Air in motion produces energy. The modern wind turbines used to harvest it have long historical roots. It is also one of the fastest growing and rapidly evolving energy technologies today. Costs of energy production from wind are falling, resulting in its adoption in many parts of the world from Africa to Asia, Europe and the Americas.

Following the invention of the electric generator, engineers began harnessing wind energy to produce electricity. Wind power generation succeeded in the United Kingdom and the United States in 1887-1888, however, modern wind power is said to have started in Denmark, where horizontal-axis wind turbines were built in Askov in 1891, and a 22.8 metre wind turbine for electric generation started operation in 1897. Since then, wind generation has spread from Europe and the United States to the world.

Global installed wind generation capacity (including both onshore and offshore capacity) has increased nearly 50 times in the past two decades, from 7.5 gigawatts (GW) in 1997 to more than 371 GW in 2014. In fact, production of wind electricity doubled between 2009 and 2013. Many parts of the world have strong wind speeds. However, good locations for generating wind are sometime remote. Offshore wind power offers tremendous potential.

The way the wind can be used to produce electricity is that kinetic energy from moving air (or wind) is transformed into electrical energy by wind turbines or wind energy conversion systems. The wind forces the turbine’s rotor to spin, changing the kinetic energy to rotational energy by moving a shaft which is connected to a generator, thereby producing electrical energy through electromagnetism.

Wind power is proportional to the dimensions of the rotor and to the cube of the wind speed. Theoretically, when the wind speed doubles, the wind power increases eight times. The main factors affecting output power are the swept area (related directly to the length of the blades) and the wind speed. Over time, the size of wind turbines has increased continually.

In 1985, turbines had a rated capacity of 0.05 megawatts (MW) and a rotor diameter of 15 metres whereas most new wind power projects have turbine capacities of around 2 MW for onshore and 3-5 MW for offshore.

The largest commercially available wind turbines to date reach 8.0 MW each, with a rotor diameter of 164 metres. The average capacity of newly installed wind turbines has increased from 1.6 MW in 2009 to 2.0 MW in 2014.

Wind hits the turbine blades causing them to rotate. The shaft of the turbine carries the mechanical energy via a gear box to a generator which transforms it into electric power.