Wind turbine noise: annoyance and alternative exposure indicators

Ecological awareness increases energy production by wind turbines, but the considerable associated annoyance risk requires carefully designed noise control strategies when they are to be installed in densely populated regions. Well-chosen operational restrictions may reduce noise annoyance while preserving cost-effectiveness. This research project investigates the relationship between the inhabitants’ wind turbine noise annoyance, exposure indicators, operational characteristics and environmental variables for a specific industrial site near a residential area. In contrast to most other research on wind turbine noise annoyance, in this study a six–month field experiment is conducted including regular on-line annoyance reports, continuous 1/3-octave band noise level registrations, periodic sound recordings, electricity production per minute and meteorological observations. Logistic regression reveals that the risk of high annoyance not only depends on the rotational speed, but also on the wind turbines’ nacelle position relative to the location of the dwellings, i.e. the wind direction. This directivity effect can be captured when noise parameters such as the background noise level caused by other sources and a so-called fluctuation-indicator are introduced. Background noise measurements incorporate wind induced vegetation and road traffic noise; their LA95-level is inversely related to the risk of high annoyance. The fluctuation-indicator is calculated from the 1/3–octave band spectra to capture the periodic part of wind turbine noise; here the risk of high annoyance increases with increasing fluctuation strength. These detailed findings can be used for designing operational restrictions that limit noise annoyance while keeping production as high as possible.