A Review of the potential impacts of wind turbine noise in the Australian context

Abstract

This manuscript describes a range of technical deliberations undertaken by the authors during their work as members of the Australian Government’s Independent Scientific Committee on Wind Turbines. Central to these  deliberations was the requirement upon the committee to improve understanding and monitoring of the potential impacts of sound from wind turbines (including low frequency and infrasound) on health and the environment. The paper examines existing wind turbine sound limits, possible perceptual and physiological effects of wind turbine noise, aspects of the effects of wind turbine sound on sleep health and quality of life, low-frequency noise limits, the concept of annoyance including alternative causes of it and the potential for it to be affected by low-frequency noise, the influence of amplitude modulation and tonality, sound measurement and analysis and management strategies. In so doing it provides an objective basis for harmonisation across Australia of provisions for siting and monitoring of wind turbines, which currently vary from state to state, contributing to contention and potential inequities between Australians, depending on their place of residence.

1. Introduction

In order to manage potential impacts from wind turbine sound, governments and regulators have established wind turbine sound limits that place an upper limit on the sound level that wind farms can generate and effectively place a limit on how close wind turbines can be placed to dwellings and population centres. There is some disparity in approach to this issue and this manuscript describes deliberations by the Australian Government’s Independent Scientific Committee on Wind Turbines (‘the committee’) aimed at optimising the approach to determining their minimum distance from noise-sensitive receivers and their management. It examines aspects of the effects on sleep health and quality of life, low-frequency noise limits, alternative causes of annoyance, annoyance attributed to low-frequency noise, management strategies, amplitude modulation, measurement of wind farm tonality, wind farm sound measurement and analysis, and the statistical power of wind turbine noise studies.

The purpose of publishing these deliberations is, by making them available to technical experts for their consideration and feedback, to facilitate and promote harmonisation across Australian states of the provisions for siting and monitoring of wind turbines. This manuscript sits alongside reports from the committee of a less technical nature, including its reports to parliament and fact sheets it intends to make available on its website. 

2 Wind Turbine Sound Limits

Committee members recently undertook a detailed review of the existing wind turbine sound limits in Australian states and several other countries with similar constraints, how these were established and a method that could facilitate their harmonisation [3]. It was found that most existing wind farm sound limits appear to have been adopted to avoid sleep disturbance but were developed using data derived from sound sources other than wind turbines. This seems to have been a reasonable approach at the time of their adoption because of the paucity of other suitable data. More recently, the concept of ‘annoyance’ has been used to encapsulate negative reactions to wind turbine sound. Given that many studies have now demonstrated a significant relationship between annoyance and wind turbine sound level, regardless of whether sound was the major source of the annoyance,
there is a logical basis for now deriving a wind turbine sound limit based on annoyance.

The committee’s analysis suggests that an appropriate noise limit to ensure that  no more than 10% of the population are ‘highly annoyed’ when exposed to wind farm noise is between 34 and 40 dB LAeq (10 min) outside the residence, with a mean value of 37 dB LAeq (10 min) [3]. The cut-off of 10% is somewhat arbitrary and itself could be a subject of informed debate. The corresponding measurement limits in LA90(10 min) are between 1.5 and 2.5 dB lower with 2 dB lower being a good practical value [4]. These values are similar to the lower maximum design limits already adopted, or proposed for use in Australia of 35, 37 and 40 dB LAeq (10 min).

Thus, this study provides a method for harmonisation of future wind farm sound limits in Australia based on direct assessments of human response to wind farm sound. 

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The committee recommends that state and territory governments consider harmonising their wind turbine sound limits by adopting the limits proposed in their paper [3]. It would also like to see more uniformity in sound measurement and compliance requirements. Although the committee believes that wind turbine sound level should be the primary determinant of how close residences can be to wind turbines, there should also be a minimum setback distance. This minimum distance may be varied under particular circumstances, such as when the residences are exposed to the same high winds as the wind turbines themselves. This produces high background noise levels at the residences and allows the residences to be exposed to a higher level of wind turbine noise and hence to be effectively closer to the wind turbines than would normally be the case. With current wind turbine
technology, this minimum distance should be in the range between the 1 km adopted by the Victorian Government and the 1.5 km recommended by the National Health and Medical Research Council and adopted by the Queensland Government. These minimum distances may need to be revised in the future due to technology changes.