MÄTNING AV LJUDIMMISSION FRÅN VINDKRAFT. VIDAREUTVECKLING AV METOD FÖR MÄTNING

Sammanfattning: The Swedish government have a goal that wind turbines shall produce 30 TWh by the year 2020, compared to about 3,5 TWh produced in Sweden during 2010. To minimize the disturbance that wind turbines create the Swedish Environmental Protection Agency has stated a guideline value that noise from wind turbines at nearby residents shouldn’t exceed 40 dBA, at 8 m/s wind speed. With advanced calculation models, like Nord 2000, the emitted sound from future wind turbines can be calculated at an early stage to optimize the power production without exceeding the 40 dBA. When the turbines have been built there is a need to verify that they really are within the guideline. To measure the sound pressure level at nearby residents, a sound immission measurement, there is a Swedish method, Elforsk 98:24 (1) with the translated titled “measuring of noise immission from wind turbines”. There is also an international standard IEC 61400-11 (2) focused on how to measure the emitted sound power level, also called sound emission measurement. To verify the sound level at a resident building a sound immission measurement is the preferred method. However this method has some practical limitations, for example the background sound level is often higher than the guideline value of 40 dBA, which makes it hard to estimate the equivalent sound pressure level of the wind turbine. A further development of this method was outlined in a draft translated “Measuring of sound from wind turbines –draft 2005” (3). The method in this draft is based on a sound emission measurement, compatible with the IEC 61400-11, in combination with a simple formula to calculate the sound immission level. The draft also contains a method for measuring the sound attenuation from the wind turbine to the resident, which can be used together with the measured sound power level to calculate the sound immission level. The intention of this thesis is to further develop today’s method for sound immission measurement of wind turbines. To achieve this, theoretical studies have been undertaken to study the elements relevant to the measurement, like sound generation, attenuation and relevant measurement equipment. Swedish and international measurement methods and guideline values have been studied. Measurements based on the draft (3) have been performed and shows that the method of measuring the sound attenuation, outlined in the draft, can provide results where the present method would fail. But the sound attenuation measuring method is still hampered by high background sound levels and has some practical limitations compared to the present method Elforsk 98:24. Conclusions from this thesis is that calculations of sound immission levels, based on measured sound power level, is a method that is and will continue to be a part of the assessment of sound levels from wind turbines. To ensure high quality of these assessments the procedure should be standardized and the use of advanced calculation models should be included. In cases where the sound attenuation path crosses hilly terrain, water or where the guideline values are exceeded, calculations with more advanced method should be advocated.