Wind turbines: Why they are noisy and what to do about it.

Abstract

Sound from modern, tall wind turbines is related to sleep disturbance and is, per decibel, more annoying than sound from common sources such as road or air traffic. Surveys among residents indicate that there are several reasons for this: the swishing character of the sound, the intrusiveness at night, and the visibility of the wind turbine(s). Residential reaction is also determined by the attitude towards wind turbines in the landscape and by economical benefits. From acoustical research different explanations have arisen as to why the sound is amplitude modulated. For a distant observer it is the result of the change in trailing sound level due to the change in wind that the revolving blades encounter. High night-time sound levels are due to an increase in rotor height wind speed simultaneously with a decrease in near-ground wind speed. Wind turbine design has been directed to higher yields per turbine. Less attention has been given to low noise blades and rotor speed reduction. Low noise design could also include a reduction in the modulation amplitude and more sophisticated speed reduction; viz., at high annoyance conditions. Also, involving residents in wind farm planning may have a high potential to reduce annoyance.