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The WINDFARMperception project shows that the sound of wind turbines causes relatively much annoyance. The sound is perceived at relatively low levels and is thought to be more annoying than equally loud air or road traffic. This may be caused by the swishing character of the sound or because at night it does not decrease in strength -which is usually the case for traffic noise. Also in this study more disturbance of sleep occurs at the highest sound levels that occurred in this study.
In the WINDFARMperception project, supervised by Frits van den Berg, the perception was investigated of modern, tall wind turbines by Dutch residents. The study shows that sound from wind farms is an important disadvantage of wind energy which in itself is positively appreciated by a majority of the participants. However, to increase public acceptance a reduction of nuisance is important. The view that noise reduction should not impair maximum efficiency does not agree very well with the general Dutch noise policy where the acceptability of a measure of annoyance determines what sound levels are acceptable.
The study further shows that having an economical benefit from a wind farm quite significantly influenced it's perception. This perception is also related to the appreciation of wind turbines in the landscape scenery and the value of the landscape. In the public debate in the Netherlands these different views often lead to polarization, but an exchange of views and ideas could lead to more understanding. Because the visibility of wind turbines is an important factor contributing to nuisance, the type of landscape and its suitability will also be important for the appreciation of and nuisance from wind farms.
Finally it appears one must be cautious with optimistic assumptions about the potential of other noise sources, especially noise from motorways, to mask the sound from wind turbines. Even much louder road traffic does not appear to reduce the annoyance due to wind turbine sound.
Wind turbine sound is annoying...
More than half of the residents in this study were positive about wind energy. A negative opinion on wind energy and especially its influence on the landscape scenery increases the probability to be annoyed. From this study it cannot be determined what is the cause or what the consequence. Sound appears to be the most annoying aspect of wind turbines: they cause more noise annoyance than equally loud traffic does. Moreover wind turbines are considered more annoying if they are visible from the dwelling or garden.
Three out of four participants declare that swishing or lashing is a correct description of the sound from wind turbines. Perhaps the character of the sound is the cause of the relatively high degree of annoyance. Another possible cause is that the sound of modern wind turbines on average does not decrease at night, but rather becomes louder, whereas most other sources are less noisy at night. At the highest sound levels in this study (45 decibel or higher) there is also a higher prevalence of sleep disturbance.
... except when there is an economic benefit
A striking result of this study is that the 14% of the participants that had an economical benefit from a wind turbine did not think the sound was annoying. The benefits exist because they own a wind turbine or have shares in a wind farm. These participants heard the sound just as well as the other participants with no benefits and gave the same characterizations of the sound, but did not find it annoying.
Participants with an economic benefit differed from the other participants in the study. ‘Benefitters' lived closer to the wind turbines, but had a more positive view in wind energy and the impact on the landscape. They were relatively better educated, younger and (hence) healthier.
The reasons for this lack of annoyance with people that have economical benefits have not been investigated, but could be due to the actual profit they have, their positive view on landscape and wind turbines, and because they have a measure of control over the turbines. One of the participants remarked: "If we are disturbed by the turbine we stop it, and we do the same for the neighbours".
Masking by road traffic?
One of the topics in the survey questionnaire was the perception of road traffic sound. It appears that people indeed do not notice wind turbine sound as often when there is more sound from road traffic, but this traffic noise does not have an effect on the perceived annoyance from the wind turbines. Wind turbines alongside busy motorways are thus not necessarily less annoying than they would be without the traffic noise.
This project is a cooperation of the former Science Shop for Physics of the University of Groningen, the University Medical Centre Groningen (UMCG) and the University of Göteborg, and was made possible by funds provided by the European Union. The study was carried out by Frits van den Berg (University of Groningen), Eja Pedersen (University of Göteborg), Jelte Bouma and Roel Bakker (both UMCG). For this study a questionnaire from a previous Swedish study was used as well as detailed calculations of the sound level due to wind turbines and their relative size in the field of view of residents. The results of this project will be available on the website of the WINDFARMperception project.
For further information: dr Frits van den Berg: tel. + 31 6 125 418 65, email: email@example.com. Dr G.P. van den Berg is a staff member of the Science & Society Group of the University of Groningen.