Final Report Summary - WINDFARMPERCEPTION (Visual and acoustical impact of wind farms on residents)
The WINDFARM project aimed to investigate the relation between:
a) the generation of wind energy by onshore wind farms; b) the exposure of the residents to noise originating from these neighbouring wind farms; and c) the impact these wind farms have on the residents' perception concerning their health and well being.
Therefore the objective of the WINDFARM perception project was:
- to provide knowledge on the perception of wind turbines by people living in proximity to wind farms;
- to evaluate human responses to audio and visual exposures from wind turbines and to give insight in possibilities to mitigate the local impact of wind farms.
The preliminary analysis of the data was performed in the second half of 2007 and the results were collected in working papers that were discussed at the progress meeting in January 2008, again in Groningen. The meeting also reviewed the project methodology and forthcoming papers. After that the final analyses were done and documented in an analysis report. This report and parts of the interim reports formed the input for the final report that was published in June 2008. Publication of the final report was accompanied by a national (Dutch) and international (English) press statement, a message including a summary of results sent to several wind energy associations, consultants and wind energy groups, and a popular summary sent to respondents who had expressed an interest to see the results. Also, a website with project results was opened.
The study included calculating the aural and visual exposure at residences due to wind farms, and a postal survey among Dutch residents to measure their response to the actual exposure. The study group was selected from all residents in the Netherlands within 2.5 km from a wind turbine. As the study aimed to address modern wind farms, wind turbines were selected with an electric capacity of 500 kW or more and one or more turbines within 500 m from the first. Excluded were wind turbines, that were erected or replaced in the year preceding the survey. Residents lived in the countryside with or without a main road close to the turbines, or in built-up areas (villages, towns). Excluded were residents in mixed and industrial areas.
The sound level at the residents' dwellings was calculated according to the international ISO standard for sound propagation, the almost identical Dutch legal model and a simple (non spectral) calculation model. The rating sound level used was the sound level when the wind turbines operate at 8 m/s in daytime -that is: at high, but not maximum power. The size of the turbines was calculated as the viewing angle between the lowest and highest part of the biggest turbine, and also as the fraction of space above the horizon occupied by all wind turbines, both from the perspective of residents' dwellings.
The study group consisted of over 50 000 addresses. To obtain sufficient statistical reliability balanced against unnecessary work we needed approximately 150 addresses per area type and per sound level class. In the high exposure classes, all addresses were used, in each of the low exposure classes 150 were randomly selected. Thus, for the survey almost 2 000 residential addresses were finally selected and a questionnaire was sent to these addresses.
37 % returned the questionnaire. A test amongst those that did not return the questionnaire (the non-respondents) showed that for two key questions they did not differ from the respondents. All questionnaire results were fed into the survey database as well as the sound levels and the visual exposures obtained from the calculation models. This was the material available for analysis.
Almost all respondents (92 %) were satisfied with their living environment, though many reported changes for the better and changes for the worst. One in two respondents was (very) positive towards wind turbines in general, but only one in five were (very) positive towards their impact on the landscape scenery. Fourteen percent of the respondents had economic benefits from wind turbines by owning them or having shares in wind turbines or otherwise.
The percentage of respondents noticing the sound of wind turbines increased with increasing sound level, ranging from 25 % at low sound levels (less than 30 dBA) to 80 % and more at higher sound levels (above 35 dBA). Percentages were the same for those who had benefits and the other respondents. The percentage of respondents that were annoyed by the sound also increased with sound level up to 40 to 45 dBA and then decreased. Respondents with economic benefits reported almost no annoyance.
In general, respondents perceived wind turbines as being louder in wind blowing from the turbine to their dwelling (and less loud the other way round), in stronger wind and at night. Respondents were more likely to be annoyed by sound from wind turbines when they noted changes for the worse in their living environment and when they had a more negative view on wind turbines in general or their impact on the landscape scenery.
There is no indication that the sound from wind turbines had an effect on respondents' health, except for the interruption of sleep. At high levels of wind turbine sound (more than 45 dBA) interruption of sleep was more likely than at low levels. Higher levels of background sound from road traffic also increased the odds for interrupted sleep. Respondents were also annoyed by wind turbines in other ways than by sound: between 4 % and 13 % were rather or very annoyed by vibrations or the movement of rotor blades or their shadows in- or outdoors.
Sound proved to be the most annoying aspect of wind turbines. From this and previous studies, it appears that sound from wind turbines is relatively annoying: at the same sound level it causes more annoyance than sound from air or road traffic. A swishing character is observed by three out of four respondents that can hear the sound and could be one of the factors explaining the annoyance. Sound is therefore an important and negative feature of wind farms and we recommend that, in the planning of wind farms, the negative impact of the sound and sound reduction should be given more attention.
Visibility of wind turbines enhances their potential to cause noise annoyance. When wind turbines are invisible, they cause less annoyance. Perhaps less visibility can also be the result of reducing the visual contrast between turbines and landscape. The possibilities to do this will depend on the landscape type. The capability of busy road traffic to mask the sound of wind turbines is apparently not straightforward: a higher level of background sound from road traffic indeed reduces the probability of noticing the sound of wind turbines, but it does not have an effect on annoyance from the wind turbines. This may be due to differences between both sounds in pitch, in character (swishing) and in diurnal variation. This issue needs further investigation.
In the course of several years a lot of new knowledge on modern wind turbines has become available. This project gives more, and more detailed information on the impact of wind farms on their environment, which is crucial information in a time when wind energy is boosted to provide a larger part of the energy needed by society, while at the same time opposition to wind farms is growing. The positive attitude towards sustainable energy is not always accompanied by a positive reception of wind farm plans locally and this study helps to explain why that is. The results support an approach were the local community is involved in the planning process with real influence on the outcome. Also, the results have helped the Dutch government to commission a review of all wind turbine noise exposure studies to obtain a general dose-response curve.
a) the generation of wind energy by onshore wind farms; b) the exposure of the residents to noise originating from these neighbouring wind farms; and c) the impact these wind farms have on the residents' perception concerning their health and well being.
Therefore the objective of the WINDFARM perception project was:
- to provide knowledge on the perception of wind turbines by people living in proximity to wind farms;
- to evaluate human responses to audio and visual exposures from wind turbines and to give insight in possibilities to mitigate the local impact of wind farms.
The preliminary analysis of the data was performed in the second half of 2007 and the results were collected in working papers that were discussed at the progress meeting in January 2008, again in Groningen. The meeting also reviewed the project methodology and forthcoming papers. After that the final analyses were done and documented in an analysis report. This report and parts of the interim reports formed the input for the final report that was published in June 2008. Publication of the final report was accompanied by a national (Dutch) and international (English) press statement, a message including a summary of results sent to several wind energy associations, consultants and wind energy groups, and a popular summary sent to respondents who had expressed an interest to see the results. Also, a website with project results was opened.
The study included calculating the aural and visual exposure at residences due to wind farms, and a postal survey among Dutch residents to measure their response to the actual exposure. The study group was selected from all residents in the Netherlands within 2.5 km from a wind turbine. As the study aimed to address modern wind farms, wind turbines were selected with an electric capacity of 500 kW or more and one or more turbines within 500 m from the first. Excluded were wind turbines, that were erected or replaced in the year preceding the survey. Residents lived in the countryside with or without a main road close to the turbines, or in built-up areas (villages, towns). Excluded were residents in mixed and industrial areas.
The sound level at the residents' dwellings was calculated according to the international ISO standard for sound propagation, the almost identical Dutch legal model and a simple (non spectral) calculation model. The rating sound level used was the sound level when the wind turbines operate at 8 m/s in daytime -that is: at high, but not maximum power. The size of the turbines was calculated as the viewing angle between the lowest and highest part of the biggest turbine, and also as the fraction of space above the horizon occupied by all wind turbines, both from the perspective of residents' dwellings.
The study group consisted of over 50 000 addresses. To obtain sufficient statistical reliability balanced against unnecessary work we needed approximately 150 addresses per area type and per sound level class. In the high exposure classes, all addresses were used, in each of the low exposure classes 150 were randomly selected. Thus, for the survey almost 2 000 residential addresses were finally selected and a questionnaire was sent to these addresses.
37 % returned the questionnaire. A test amongst those that did not return the questionnaire (the non-respondents) showed that for two key questions they did not differ from the respondents. All questionnaire results were fed into the survey database as well as the sound levels and the visual exposures obtained from the calculation models. This was the material available for analysis.
Almost all respondents (92 %) were satisfied with their living environment, though many reported changes for the better and changes for the worst. One in two respondents was (very) positive towards wind turbines in general, but only one in five were (very) positive towards their impact on the landscape scenery. Fourteen percent of the respondents had economic benefits from wind turbines by owning them or having shares in wind turbines or otherwise.
The percentage of respondents noticing the sound of wind turbines increased with increasing sound level, ranging from 25 % at low sound levels (less than 30 dBA) to 80 % and more at higher sound levels (above 35 dBA). Percentages were the same for those who had benefits and the other respondents. The percentage of respondents that were annoyed by the sound also increased with sound level up to 40 to 45 dBA and then decreased. Respondents with economic benefits reported almost no annoyance.
In general, respondents perceived wind turbines as being louder in wind blowing from the turbine to their dwelling (and less loud the other way round), in stronger wind and at night. Respondents were more likely to be annoyed by sound from wind turbines when they noted changes for the worse in their living environment and when they had a more negative view on wind turbines in general or their impact on the landscape scenery.
There is no indication that the sound from wind turbines had an effect on respondents' health, except for the interruption of sleep. At high levels of wind turbine sound (more than 45 dBA) interruption of sleep was more likely than at low levels. Higher levels of background sound from road traffic also increased the odds for interrupted sleep. Respondents were also annoyed by wind turbines in other ways than by sound: between 4 % and 13 % were rather or very annoyed by vibrations or the movement of rotor blades or their shadows in- or outdoors.
Sound proved to be the most annoying aspect of wind turbines. From this and previous studies, it appears that sound from wind turbines is relatively annoying: at the same sound level it causes more annoyance than sound from air or road traffic. A swishing character is observed by three out of four respondents that can hear the sound and could be one of the factors explaining the annoyance. Sound is therefore an important and negative feature of wind farms and we recommend that, in the planning of wind farms, the negative impact of the sound and sound reduction should be given more attention.
Visibility of wind turbines enhances their potential to cause noise annoyance. When wind turbines are invisible, they cause less annoyance. Perhaps less visibility can also be the result of reducing the visual contrast between turbines and landscape. The possibilities to do this will depend on the landscape type. The capability of busy road traffic to mask the sound of wind turbines is apparently not straightforward: a higher level of background sound from road traffic indeed reduces the probability of noticing the sound of wind turbines, but it does not have an effect on annoyance from the wind turbines. This may be due to differences between both sounds in pitch, in character (swishing) and in diurnal variation. This issue needs further investigation.
In the course of several years a lot of new knowledge on modern wind turbines has become available. This project gives more, and more detailed information on the impact of wind farms on their environment, which is crucial information in a time when wind energy is boosted to provide a larger part of the energy needed by society, while at the same time opposition to wind farms is growing. The positive attitude towards sustainable energy is not always accompanied by a positive reception of wind farm plans locally and this study helps to explain why that is. The results support an approach were the local community is involved in the planning process with real influence on the outcome. Also, the results have helped the Dutch government to commission a review of all wind turbine noise exposure studies to obtain a general dose-response curve.
