Effect of a common wind shear adjustment methodology on the assessment of wind farms when applying ETSU-R-97
This research paper has been commissioned by MAS Environmental Ltd. It challenges many of the commonly accepted assumptions on the influence of wind shear on wind turbine noise introduced by an article published in 2009. The article outlined changes to the assessment of wind shear reasoning that by altering background noise levels for wind shear, permitted turbine noise limits would be lowered.
The 2009 article method for assessing wind shear was not based on research and was developed following some widely stated, but now shown to be incorrect, assumptions about the effects of wind shear.
This paper investigates the differences in turbine noise assessment as recommended in the article method and as recommended in ETSU-R-97, the current UK guidance for assessing wind farm noise. Using data measured at a number of wind farm sites around the country comparison is made between the difference in margin between predicted turbine noise level and associated limits as calculated by the article method and by the application of ETSU-R-97 as written. This paper explores whether there are any benefits to using the article method, however small, and reviews the consequences for local communities in adopting this change.
The study concluded that the desired benefit using the article method at all wind speeds, and especially at 5-7m/s where the article method was expected to perform best, is not realised. Where standardised wind shear conditions as implemented by the article, which do not relate to those conditions causing complaint, were substituted for the actual wind shear conditions likely to cause complaint more turbine noise was allowed. Further, the comparison showed that in all cases analysed there was a loss of community protection when adopting the article method.
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