Renewable Energy Sources in the United States

Hydropower refers to using water to generate electricity. Water is the most common renewable source of energy in the United States today. Many hydroelectric power plants use a dam on a river to store water. Water released from behind the dam flows through a turbine, spinning it, which then turns a generator to produce electricity. Electricity generated this way is known as hydroelectricity, and it accounts for about 7% of the electricity used by the nation. Hydroelectric power doesn't necessarily require a large dam – some hydroelectric power plants just use a small canal to channel the river water through a turbine. A small or micro-hydroelectric power system can produce enough electricity for a home, farm, or ranch.

The Tazimina project in Alaska is an example of a diversion hydropower plant. No dam was required.Dam sites for hydropower plants are limited both by available rivers and by competing uses for those rivers, such as recreation, tourism, industry, and human settlements. Because of such limitations, water power could never generate all the electricity used in the United States. In addition, environmental impacts are considered when locating dams. While all hydroelectric dams have some environmental impact, the impacts vary widely, and current regulations and policies attempt to address environmental concerns. A dam may either create a reservoir or may be a run-of-river project that does not store large amounts of water but simply takes advantage of a river's natural flow. A dam that Fish ladder.creates a reservoir may flood a large area upstream, and can change flow patterns and impact flooding downstream with resulting environmental consequences, either positive or negative. Fish migration, which has long been a concern associated with dams, is often addressed with fish ladders and other structures to ensure the successful movement of fish both upstream and downstream. In addition to power, dams often provide other benefits such as recreation opportunities on upstream reservoirs, habitat for a wide variety of aquatic and terrestrial species, diversion of water for irrigation, and control of destructive flooding and environmental damage downstream. Hydropower is one of the least expensive sources of electricity and areas with good sources of hydropower tend to attract industries with large needs for electricity. Major hydroelectric dams in the United States are found in the Northwest, the Tennessee Valley, and on the Colorado River.