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Hydropower

Impoundment Example Courtesy of HowStuffWorks, Inc.
Impoundment Example Courtesy of HowStuffWorks, Inc.

Hydropower systems are sustainable ways of harnessing energy in order to produce electricity from flowing water.  There are three different systems that are generally used to harness water’s energy, typically based on the amount of available energy.  The amount of energy is determined by the head and flow of the water.  Head is the water’s vertical change of elevation, while flow is the volume of the water passing a specific point over a certain time.  The volume is typically measured in cubic meters per second. 

The four different hydropower systems or micro-hydropower systems are an impoundment facility, diversion system, pumped storage system, or run-of-the-river.  An impoundment facility, which is usually a large hydropower system, uses a dam to hold water in a reservoir and then release the water in order to produce electricity by spinning a turbine.   A Diversion system does not use large reservoirs, but rather diverts a portion of water from the river into a water conveyance which leads the water to a turbine or waterwheel.  The water turns the turbine or waterwheel which causes a shaft to spin in order to power an alternator or generator to produce electricity.  A pumped storage system is only used when electricity need is low. 

Diversion or "Run of the River" Example Courtesy of U.S. DOE EERE
Diversion or "Run of the River" Example Courtesy of U.S. DOE EERE
Water is pumped from a lower reservoir to a higher reservoir and then released when power is needed as with an impoundment system.  A run-of-the-river system uses the flow of water in the river or stream to turn a turbine positioned directly in the river.

Within these systems, there are two different types of turbines: impulse and reaction turbines.  Impulse turbines are generally used when there is high head and low flow. This turbine uses the velocity of the water to move the turbine and create electricity.  Reaction turbines are used for low head and higher flow.  This turbine uses the combined power of pressure and water flow to create electricity.



Reference:

U.S. DOE Energy Efficiency and Renewable Energy. 2005 August 20. Hydro Plant Types.  http://www1.eere.energy.gov/windandhydro/hydro_how.htmlhydro/hydro_plant_types.html. Accessed July 2008.