Finally, fossil fuel use also produces particulates, including dust, soot, smoke, and other suspended matter, which are respiratory irritants. In addition, particulates may contribute to acid rain formation. This is the reason why there has been exploration into clean power sources.
Hydroelectric is one of the oldest forms of clean power. Hydropower converts the energy of flowing water into electricity. Today's hydropower plants generally range in size from several hundred kilowatts to several hundred megawatts, but a few large plants have capacities up to 10,000 megawatts and supply electricity to millions of people. Most hydropower plants are conventional in design, meaning they use one-way water flow to generate electricity. There are two categories of conventional plants, run-of-river and storage plants. The Run-of-river plants use little, if any, stored water to provide water flow through the turbines. Although some plants store a day or week's worth of water, weather changes especially seasonal changes cause run-of-river plants to experience significant fluctuations in power output. Where as the Storage plants have enough storage capacity to offset seasonal fluctuations in water flow and provide a constant supply of electricity throughout the year. Large dams can store several years" worth of water. Then there is pumped storage which reuses water. After water initially produces electricity, it flows from the turbines into a lower reservoir located below the dam. During off-peak hours some of the water is pumped into an upper reservoir and reused during periods of peak-demand. Most hydropower plants are built through federal or local agencies as part of a multipurpose project. Hydroelectric plants have a preventive start up cost, but once it is built the cost to maintain it is low. In addition to generating electricity, dams and reservoirs provide flood control, water supply, irrigation, transportation, recreation and refuges for fish and birds.
