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	Hydroelectric

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Francis turbine (click for details) Pelton turbine (click for details)	Kaplan turbine (click for details)
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A hydraulic turbine is essentially composed of a modulating body, a distributor, and a wheel or impeller. The first convoys and regulates the water flow, the latter converts the kinetic energy taken from the water into rotational energy. From a construction point of view, to obtain the highest possible return there are 3 different types of turbine:

Pelton
A hydraulic turbine typically used with high jumps (50-1300 m) and small flows. Pelton turbines consist of a distributor with one or more nozzles (usually up to 6) in relation to the scope to be sent to the impeller and by a wheel, keyed on the drive shaft that transmits rotation to the electricity alternator. Each nozzle creates a stream, whose flow is regulated by a needle valve.

Francis
A hydraulic turbine with fixed rotor blades, typically used with medium or low jumps (from 10 to 250 meters) and medium flows. Francis turbines are characterized by the fact that water enters the impeller in a radial centripetal direction, and also by an axial exhaust. In fast Francis turbines, the feeding is always radial, while the discharge of water is usually axial; in these turbines the water moves as in a pressurized pipe: through a distributor (fixed body) it reaches the wheel (moving body) to which it gives up its energy, without entering at any time in contact with the atmosphere.

Kaplan
Hydraulic turbine with adjustable impeller blades typically used with high flow and low jump (from 5 to 30 meters). These are axial flow turbines, generally used for low jumps (2-20 meters). In Kaplan turbines, the blades of the wheel are always adjustable, while the ones of the distributor can be either fixed or adjustable. When both turbine blades and those of the distributor are adjustable, the turbine is a real Kaplan (or ‘double setting turbine’); if only the lades of the wheel are adjustable, then the turbine is a semi-Kaplan (or ‘single setting’).

The term “small hydro” is conventionally used for hydroelectric systems with a capacity up to 10 MW, which differ from plants with a higher capacity. In fact, while the latter require large barrages (dams) and extended artificial lakes for water accumulation, small hydro systems practically work like the old wind mills (obviously as a high-tech version), without almost any environmental impact.
On the contrary, they offer several environmental advantages. First of all they supply energy without emitting polluting substances, dust particles, heat and greenhouse gasses, thus helping to reduce local pollution and global warming.
From the point of view of energy, even if small hydro plants do have a limited individual capacity, they can be installed in arrays that include several systems, thus making a significant contribution to the national electricity production. In fact, this is an energy source that is considered essential to achieve European emissions reduction targets by increasing the amount of renewables that is deployed.