By: Rosemary Stephen PMed, (cert) EOH, IPM, Elements: Environmental Health Intelligence
Parts I and II of this series looked at a small segment of the population who experience physical discomfort when living in close proximity to wind turbines due to infrasound. Approximately 15% of the total population experience health issues caused by infrasound, including disrupted sleep, noise irritation and other physical ailments, and of this number 3% suffer severe symptoms. So far, however, the World Health Organization (WHO), and numerous other agencies which have studied wind turbines, have concluded there are no human health risks associated with this green energy source [1].
The wind industry, along with other health agencies, have, however, expressed concern even if studies seem to rule out health risks. Wind turbine engineers have instituted a steady series of design changes to decrease both noise emissions and the environmental impact. Part III of this series will discuss the results of these changes.
Wind Farms
Not all geographical areas are ideal for wind turbines. Forests, large cities, rough terrain and bodies of water can create obstacles that greatly affect wind speeds. Each element or land feature is given a classification number, for example, sea level is zero, farming areas are two, trees and buildings are 3 to 4. These numbers indicate amount of interference created and their affect on wind speeds [2].
Turbulence behind an obstacle slows wind speed for approximately three times the distance of the height of the obstacle. This area, known as the shade of the obstacle, will have a marked influence on the wind speed close to the obstruction, and close to the ground. This means that a turbine located closer than five times an obstacle’s height may not receive an adequate amount of wind [3]. In an offshore installation, wind shade effects may extend up to 20 kilometers (12.4 miles) from land [4].
The two elements of the turbulence classification number and the shade will dictate the height of the turbine [5].
Spacing of wind turbines is another element to consider when siting multiple towers because of the downwind turbulence they create. The recommended spacing to prevent turbulence is usually each turbine spaced between 5 and 9 rotor diameters apart in the prevailing wind direction, and between 3 and 5 diameters apart perpendicular to the prevailing winds [6]. The windy side of buildings or mountains is an ideal location wind turbines because these obstacles create a tunnel effect that focuses winds hence increasing wind speed. They, however, also increase turbulence [7]. Other ideal locations are round hills and regular ridged terrain. These features create the hill effect which channels winds as well as modifying wind speeds [8].
Another consideration in the location of wind turbines is the setback distance of wind farms from residential areas. The setback varies around the world [9]. In Europe each country has their own setback [10] while in the United States each individual state has its own regulated setback distance. In Canada, setbacks are influence by legislation from federal and provincial governmental acts, including the Canadian Fisheries Act, Migratory Birds Convention Act and the National Parks Act which protects wildlife [11]. Hospitals, schools, places of worship and First Nations sacred sites also affect Canadian setbacks. As well, the Canadian wind industry must go through a local, provincial and federal approval process for noise emissions [12]. Depending on the sites, setbacks in Canada range from 300m to 600 m (984 ft to 1,968 ft) [13].
Rotor blades and noise
Rotor blades are angled to achieve an optimal angle to cut into the wind for the full length of the blade [14]. The blades slow the wind to transfer energy to the rotor which this causes the emission of white noise. Most of the noise is produced by the back edge — the trailing edge — of the blade and the blade tip [15]. Research has been concentrated in creating newer blade designs in order to produce less infrasound as well as increase the energy output from the turbines. The new blade designs have also allowed wind turbines to be sited closer together, averaging about 7 rotor diameters or 300 m (1000 ft) apart [16].
Birds, bats and air strikes
Wind farms have an environmental impact, especially on bird and bat populations. Denmark’s Ministry of the Environment carried out a study in 2003 on the effect of offshore wind turbines on migratory birds. They found that, surprisingly, migratory birds adapt more quickly to wind turbine rotor blades than local bird populations [17]. Similar studies were carried out in Canada and the United States both for onshore and offshore installations. Here results identified a high rate of mortality among bird and bat populations, especially during migration season, caused by rotor blade strikes [18].
Klickitat County, Washington, USA has the highest numbers of bird casualties of all US regions [19]. Unfortunately, a number of these are threatened raptors species [20]. Not all areas, however, have experienced birds casualties. They appear to be more pronounced in very specific geographical areas and at specific time of the year [21]. Fatalities generally tend to peak in late summer and early fall, coinciding with the migration of many species [22]. Bad weather and take-off and landing patterns in proximity of the wind turbines are the cause of many bird and bat casualties [23].
Bats casualties are similar to birds, but occur mostly at night, immediately before and after the passage of storm fronts and during spring migration [24]. Autopsies on bats identified the cause of death as barotrauma — injuries resulting from sudden changes in air pressure as they pass through vortices and turbulence caused by the wind turbine blades [25, 26]. Barotrauma can cause internal injuries leading to death. Germany, Canada and the United States have tested whether or not increasing the minimum turbine cut-in speed would reduce bat fatalities. Tests resulted in a reduction of bat fatalities by 50% to 87% [27]. The province of Alberta, Canada, has suggested slowing down wind turbine blades to near motionless in low-wind periods. This action decreases bats mortality rates by as much as 60 percent [28].
The United States Federal Aviation Administration (FAA) regulates lighting on all tall structures. If wind farms contain more than three (3) turbines over 200 feet tall they require regulation lighting [29]. The turbines are generally lit with white and/or red strobe or strobe-like lights that produce momentary simultaneous flashes interspersed with dark periods up to 3 seconds in duration [30]. Studies have indicated that this lighting does not appear to influence bat and songbird fatalities.
Other environmental impacts of wind farms include habitat disruption. A single example is the Canadian Prairie Grouse. These birds are very sensitive to their environment and will shy away from displaying, nesting, or brooding in close proximity to roads, utility poles or lines, trees, oil and gas platforms, and human habitation [31]. Researchers worry that these birds, and other shy species, would not adapt to the presence of wind turbines causing a threat to their existence.
Conclusion:
The wind industry has made changes to wind turbine design to decrease noise emissions and environmental impact to wild life and humans. Before any wind turbine is installed, a survey of the site must be done to identify elements which will affect wind speed. Land features or obstacles receive a classification number. Higher classification numbers indicate that turbulence and shadows will decrease the wind speed and will dictate the height of the future wind turbines. In an offshore installation wind shade effects may extend up to 20 kilometers (12.4 miles) from land. Spacing of turbines is very important when trying to avoid turbulence. Areas that create tunnel affects, round hills and regular surface ridges are ideal location to take advantage of wind speeds. Setback for siting wind turbines varies from country to country. In the States and in Canada, siting will depend on existing local, provincial, federal or States legislation. Rotor blade design changes have reduced noise emissions in turn allowing closer spacings and smaller setbacks.
Wind farms are seen as a source of green energy, but they do have an environmental impact. Habitat disruption is a problem as well as bird and bat strikes. Strikes are common to specific geographical areas and in specific seasons, especially during migration. The number of bat casualties is similar to birds, except they are more pronounced during spring migration. The Federal Aviation Administration has done studies on bird and bat reaction to wind turbine lighting. Its appear that white and/or red strobe or strobe-like lights do not affect fatality rates of bats and songbirds.
Rosemary Stephen PMed, (cert) EOH, IPM (2010). Wind Turbine Syndrome, Part III Elements: Environmental Health Intelligence
End notes
Tunnel Effect and Hill Effect: affects on wind speed and the wind path in the lower layers of the atmosphere caused by buildings, natural hills and ridges.
Macías, F., Nieto, C. and García A. Environmental Impacts caused by Eolic Energy (2010) Environmental Technology Laboratory. Technological Research Institute, University of Santiago de Compostela. (On-line) Available: http://www.icrepq.com/pdfs/PE4.MACIAS.pdf. Cited 2010 Jul 26.
White noise: a noise produced by a stimulus containing all of the audible frequencies of vibration.
Definitions of white noise on the Web. (2010) Princeton word net web. (On-line) Available: http://wordnetweb.princeton.edu/perl/webwn?s=white%20noise. Cited 2010 Jun 04.
Barotrauma: physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and its surroundings.
Barotroma, (2010) Wikipedia the free encyclopedia. (On-line) Available: http://en.wikipedia.org/wiki/Barotrauma. Cited 2010 Jul 23.
References:
[1] Addressing Concerns with Wind Turbines and Human Health (2009) Canadian Wind Energy Association. (On-line) Available: http://www.canwea.ca/pdf/CanWEA%20-%20Addressing%20concerns%20with%20wind%20turbines%20and%20human%20health.pdf. Cited 2010 Apr 26.
[2] Designing for Low Aerodynamic Noise from Wind Turbines (2003) Danish Wind Industry Association. (On-line) Available: http://windwithmiller.windpower.org/en/tour/design/quietae.htm. Cited 2010 Apr 28.
[3] Ibid. Cited 2010 Apr 28.
[4] Ibid. Cited 2010 Apr 28.
[5] Ibid. Cited 2010 Apr 28.
[6] Ibid. Cited 2010 Apr 28.
[7] Ibid. Cited 2010 Apr 28.
[8] Ibid. Cited 2010 Apr 28.
[9] European Platform Against Windfarms. European Setbacks (minimum distance between wind turbines and habitations) (2009) National Wind Watch. (On-line) Available: http://www.wind-watch.org/documents/european-setbacks-minimum-distance-between-wind-turbines-and-habitations/. Cited 2010 Jul 22.
[10] Ibid. Cited 2010 Jul 22.
[11] Wildlife Guidelines for Alberta Wind Energy Projects (2006) Alberta Sustainable Resource Development – Fish and Wildlife Division. (On-line) Available: http://www.srd.alberta.ca/ManagingPrograms/FishWildlifeManagement/documents/inventoryguide/Wildlife_Guidelines_for_Alberta_Wind_Energy_Projects_April52006.pdf. Cited 2010 Jul 22.
[12] Wind Turbines and Sound: Review and Best Practice Guidelines (2010) HGC Engineering. (On-line) Available: http://www.canwea.ca/images/uploads/File/CanWEA_Wind_Turbine_Sound_Study_-_Final.pdf. Cited 2010 Jul 22.
[13] Ibid. Cited 2010 Jul 22.
[14] Designing for Low Aerodynamic Noise from Wind Turbines (2003) Danish Wind Industry Association. (On-line) Available: http://windwithmiller.windpower.org/en/tour/design/quietae.htm. Cited 2010 Apr 28.
[15] Ibid. Cited 2010 Jul 13.
[16] Ibid. Cited 2010 Apr 28.
[17] Birds and Wind Turbines (2003) Danish Wind Industry Association. (On-line) Available: http://www.talentfactory.dk/en/tour/env/birds.htm. Cited 2010 Jul 13.
[18] Impact on Wildlife (2010) Industrial Wind Action Group. (On-line) Available: http://www.windaction.org/news/c38/. Cited 2010 Jul 14.
[19] Chumley, C.K. Wind Turbines Killing Thousands of Birds in Northwest (2010) The Heartland Institute. (On-line) Available: http://www.heartland.org/full/28021/Wind_Turbines_Killing_Thousands_of_Birds_in_Northwest.html. Cited 2010 Jul 14.
[20] Ibid. Cited 2010 Jul 14.
[21] Ibid. Cited 2010 Jul 14.
[22] Wind Turbine Interactions with Birds, Bats, and their Habitats: A Summary of Research Results and Priority Questions (2010) National Wind Coordinating Collaboration. (On-line) Available: http://www.nationalwind.org/assets/publications/Birds_and_Bats_Fact_Sheet.pdf. Cited 2010 Jul 14.
[23] Ibid. Cited 2010 Jul 14.
[24] Ibid. Cited 2010 Jul 14.
[25] Ibid. Cited 2010 Jul 14.
[26] Baerwald, E, D’Amours, G., Klug, B, and Barclay, R. Barotrauma is a significant cause of bat fatalities at wind turbines (2008) National Wind Watch. (On-line) Available: http://www.wind-watch.org/documents/barotrauma-is-a-significant-cause-of-bat-fatalities-at-wind-turbines/. Cited 2010 Jul 16.
[27] Wind Turbine Interactions with Birds, Bats, and their Habitats: A Summary of Research Results and Priority Questions (2010) National Wind Coordinating Collaboration. (On-line) Available: http://www.nationalwind.org/assets/publications/Birds_and_Bats_Fact_Sheet.pdf. Cited 2010 Jul 14.
[28] Scientists Find Successful Way To Reduce Bat Deaths At Wind Turbines (2009) Science Daily. (On-line) Available: http://www.sciencedaily.com/releases/2009/09/090928095347.htm. Cited 2010 Jul 19.
[29] Marking and Lighting Wind Turbine Farms, Construction Marking and Lighting (2007) US Department of Transportation. (On-line) Available: https://oeaaa.faa.gov/oeaaa/external/content/AC70_7460_1K.pdf. Cited 2010 Jul 23.
[30] Wind Turbine Interactions with Birds, Bats, and their Habitats: A Summary of Research Results and Priority Questions (2010) National Wind Coordinating Collaboration. (On-line) Available: http://www.nationalwind.org/assets/publications/Birds_and_Bats_Fact_Sheet.pdf. Cited 2010 Jul 14.
[31] Chumley, C.K. Wind Turbines Killing Thousands of Birds in Northwest (2010) The Heartland Institute. (On-line) Available: http://www.heartland.org/full/28021/Wind_Turbines_Killing_Thousands_of_Birds_in_Northwest.html. Cited 2010 Jul 14.
