Technologies and applications

The yield of wind turbines depends significantly on wind speed. Because winds are stronger and steadier the further they are from the earth’s surface, turbines are mounted on towers as high as possible. Local limits on turbine height may thus hamper the exploitation of a turbine’s maximum potential efficiency. In some German states, for instance, a 100 m limit on turbine height is common.

Currently, most of the world’s turbines are installed on land. In future, their numbers will continue to grow mainly on land, both in Europe and worldwide. But the development of offshore wind farms will become more important over the next few years. Much experience with offshore projects has also already been gained in over 30 offshore wind farms built off the coasts of Great Britain, Denmark, Sweden, Ireland, the Netherlands and Germany. Given the consistent wind conditions and higher average wind speeds at sea, the expected energy yields are up to 35 % higher than those on land. The German government has forecast an installed capacity of up to 25 GW by 2030, so German maritime wind farms could meet up to 15 % of the country’s power requirements in the long term. Construction of the first commercial offshore wind farms ‘Baltic 1’ in the Baltic Sea and ‘Bard Offshore 1’ in the North Sea in 2010 was a major milestone in the development of offshore wind energy use.

One of the main challenges for offshore systems is the strong dependence on weather conditions during construction. The main construction phase is limited to a period between April and November and is very dependent on wave heights and wind speeds. These incalculable parameters can significantly impact the overall cost of a project. During operation, salty air also makes heavy demands on the materials used. The multi-megawatt turbines and components used in offshore areas were for the most part developed, manufactured and tested in small series on land in Germany.

The use of small wind energy turbines (small wind turbines) is also becoming more important. Small wind turbines are defined by the international IEC 61400-2:2006 standard (‘Design requirements for small wind turbines’), which describes small wind energy turbines as those with a rotor sweep area of less than 200 square metres at 350 W/m², providing a maximum output of 70 kW. Their towers are usually not higher than 20 metres. Most turbines currently on the market generate outputs in the 5 to 10 kW range. Small wind turbines are especially suitable for providing a basic supply of electricity in regions far from power grids.