Analytical assessment of wind turbine noise impact at receiver by means of residual noise determination without the wind farm shutdown

Wind turbine noise (WTN) assessment by means of outdoor measurements at the receivers living nearby an operation wind farm results a complex task. Both the background noise and the source noise are related to wind speed and both contribute to the overall measured noise levels (environmental noise). Especially in hilly areas, many physical phenomena increase the wind shear, leading to an unpredictable relation between noise and wind speed. In many countries, this kind of assessment is even more difficult due to the national regulations requiring to compute the difference between environmental and background noise levels acquired in the same weather conditions. Thus, the residual noise is generally evaluated turning off the wind farm, with a consequent disagreement. This study suggests a procedure to simultaneously estimate the immission and the residual noise components measured nearby a wind farm when the residual noise is mainly generated by wind. This allows the evaluation of the noise impact produced by operational wind farms, without requiring the farm shutdown. An engineering method with the required scientific basis to be used as an assessment procedure by consultants and public bodies is thus developed. Particular attention will be put on the parameters involved in the procedure and an example of application is provided.