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ReferenceLow Frequency Noise and Wind TurbinesKeele University Rejects Renewable Energy Foundation's Low Frequency Noise Research ClaimsAugust 2005 Following a press release from the Renewable Energy Foundation (REF) and the associated article in the Scotsman at the beginning of August 2005, Professor Styles's team at Keele university have put together a rebuttal to what was a misinterpretation and confusion of various studies. Below is also included the original REF release and Scotsman article. Wind farm noise
We are writing to clarify some misconceptions in your report (8 August) about wind farm noise. While it is technically correct that "vibrations can be picked up as far away as 10km", to give the impression that they can be felt at this distance is highly misleading. The levels of vibration from wind turbines are so small that only the most sophisticated instrumentation and data processing can reveal their presence, and they are almost impossible to detect. The Dunlaw study was designed to measure effects of extremely low level vibration on one of the quietest sites (Eskdalemuir) in the world, and one which houses one of the most sensitive seismic installations in the world. Vibrations at this level and in this frequency range will be available from all kinds of sources such as traffic and background noise - they are not confined to wind turbines. To put the level of vibration into context, they are ground vibrations with amplitudes of about one millionth of a millimetre. There is no possibility of humans sensing the vibration and absolutely no risk to human health. It is, however, an issue for the Eskdalemuir seismic array, as it can detect this level of vibration. It is designed to detect explosions and earthquakes of a low magnitude from all over the world. The infrasound generated by wind turbines can only be detected by the most sensitive equipment, and again this is at levels far below that at which humans will detect the low frequency sound. There is no scientific evidence to suggest that infrasound has an impact on human health.
Wind-farm noise rules 'dated'
Guidelines on noise from wind farms urgently need to be revised, research suggests. One study on the modern, tall turbines now used, conducted at Dunlaw wind farm in the Borders, found that when the 60-metre turbines start to generate electricity, even at low wind speeds, vibrations can be picked up as far away as 10km. Earlier studies concluded there was no significant risk to health from vibrations produced by wind farms. But campaigners say this research was done on much smaller turbines than those used today. The research on the Dunlaw wind farm is backed up by a study just published by acoustic experts at the University of Groningen in the Netherlands. It also claims that measurable, low-frequency noise is present and is relevant to the audible noise nuisance often reported. Professor Peter Styles, who led the team from Keele University that studied Dunlaw wind farm, said: "We have clearly shown that wind turbines generate low-frequency sound [infrasound] and acoustic signals which can be detected at considerable distances [many kilometres] from wind farms on infrasound detectors and on low-frequency microphones. "When the wind farm starts to generate at low wind-speeds, considerable infrasound signals can be detected at all stations out to 10km." Professor John Ffowcs Williams, professor of engineering at Cambridge University and a world expert on acoustics and noise reduction, said: "The regulations are dated and in other ways inadequate. It is known that modern, very tall turbines do cause problems, and many think the current guidelines fail adequately to protect the public." Jason Ormiston, wind energy officer for the industry body Scottish Renewables, said: "Expert opinion recognises there is no direct effect on human health from noise at the level generated by wind turbines." Dr Geoff Leventhall, consultant in noise, vibration and acoustics and the author of a government report on low-frequency noise and its effects, says: "I can state quite categorically that there is no significant infrasound from current designs of wind turbines."
REF PRESS RELEASE
Studies on Wind Turbine Noise Raise Further Concerns Two studies recently analysed by the Renewable Energy Foundation have today raised further concerns over Wind Turbine noise. REF supported further research by G. P. van den Berg, of the Faculty of Mathematics and Natural Sciences, University of Groningen into the presence of low frequency components in wind turbine noise. G. P. van den Berg's work establishes that measurable low frequency noise is present, and is relevant to the audible noise nuisance commonly reported. This reinforces doubts shared by many acousticians with regard to the continuing usefulness of current UK noise regulations relating to wind turbines, ETSU-R-97, which are now some ten years old, and refer to a previous generation of much smaller turbines. Hitherto, it has been assumed that low-frequency sound from wind turbines has not been a major factor contributing to annoyance as the blade passing frequency is of the order of one hertz where the human auditory system is relatively insensitive. This argument, however, can now been seen to obscure a very relevant effect: the blade passing frequency modulates well audible, higher-frequency sounds and thus creates periodic sound. This means that residents near wind turbines have observed that, often late in the afternoon or in the evening the turbine sound acquires a distinct 'beating' character, the rhythm of which is in agreement with the blade passing frequency, and that this effect is stronger for modern (tall) wind turbines. Professor Peter Styles and his team at Keele University have very recently also published a major study on vibrations from the 60m high wind turbines at Dunlaw. Interesting findings in this second report include that 'When the windfarm starts to generate (even) at low wind speeds, considerable infrasound signals can be detected at all stations out to c 10km' (p. 66). We have clearly shown that wind turbines generate low frequency sound (infrasound) and acoustic signals which can be detected at considerable distances (many kilometres) from windfarms on infrasound detectors and on low-frequency microphones.' Whilst earlier studies conclude there was no significant risk to human health from vibrations produced by wind-farms, these studies are dated, and refer to older, much smaller turbines. Concern is increased as most modern wind turbines are in excess of 100m (much bigger than those at Dunlaw), and developers are proposing to install these devices as close as 650m to human habitation (sometimes closer). Professor Ffowcs-Williams, Emeritus Rank Professor of Engineering at the University of Cambridge, one of the UK's leading acoustical experts and an advisor to REF, said: "Van den Berg's paper adds weight to the criticisms frequently offered of UK regulations covering wind turbine noise, ETSU-R-97. The regulations are dated and in other ways inadequate. It is known that modern, very tall turbines, do cause problems, and many think the current guidelines fail adequately to protect the public. This is a rapidly evolving field, and knowledge is growing fast. The Keele report, for example, is very important, and raises further questions with regard to the effect that modern wind turbines have on local residents. Sensitivity to lower frequency vibration varies considerably between individuals, and with Professor Styles providing clear evidence of detectable low frequency vibration at very large distances (10km), even from smaller turbines, it is entirely sensible to ask whether these cause problems for sensitive individuals living in much closer proximity. It really is time for the DTI to clear the air on this one, and institute a comprehensive and fully transparent study, obtaining data from the United States and Europe, as well as the United Kingdom."
For more information and an extensive Technical Annex on low frequency noise studies, see BWEA briefing on Low Frequency Noise and Wind Turbines. |
