Wind turbine sound – how often is it heard by residents living nearby?

Sound power levels of wind turbines and consequently also the immission sound pressure levels at nearby residents vary with the wind speed. A standard meteorological situation is therefore commonly used when the immission levels are discussed; wind speed 8 m/s at 10 m height downwind. There is a need for a more comprehensive description of the sound that could be included in the Environmental Impact Assessment. The objectives of this study were to explore if it is possible to measure how often the sound is heard, and if the occurrence could be related to the standardized immission levels or the performance of the wind turbine. Twenty four people living in three wind turbine areas (A-weighted sound pressure levels 29.6 – 45.9 dB) filled in diaries for three weeks, noting when they were at home, when they were outdoors, and when they could hear sound from wind turbines. The incidents when the wind turbines were heard varied largely from 0% to 100% of the times spent outdoors. The percentage increased with increasing standardized immission levels (r = 0.56, p < 0.01). In two of the areas it was possible to get data from the nearest turbines for the study period. The sound was more easily heard at wind speeds above 5 m/s than at lower wind speeds. No indication of a decreased possibility to hear the sound when the wind increased further was found. Possibility to hear the sound was most closely related to the electrical power generatio