The warming of the Earth, caused by radiation from the Sun, causes differences in temperature and pressure between the masses of atmospheric air at different points on the planet.
When these air masses reorganize and move, seeking to be all at the same temperature and pressure, wind appears (air in motion). On a global scale, the Earth's rotation on itself and the temperature difference between the equatorial and polar zones are the causes that originate the air currents; while, on a local scale, it is the particularities of the terrain's orography that determine the presence and characteristics of the wind.
The possibilities of using the wind as an energy resource are conditioned by the variability of this atmospheric phenomenon and by the minimum technical requirements necessary for the operation of the facilities.
Wind conditions change permanently, both in intensity and direction. Therefore, it is necessary to know these variations in detail. The devices that allow measuring the speed and the predominant direction of the wind are the anemometer and the weather vane, respectively.
Regarding the operation of wind farms, with current technology, wind speeds of at least 6.5 m/s are required, and some 2,400 equivalent hours per year, to guarantee good performance.