RenewableUK will today release in-depth new research revealing the cause of certain wind turbine noises and the technical measures needed to tackle the problem, alongside proposed planning conditions to help ensure developers take steps to minimise turbine noise.
Wind turbines are known to result in two types of noise: the common “swishing” sounds caused by the blades and known technically as Normal Amplitude Modulation (NAM), and rarer “whumph” noises known as Other Amplitude Modulation (OAM), the cause of which has to date been uncertain.
However, new research to be published today by trade association RenewableUK and carried out by a group of independent experts, including academics from the Universities of Salford and Southampton, and the National Aerospace Laboratory of the Netherlands, Hoare Lea Acoustics, Robert Davies Associates and DTU Riso in Denmark, identifies the cause of OAM noise as sharp changes in wind speed and direction.
The report concludes that sudden changes in wind speed and direction can on occasion lead to a partial stall of a turbine, resulting in the “whumph” noise.
The study stresses that OAM is infrequent – an analysis of 133 wind farms found it had occurred at four sites and may have been a factor at an additional eight locations – and is no louder than the more common NAM, with both noises recording 35 to 40 decibels at a distance of one kilometre from a wind farm, a level comparable to the sound from traffic on a single carriage A road at the same distance.
However, an analysis of individuals’ response to the noise carried out by the University of Salford found that some people found the intermittent nature of OAM noise and its lower pitch more annoying than the more common “swishing” noise from turbine blades.
Speaking to BusinessGreen, RenewableUK deputy chief executive Maf Smith said that in addition to identifying the cause of the noise the research had worked out how to combat the problem. “Because of the research we now understand how the stalling of turbines can happen when the wind changes suddenly,” he explained. “We’re are very confident manufacturers have the ability to monitor sites and use existing software systems in turbines to change the angle of the blades to stop the noise if it turns out OAM is occurring.”
The research also found that while OAM is infrequent, it is currently impossible to predict if a site or turbine is likely to be susceptible to the problem. As such, alongside the research RenewableUK will today release a new planning condition, developed in conjunction with some of its members and the Institute of Acoustics, that planning authorities can adopt to minimise the risk of disruption caused by OAM.
The proposed condition would require wind farm operators to measure instances of OAM and set a threshold in decibels above which they would be required to act immediately to change blade angles to minimise the noise.
Smith said the condition would benefit both developers and local communities that host wind farms, by reducing the risk of complaints and allowing operators to tackle noise issues without the need for planning authorities to issue orders restricting turbine operation.
RenewableUK stressed that despite repeated studies on the subject there was no evidence wind turbine noise has any impact on public health and highlighted the latest research as a further demonstration of the industry’s commitment to acting as “good neighbours to the communities in which we operate”.
However, the new research is likely to be seized on by critics of wind power as further evidence of the local environmental impact turbines can have.
The sector has faced fierce criticism from some segments of the media in recent months and there are growing concerns that the government is seeking to restrict onshore wind farm development after ministers last month agreed to fresh cuts to subsidies for new projects.
But Smith insisted that far from highlighting the extent of wind turbine noise the latest research demonstrated both the relatively low level of noise generated by turbines and the industry’s commitment to minimising it further.
“We’re proud to have commissioned this ground-breaking research as it pushes the boundaries of our knowledge of wind turbine acoustics considerably further forward,” he said. “It’s a tangible example of the wind industry acting in a responsible manner, demonstrating that we’re continuing to be good neighbours to the communities who host wind farms in the UK.”
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