Virginia Renewables - Hydroelectricity
"Hydropower" (or the energy exerted by water, as it moves in response to the force of gravity) is one of the oldest sources of energy harnessed by humans. The earliest hydro facilities (called "mills") supplied mechanical energy. Early mills ground grain, powered textile mills, and supported other early industrial processes. Today, the vast majority of the world’s hydro power facilities are used to generate electricity (see http://www1.eere.energy.gov/windandhydro/.
Hydroelectric generating facilities are essential the electrical generation, both within Virginia and nationally. In 1999, hydroelectric plants generated more than 8 percent of our nation’s electrical energy. In Virginia, more than 16 percent of the state’s combined utility and non-utility generating capacity is hydroelectric. Virginia hydroelectric plants include both conventional hydroelectric generators and pumped-storage generators.
Conventional Hydroelectric Generating Facilities
Conventional hydroelectric generating units are located on rivers primarily in the southern part of the state. These units are constructed by placing a dam across a river, generally in a location where its channel is constrained by mountains or hills. Water flowing across the dam is sent through channels, to flow through electricity-generating turbines. In some cases, the lakes created by the damming are sufficiently large to allow use for recreation, home development, and flood control. Operators of hydroelectric facilities may control the flow of water through the facility (and hence the rate of electricity generation) so as to increase generation during times of day when electrical demand is highest.
Pumped-Storage Hydro Facilities
The state is also home to two very large pumped-storage hydro facilities, both in western Virginia: Dominion Generation Company's Bath County pumped storage unit, and American Electric Power's Smith Mountain Lake facility. Both of these units generate energy using conventional hydroelectric turbines. However, they differ from conventional hydroelectric plants in that they include basins to hold water both above and below the turbines. During times of peak demand, water from the upper basin is moved through the turbine into the lower basin, generating electricity to satisfy customer demand. During times of low demand for electric power, excess electricity from the firms' "base loaded" generating units (generally, coal-fired and nuclear units that operate most efficiently when run continuously, regardless of customer demand) is used to pump water from the lower to the upper basin. This stored water can be available to generate electricity during those portions of the day or week when customer demand increases.
Map of Major Hydroelectric Plants