How Do Hydroelectric Dams Work?

Hydroelectric dams provide a source of renewable energy all over the world. Their basic principle of operation is not difficult to understand. For years, and even today, water wheels were used for grinding grain into flour and the same wheel principle can produce electricity.

In the case of a hydroelectric dam the wheel is a turbine. As water flows from a high point to a lower point by gravity it must turn the turbine propeller. The flowing water produces a mechanical energy. The mechanical energy is what turns the turbine propeller. A shaft is attached to the propeller that goes up into a generator. This generator contains a rotor and a stator.

The generator operates on principles discovered by Michael Faraday, (1791 - 1867). When a magnet moves past a conductor, electricity will flow. The rotor on the generator is basically a large magnet. As it turns from the mechanical energy of the water it moves rotationally inside the stator. The stator is the conductor in this power process. The movement of the magnetic rotor past the conductive stator produces electricity and creates voltage that will develop at the output terminals of the generator.

A dam must be built on a large river or body of water that has a sizable drop in elevation. The dam itself builds up the pressure of the water that it is holding back. At the bottom of the dam wall will be an opening, or penstock, that the water will flow through due to gravity. The turbine is on the other end of the penstock, before the opening to the next section of river or lake. The higher the elevation of the first body of water, and the more water the dam is holding back, the more mechanical power that can be produced. The more mechanical power that is obtained, the more electrical power that can be generated.

Any moving water source can be used to produce energy, even ocean waves and tide movement can be used. Hydropower dams are considered to be about 90 percent efficient. Water is not destroyed by its use to create power and it is therefore considered to be a renewable energy source.

About 24 percent of the world's power is supplied by hydropower. The global output is approximately 675,000 megawatts and is equivalent to over 3.5 billion barrels of oil. There are more than 2,000 of these hydropower plants operating in the U.S. alone. The Hoover dam and Niagara Falls are only two of the many power plants operating today.

References:

http://ga.water.usgs.gov/edu/hyhowworks.html

http://www.phy.hr/~dpaar/fizicari/xfaraday.html

http://www.globalchange.umich.edu/globalchange2/current/lectures/dams/dams.html

http://www.howstuffworks.com/hydropower-plant.htm