The main concept hydroelectric plants are based on is to transform the potential energy of resting mass of water and/or the kinetic energy of a water current into mechanic energy. Subsequently this energy will be converted into electric energy.
Hydroelectric plants are subdivided into big hydroelectric plants (or simply hydroelectric plants) and minor hydroelectric plants (or mini-hydroelectric plants). This subdivision depends on the power installed inside the plant and can take 10 MW as a reference value (actually in Italy minor hydroelectric refers to a maximum power of 3 MW).
This subdivision is usually reflected on different types of plants: while large hydroelectric plants usually require wide surfaces to be submerged, with a significant environmental and social impact, small hydroelectric plants perfectly integrate with the local ecosystem (it directly exploits the river current).
Hydroelectric power plants are also marked by great flexibility of use. Thanks to the modern automation systems, a few minutes are enough to make the power plant pass from the stand-by to the full power state. Thanks to this peculiarity, hydroelectric power plants are faster than thermoelectric power plants in increasing their production of electric energy during peak consumption hours. Therefore, the hydroelectric production process is convenient not only from the economic and environmental viewpoint, but also from the viewpoint of operating efficiency. Hydroelectric plants can also be defined according to the type of plant, i.e. regulated flow plants or flowing water.
Regulated outflow power plants
These plants are natural water basins (lakes) or artificial lakes (like many tanks) and sometimes the capacity of water basins increases by means of barriers (many times barriers are dams that are tens of metres high).
Flowing-water power plants
Flowing-water power plants were much more used at the beginning of the last century, above all to activate machine tools in some workshops. The potential of these plants today is less exploited than it could be.
How is a plant made
A hydroelectric plant usually includes five elements: a water collection system, a penstock a turbine transforming potential energy into mechanic energy, a generator converting mechanic energy into electric energy and a control system regulating the water flow.
Barrages intercept the watercourse in a specific area. There can be two different types of barrages which differ according to their dimensions: dams or weirs.
Small plants, small impact
In order to overcome the problems regarding the protection of the environment which the realization of hydroelectric power plants in areas that are particularly vulnerable and sensitive involve, the trend of the past years has been to progressively abandon the construction of large plants with a heavy impact on the environment.
Just like other types of renewable sources, hydroelectric energy is characterised by remarkable advantages as compared to the production of electric energy from fossil fuels. To begin with, it is a renewable and endless source.
Secondly, emissions of polluting substances into the air and water are virtually absent, since no combustion process is involved. In particular, carbon dioxide (CO2) emissions are reduced by 670 grams for each kW/h of energy output. Other advantages are: a low dependence on ester energy sources, source diversification and the regional re-organization of energy production.
Moreover, mini-electric plants, in many cases, thanks to their hydraulic arrangement, create many advantages to the watercourse (in particular to the regulation of floods in water streams, especially on the mountains characterized by soil deterioration), and can efficiently contribute to the protection and safeguarding of the territory.
In some cases, the artificial lake that forms as a consequence of a weir o dam can improve the surrounding area, by allowing the development of tourist, sports and productive activities that can coexist together with hydroelectric exploitation. The chance to accumulate water and then regulate its flow downhill can also contribute to reduce floods and encourage a better use of water resources, which are becoming more and more precious and rare.
Really clean energy?
Hydroelectric power suggests, in our mind, the idea of a clean source of energy, that is eco-compatible and especially a source of energy that is renewable. Actually, a large power plant has problems in connection with the environmental impact, problems of an aesthetical nature, electromagnetic pollution and overload of the ground.
With reference to the visual impact of large hydroelectric plants, they are difficult to hide and quite eye-catching. This is why it is necessary to carry out a careful assessment of the plant on the territory, by also making an aesthetical assessment.
Relation with the ecosystems
The relation with the ecosystems is fundamental when designing a hydroelectric power plant. Two aspects are strictly linked to the collection of superficial water and can provoke two different impacts…
Dams and the local climate
The presence of a dam influences the microclimate of the territories all around due to the large mass of water that collects upstream of the dam.