Whenever the sound of a wind farm hits the press or the environmental courts, there are usually two polarised sides of the argument: complainants who say they can’t sleep at night and/or concentrate during the day, and those who suggest the complainants are hearing things.
Whether the noise generated by wind farms is unreasonably intrusive is a moot point and has been for some time. Which is why engineers at the University of Adelaide are researching the specific character of the sound of the modern wind farm.
“More understanding is needed,” says Con Doolan, the engineer leading the study at the University’s School of Mechanical Engineering. “So many people have talked to us, and there are a lot of people who are annoyed by the noise, so there is something in it. And we’d like to get to the bottom of it, and then control it.”
Sound is a complicated business; the way people respond to it invariably involves a number of subjective factors, such as the level of background noise, their attitude toward the source of the sound and even what they’re capable of hearing.
A few years ago The Hum, a mysterious low-frequency sound, kept some residents of Auckland’s North Shore awake at night. Researchers at Massey University never did identify the source, but they managed to record a sound that was probably industrial, which some could hear and others couldn’t. Those who could were driven to despair. (Similar Hums have bothered people in towns around the world throughout recent history.)
Some studies, by both physicians and acoustic engineers, have reported on wind-turbine noise problems, such as sleep deprivation, headaches, dizziness, anxiety and vertigo. Some have called this wind turbine syndrome, but a comprehensive study published in 2009 by researchers commissioned by the Canadian Wind Energy Association and American Wind Energy Association concluded it didn’t exist, that wind turbines do not make people sick. They acknowledged that some people were stressed out by the “swishing” sound the turbines often make, but argued that all sorts of sounds can annoy people and “annoyance is not a disease”.
But annoyance is not pleasant, either, and as Doolan notes, studies in Europe have also shown the noise that wind farms generate is often considered more annoying than other industrial noises. Wind farms may generate less noise than normal road traffic or the average office, but it’s less about the loudness of the sound and more about its idiosyncratic character. “People complain about hearing an endless train, a pole-driving noise … It’s like a hissing noise that goes up and down in volume – it’s an amplitude-modulated broadband noise. This is what we think makes it so annoying. A constant hiss you could get used to.”
It could be something to do with the shape of the blade: as the turbulent air flows over the blade’s sharp edge, sound is radiated extremely efficiently, and all in one direction. “So someone living at the base might not have a problem, but 2km away, it might be keeping them awake at night.”
It could be something to do with the way the blade interacts with its tower, or the wind farm’s terrain, or the effect of having many wind turbines interacting together; most research on the sound of a wind turbines has focused on single turbines, rather than the sound of several dozen rotating in unison. “And this might require a really simple solution, like slowing some down and making them less synchronised.”
To take complaints about the sound of wind farms seriously is not to undermine the virtue of wind farms as a clean source of energy. But once we better understand what can make wind farms so acoustically annoying, we can develop less acoustically annoying solutions. “We have some ideas about controlling it, but first we need to pinpoint exactly what noise-generating mechanisms are the most dominant.”
But will people who never wanted wind turbines in their midst always find something to complain about? “There probably is an element of that. But there are also people who have welcomed wind turbines into their communities, and who have now had to move out of their homes.”