Hydro power is a significant source of California's and the nation's electricity. In 2004, about 16.5 percent of the total electricity in California is from hydro -- 14.9 percent from large hydroelectric plants, and about 1.6 percent is from small hydro facilities, which are 30 megawatts or smaller in size. Nationally, according to the U.S. Department of Energy, hydro accounts for about 10 percent of the country's total electricity production - about 95,000 megawatts.
The larger hydro plants on dams in California (such as Shasta, Folsom, Oroville, etc.) are operated by the U.S. Bureau of Reclamation and the state's Department of Water Resources. Smaller plants are operated by utilities, mainly Pacific Gas and Electric Company and Sacramento Municipal Utility District. Licensing of hydro plants is done by the Federal Energy Regulatory Commission with input from state and federal energy, environmental protection, fish and wildlife, and water quality agencies.
Hydroelectric power, a renewable resource, is generated when hydraulic turbines are turned by the force of moving water as it flows through a turbine. The water typically flows from a higher to a lower elevation. These turbines are connected to electrical generators, which produce the power. The efficiency of such systems can be close to 90 percent.
How hydro power works
Hydro means "water". So, hydropower is "water power." Potential energy (or the "stored" energy in a reservoir) becomes kinetic (or moving energy). This is changed to mechanical energy in a power plant, which is then turned into electrical energy.
Water is stored behind a dam in a reservoir. In the dam is a water intake. This is a narrow opening to a tunnel called a penstock.
Water pressure (from the weight of the water and gravity) forces the water through the penstock and onto the blades of a turbine. A turbine is similar to the blades of a child's pinwheel. But instead of breath making the pinwheel turn, the moving water pushes the blades and turns the turbine.
The turbine spins because of the force of the water. The turbine is connected to an electrical generator inside the powerhouse. The generator produces electricity that travels over long-distance power lines to homes and businesses. The entire process is called "hydroelectricity".
Types of hydro facilities
The water used by hydro plants can be flowing in natural streams or rivers, or contained in man-made facilities such as reservoirs, pipelines, or canals. There are two main categories of hydroelectric power generation: conventional methods, which produce electricity via water flow in one direction; and pumped storage methods, which are both producers and consumers of electricity. In a pumped storage facility, water from a higher elevation reservoir flows to a lower elevation reservoir during peak demand periods -- such as during hot afternoons. During off-peaks periods, the water is recycled and pumped from the lower reservoir back to the higher reservoir to be used again during the next peak period.
Two types of conventional hydro plants are dams and run-of-the-river. Dams raise the water level of a stream or river to an elevation needed to create water pressure or "head." Dams can be constructed of earth, concrete, steel or a combination of such materials. Dams may create secondary benefits such as flood control, recreation opportunities and water storage.
Run-of-rive, or water diversion, facilities typically divert water from its natural channel to run through a turbine. The water it uses is usually returned to the channel downstream of the turbine.
Small or low-impact hydro may be a misnomer. Size of energy-producing facilities doesn't necessarily mean smaller environmental impacts. Hydro plants along small rivers or streams may be harmful to fish and other aquatic species. Of the roughly 2,000 private hydro facilities in the United States, about 89 percent can be categorized as small hydro.
The Low Impact Hydropower Institute, a nonprofit organization based in Portland Maine, is promoting the certification of environmentally responsible, "low-impact" hydropower. To date, the Institute has certified 19 hydropower facilities as Low Impact.