Conoscere l’energia eolica

Aeolian energy is the energy that derives from the wind. Men have used its power since ancient times to navigate or to move windmill blades, to grind cereals, to squeeze olives or pump water. Only in the last few decades wind energy has been used to produce electricity. The word “Aeolian” comes from Aeolus, the Greek god of wind, whose name “aiolos” means “fast”.

Electric power is obtained by exploiting the kinetic energy of the wind that makes the propeller blades move. These are connected to a generator that transforms mechanic energy (blade rotation) into electric power. These modern windmills are called aerogenerators.

Wind formation

Wind is an atmospheric phenomenon due to the heating of the sun. The sun radiates on the Earth a power of 1.74 x 1017 Watts: about 2% of it is converted into wind energy. The Earth releases the heat received from the Sun, but this is hardly homogeneous.

How to measure the wind

A wind is described by two parameters: the strength (related to speed) and direction. We all know that the wind is not constant, as its strength and direction change. The wind direction can be observed by simply using a weathercock.

Wind circulation on the Earth

Air masses are moved by solar heating and in particular by the difference in temperature (gradient) between equatorial and tropical areas. Solar radiation in equatorial areas is more intense than in tropical areas.

The wind and land roughness

The speed of the wind depends, as well as on atmospheric parameters, on land conformation. The rougher the land, the more sudden inclination variations it has, the more forests, buildings and mountains, the more obstacles the wind will meet, the more its speed will be reduced.

A bit of history

Man learned how to use the kinetic energy of the wind thousands of years ago. Sailing dates back to at least 10,000 years ago. The first wind mills of which rests were found were Persian and date back to 200 B.C. They were built in a very simple way, with sails mounted on wooden frames.

Research is trying to solve what at present is the major problem of the production of wind energy: the discontinuous nature of the supply of energy due to the irregular wind regime. It must be pointed out that the gross efficiency of wind power plants, expressed in MW, defines the quantity of energy that can be produced in a determined period of time in which the plant operates, and it is the parameter that is considered in order to compare the productive possibilities of wind power generators with one another. However it must be considered that due to various factors, and first of all the variability of the wind, a wind power generator never operates for 24 hours a day for the whole year, but only for a certain number of hours. When the wind blows at speeds that are too low (v < 5-4 m/s) the generator does not produce energy, while when the wind speed is too high (v > 20-25 m/s) the plants must be shut down for safety reasons. Therefore, a very important factor, in order to determine the productivity of the plants, is the number of hours of operation. In Italy the plants that operate for the greatest number of hours generally operate for about 3,200 hours a year (i.e. for about 38% of the time, considering that in a year there are 8,760 hours). However, the Italian national average is much lower, it amounts to 1,700 hours a year. In order to solve this problem and increase the number of hours of utilization, research is trying to develop rotors that can produce energy and operate safely also with very low or very high speed winds. However, there are limits beyond which no further improvement is possible, especially with regard to the efficiency at low speeds.

Aeolian production worldwide

In the last years we have assisted at an exponential growth of aeolic power installed and production of electricity generated by wind. In 2021 a power of 102 GW has been installed worldwide, reaching a total power rising up to 845 GW: biggest contributors were China (282 GW), USA (178 GW), Germany (62 GW), India (38 GW), Spain (27 GW), with Europe as a whole covering 29% of world aeolic power.

Aeolic production in Europe

Wind power installed in Europe by end of 2020 reached 216,580 MW. The field is monitored, in Europe, by Wind Energy (ex European Wind Energy Association (EWEA)), a non-profit NGO established in 1982, counting up to 700 members among which the main firms in aeolic plants making, and the most influential research institutes: it is the biggest sustainable resources association in the world.

Aeolic production in Italy

In 2020 Italy was at 10th place of biggest aeolian energy producers' ranking, with an installed capacity of 10.8 GW. A placement that deserves respect, if we think at country's smallness if compared to "giants" like USA, China or India.