Wind-energy Technology

Although conventional sources of power dominate the energy needs of European countries, wind energy is growing rapidly. Renewable energy sources currently provide nearly 5.4% of the European Union's primary energy needs, and have the potential to provide much more.

Almost all wind turbines producing electricity for the national grid consist of rotor blades which rotate around a horizontal hub. The hub is connected to a gearbox and generator, which are located inside the nacelle. The nacelle houses the electrical components and is mounted at the top of the tower. This type of turbine is referred to as a 'horizontal axis' machine.

Rotor diameters range up to 80 metres, smaller machines (around 10 meters) are typical in developing countries. Blades are made of fibreglass-reinforced polyester composites.

The blades rotate at 10-30 revolutions per minute at constant speed, although an increasing number of machines operate at a variable speed. Power is controlled automatically as wind speed varies and machines are stopped at very high wind speeds to protect them from damage. Most have gearboxes although there are increasing numbers with direct drives.

The yaw mechanism turns the turbine so that it faces the wind. Sensors are used to monitor wind direction and the tower head is turned to line up with the wind.

Towers are mostly cylindrical and made of galvanized steel and often painted. Lattice towers are used in some locations. Towers range from 25 to 75 meters in height.

Commercial turbines range in capacity from 50 kilowatts to over 2 megawatts. The crucial parameter is the diameter of the rotor blades - the longer the blades, the larger the area 'swept' by the rotor and the greater the energy output.

There are two main methods of controlling the power output from the rotor blades. The angle of the rotor blades can be actively adjusted by the machine control system. This is known as pitch control. This system has built-in braking, as the blades become stationary when they are fully 'feathered.' Most wind turbines start operating at a speed of 4-5 metres per second and reach maximum power at app. 15m/s.

Most important is how windy the site is. The power available from the wind is a function of the cube of the wind speed. Therefore a doubling of the wind speed gives eight times the power output from the turbine. All other things being equal, a turbine at a site with an average wind speed of 5 meters per second (m/s) will produce nearly twice as much power as a turbine at a location where the wind averages 4 m/s.

Europe is the world leader in wind energy, with more installed capacity than any other region of the world. Improvements in wind energy technology would mean that the trends which have led to the dramatic fall in the cost of wind energy are set to continue.

Countries all over the world are setting targets for wind power. It is estimated that 22,000 megawatts of wind energy capacity, in the form of 40,000 wind turbines will be installed in the next 10 years. This represents an annual market of around 2.4 billion Euros . Europe is the core of this global business, and stands to benefit greatly from this move towards sustainability.