The water cycle, triggered by the evaporation of the Earth’s water, the formation of clouds and rain, provides mankind with the most extraordinary renewable energy source, the second after biomass. Its origin is once again the sun, the radiation of which causes evaporation. Although only 0.33% of solar energy received by the Earth leads to rainfall, it is still a remarkable amount of energy. Water includes two types of energy: potential and kinetic.
Both when it falls down as rain and when it comes out of a spring, water is forced to go “downwards” due to force of gravity. We all can see the energy of a waterfall; the higher the jump, the more energy will be produced by the water when it falls. Therefore, the higher the water is located with respect to the point of arrival, the more the energy that can be potentially developed. Potential energy is therefore the energy of the water mass at rest, according to the initial position of water and its point of arrival. It corresponds to the energy contained in the glaciers and natural or artificial basins located at high altitude.
Water kinetic energy is the energy of a moving water mass and corresponds to the energy contained in the water of rivers, water streams and the sea. It depends on the speed and the volume of the moving water. Hydraulic machines transform water movement into mechanic energy. It is simple to convert mechanic energy into electric energy.
How to obtain energy
Two procedures are available to obtain energy from fresh water: water wheels and hydroelectric power plants. The former produce mechanic energy, the latter electricity. Water is a source of energy marked by numerous advantages known by mankind.
Where it is
Water energy turned into hydroelectric energy a little more than a century ago and it has undergone a very rapid development which is still continuing in industrialised countries and developing countries of Asia and Latin America, potentially rich in resources. Also in terms of exploitation of available hydroelectric resources, Western Europe and the United States are the world leaders and use almost all the available resources.
Hydroelectric power in Italy
In Italy 40.7% of energy produced in 2020 by renewable sources comes from hydroelectric. According to the data of GSE (Gestore dei Servizi Elettrici), at the end of 2020, the hydroelectric power produced in Italy amounted to 47.552 GWh.
Compared to the other renewable sources, hydroelectric power has already reached a very high level of utilization of resources. The large hydroelectric power plants in fact have almost all been built. The road to follow in the future will be that of minor hydroelectric plants (mini-and micro-hydroelectric) with small plants serving isolated utilizers, that have the possibility of exploiting the water resource that is available in the vicinity.
A bit of history
Thousands of years ago mankind learned how to exploit the mechanic energy produced by falling water. The Greeks and Romans already used water mills to grind wheat. In Barbegal, France, and near Arles, an important port supplying Rome with wheat, 8-wheel water mills were found exploiting the same river at the same time (310 A.D.).
Most of the mountain regions in areas with a humid and temperate climate, including Italy, have a high production of hydroelectric power. This is an important item in the national energy accounts.
The water of the mountain torrents flows down great drops, which determine an optimum energetic potential, but generally the outputs of the torrents are too variable to be exploited continually. Glacier melt waters guarantee a supply of large quantities of water in the summer season, when the other courses of water have run dry. It is sufficient to compare, with equal precipitation, the summer output of water courses in the Alps and in Central and Southern Italy, to realize the importance of the existence of glacier bodies in the surface water regimen.
For this reason many hydroelectric plants in the mountain areas are fed by ice melt waters, and in very many cases water is tapped directly from the torrents that form from the glaciers. Countries like Switzerland, Austria, Italy and New Zealand were among the first to exploit the productive potentiality of ice waters. At the start of the Seventies, 64% of the energy requirement in Switzerland was covered by the production of the hydroelectric power plants, that were mostly fed directly or indirectly by water melting from the glaciers. In the Italian Alps, there are a number of examples in the mountain regions in the north, in the regions of Piedmont, Valle d’Aosta, Trentino-Alto Adige and Lombardy, where the presence of glaciers enables an intensive use of water as a source of energy.
The state of the glaciers
With only very few exceptions, glaciers around the world are receding, a phase which began at the beginning of the last century and briefly interrupted by a small advance of the alpine area around the 1980s.
Advantages of power from glaciers
There are many advantages in using glacier melt waters for the production of hydroelectric power. Glaciers are a source of water that is constant and sure during the summer months, unlike the water of rivers and torrents whose capacity is subjected to remarkable variations depending on precipitation.
Problems and solutions
Apart from the problem of having almost reached the maximum limit in the exploitation of this resource, a fact that has already been mentioned, the utilization of glacier melt waters for the production of hydroelectric power involves some technical problems, which have important economic repercussions.