An approach to on/off testing for wind farm noise assessment

In Victoria, assessment of operational wind farm noise is usually undertaken using a regression approach based on NZS6808. This adopts a comparison of long-term operational sound level and wind speed measurements with background sound levels measured prior to the construction of the wind energy facility (WEF), taken at sensitive receivers near to the site. Where no background noise levels have been measured or there are changes in the environment that may make background noise levels unrepresentative, it can be difficult to positively demonstrate compliance with required noise limits, and the results can be inconclusive. On/Off testing is described in NZS6808 as an alternative to conducting sound measurements correlated with wind data, and relies on the wind farm being turned off for a short period to allow a short-term background noise level to be determined, against which the “adjacent” operational noise levels can be compared. However, the approach is not documented in detail in NZS6808 and on/off testing is rarely undertaken in Australia. This paper describes a detailed approach that has been adopted for recent on/off testing undertaken at a large WEF in Australia and outlines the key aspects of the testing which are necessary to conduct a meaningful assessment.