Solitary wind turbine near Bergen in Germany (Image: Jason, Flickr)
Over recent years, the wind industry all over the world has had to endure a spate of protest against the construction of onshore (and offshore) wind farms. At first, the complaints were concerned with visual impact, but more recently wind turbine noise has also been a major source of complaints. Collectively, this level of opposition has been enough, in many cases, to completely thwart the development of wind farms in certain areas.
However, is there really any evidence to suggest noise, if indeed wind turbines produce any of any real significance, is a major problem? Survey after scientific survey on the matter has rejected the suggestion after prolonged and careful analysis.
According to GE, the manufacturer of several models of onshore and offshore wind turbines, the closest distance a wind turbine can be placed to a home is about 300 meters or more. At this distance, a wind turbine will emit noise levels of 43 decibels, which is less than the noise produced by the average air conditioner (50 decibels) while most refrigerators emit noise of around 40 decibels. This noise level falls to 38 decibels at a distance of 500 meters. Keith Longtin of GE Renewable Energy says that most background noise reaches a level of 40-45 decibels, which means that noise from a wind turbine would be completely drowned out by it.
You would think that such information from industry experts and scientists would be enough to quell the matter, but as we’ve seen from climate change denial around the world, if anything, such information is completely ignored by those with a potential axe to grind.
Those making complaints about wind turbine noise argue that they create noise from either the movement of the blades through the air or from the mechanical hub that generates the electricity. The argument goes that the movement of the blades can produce an oscillating or pulsing sound while the hub emits a whining or screeching sound.
Sound fades with distance, following the Inverse Square Law, a law of physics that has been known since the 17th century and basically relates to any sound originating from a distinct source, such as a wind turbine. In essence, at double the distance from the source, the loudness of a sound decreases to a quarter. Trebling the distance reduces the loudness to a ninth. Four times the distance reduces it to a sixteenth, and so on. This means that the measurement of sound from a wind turbine at distances of a kilometer or more is very complicated. In turn, this indicates that complaints regarding noise from wind turbines at a distance of 5 kilometers or more are highly unlikely to have any substance whatsoever, according to the Inverse Square Law and the principle of attenuation, which stipulates that air absorbs energy from sound waves, something that is increased if there is dust or mist in the air.
Unfortunately, complainants very often accuse acoustic scientists employed by the wind industry to assess noise levels as having a ‘vested interest’, and are thereby minded to disprove complaints about noise when investigating the matter. For example, the website Windbyte argues that the proper response should be to employ clinicians and researchers with experience in analyzing low frequency noise and its impacts on the human body, particularly with regard to the cochlea and interruption of sleep.
The type of noise most commonly associated with wind farms, according to complainants, is known as Amplitude Modulation (AM). The term is basically used to describe a fluctuation in noise levels, causing a general ‘swish’ ‘whoomph’ or ‘thump’ noise, which those opposed to wind turbines claim is related to the rotational speed of the blades. In 2007, the Department of Energy & Climate Change (DECC) commissioned Hayes McKenzie Partnership and the University of Salford to investigate this phenomenon by means of a survey of wind farm noise complaints submitted to local authorities. In 2009, the survey data was released, concluding that a substantial number of noise complaints could be attributed to AM.
Wind farm in the UK (Image: Steve P2008, Flickr)
Typical of complaints regarding AM is that concerning the Den Brook wind farm in Devon, to which a specific planning condition regarding AM was attached as part of the consent awarded to it in 2009. This followed two public inquiries, the second of which saw extensive discussion of noise issues. The Den Brook AM condition states the wind farm operator must, at its own expense, “employ a consultant approved by the local planning authority to assess whether noise emissions at the complainant’s dwelling are characterized by greater than expected amplitude modulation”. In the event, opposition to this wind farm failed to win its case, and construction of the project began in 2015. Nevertheless, some have argued that the planning condition attached to the consent, the Den Brook AM noise condition, may be useful in assessing whether there is a noise problem or not.
Dr Lee Moroney and Dr John Constable, writing on the website of the Renewable Energy Foundation (REF), having examined some of the data gathered by the Hayes McKenzie survey, argue that the Den Brook AM noise condition could potentially be used to assess alleged wind turbine noise if it was verified against SCADA (Supervisory Control and Data Acquisition) data, which is automatically gathered from each turbine, assuming this data was made accessible that is. The major problem is that there is considerable controversy over whether AM can be effectively distinguished from other noises in the local environment.
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How have other countries around the world fared in the study of this issue?
In 2014, Health Canada released a report entitled Wind Turbine Noise and Health Study: Summary of Results. The study concluded that quality of life was largely unaffected by wind farms. It rejected various accusations that wind turbines cause sleep disorders, dizziness, tinnitus, migraines and headaches, high blood pressure and diabetes.
Some complaints concern alleged infrasound, which can be described as resulting from acoustic oscillation with a frequency below that of audible sound (16 Hertz). In essence, it is inaudible to humans. A report by the South Australian Environmental Protection Agency (EPA) published in 2013 found that infrasound levels at sites close to wind farms are no higher than levels at more distant locations and there did not seem to be any credible contribution to infrasound level from wind farms. This is supported by other research from the Association of Australian Acoustical Consultants finding that infrasound levels adjacent to wind farms are below the threshold of human perception and below currently accepted limits. Similar findings have been obtained by the Victorian Department of Health in Australia, Hideki Tachibana, Professor Emeritus at the University of Tokyo and the Bavarian Environment Agency in Germany, among others.
Albany wind farm in Western Australia (Image: Lawrence Murray, Flickr)
The Massachusetts Department of Environmental Protection has also found very little evidence of so-called ‘wind turbine syndrome’, and no evidence of ‘wind turbine flicker’ causing seizures or any other illness.
The most likely explanation for all this is mere suggestion, the conclusion reached by Crichton, F. et al in a study published in Health Psychology. The study found that healthy volunteers, accessing information about an expected physiological effect of infrasound, tended to report symptoms associated with that information. Thus the issue is almost certainly to do with psychological expectation. Or to put it more simply, the tendency among impressionable individuals to literally ‘worry themselves sick’, a phenomenon known as the ‘nocebo’.
There is just one final point to make here. Where wind turbine maintenance has been neglected, there is indeed the potential for the working parts to emit unpleasant noise. However, that is just what you would expect, as with any other piece of machinery.
With well-maintained turbines (the vast majority), it is now pretty clear, following repeated studies around the world, that wind turbine noise is just not an issue to be taken seriously.