Minnesota DOH

III.           Public Health Impacts of Wind Turbines- Minnesota Department of Health

The Minnesota Department of Health was asked by the Office of Energy Security (OES) in the Minnesota Department of Commerce to evaluate possible health effects associated with low frequency vibrations and sound arising from large wind energy conversion systems. The report begins by explaining hearing and the vestibular system as well as sound levels and frequencies.

Exposures of Interest

  Wind turbines create mechanical noise and aerodynamic noise. The gearbox, generator, motors, ventilation, and transformers make mechanical noise. These sounds are not prevalent in newer model wind turbines.

Aerodynamic noise occurs when air passes over the blades of the wind turbine. Rhythmic noises, like that of turbine noise, are found to be more irritating than constant tones or frequencies. The further away from the turbine tower, the rhythmic noise begins to sound steadier. Turbine blade tips can travel over 140 mph. The design of the blade can minimize noise, but it cannot be eliminated. Aerodynamic noise is hard to estimate and may be underestimated in planning. Blade angles can be adjusted to maximize productivity, but if the blade is not angled properly it will make more noise. Aerodynamic modulation is when horizontal layers of varying wind speeds or directions occur and turbine blades pass through these areas creating different noises in each horizontal layer. These horizontal layers, called shear, can be caused by various terrains or by structures on the ground.

Shadow flicker is another common problem with wind turbines. In sunny conditions, blades can create moving shadows. It has been shown that these shadows move to slow to trigger epileptic responses. To avoid this, setbacks of 1km have been suggested for houses and other dwellings and 300 meters from roads to avoid distraction.

Impacts of wind turbine noise

Every individual has a different reaction to sounds. Stress from noise does not correlate with loudness, but in some circumstances (wind turbines) interest in the project may decrease annoyance. Unlike higher noise frequencies, low frequency noise can be accompanied by shaking, vibrating, or rattling, which will increase annoyance for these sounds.

Studies of wind turbine noise impacts on people

Two Swedish studies used questionnaires to study the relationship between turbine noise and annoyance. With noise levels above 40 dB more residents could hear the noise in their homes. Annoyance was found to have a correlation with the noise level. When turbines were above 40dB, at least 50 percent of people surveyed were annoyed. When the turbine noise was between 35 and 40 dB, half as many people were irritated. “Noise annoyance was more likely in areas where turbines were visible.”

The United Kingdom conducted a study in which they analyzed the different complaints made about wind farms. Out of 133 wind farms, 27 of those received formal complaints. Many of the earlier complaints were about the noise from the gearbox and other mechanical devices. The rest of the complaints were from the aerodynamic noise. For two of the wind farms, complaints have stopped and one farm is taking steps to reduce noise.

A study in the Netherlands sent out questionnaires to anyone living within 2.5 km of a wind turbine. In this study, when turbine noise went 40 dB, up to 25 percent of people were annoyed. However, above 45 dB, most residents reported economic benefits from the turbines, so annoyance levels dropped to 5 percent.

Herbrandson, C., Messing, R. (2009). Public Health Impacts of Wind Turbines. Minnesota Department of Health. Retrieved from: http://energyfacilities.puc.state.mn.us/Resources.html?Subject=Wind%20power