Effects of the wind profile at night on wind turbine sound

This significant research by van den Berg explains why turbine noise as far away as 1900 meters (more than 6,000 feet) is resulting in complaints by residents particularly at night. The paper concludes that noise immission predictions are not accurate and result in the understating of turbine noise levels, particularly during nighttime conditions.


Since the start of the operation of a 30MW, 17 turbine wind park, residents living 500 m and more from the park have reacted strongly to the noise; residents up to 1900 m distance expressed annoyance. To assess actual sound immission, long term measurements (a total of over 400 night hours in 4 months) have been performed at 400 and 1500m from the park. In the original sound assessment a fixed relation between wind speed at reference height (10 m) and hub height (98 m) had been used. However, measurements show that the wind speed at hub height at night is up to 2.6 times higher than expected, causing a higher rotational speed of the wind turbines and consequentially up to 15 dB higher sound levels, relative to the same reference wind speed in daytime. Moreover, especially at high rotational speeds the turbines produce a ‘thumping’, impulsive sound, increasing annoyance further. It is concluded that prediction of noise immission at night from (tall) wind turbines is underestimated when measurement data are used (implicitly) assuming a wind profile valid in daytime.

G Pvanden Berg

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SEP 22 2003
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