TABLE OF CONTENTS The wind is characterised by its speed and direction, which are affected by several factors, e.g. geographic location, climate characteristics, height above ground, and surface topography. Wind turbines interact with the wind, capturing part of its kinetic energy and converting it into usable energy. This energy conversion is the result of several phenomena that are explored in this chapter.
This section is devoted to the study of the patterns, strengths and measured values of wind and their effects on its interaction with turbines.
In a macro-meteorological sense, winds are movements of air masses in the atmosphere mainly originated by temperature differences. The temperature gradients are due to uneven solar heating. In fact, the equatorial region is more irradiated than the polar ones. Consequently, the warmer and lighter air of the equatorial region rises to the outer layers of the atmosphere and moves towards the poles, being replaced at the lower layers by a return flow of cooler air coming from the polar regions. This air circulation is also affected by the Coriolis forces associated with the rotation of the Earth. In fact, these forces deflect the upper flow towards the east and the lower flow towards the west. Actually, the effects of differential heating dwindle for latitudes greater than 30 N and 30 S, where westerly winds predominate due to the rotation of the Earth. These large-scale air flows that take place in all the atmosphere constitute the geostrophic winds.
The lower layer...
