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How a small hydroelectric plant works

A small hydroelectric plant does not always require tall waterfalls and large quantities of water.

In addition to “water drop” plants, there can also be some small “running water” hydroelectric plants, which exploit the flow of water instead of the power generated from the drop. Small hydroelectric plants exploit the kinetic energy (related to movement) of streams and rivers.

Water is collected via intakes and conveyed through channels or pipes to a charge basin where the upper free surface needed to calculate the drop required by the small hydroelectric plant is determined. From this point onwards, water reaches the turbines by means of penstocks and its passage through the moving parts, also known as impellers, produces rotation.

The impeller shaft is connected to an alternator that generates electricity. The water leaving the turbine is released, by means of the restitution works, into its original channel at a level which determined by the lower free surface.


A small hydroelectric plant is made up of civil and hydraulic components:

  • intake works: these change the configuration according to the type of watercourse used and the orography of the area;
  • filtering works: these serve to remove large suspended bodies from the water and the type of works depends on the amount of water involved and the type of the solids in the water flow;
  • conveying works: these consist of channels or penstocks depending on the orography and consequently the type of plant with a low or high water drop;
  • restitution works: these channel the water back to the main watercourse.