The main renewable energy source for producing electricity in Italy comes from hydropower. Hydropower is renewable, that is, it can be considered inexhaustible as long as the water cycle exists. In fact, the two main characteristics of hydropower are:

  • The water cycle: water evaporates from the oceans by the heat of the sun’s rays. Water vapor rises into the sky and condenses due to low temperatures, shaping clouds. Reaching a certain weight, the water droplets enclosed in the new ones precipitate to earth as rain, hail or snow, which give rise to rivers and streams or fall into the seas and oceans;
  • The force of gravity, which guides the water in rivers to flow to the sea and to some extent also that in lakes. Melting glaciers also form water that flows to the sea or oceans, feeding the water cycle. All water masses found at high altitudes are endowed with a considerable amount of gravitational potential energy.

The most important component of a hydroelectric plant is undoubtedly the hydroelectric turbine, which converts the kinetic energy of water into mechanical energy; the latter sets the alternator in motion, transforming it into electrical energy, which, through the transformer, increases its intensity to be fed into the grid.

Depending on the water flow rate and elevation difference, three types of water turbines are distinguished:

  • Pelton turbine: this is the highest efficiency action turbine, that is, it can totally convert the potential energy of water into kinetic energy. It works like the water wheel in old mills, but much more efficient: water is conveyed into a pipe that sends it to a nozzle, which increases the speed of the water jet hitting the impeller blades. It is used for large jumps, from 300 to 1,400 meters, and for small water flows, less than 50 cubic meters per second, in order to achieve higher speeds. It can generate a power of up to 200MW.
  • Francis turbine: this is the most widely used type of hydraulic turbine. It is called reaction driven, because in addition to the speed of the water it also exploits its pressure, and it is centripetal flow, because the water reaches the impeller through a spiral duct and invests its blades thanks to a distributor that directs the flow of water by moving axially.

It is used for medium height differences, from 10 to 300-400 meters, and water flow rates from 2 to 100 cubic meters per second. It can generate up to 800MW.

  • Kaplan turbine: is an axial-flow reaction turbine. It works like a ship’s propeller: the flow of water that turns the impeller blades moves axially with respect to the axis of rotation of the impeller. Its special feature is the ability to adjust the angle of incidence of the blades: this provides excellent performance for small gradients and large variations in load.

It is used for minimal gradients, from 2 to a few tens of meters, and large water flow rates, above 200-300 m³/s. It can generate up to 400MW.


Hydropower includes several applications that take advantage of water turbine technologies both for their own self-consumption and for the sale of energy itself. These include:

  • natural watercourses;
  • irrigation canals;
  • aqueduct penstocks (for drinking or industrial use);
  • discharges of industrial wastewater or sewage treatment plants.

In particular, hydropower plants enable the reclamation of marshy areas and reduce the risk of flooding by containing watercourses by means of artificial dams. In this way, they can precisely control the amount of water that is released.

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Hydropower plants also make it possible to replenish water supplies in preparation for periods of drought. Reservoirs can act as water reservoirs that allow irrigation of fields even when there is little water available.

Hydropower plants fall into three types:

  • Run-of-river: they make use of the natural flow, that which is available, of watercourses, and because of this, power generation is not constant, but depends on seasonality and weather conditions. They are installed near rivers or streams to channel the water to a reservoir with a system of pipes (not forced) and made to flow to a restitution channel located lower down, which feeds it back into the river or stream. In the middle of this journey, the water passes through the hydroelectric turbine blades producing electricity. In this way, electricity is produced without any waste of water.
  • Reservoir: they function like run-of-river ones, except that the water comes not from a river or stream, but from a reservoir, that is, a natural lake or an artificial dam that acts as a reservoir. In this case, the water passes through penstocks to reach the hydraulic turbine.
  • Pumped: these are formed by two reservoirs placed at different levels, into which water can descend by penstock from the upper reservoir or can be pumped from the lower reservoir using electricity. When the demand for electricity is reduced, such as during the night, excess energy is used to return water to the upper basin, thus ensuring the stability of the power grid.

This mechanism allows electricity to be produced in a short time. In fact, the speed with which electricity is produced is one of the major advantages of hydropower plants.


Hydropower is considered the energy of the future. It is one of the cleanest sources of energy supply, with a potentially infinite renewability rate.

Its main advantages are:

  • Zero CO2 emissions: it is a completely clean energy that does not pollute the environment
  • Efficiency of 90 percent or more, thanks to water turbines: this means that almost all the potential energy of water becomes electricity
  • Flexibility: they make it possible to quickly vary the production of electricity according to the amount of water being delivered to the turbine, allowing a rapid restoration of grid balance should the need arise, in a time on the order of a few minutes
  • Minimal maintenance and operating costs.

However, there are also disadvantages:

  • High initial investment, since in addition to the cost of water turbines, generators, switchboards and control systems, various civil and hydraulic works have to be carried out, such as dams with weirs, penstocks, the power plant building, etc;
  • Weather dependence, as hydropower plants are very sensitive to climate change and possible drought periods
  • Ecosystem changes: construction of dams and penstocks could not only experience coastal erosion phenomena but can also alter flora and fauna.

Salmon, for example, are unable to spawn during migration, although some technologies such as the mound ladder are able to help them cross dams.

Finally, hydropower plants can damage riverbeds due to lack of oxygen in the water, altering the chemical balance of ecosystems there.

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