Wind turbines generate infrasound - as do many other sources, including heating and air conditioning systems or road traffic. Infrasound is also generated in the natural environment from various sources such as waterfalls or ocean waves. With the expansion of wind energy, concerns arose regarding the impact of wind turbines on human health. Opponents of wind power projects repeatedly claim: the sound produced by the turbines makes people ill. Here you can learn more about what infrasound actually is, how it is generated by wind turbines, and whether the claims are justified.
Infrasound refers to sound waves with very low frequencies below 20 Hertz. The human ear can only perceive frequencies between 20 Hertz and 20,000 Hertz. Infrasound is therefore below the normal hearing threshold of humans.
The rotors of wind turbines generate sound with very low frequencies. When the rotor blades move through the air, pressure fluctuations are created, which are emitted as low-frequency sound waves. The intensity of the generated infrasound depends on various factors, including the size and speed of the rotor blades, as well as the wind speed.
Rotor speed is a key factor in the generation of infrasound by wind turbines. Modern wind turbines are equipped with large rotor blades that rotate relatively slowly - typically, a rotor blade brushes past the tower about once per second. These slow movements lead to the generation of more infrasound compared to, for example, smaller rapidly rotating propellers. The latter, on the other hand, produce more audible sound. Understanding this dynamic relationship between rotor speed and sound frequency is crucial for the design and placement of wind turbines to minimize the impacts on the surrounding environment.
The design of the wind turbine also plays an important role in the amount of generated infrasound. In modern turbines, the rotor blades are located in front of the tower, facing the wind. This arrangement minimises the generation of infrasound. In older turbines, the rotor blades sweep behind the tower. These older models generate significantly more infrasound due to the frequent entry of the rotor blades into the wind shadow of the tower.
Although the low frequencies of infrasound are not consciously perceived, there are concerns that they could still have an impact on the human body. "Measurements show that the infrasound from wind turbines is well below the threshold of hearing and perception," write the experts from the Bavarian State Office for the Environment (LfU): "This is even true in the vicinity of the turbines." The lower a sound is, the higher the volume must be for it to be perceived by the human ear. However, the sounds emitted by the rotors always remain low. Various studies have not yet found any health effects below the threshold of hearing and perception, as a summary from the LfU shows .
Although no harmful health effects are known, wind farm operators and authorities take the issue seriously. In some federal states, minimum distances between wind turbines and residential buildings have been increased. Turbine manufacturers are also researching quieter rotor blades and new bladeless Vortex turbines. The system developed by the Spanish company Vortex Bladeless consists of a slim, conical tower that is set into oscillation by vortex currents. This kinetic energy is then used in the generator to generate electricity.
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