Water that falls from a certain height to a lower level provokes the movement of hydraulic wheels or turbines producing kinetic energy and finally electricity. Its production costs are very low which makes it a very profitable energy with high installation costs.

To develop this form of energy, reservoirs, dams, derivation channels need to be built, along with large turbines and electricity-generating equipment. All these elements mean that large sums need to invested. For this reason, hydraulic energy is not competitive in areas where there are large amounts of oil or coal.

A little history
The Romans and Greeks already knew how to harness the power of water to grind wheat. However, the use of slaves and beasts of burden slowed down the generalised use of this type of energy until the 12th century.

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In the Middle Ages, mills equipped with large hydraulic wooden wheels developed a maximum power of 50 horse power. Hydraulic energy owes its great development to the British civil engineer John Smeaton, who was the first to incorporate large cast iron hydraulic wheels.

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Hydroelectricity was of vital importance to the Industrial Revolution. Although steam engines were already in use, coal was scarce and wood was not efficient enough as a fuel. Hydraulic energy helped the new industrial cities to grow in Europe and the United States up until the construction of canals in the mid-19th century, which supplied coal at low cost.

The development
The first hydraulic plant was built in 1880 in Northumberland in the north of England. The rebirth of hydraulic energy came about as a result of the development of the electric generator, followed by the improvement of the hydraulic turbine and the increase in demand for electricity that coincided with the start of the 20th century.

In 1920 the hydraulic plants generated a large proportion of the total electricity production. The technology of the first installations has remained basically the same throughout the 20th century.

There are now large numbers of hydraulic plants, which are classified according to their technical characteristics, their location and their function. Some use water that runs naturally along a riverbed and some use water that is stored in a reservoir or in a lake. Depending on the height of the waterfall or the drop, the plants can be of high, medium or low pressure, and so on.

Negative effects
-Hydraulic energy alters the course of a river and, in turn, the natural development of the animal and vegetal life of the river.
-The reservoir plants provoke the evaporation of the water, which increases the relative humidity of the areas in which they are located.
-Some studies have suggested that the reservoir plants located in tropical areas can become focal points for infections, bacteria and diseases as a result of the water's stagnation.

Did you know...?

-Hydroelectricity accounts for around a quarter of global electricity production. In Norway (99%), Zaire (97%) and Brazil (96%) this type of energy constitutes the most important source of electricity.

-The Itaip� plant, along the Paran� river between Brazil and Paraguay, was inaugurated in 1982 and boasts the world's largest generating capacity: 14,800 MW (megawatts).

-Reservoirs have a limited life. This is generally shorter than expected due to the accumulation of organic and mineral elements that are carried along by the rivers. It is estimated that around 50 cubic kilometres of sediments (around 1% of the total storage capacity) are caught every year in the reservoirs.

-The sea can also produce electricity. The movement of waves moves small generators that supply electricity to signalling buoys and low power sea lighthouses. The rise and fall of the tide, trapped by dams, can move large generators as, although the height difference is not large, the quantity of water displaced is enormous.