Opponents of wind farms claim that there are high levels of infrasound and low frequency sounds that are generated by wind turbines and that these pose a potentially serious threat to communities near wind farms. This is called wind turbine syndrome by some people, and a lot of research and experimentation by manufacturers of turbines, government research institutes and Universities have been carried out into the phenomenon.
The main source of sound from wind turbines is usually aerodynamic noise, which is created when the wind passes over the rotating blades. This sound is often heard as a swishing or whooshing sound, when close to a turbine. Turbines can also produce some mechanical noise from the operation of the generator and gear box, but this is less common. Improvements in turbine design over the last twenty years have greatly reduced the mechanical sound emitted from modern wind turbines, and the aerodynamic sounds have also been reduced by more efficient blade design.
Sound from wind turbines will vary considerably within and around wind farms. Sometimes the lay of the land can dampen or artificially increase the apparent volume of turbines, but there are sophisticated computer programmes that can map the land where a turbine is to be sited and predict the effect the area will have on sound waves emanating from the turbine. However, I have recently stood beneath a functioning wind turbine in a 20 mph wind and conducted a perfectly normal conversation with a colleague, without having to raise my voice, or ask her to do the same.
Wind turbines will create more sound as the wind speed increases. But it is important to remember that the background sound will also increase, as the wind blows through trees, past buildings, through heather and brush, and through power lines and other objects. At the high wind speeds, it will often be hard to distinguish between these background sounds and the sound from the operating wind turbines.
Most countries have regulations saying that wind turbines should be sited a certain distance from homes or places of work to minimise sound causing distraction to people. But that said, there are many people who have chosen to have a home wind turbine sited near their property, and who have found the sound of the turbine not a problem, and even comforting- knowing that with each rotation it is generating clean carbon-free energy for their home. I know of one gentleman in California who has difficulty sleeping when his nearby wind turbine isn't operating; it seems that he finds its sound rather like a lullaby!
In 2009 an international panel of experts released a report, Wind Turbine Sound and Health Effects: An Expert Panel, based on a review of a large body of scientific literature on sound and health effects, and specifically with regard to sound produced by wind turbines.
The panel concluded:
- There is no evidence that the audible or sub-audible sounds emitted by wind turbines have any direct adverse physiological effects.
- The ground-borne vibrations from wind turbine masts are too weak to be detected by, or to affect, humans.
- The sounds emitted by wind turbines are not unique. There is no reason to believe, based on the levels and frequencies of the sounds and the panel's experience with sound exposures in occupational settings, that the sounds from wind turbines could plausibly have direct adverse health consequences.
Basically they found that Wind Turbine Syndrome was not supported by the facts in their study. However another study noted that if winf turbines were not regularly maintained and occasionally refurbished, the longer they were in operation, the more mechanical noise they could generate.
If you look on YouTube you will see a number of clips of wind turbines with sound. Some of these have clearly had the sound portion tampered with to make it louder and more intrusive. That said there are other clips from pro-wind supporters where the turbines sound suspiciously quiet! Here are some:
I urge you to go and visit a wind farm and hear for yourself if you want to hear how they sound.