10 Sep Wind Turbine Noise Conference Presentation
BKL Partner Mark Bliss prepared a paper and presentation about environmental noise assessment of proposed wind farms for the 5th International Conference on Wind Turbine Noise, which was held in Denver, Colorado, in August 2013.
In British Columbia, environmental noise from proposed wind farms is currently evaluated based on assumed worst-case conditions using ISO 9613-2 Acoustics — Attenuation of sound during propagation outdoors — Part 2: General method of calculation. Around the world, however, it is generally accepted that human annoyance due to environmental noise — including noise from wind farms — is based on long-term conditions and annual average noise levels. “Wind farm noise heard by people at their homes tends to be highly variable,” says Bliss. “And residents who are downwind of a wind farm for 5 per cent of the year would be less annoyed than residents who are downwind for 50 per cent of the year, everything else being equal.”
One approach to take this into account is to calculate the annual average noise level based on a distribution of noise emission and propagation classes using real weather statistics. Bliss performed example sound predictions and compared them with conventional modelling best practice using ISO 9613. “One could arrive at significantly different conclusions based on the approach taken,” says Bliss. “We can provide a more realistic picture of future effects if we consider real-world weather conditions but we still need to work on validating prediction methods.”
One could arrive at significantly different conclusions based on the approach taken.
His paper summarizes a case study that investigates results produced by a range of available approaches with ISO 9613 and Harmonoise/ IMAGINE predictions.
Bliss concludes, “I think the next step to getting a better picture of potential effects is to change how the noise limit is set and how wind turbine sound power levels are used. We should keep using ISO 9613 for noise predictions for now but annual average noise limits should be adopted so that assessments would consider the variation in wind turbine sound power levels due to varying hub-height wind speeds.” Ultimately, more field validation work will be required before assessments incorporating varying weather conditions can be considered industry best practice.