[D]ue to the typical size of turbines and their airspace configuration, they can adversely impact the natural environment posing potential hazards such as noise emission, vibrations, non-ionizing radiation effects, emergency situations, the shadow flicker effect, and permanent shade conditions. Turbines may have also a negative effect on the local fauna (particularly birds) as well as the landscape.
In case of wind turbines, both low-frequency noise and audible noise is produced by various aerodynamic noise sources (turbulent layer tearing off from blade edges, boundary layer tearing off, onset of vortex air flows, induction of a boundary vortex, vortices of laminar layer, turbulence of the inflowing air stream) as well as by mechanical noise sources (gearboxes, generators, devices altering the headstock direction, cooling system pumps, ancillary facilities, etc.) .
Despite the fact that modern wind turbines operated at daytime generate far less noise than their prototypes, they still appear to strongly affect people. Under certain weather conditions, this noise is transmitted over large distances and exceeds (by about 10–15 dB) the noise levels obtained from numerical models . In most cases, this effect can only be sensed in a subjective manner which means that the very presence of wind turbines may bring about acoustic or beyond-acoustic annoyance reactions in humans (distraction, irritation). These factors are accounted for in the sound level models and questionnaire tools that were a part of experiments conducted mainly in Holland and Sweden and connected with the level and spectral composition of sound generated by wind turbines emitted over the neighboring areas (residential areas). When addressing the issue, other aspects have to be considered as well: time of the day, atmospheric conditions (wind speed and direction), personal attitude towards wind power generation (ardent supporters and fierce opponents), the actual distance from a wind mill farm or the age of people being interviewed [3–6].