Feature Report: Wind Power

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Harnessing the Wind

The wind’s energy has been harnessed for centuries. Wind turbines are the machines that convert this energy into electricity. Equipped with state-of-the-art technology, the turbines operate like mini power plants. 

Wind turbine blades can have a diameter of up to 120 meters. © Thinkstock

Wind is caused by the uneven heating of the earth's surface, which creates different temperature and pressure areas known as anticyclones and depressions. As the atmospheric forces try to balance, air masses move from anticyclones to areas of depression. The larger the depression, the stronger the wind.

Wind force has long been used to propel boats and drive windmills. Today it is being converted into electricityForm of energy resulting from the movement of charged particles (electrons) through a conductor... thanks to wind turbines.

Wind Speed and Swept Area

A number of principles govern the design of wind turbines:

The maximum wind speed a turbine can withstand is 90 kilometers per hour

Tower, Rotor and Nacelle

Wind turbines have three main components.

  • The tower supports the nacelle and the rotor. It is generally made of metal and set in a concrete foundation anchored by long piles. Offshore turbines are anchored to the seabed in the same way.
  • The rotor converts the wind's kinetic energyThe energy of an object due to its motion. (or movement) into mechanical energySum of the potential energy and kinetic energy of an object or system.... It consists of a hub and an impeller comprised of three, or sometimes two, blades. The propeller-like blades are manufactured from composite materials, such as polyester- or carbon-reinforced fiberglass, that are light, rigid and resilient.
  • The nacelle is located at the top of the tower behind the rotor. It houses the generator that uses the moving rotor's mechanical force to produce electricity. The electricity is transmitted to the ground via electric cables inside the tower.

The nacelle has an installed capacityThe power generation capacity of a particular plant. It is usually expressed in megawatts (or sometimes even gigawatts)... (power generation capacity) of up to 5 megawatts.

The rotor diameter of a giant wind turbine can span a football field. 

Wind turbines are equipped with a controller that:

  • Positions the rotor so it is perpendicular to the direction of the wind, to capture as much motive force from the wind as possible.
  • Changes the blades' angle of attack with the wind direction, to maximize energy recovery.

Thanks to this system, the turbine can be shut down quickly and automatically if necessary, thus ensuring safe operation at all times.

A Wind Turbine is a Mini Power Plant

A minimum wind speed of 10 to 15 kilometers an hour is required to start the turbine. The turbine also has an upper limit wind speed of 90 kilometers an hour — sometimes higher for the most recent models. The limit was established for financial as well as safety reasons: fast-moving parts experience increased wear and tear, while the extra electricity output is minimal.

An internal gearbox multiplies the basic rotor speed of 12 to 15 rotations per minute to 1,500 rotations per minute so that the generator can operate effectively.

Electronic power converters adjust the frequency of the current generated by the turbine to match that of the grid (50 Hz in Europe), while allowing for a variable rotor rotation speed depending on the wind.

Connecting Wind Power to the GridA power transformer located in the nacelle or inside the tower steps up the voltage from 600-1,000 volts to 20,000-30,000 volts so that the electricity can be transferred to the grid connection point. For a 10 to 15-megawatt wind farm in France, the voltage level at the connection point is generally 20,000 volts. For higher capacity wind farms, the voltage level can rise to 60,000 to 90,000 volts, and even up to 225,000 volts in some cases.