Since ancient times, wind has been exploited in different ways, mainly for grain milling and water pumping. With the advent of the industrial era, wind energy was gradually replaced by fossil fuels, the windmills being practically relegated to pump water for agricultural use. In the 20th century, new designs enabled electricity generation at small-scale levels for battery charging uses. After the early 1970s oil crisis, wind technology experienced a revolution. Motivated by the oil price boost, many countries promoted ambitious wind energy R&D programs. As a result, new materials and modern turbine designs were developed, initiating the age of large-scale wind electricity generation. During the last decades, the increasing concern about the environment and the trends towards the diversification of the energy market have been reinforcing the interest in wind energy exploitation.

Nowadays, wind energy is by far the fastest-growing renewable energy resource. The progress of wind power around the world in recent years has exceeded all the expectations, with Europe leading the global market. In numbers, the wind turbine capacity installed in Europe increased during the last years at an average annual growth rate superior to 30% [24].

The wind energy industry so far has been supported by market incentives backed by government policies fostering sustainable energy resources. Anyway, the cost of electricity provided by wind power facilities has been dropping drastically since the 1980s. These cost reductions are due to new technologies and higher production scales leading to larger, more efficient and more reliable wind turbines [2, 8,...