A quiet revolution

In the clamour to cut carbon, are wind farm concerns going unheard? E&T investigates.

When American paediatrician Dr Nina Pierpont publishes her book 'Wind Turbine Syndrome' later this month, the wind industry will dismiss it. Already the British Wind Energy Association has published a three-page document stating that her research is not credible. Meanwhile, the trade body's US counterpart, the American Wind Energy Association, asserts her syndrome is not a genuine medical condition. Why the backlash?

For more than five years, self-funded and in her spare time, Pierpont has studied the symptoms displayed by ten families living within 1.5km of wind turbines. These range from sleep disturbance and headaches to concentration problems and panic episodes.

She describes this set of symptoms as 'wind turbine syndrome', due to abnormal stimulation of the inner ear's vestibular system by turbine infrasound and low-frequency noise. She also claims as more turbines are erected, the syndrome is likely to become an "industrial plague".

Government and industry bodies have responded quickly and sharply. Whereas Pierpont claims her work has been peer reviewed, the BWEA says it is self-published and points out it hasn't been published in a peer-reviewed medical journal.

And, while Pierpont is adamant her book documents a "consistent and often debilitating complex of symptoms experienced by adults and children living near to industrial (1.5 to 3MW) wind turbines", the UK National Health Service states: "this study provides no conclusive evidence that wind turbines have an effect on health or are causing the set of symptoms described as 'wind turbine syndrome'".

For her critics, Pierpont's fatal flaw is that her syndrome hangs on the premise that infrasound and low-frequency noise, emitted by turbines at frequencies of 10 to 200Hz, is harmful. But, as Geoff Leventhall, consultant in noise vibration and acoustics, says: "The physics in Nina Pierpont's work is rubbish. While her work is all about infrasound, the levels from wind turbines are much too low to produce any of the effects she claims."

Leventhall has been looking into low-frequency noise since the 1970s and authored the DEFRA review 'Low-Frequency Noise and its Effects'. His no-nonsense comments are supported in his recent paper, 'Infrasound from wind turbines - fact, fiction or deception', as published in Canadian Acoustics journal. Here he simply states: "Infrasound from wind turbines is... of no consequence."

But, while Leventhall's views on Pierpont's research are clear, he is certain that noise can be an issue for some people living close to wind farms and the symptoms that the paediatrician describes are very real.

"The wind developers are going to rubbish her book, and quite rightly so, but what must be accepted - and developers don't want to accept this - is that yes, people are disturbed," he says. "If people are consistently disturbed, and their sleep is consistently disturbed, then they will develop some very 'unclever' stress symptoms. That will lead to stress-related illness."

Leventhall's warning is echoed in research carried out by Dr Eja Pedersen of Halmstad University, Sweden. In the past decade, Pedersen has surveyed thousands of people, typically living within 2.5km of wind farms in Sweden and the Netherlands. Statistical analysis has uncovered a link.

While she cannot directly relate wind turbine noise levels to health symptoms, she has established a relationship between people who are annoyed by turbines and stress symptoms such as headaches and sleep disturbance.

"The main adverse effect from wind turbines is annoyance due to sound," she says. "Our research indicates that people get annoyed by the noise and this lowers their wellbeing. In addition, there are people who are already vulnerable - perhaps they are stressed at work - and already have a lowered wellbeing. These people need to find places to rest, and if they have chosen their homes, they will not benefit from extra noise they can't control."

So how can you reduce annoyance? Pedersen first suggests taking a look at building construction. As she points out, many dwellings in Sweden are triple-glazed, blocking out a lot of noise.

"However, sometimes I think it's just a case of moving the wind turbines a little bit further from people's homes, so the noise is a little bit lower," she adds.

Pierpont would agree. In her book, she recommends wind turbines be built at least 2km away from people's homes. So, are wind farms too close for comfort? Dick Bowdler, a noise consultant specialising in wind farm noise, believes this could be the case in the countryside.

"Although there is no evidence that low-frequency noise from wind turbines would be a problem, the findings of Nina Pierpont don't surprise me at all," he says. "I would expect there to be a significant proportion of people who would be annoyed living that close to turbines. I've always said you need to get 2km away in a rural area, where there is no noise apart from the wind. At this distance you probably won't hear the wind farm, and if you do, it will be very rare you notice it."

Clearly, such a large set-back distance would hamper wind-farm development. "I have sympathy with the argument that this limits the development of wind power," agrees Bowdler. "And if I were party to an agreement to determine [a set-back distance] then I would consider something less than 2km, if I had full information on noise issues and other considerations."

Leventhall is more bullish on distance restrictions. "With a 2km set-back, there would be no need for calculations and no need for consultants, but far fewer wind farms would be built and these would be rather small," he states. "Today's set-backs have to comply with criteria. It may be that the current criteria aren't strict enough, that's up to somebody else to decide, but each situation should be determined separately. I believe a 2km set-back is too large and that around 500m will be fine in many cases."

ETSU-R-97 noise restrictions

The distance between homes and turbines is not the only contentious issue when planning wind farms. Bowdler also believes UK government restrictions on wind farm noise are too lax.

Today's government guidelines for wind farm noise were drawn up by a working group of wind farm developers, noise consultants and environmental health officers, and released in September 1996. Known as ETSU-R-97, Bowdler describes them as flawed and bearing no resemblance to the standards used for other industrial developments.

The guidelines first advise that noise from a wind farm should be limited to 5dB above day-time and night-time background noise levels, in line with other renewable energy developments. However, these limits are then relaxed.

In areas where background noise is particularly low, the document states the daytime noise from a wind farm need not be limited to this level plus 5dB, as long as it doesn't exceed 35 to 40dB. Meanwhile the limit for night-time should be 43dB.

As Bowdler highlights, the higher noise limits are likely to prove more problematic in rural regions. "During the middle of the night in rural areas, background noise is down to 20dB," he says. "A noise level measuring 40dB is actually four times as loud as 20dB, and anything up to 43dB is permitted in the UK at night."

While these limits are approximately in line with other European countries - Denmark, Germany and Holland stick to a 40dB limit - US limits can be as high as 55dB. And this means wind farms can be built closer to people's houses.

Bowdler is convinced lenient noise limits are the major cause of complaints. As he puts it: "The levels are far too high and, personally, I think this is the fundamental problem that causes complaints. If you look at Pierpont's people, they will be exposed to noise levels in excess of 40dB."

Amplitude modulation

In contrast, Leventhall believes limits of roughly 40dB are "okay". That is, he states, unless a sound phenomenon known as 'amplitude modulation' comes into play.

Amplitude modulation is a little-understood noise phenomenon identified at a handful of wind farms across the UK. Typically described as a 'swishing' or 'thumping' noise, noise levels go up and down, and many wind farm noise complaints appear to be linked to this phenomenon.

"We don't really know what causes it, it could be due to wind gradients or wind shears between the top and bottom of the blades," explains Leventhall. "However, if there is significant amplitude modulation, you get a fluctuating noise which is more difficult to accept than a steady noise of the same average level."

Julian Davis is only too aware of this fact. He and his family left their farm at Deeping St Nicholas, Lincolnshire, in May 2007, after a wind farm started operating 930m away (see 'The Family That Left', below). While they report hearing a range of noises, they cite amplitude modulation as the most disruptive.

"This [sound] was quite severe," he says. "When we first heard it we thought 'there must be something wrong with the turbines, they can't surely do that', it was horrendous."

But, despite anecdotal evidence, research to date indicates amplitude modulation is not a problem at most wind farms. A report from Salford University, commissioned by the Department for Business, Enterprise and Regulatory Reform (BERR) and published in July 2007, confirmed the phenomenon was taking place at four of the UK's wind farms and could be occurring at a further eight.

The researchers stated however that further research was difficult to justify. As their report concluded, amplitude modulation would not be present on most days, and complaints had 'subsided' at three of the four sites. In the remaining site, Deeping St Nicholas, they noted investigations were ongoing.

Nick Medic, communications manager of the BWEA, supports Salford University's work. "Within the context of how significant other sources of noise pollution are, this is a negligible problem," he says. "Our awareness work shows that so much is currently being written about wind farm noise that people expect to encounter a deafening roar of turbines when they visit a wind farm. The first thing they comment on is how quiet the turbines are."

Bowdler disagrees. "The 'headline' result of the Salford report was that there are four amplitude modulation-affected sites. My view is that's not borne out of evidence in the report and there are more," he says.

Indeed, as the Salford report was released, Bowdler, as part of a Noise Working Group advised BERR that a greater understanding of amplitude modulation was crucial as incidents could grow as more wind farms come online. BERR ignored the advice.

Clearly issues around wind farms and noise are many, complex, and are not going away. At the time of writing, Dr Nina Pierpont is preparing to send copies of her book to major clinical journals for review. She then hopes to testify before US congress. Her website states: "With Congress alerted to 'wind turbine syndrome'... efforts to get [wind turbines] removed from your backyard will be much more likely to succeed."

But, as Geoff Leventhall points out, her efforts to pin down 'wind-turbine syndrome' could prove counter-productive. "Objectors like Pierpont have gone out of their way to frighten people and make them anxious about noise from wind turbines," he asserts. "Many publications show that if you are anxious about a noise source, then your reaction to it is more adverse. Pierpont denies this, but I think she's probably caused a lot of harm."

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