Studies On Wind Turbine Noise Raise Further Concern

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.