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
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
technologies, visit the website of NWHA members who are
exploring these new methods.
For more information download following the pamphlet:
Managing Water in the West
by the U. S. Department of the Interior, Bureau of Reclamation,
Power Resources Office, July 2005.