Hydroelectric energy

The hydroelectric energy , or hydroelectricity , is a electrical energy obtained by conversion of the hydraulic power of various flows of Eau (rivers, rivers, falls of water, currents marine…).

The kinetic energy of the water current is transformed into mechanical energy by a Turbine, then in electrical energy by a Alternateur.

Hydroelectric energy is a renewable energy. She is also regarded as a clean energy, although she is the subject sometimes of environmental disputes, either because of its land influence, or more recently on its assessment carbon.

The hydroelectric power installed in the world in 2004 was estimated at 715 gigawatts (GW), that is to say approximately 19% of the world electric output. Nearly 15% of the electric output installed in Europe hydraulic east of origin.

However, the hydroelectric proportion of energy is quite less (of about a 10%) that the working installed capacity can make it believe, because this last cheek a particularly important role to ensure the instantaneous balance of the production and consumption of electricity. Indeed, electrical energy is practically not stored and this is why hydroelectric energy is often a variable of adjustment. In France, for example, the working installed capacity is of 25 GW, that is to say 22% of the whole of the power stations contributing to the food of the public networks whereas the production accounts for only approximately 15%.

Techniques of hydroelectric energy production

Electrical energy is produced by the kinetic energy conversion of water, via a wheel actuating a rotor of alternator. The mechanical unit located around the driving wheel is called " the turbine". There exist 3 types of turbines, quoted below. The choice of the type of turbine more adapted is made by the calculation of the noted specific Speed NS .

Turbine Pelton

Adapted to the high falls, with a scoop wheel, invented by To ballast Allan Pelton.

Turbine Francis

Rather gone up for average falls, to see the high ones, with a paddle wheel simple or double. Conceived by James B. Francis.

Turbine Kaplan and Hélice

Perfectly adapted to the low falls and strong flows, with a standard wheel propeller, like that of a boat. Viktor Kaplan developed a wheel with propeller whose blades can be directed according to the flows usable.

Various forms of hydroelectric energy production

One can distinguish three principal forms from hydro-electric energy production:
  • the power stations known as gravitating for which the contributions of water in the reserve are only gravitating
  • the stations of transfer of energy per pumping, for which an artificial device makes it possible to pump the water of a lower basin towards an upstream reservoir. Besides those Ci include/understand frequently a gravitating part.
  • the tidal power plants in the broad sense which use the energy of the movement of the seas, that it is about the alternate flow of the tides (tidal in a strict sense), the permanent marine currents (hydroliennes in a strict sense) or of the movement of the waves.

Gravitating power stations

See also: Small hydroelectric station

One can classify them according to three types of operation, determining a different service for the electric system. This classification is done according to the constant of emptying, which corresponds to the theoretical time which would be necessary to empty the reserve while harnessing with the maximum power.

In France one distinguishes as follows:

  • power stations called to the current whose constant of emptying is lower or equal to 2 a.m.;
  • the lockfuls whose constant of emptying lies between 2 and 200 hours;
  • the lakes whose constant of emptying is higher than 200 hours.

The power stations known as with the current , mainly installed in zones of plains present for these reasons of reserves low height. They use the flow of the river such as it is presented, without significant capacity of modulation per storage. They provide an energy bases some far from expensive. They are typical the installations carried out on the important rivers like the Rhone and the Rhine.

The lockfuls present more important lakes, allowing them a modulation in the course of the day even the week. Their management makes it possible to follow the variation of consumption on these horizons of time (peaks of consumption of the morning and the evening, difference between working days and week end…). They are typical installations carried out on average mountain.

The lakes correspond to the works presenting the most important tanks. Those allow a seasonal storage of water, and a modulation of the production to pass the peaks of load of electricity consumption: the summer for the countries where the peak demand is determined by air-conditioning, the winter for those where it is determined by the heating. They are typical installations carried out on average and high mountain.

It is also possible to classify the power stations according to the characteristics of filling of their tank, which induces certain constraints in the electric use which can be made about it. One will distinguish for example, the tank whose filling can statistically be obtained in a weekly way, seasonal, even pluri-seasonal.

Finally one can also classify the works according to their drop height, i.e. the difference in altitude between the theoretical mirror of the full tank and the turbine. This drop height notably determines the types of turbines used.

One distinguishes as follows:

  • the high falls (> 200 m)
  • average falls (between 50 and 200 m)
  • the low falls (< 50 m)

Between these three types of classification, there does not exist strict equivalence but a strong correlation. The power stations with the current in general have characteristics of filling daily with regular contributions, and low drop height; the lockfuls have characteristics of filling daily influenced by the season (season of raw) and drop heights average, more rarely high; finally the lakes have filling in general seasonal (cast iron of snows or rain season) and important drop heights.

STEP: Station of Transfer of Energy per Pumping

These power stations do not produce their energy solely starting from the natural flow, but they allow, in pumping mode, to store the energy produced by other types of power stations when consumption is the low for example night and to redistribute it, in treatment by turbine action mode, at the time of the peaks of consumption.

These power stations have two basins a superior and an inferior between whom is placed a reversible hydroelectric machine: the hydraulic part can function as well in Pompe, as in Turbine and the electric part as well in Moteur as in Alternateur (synchronous Machine). In accumulation mode the machine uses the current provided to go up the water of the lower basin towards the upstream reservoir and into production mode the machine converts the gravitational potential energy of water into electricity. The output (relationship between electricity consumed and produced electricity) is about 82%.

This type of power station is interesting for the regulation between supply and demand, in countries equipped with large production centres (such as nuclear plants) and not having sufficient natural capacities hydroelectric production in the form of stoppings. It can also find its interest in the storage of the energy produced starting from less controllable modes of production, such as the wind energy, and compensate for the falls of wind.

The energetic efficiency is not very significant since the energy used at the base is an energy which would be lost (stoppings with the current, nuclear vapor of origin), on the other hand, restored energy thus replaces supplements made up of fossil energy with greenhouse effect (coal, gas turbines), consequently, the financial output is very favorable since at this hour of restitution, the industrial connections see gratifier of tariffs of point and very high penalties in the event of going beyond of the contractual demand (integration of the strongest power over one 10 minutes period and observed over one month). On the other hand, the annual peak hour (expenditure of production) increases three times more quickly than the yearly consumption (receipts of production) and is located at the neighborhoods 19 hours in France.

The most known STEP in France is in the valley of the Water of Olle (in the Alps), and connects the lake of Verney (retained downstream) to the Barrage of Grand' Maison (retained upstream).

On the other hand, oldest seems to be that of the Black Lac in the the Vosges, slope Alsatian, of the name of the lake associated with the White Lac. Conceived, in the Years 1930, to control the production of the stopping to the current of Kembs, on the the Rhine, its introduction was the theater of a tragedy where all the personnel perishes except for a survivor. It was brought into service after having equipped the pipe pressure, of a hundred meters of unevenness, of a chimney of balance against the water hammers and located at horizontal at the top of the rebuilt building.

A great project of construction supported by hydroelectric Europe of factory called to produce 560 million kWh per annum, is the equivalent of the food of a town of 280.000 inhabitants will be completed in the years to come, it is the " project; Romanche" news; on the commune of Livet-and-Gavet, the amount of the investment amounts to 150 M€, assured to a total value of 80 to 90% by EDF. It is an underground power station equipped with two Francis turbines, built with the current, which will allow a better use of the hydraulic force in the Vallée of Romanche.

Leif-Erik Langhans, of the the Ruhr-Universität of Bochum, also studied a system of wind coupled to a hydro-electric power station with pumped reserve. Surplus wind energy is used to bring water in an elevated basin. In the event of deficit of energy, this water reserve passes through producing turbines of electricity.

Tidal power plants

See also: tidal Energy

A tidal power plant is an hydroelectric station which uses the energy of the Marées to produce electricity.

starting from the waves

See also: energy of the waves

The Japan was interested the first in the resources of the Houle as from 1945, followed by the Norway and the the United Kingdom. At the beginning of the month of August 1995, the Ocean Swell Powered Renewable Energy (OSPREY), the first powerplant using the energy of the waves, is installed in the north of the Scotland. The principle is the following: the waves penetrate in a kind of Caisson immersed, opened at the base, push air in the turbines which actuate the alternators generating electricity. The latter is then transmitted by underwater Câble to the coast, distant of approximately 300 meters. The power station had a power of 2 MW. Unfortunately, this work, damaged by the waves, was destroyed one month later by the tail of the Cyclone Felix. Its creators do not discourage themselves. A new machine, less expensive and more powerful, is currently developed. It must make it possible to provide electricity to the small islands which miss some and, to feed a desalination plant of sea water.

starting from the marine currents

See also: Hydrolienne

A project of the British company Marine Current Turbines envisaged to use hydroliennes (kind of underwater “wind mills”) which would use the marine currents in a way similar to a propeller of boat to produce electricity.

Cost of the hydroelectricity

In spite of generally high costs of realization, the costs of maintenance are reasonable, the installations are designed to last a long time, and the energy of water is free and renewable if it is well managed. Thus the assessment is rather positive, it is one of the most profitable systems of production of electricity; moreover it is one of most flexible.

Use of the hydroelectricity

Hydroelectric energy is storable, it can thus be used points of it, i.e. when the demand is keenest on the electric public network of distribution.

On the other hand, the production of hydroelectricity is limited by water reserve available, which depends on the Climat and pumpings carried out upstream of reserve for domestic water and the Irrigation.

Environmental impacts

The hydroelectricity is regarded as an clean energy and inexhaustible, contrary to the Pétrole or the Natural gas.

The use of energy of hydraulic pressure supply rather than coming from nonrenewable sources is overall positive for the environment. However the environmental impacts can be very important, especially at the time of the installation of often heavy structures allowing the hydraulic recuperation of energy.

These impacts vary with the type and the size of the structure installation: they are weak if it is a question of exploiting the natural water falls, the marine currents, the waves, but they become very important if it is a question of creating stoppings and artificial reserves of water. It should be noticed that in the projects of stoppings, the production of hydroelectricity is, most of the time, secondary compared to other aspects such as the control of the flow of a river (avoidance of the floods), the water supply of channels, the accumulation of water stocks.

Whatever the size of the installation, it is necessary nevertheless to make serious studies of incidence on the environment before building a hydraulic installation and adopting compensatory measures such as scales with fish. In the past, the built stoppings led to the depopulation of the river migrating in cash (eels, salmons,…). To this point of view, the situation of the European rivers tends to improve slowly.

The gas assessment with greenhouse effect of the hydroelectric systems is definitely positive. It is necessary nevertheless to hold account which it is necessary several years before the CO {{sub|2}} spent during its construction is compensated by produced electricity.

Called into recent question of the environmental impacts

Certain recent research expresses very serious doubts on the gas assessment with greenhouse effect of the hydroelectric systems. The bacteriological activity in the water of the stoppings (especially in tropical areas) would slacken enormous quantities of methane (gas having an greenhouse effect 20 times more powerful than CO2) (See: Stoppings more polluting than the coal stations or the original article in English: . See also)

See too

External bonds

  • Large Dixence
  • Article detailed on the stoppings and hydroelectric energy
  • Hydro Quebec
  • hydroelectric Energy
  • Center of expertise on the hydroelectricity and its impacts on fish and the habitat of the fish Fishings and Oceans Canada

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