Thursday, 8 September 2011

Shh, quiet please - I'm trying to sleep

This is the first of a series of posts looking at ETSU-R-97 - The assessment & Rating of Noise From Wind Farms. This document is essentially used as a guiding standard for minimising the audible noise output from wind farms. This document was commissioned by the Department for Trade and Industry (DTI) in the mid 1990s, and published in September 1996. The document itself is lengthy, and in parts quite technical. It can be accessed via the Reference Documents links on the right hand side of this blog, but be warned - it's pretty big.

Perhaps you are one of those who is not convinced that wind turbines can make a noise and perhaps do not understand what the fuss is about - maybe this video will change your mind:

OK, so it appears that wind turbines can make an audible noise, and in that case there seems to be a need to ensure that the noise output is kept under control. Enter ETSU-R-97. First of all, we should consider the title: The assessment & Rating of Noise From Wind Farms. The title is not something along the lines of 'The Mitigation and Management of Wind Farm Noise', or 'A Method for Protecting the Audio Amenity of Wind Farm Neighbours'. The document is not a standard, a technical paper or a reviewed study. In all honesty, I struggle to find words to describe it. The Introduction to the Executive Summary (Part 1) probably gives the best indication of the purpose of the document: This document describes a framework for the measurement of wind farm noise and gives indicative noise levels thought to offer a reasonable degree of protection to wind farm neighbours, without placing unreasonable restrictions on wind farm development or adding unduly to the costs and administrative burdens on wind farm developers or local authorities. I have placed additional emphasis on the final part of the introduction as this phrase or something similar crops up a great many times in the document.

As a document, ETSU-R-97 is used throughout the United Kingdom as the standard by which the noise output from wind farms is 'controlled'. Developers seem to make no effort in going the extra mile in terms of bettering its recommendations. The document itself has been quite extensively criticised, and I include a couple of links to such criticisms: Philip Mullen - Chief Executive Environmental Protection UK Ltd and Richard Bowdler - who was a member of the original working group who drew up ETSU-R-97, but resigned and therefore is not credited as being part of the group in the final report.

Some of the major flaws in the document as far as I am concerned are:

  • The maximum noise limits for night time wind farm operation exceed those set for daytime operation.
  • The maximum noise limits for night time wind farm operation are not set relative to the established background noise levels, but are established as an arbritary value.
  • No protection is offered by the document's methodology for mitigating the effects of amplitude modulation of aerodynamic noise.
  • Background noise levels can be established over a very short time frame - just 4 weeks.
  • Sounds below the audible hearing range (so called infrasound) are not catered for at all.
  • Too much emphasis is placed upon 'not inconveniencing the operator'.
  • Wind farm operations are permitted far higher operating noise levels than other types of industrial machinery.

ETSU-R-97 is a document that is now 15 years old - and turbines have got a lot bigger since it was written. It has never had the status of a 'standard' bestowed upon it, doesn't address all the types of sound emitted from wind farms and is in desperate need of a thorough review. A far better understanding of the noise emissions from wind farms is now being gained, but this better understanding is both wasted and ignored. The document itself curiously - is actually fit for purpose (just not the purpose for which it is most often used): go back to that introductory paragraph I quoted just under the video and re-read it. You see, ETSU-R-97 is not designed to ensure that quiet rural properties remain quiet, it is a document that '.... describes a framework for the measurement of wind farm noise and gives indicative noise levels thought to offer a reasonable degree of protection to wind farm neighbours'. The really key phrase here is 'thought to offer a reasonable degree of protection' - unfortunately, the words thought and reasonable ensure this document has a built in get out clause.

Finally, I would like to set the record straight. I do believe that the audible sound emitted from wind turbines is decreasing as better designs are rolled out. However, by not updating this document and by setting such relatively high acceptable noise emission for wind farm operations, ETSU-R-97 effectively allows bigger and bigger turbines to be installed and still stay within the 'accepted' noise emission standard. Perhaps this is the real reason why we don't see this document being updated.

If you are interested in finding out more about the health implications of the noise emissions from wind farms, click on the Medical Data link at the top of this blog. It will be a few more months before the list of documents can be considered approaching complete, but there is some pertinent reading material there in the meantime.


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