The greater the flow and head, the more electricity produced. The electricity is then transmitted to a substation where transformers increase voltage to allow transmission to homes, businesses and factories. Most hydropower plants are conventional in design, meaning they use one-way water flow to generate electricity. These plants use little, if any, stored water to provide water flow through the turbines. These plants have enough storage capacity to off-set seasonal fluctuations in water flow and provide a constant supply of electricity throughout the year.
Large dams can store several years worth of water.
In contrast to conventional hydropower plants, pumped storage plants reuse water. After water initially produces electricity, it flows from the turbines into a lower reservoir located below the dam. Most hydropower plants are built through federal or local agencies as part of a multipurpose project. In addition to generating electricity, dams and reservoirs provide flood control, water supply, irrigation, transportation, recreation and refuges for fish and birds. Private utilities also build hydropower plants, although not as many as government agencies.