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IoA Supplementary Guidance Notes on Wind Turbine Noise

REF has responded to the latest consultation by the Institute of Acoustics on the Supplementary Guidance Notes designed to accompany their Good Practice Guide to the Application of ETSU-R-97 for the Assessment and Rating of Wind Turbine Noise.  The summary follows and access to the full text of the consultation response is below.


1.1 The Renewable Energy Foundation (REF) welcomes the opportunity to respond to the Institute of Acoustics (IoA) on the Supplementary Guidance Notes that have been produced to follow the publication in June 2013 of A Good Practice Guide to the Application of ETUS-R-97 for the Assessment and Rating of Wind Turbine Noise (hereafter the GPG).

1.2 We are perturbed that the first round of consultation that preceded the publication of the Good Practice Guide itself was not followed up by a consultation response document in which the IoA addressed the issues raised by the consultees. There were a number of technical responses from well-qualified engineers drawing the IoA’s attention to technical flaws in the fundamental science underpinning the GPG, and these required an answer. The credibility of the GPG is undermined by the failure of the IoA to provide an evidence-based defence of the guidance.

1.3 We consider that there are two fundamental problems with the IoA Supplementary Guidance, firstly the treatment of wind shear in Supplementary Guidance Note 4, where the IoA proposes two conflicting methodologies for measuring the wind speeds which are used to assess the noise impacts and to set the noise condition limits for a wind farm. We demonstrate below that the new and IoA-preferred methodology using the so-called ‘standardised’ 10m wind speeds results in increased noise limits compared with those formulated in ETSU-R-97, which are based on measured 10m wind speeds and already widely acknowledged to offer inadequate protection to residents.

1.4 The presentation of two conflicting methods will lead to further confusion and debate as to which of the two methodologies a planning Inspector or local authority should use in setting noise condition limits. We see this outcome as an inevitable (though unintended) consequence of the increasing complexity of wind farm noise guidance, which is poorly understood even by professionals, and even, apparently, by the IOA GPG authors.

1.5 Furthermore, the IoA have previously made it clear that their remit in producing the GPG was not to increase noise limits above the ETSU-R-97 limits, but unfortunately, this is, in point of fact, the effect of their recommended wind shear methodology. Moreover, the IoA methodology provides extra headroom for extra wind farm noise at times of high wind shear which occurs during evenings and night times when low background noise levels prevail. Consequently, the impact of these changes will be very significant and negative for wind farm neighbours.

1.6 The second major problem concerns the guidance provided for turbine noise predictions used in the planning system when assessing probable noise impacts. The key parameters are the turbine sound power levels, which are provided by turbine manufacturers, and a ground parameter used to account for sound reflected from the ground surface and interfering with the sound propagated directly from turbine to receiver.

1.7 Recommendations for these key parameters are made in the GPG and in Supplementary Guidance Note 3. However, no data is produced to demonstrate that these parameters correctly predict turbine noise. We have commented in the past that the code of conduct of the IoA includes the requirement that primary data used in any publication or report are available in a form that would allow for independent scrutiny. However, the GPG is not consistent with this recommendation since the evidence base for the recommended noise prediction methodology has, in spite of requests, not been published. Consequently, the reliability of the recommended method cannot be objectively tested, and must be regarded as of doubtful quality.

1.8 In fact, we have investigated in some detail two publications that cite results for a number of un-named wind farms, and find from that analysis that the conclusions adopted by the IoA GPG are not supported by this data.

1.9 Furthermore, we provide results of independent turbine noise measurements that not only exceed the predicted noise levels when derived using the IoA GPG methodology and parameters, but exceed them by a considerable margin.

1.10 The IoA must as a matter of urgency address the faults outlined above, and revise the Good Practice Guidance accordingly. Without such validation and revision the GPG has no credibility, and is manifestly unfit for purpose. Where it sought to clarify matters it has introduced further confusions; where it promised to give neighbours increased confidence in the protection, it has exposed them to a higher risk of noise disturbance.