Wind power becomes usable for electricity generation above a wind speed of 3 to 4 m/s, depending on the turbine type. The rotor blades begin to turn above this wind speed. The output increases with the cube of the wind speed. If the wind speed doubles, the output increases eightfold. The generators achieve the rated power, that is the maximum energy yield, at 12 to 15 m/s, which they then keep constant even at higher wind speeds. The active blade pitch at different wind speeds optimises the energy yield of the pitch-controlled Enercon systems. This state-of-the-art, efficient control technology in which the power is adjusted to the wind speed by rotating the rotor blades (controlling the angle of incidence), guarantees operation of the wind turbines even in strong winds and storms (above 25 m/s). Only above a wind speed of 30 m/s (hurricane strength) are the Enercon wind turbines switched off automatically due to the wind being too strong.

When converting energy into the various energy forms, some of the energy utilised is released into the environment unused. Thus, purely physically, a wind turbine can only use 59% of the kinetic energy contained in the wind and convert it into mechanical energy. However, due to aerodynamic, mechanical and electrical losses, this theoretical maximum calculated by Albert Betz is not achieved in practice. Thus, aerodynamic losses arise due to friction and turbulence on the rotor blade and the swirl effect in the rotor’s wake. Mechanical losses are caused by friction in the bearing and the gearbox as well as in the generator itself. Heat generated by electrical resistances in the converter and cables cause electrical losses. Due to these conversion losses, our state-of-the-art Enercon wind turbines now achieve a yield of between 40 and 50%.

In addition to the coastal areas, good wind regions in Germany are increasingly inland locations. In view of the steadily rising mast heights, the exposed positions of the low mountain ranges are becoming very attractive for the erection of wind turbines.

When designating wind priority areas in the regional plans of the German states, the minimum distances to residential areas and traffic routes, to nature reserves and biotope areas, to bodies of water as well as to military bases and airports serve as a basis for decision-making. When priority areas are found and designated, more refined site planning must take into account nature conservation interests, particularly species protection. An environmental impact study is conducted to assess interventions in the natural surroundings and landscape and to define any necessary compensation measures. In addition, the local wind conditions of the site selected are analysed in detail and the noise and shadow emissions are determined. The exact layout of the wind farm is ultimately determined based on the results of the preceding studies.

The rotating movements are converted in the generator into electrical current with a voltage of 400 volts. The amount of electricity generated depends essentially on the diameter of the rotor, the hub height, and the wind strength.

To feed electrical energy into a grid, this electricity must be adapted to the line frequency, phase difference and voltage.

Like the majority of today’s wind turbines, our planned Enercon turbines are operated at a variable rotor speed. With the aid of a converter, the generator’s variable frequency is then adapted or synchronised to the desired line frequency - in Europe this is 50 Hz.

The electricity generated is transferred to the nearest substation via a transformer which raises the voltage to 20 kV depending on the local line voltage. From here the electricity is fed into the power grid from which the end consumer obtains its electricity.

The power grid as a transmission medium for electrical energy between wind turbine and end consumer is divided into a transmission and a distribution grid level. Wind turbines are mainly connected to the distribution grid system. Grid connection here is usually carried out at the medium and high voltage level.

Repowering is now a key tool for increasing wind power generation on land. Older, smaller wind turbines with low yields, such as were built in the early days of the wind industry, are replaced by state-of-the-art and more powerful turbines. This results in several advantages:

• Increase in energy efficiency with decreasing number of wind turbines
• Increase in municipal revenues due to business tax
• Restoring the natural character of the landscape by reducing the number of wind turbines and eliminating individual wind turbines
• Improvement of grid integration

Wind turbines have a long service life of 25 to 30 years. Due to the great advances in technology, however, it makes sense to replace older wind turbines before the end of their service life to take advantage of the benefits of progress, relieve the strain on nature and landscape, and achieve higher yields. Repowering also provides the opportunity to correct design errors from the pioneering years thus leading to greater acceptance within the population.