Low-frequency noise from large wind turbines – additional data and assessment of new Danish regulations

Previous studies have shown that the noise becomes more low-frequency in character, when wind turbines get larger, and with todays’ megawatt turbines the low-frequency noise may cause annoyance for the neighbors. Therefore, low-frequency noise has been included in the noise regulations on wind turbines in Denmark. In this study, the data material has been increased to include more data on noise from modern production turbines up to 5 MW. In addition, the new Danish regulations are assessed. The previous result that the relative amount of low-frequency noise is higher for large turbines (> 2 MW) than for small turbines (≤ 2 MW) is confirmed. Due to the air absorption, the higher low-frequency content becomes even more pronounced, when sound pressure levels in relevant neighbor distances are considered. Even when A weighted levels are considered, a substantial part of the noise is at low frequencies, and for several of the investigated large turbines, the one-third-octave band with the highest level is at or below 250 Hz. It is thus beyond any doubt that the low-frequency part of the spectrum plays an important role in the noise at the neighbors. The new Danish regulation is based on calculations of the indoor noise at the neighbors, but unfortunately, the calculation underestimates the level that would be measured, thus the regulation does not adequately prevent potential annoyance and sleep disturbance effects from future wind turbines in Denmark.