Hydroelectric power units use flowing water to spin a turbine connected to a generator. There are many types of hydroelectric generating systems; the most common are storage projects and run-of river projects. These projects are often referred to as “conventional hydropower.”
In a storage or “falling water” system, water is accumulated in reservoirs created by dams, then released through conduits to apply pressure against the turbine blades to drive the generator. The major benefit of storage systems is that water may be retained and released for generation at a later time. For example, storage projects can help collect plentiful water during some seasons of the year and release it later when water for electric generation is scare. This storage ability may also be utilized on a smaller scale, allowing electricity demand to be met on a daily or weekly basis. These storage projects can provide irrigation water, reservoir recreation opportunities, and flood control.
Run-of-river projects have smaller reservoirs that can sometimes store water for daily or hourly periods, but generally inflow equals outflow over a short-term period. River water flowing downstream is diverted through penstocks or canals to turn hydropower turbines before being returned to the river. These projects have an excellent ability to release water quickly in response to peaking electric demand by the hour or minute. Such projects can more efficiently respond to varying demand signals than thermal units and help to stabilize the Northwest’s electric transmission grid.
Another type of hydropower system that manages water in accordance with short term electric demand is pumped storage. These systems use reversible pumps to move water from a lower reservoir to an upper reservoir during periods of low demand. This same water is then released through generating units when demand for electricity is high. While some electricity is used in the pumping process, the value of power during periods of higher demand can make it economic.
The force of moving water can be captured in other ways as well. Irrigation projects and canal and aqueduct systems can incidentally capture moving water for power generation. Newer technologies that capture tidal or wave energy or hydrokinetic energy are receiving increased attention in recent years. To learn more about new hydropower technologies, visit the website of NWHA members who are exploring these new methods.
For more information download following the pamphlet:
by the U. S. Department of the Interior, Bureau of Reclamation,
Power Resources Office, July 2005.