, Hydropower

Large hydropower projects are the most common type of hydropower, and also the most controversial and environmentally damaging. These projects use dams to store water in reservoirs, and then run channel water through turbines, which drive generators to produce electricity. Hydropower energy can also be stored by pumping water from a lower reservoir to an upper reservoir, and releasing the water through turbines to produce electricity when it is needed.

Dams, especially the large dams required for large hydropower projects, can cause environmental impacts, such as:

Inundating homes and wildlife habitat when reservoirs are filled;
Interfering with fish migration patterns;
Altering, reducing, or eliminating downstream flows;
Changing river temperatures by releasing colder water from the reservoir bottom, which changes downstream river habitat;
Interfering with the movement of sediments and deposition along riverbanks; and
Creating conditions that favor non-native species over native species.

On the other hand, dams can create benefits beyond electricity generation, such as flood control, recreational activities, and jobs. These benefits and disadvantages of large hydropower should be weighed carefully before making the decision to build a large hydropower project.

For more information, see the Wind Energy and Hydropower sections of DOE's website (www1.eere.energy.gov/windandhydro).

Small Hydroelectric Power
Electricity can also be generated without building dams, by capturing the energy from the flow of a running river. These "Run of River" projects channel water through a small canal and then through a turbine to generate electricity. Run of river hydropower projects are generally much smaller than projects that involve dams, and have less environmental impact.

Run-of-River projects are dramatically different in design, appearance and impact from conventional hydroelectric projects. There are two main differences. First, there is no water storage other than the limited amount required to submerge the intake pipe. Second, there is no alteration of downstream flows, since all diverted water is returned to the stream below the powerhouse.

A typical run-of-river project consists of the following: an intake structure at which water is diverted, a pipeline (penstock) through which it travels downhill, a small powerhouse, and a tailrace where the water is returned to the stream above — or as close a possible to — a barrier to fish movement.

For more information, see the Hydropower section of Home Power Magazine (www.homepower.com).