The government guidance for measurement of wind farm noise is a document known as ‘ETSU 97’.
This guidance was produced over 10 years ago and since it was drafted, wind turbine size has dramatically increased and problems – which the ETSU methodology does not address – have come to light at several established wind farms.
Although it is still official government guidance, most noise experts now accept that ETSU 97 does not adequately deal with certain potential noise impacts of wind farms.
One potential wind farm noise problem is a phenomenon known as ‘amplitude modulation of aerodynamic noise’ or, more commonly, ‘AM’.
In simple terms, AM is the increased swishing of turbine blades as they pass – the ‘whoomph, whoomph, whoomph’ of the turning blades – which is increased significantly in certain conditions.
The ETSU 97 guidance does not deal with AM. This is because it was written when smaller turbines and smaller turbine blades were being used and when wind farm developments were still fairly new. Those that had been built were, on the whole, sited well away from residential areas and as a result, AM problems had rarely been reported. They only became apparent as more and bigger developments were built. As a result, a wind farm can comply in all respects with ETSU 97 government guidance – but if it is in an area where local land, weather and atmospheric conditions are such that AM occurs, it can create horrendous noise problems for those in the locality.
A worrying example
Near Deeping St Nicholas in the Fens, Jane Davis and her family have been forced to move out of their house by frequent and intrusive noise from a neighbouring wind farm development. They were unable to sleep properly at night and have recently been unable to get a valuation of their house because of the ongoing problems. The Davis story is the stuff of nightmares. Their case is still being investigated but because the wind farm has already been built and background noise levels at their house were not monitored beforehand – nor was AM considered to be a potential problem – there are no safeguards at all in the wind farm planning permission. It seems that there is nothing they can do to stop the noise.
AM is not the only potential problem with the Den Brook proposal.
As part of its assessment, RES took background noise measurements at two local properties. These measurements were analysed and used to set noise limits against which increased noise levels at any property resulting from the operation of the wind farm, could be measured. In effect, the noise at a property when the turbines are working must not go above these limits.
DBJRG believe that because RES’s analysis of the background noise data was proved to be wrong, the noise limits set are unfairly high. As a result, there could be a significant increase in noise levels at surrounding properties once the wind farm is in operation that residents can do nothing about. They would have no recourse to the developer or to the local authority.
Research suggests that about 20% of wind farms cause noise problems – but experts admit they don’t know how to predict which ones will. It depends on the size of the turbines, how they are spaced, what the land is like, where a house is and the atmospheric conditions in the area. We don’t know for sure that there will be a noise problem if the Den Brook wind farm is built – but we DO know that RES’s noise assessment for the project is wrong. We also know that the turbines are of similar size and layout to those that are causing huge problems for the Davis family – and we strongly suspect that atmospheric conditions and land layout in the Den Brook valley are such that AM is very likely to occur. This means it is absolutely essential that proper investigations and monitoring are carried out before the wind farm is built.
A summary of DBJRG concerns
1) RES’s original noise assessment has been shown to be wrong. It contains basic data processing errors and there are also further errors and discrepancies in the noise assessment methodology used. A new noise assessment is required to properly and thoroughly assess the noise impacts of the proposed development and to set accurate and realistic noise limits.
2) Not only were there errors in the original noise assessment, which was therefore in breach of government guidance in the form of ETSU 97, any new assessment needs to go beyond the requirements of the outdated ETSU 97 guidance. If those living close to modern turbines are to be adequately protected, potential noise impacts needs to be fully assessed using current understanding of noise issues – not only by reference to outdated, unrevised guidance.
3) Without a comprehensive, trustworthy and site-specific noise assessment, the potential benefits of the Den Brook development in terms of its contribution to ‘green’ targets cannot be properly weighed up against the detriment it will cause by way of increased noise levels and other impacts on the area, its wildlife and the lives of those living around the site.
4) DBJRG’s concerns about mistakes RES has made, about the deficiencies in ETSU 97 and the possibility of AM and other noise problems from the development are being magnified enormously by RES’s unhelpful attitude. RES originally promised to share noise data – then failed for 3 years to provide it. RES assured local people and the Planning Inspector at the first Public Inquiry that its noise assessment was accurate – then admitted it contained errors. RES tried to dismiss the errors – then agreed they were sufficient to require quashing of the planning permission. RES claims other discrepancies are a matter of opinion only – but now uses different methods for assessment. To add to all of this, RES is still refusing to share information. In November 2008 it promised to supply supplementary environmental information, including information about wind speeds and wind directions used in its noise assessment. This will enable DBJRG’s experts and any other members of the public who wish, to make their own independent assessment of the data before a second Public Inquiry. RES gave assurances that details of when that information would be made available would be with us at the end of November 2008 – but in the middle of January 2009 still nothing had been supplied. RES claims to want a fair and open hearing of all the issues at a second Public Inquiry, yet consistently refuses to make information publicly available.
5) A second Public Inquiry is necessary because RES got it wrong first time around – but the taxpayer, not RES, will be bearing the cost.
6) If the wind farm is built RES will benefit through the government subsidy programme (which is paid for by us, the consumer). It can take the benefit with little regard to the harm. We’ve also heard from residents living close to a wind farm in Scotland where there are ongoing noise problems that RES built then sold. Whatever verbal assurances RES might give, we don’t know who we’ll be dealing with in future. We need to sort out possible problems now.
Please support the Den Brook Valley communities of Spreyton, Bow & North Tawton.
This article is the work of the author(s) indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.
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