How does it work?
A wind farm comprises several wind turbines. A wind turbine, also referred to as an aero generator, is the fusion of several advanced technologies uniting mechanics, electronics, computer technology, composite materials…
Composition of a wind turbine
An onshore wind turbine is made up of three main parts:
- The tower: most often metallic and cone shaped, it is usually white and meets aeronautical requirements. It is 40 to 110 meters tall, with a base diameter of 4 to 7 meters. It contains an opening on the ground to allow access to variety of equipment. The rotor is located upwards where the wind is strongest, and which allows for a lengthy blade.
- The rotor: It is made up of three blades of composite material from 25 to 60 meters in length, connected by a hub. The rotor pivots 360° to face the wind and to allow a maximum production of electricity. The height at the tip of the blade varies between 90 and 150 meters for the largest wind turbines. The blades of a wind turbine turn at an average speed of 10 to 20 rotations per minute.
- The pivoting nacelle: located at the peak of the tower, it houses the generator that transforms the mechanical wind energy into electric energy. The nacelle pivots automatically depending on the direction of the wind. Access to the nacelle is made by a ladder and/or a lift located inside the tower.
The primary characteristic of a wind turbine is its power or capacity. It is measured in kilowatts (kW) or in megawatts (MW). Wind turbines installed today range from 850 kW to 3,000 kW (or 3 MW). The energy produced by a wind turbine during its operation is measured in kilowatt hours (kWh) and mainly depends on the wind speed.
The idea of its operation is simple: the strength of the wind makes the blades turn and initiates the rotor that transmits the energy received to a generator that produces electric energy. The electricity is channeled by an underground electric cable to the public grid.
The transformation from wind to electricity
The difference in pressure between the two sides of the blade creates an aerodynamic force that puts the rotor in motion. This motion is generally accelerated by a gear-box and the mechanical energy transmitted by the gear-box is transformed into electrical energy by the generator.
The generator’s rotor turns at a high speed and produces an electric charge of around 690 volts. This electricity cannot be used directly. It is handled thanks to a converter, then its charge is increased to 20,000 volts by a transformer.
The wind turbines are set in the ground thanks to reinforced concrete foundations, often circular, covered over with seeded soil. They are interconnected among themselves by underground electric cables.
Each wind turbine is connected to the transformer located at the foot and inside the tower. The electric energy produced is sent towards the public distribution grid through a delivery station.
A computer system, linked to the phone network, allows for long distance monitoring and control of each turbine.
To start, a turbine needs wind of at least 12 to 15 km/hr. So that the machine operates at full capacity, winds needs to go from 45 km/hr to 90 km/hr. Beyond 90 km/hr, the turbine is stopped and enters a protection mode for security reasons.
For 1 MW of installed capacity, the annual average production of a wind farm owned by the Group can vary from 1.6 to 3.7 GWh, depending on the quality of the site (wind conditions) and the type of machines (power curve and availability) and meets the electricity needs of 600 to 1,500 households (1).
(1) Calculation assumption: a household consumes approximately 2,500 kWh/year excluding heating.
Wind turbines are more and more productive: their average capacity increases constantly and the turbine manufacturers continue to make improvements. Significant technological progress has been made over the past ten years. In 1999, it took 30 wind turbines to constitute a wind farm of 12 MW. Today, only 4 are needed.