Introduction

Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator.Less common variations make use of water's kinetic energy or undammed sources such as tidal power.Hydroelectricity is a renewable energy source..
For more information about the topic Hydroelectricity, see the following related articles:

Power station — A power station or power plant is a facility for the generation of electric power. At the centre of nearly all power stations is a generator.

Water turbine — A water turbine is a rotary engine that takes energy from moving water. Water turbines were developed in the nineteenth century and were widely used.

Distributed generation — Distributed generation is a new trend in the generation of heat and electrical power. The concept permits the "consumer", who is generating heat.

Electric power — Electric power is the amount of work done by an electric current in a unit time. When a current flows in a circuit with resistance, it does work.

Hydro energy is a Renewable source of energy that can be replenished on a time scale appropriate to human use. Solar energy for growing plants for food is renewable because light flows continuously from the sun, and plants can be reproduced on a time scale suitable for human needs. Coal is produced continually in some geologic formations, but the time scale is on the order of hundreds of thousands of years. Accordingly, coal is considered a nonrenewable energy.

The Department of Energy categorizes sources of nonrenewable energy production as fossil fuels, nuclear electric, and pumped hydroelectric. Sources of renewable energy are delineated as conventional hydroelectric, geothermal, biofuel, solar, and wind. Conventional hydroelectricity and energy from biofuels are considered mature sources of renewable energy; the remaining types are thought of as emerging.

More electric energy is invested in pumping water for pumped storage hydroelectricity than is produced by the electric generators. Therefore, the net production of electricity from pumped hydro sources is slightly negative and does not appear on the chart inFigure 1. A breakdown of the 9.57 percent contribution from renewable sources is shown in Figure 2. The great bulk of the energy produced from renewable sources is from biofuels and conventional hydroelectric systems, both of which are considered mature.

Nonrenewable energy such as coal, petroleum, and natural gas are vast but not inexhaustible. A nonrenewable resource can be preserved if it can be replaced with a renewable one. This is the prime attraction of renewable energy. Sometimes a renewable resource offers an environmental advantage. If a house heated by burning fuel oil could instead use a solar heating system, then products from burning that might contribute to environmental problems would not be released into the atmosphere. On the other hand, damming a river to make a reservoir for a hydroelectric power plant might inflict damage to the environs by destroying plant and animal habitat.

Most use of renewable energy involves the sun. Solar energy is converted to thermal energy for space heating, heating hot water for domestic use and, to some extent, for generating electricity. A photovoltaic cell, which functions like a battery, converts solar energy directly to electric energy. Biomass energy has its origin in plants grown with the help of solar radiation. Wind energy is due to unequal heating of Earth's surface by the sun. A hydroelectric plant converts the gravitational energy of water into electricity, but the mechanism that replenishes the water is powered by the sun. Roughly, 95 percent of all renewable energy is solar in origin. The remainder is from geothermal energy. Tidal energy, having its origin mainly in the gravitational force between Earth and Earth's moon, is used in some parts of the world (France, for example), but is yet to be exploited in the United States.