energy-science

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Energie hydraulique / Hydropower

Hydropower is power that is derived from the force or energy of moving water (water at work, water in motion). It can be seen as a form of solar energy, as the sun powers the hydrologic cycle which gives the earth its water. In the hydrologic cycle, atmospheric water reaches the earth=s surface as precipitation. Some of this water evaporates, but much of it either percolates into the soil or becomes surface runoff. Water from rain and melting snow eventually reaches ponds, lakes, reservoirs, or oceans where evaporation is constantly occurring.


Moisture percolating into the soil may become ground water (subsurface water), some of which also enters water bodies through springs or underground streams. Ground water may move upward through soil during dry periods and may return to the atmosphere by evaporation. Water vapor passes into the atmosphere by evaporation then circulates, condenses into clouds, and some returns to earth as precipitation. Thus, the water cycle is complete. Nature ensures that water is a renewable resource.

 

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Generating Power
To generate electricity, water must be in motion. This is kinetic (moving) energy. When flowing water turns blades in a turbine, the form is changed to mechanical (machine) energy. The turbine turns the generator rotor which then converts this mechanical energy into another energy form -- electricity. Since water is the initial source of energy, we call this hydroelectric power or hydropower for short.


At facilities called hydroelectric powerplants, hydropower is generated. Some powerplants are located on rivers, streams, and canals, but for a reliable water supply, dams are needed. Dams store water for later release for such purposes as irrigation, domestic and industrial use, and power generation. The reservoir acts much like a battery, storing water to be released as needed to generate power.

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The dam creates a head or height from which water flows. A pipe (penstock) carries the water from the reservoir to the turbine. The fast-moving water pushes the turbine blades, something like a pinwheel in the wind. The waters force on the turbine blades turns the rotor, the moving part of the electric generator. When coils of wire on the rotor sweep past the generator’s stationary coil (stator), electricity is produced.  This concept was discovered by Michael Faraday in 1831 when he found that electricity could be generated by rotating magnets within copper coils. When the water has completed its task, it flows on unchanged to serve other needs.

 

The diagram of a hydroelectric generator:

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Une production majeure dans de nombreux pays:
Dans le monde, une vingtaine de pays produisent plus d’un cinquième de leur électricité grâce à l’énergie de l’eau. Une dizaine de pays, dont quatre en Europe (Norvège, Islande, Autriche et Suisse), produisent plus de la moitié de leur électricité grâce à l’hydraulique. Contrairement à une idée reçue, les plus grands producteurs d’hydroélectricité ne sont pas des pays de montagne, mais des pays traversés par de nombreux fleuves et des rivières à gros débit et qui bénéficient, de ce fait, d’une ressource abondante.

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Une croissance continue dans le monde :
La production hydroélectrique est en croissance dans le monde, passant d’environ 1 000 TWh en 1965 à plus de 3 000 TWh aujourd’hui. Cette croissance est particulièrement importante en Amérique du sud ainsi qu’en Asie. Avec plus de 27 % de la production mondiale, l’Asie est le premier producteur d’hydroélectricité, devant l’Amérique du nord. Ce continent est également celui dont la croissance est la plus forte, avec une production ayant doublé ces 15 dernières années. Le potentiel de développement reste encore extrêmement important, notamment en Afrique, en Amérique latine et en Asie.
La croissance la plus forte provient de Chine, dont la production augmente d’environ 10% chaque année. Ce pays est devenu en 2004 le premier pays producteur d’hydroélectricité au monde devant le Brésil, le Canada et les États-Unis.

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Exemple de coûts moyens d'une centrale hydraulique

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