Compared to the environmental impact of traditional energy sources, the environmental impact of wind power is relatively minor. Wind power consumes no fuel, and emits no air pollution, unlike fossil fuel power sources. The energy consumed to manufacture and transport the materials used to build a wind power plant is equal to the new energy produced by the plant within a few months. While a wind farm may cover a large area of land, many land uses such as agriculture are compatible, with only small areas of turbine foundations and infrastructure made unavailable for use.[2]
There are reports of bird and bat mortality at wind turbines as there are around other artificial structures. The scale of the ecological impact may[3] or may not[4] be significant, depending on specific circumstances. Prevention and mitigation of wildlife fatalities, and protection of peat bogs,[5] affect the siting and operation of wind turbines.
There are anecdotal reports of negative effects from noise on people who live very close to wind turbines. Peer-reviewed research has generally not supported these statements.[6][7]
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Wind power consumes no fuel and no water[8] for continuing operation, and has no emissions directly related to electricity production. Wind turbines produce no carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen dioxide, mercury, radioactive waste, particulates, or any other type of air pollution, unlike fossil fuel power sources. Wind power plants consume resources in manufacturing and construction. During manufacture of the wind turbine, steel, concrete, aluminium and other materials will have to be made and transported using energy-intensive processes, generally using fossil energy sources. The wind turbine manufacturer Vestas states that initial carbon dioxide emissions "pay back" is within about 9 months of operation for off shore turbines.[9]
A 2006 study found the CO2 emissions of wind power to range from 14 to 33 tonnes (15 to 36 short tons) per GWh of energy produced. Most of the CO2 emission comes from producing the concrete for wind-turbine foundations.[10]
A study by the Irish national grid stated that "Producing electricity from wind reduces the consumption of fossil fuels and therefore leads to emissions savings", and found reductions in CO2 emissions ranging from 0.33 to 0.59 tonne (0.36 to 0.65 short ton) of CO2 per MWh.[11]
The UK Energy Research Centre (UKERC) study of intermittency also states that wind energy can displace fossil fuel-based generation, reducing both fuel use and carbon dioxide emissions. [12]
The production of permanent magnets used in some wind turbines makes use of neodymium.[13][14] Primarily exported by China, pollution concerns associated with the extraction of this rare-earth element have prompted government action in recent years,[15][16] and international research attempts to refine the extraction process.[17] Research is underway on turbine and generator designs which reduce the need for neodymium, or eliminate the use of rare-earth metals altogether.[18] However, Enercon did choose very early not to use permanent magnets for its direct drive turbines, in order to avoid responsibility in the bad environmental imprint of rare earth mining.[19]
The initial carbon dioxide emission from energy used in the installation is "paid back" within about 9 months of operation for off shore turbines. Any practical large-scale energy source must replace the energy used in its construction. The energy return on investment (EROI) for wind energy is equal to the cumulative electricity generated divided by the cumulative primary energy required to build and maintain a turbine. The EROI for wind ranges from 5 to 35, with an average of around 18, according to wind-energy advocates. EROI is strongly proportional to turbine size,[20] and larger late-generation turbines are at the high end of this range, at or above 35.[9] Since energy produced is several times energy consumed in construction, there is a net energy gain.[2]
Wind farms are often built on land that has already been impacted by land clearing. The vegetation clearing and ground disturbance required for wind farms is minimal compared with coal mines and coal-fired power stations. If wind farms are decommissioned, the landscape can be returned to its previous condition.[22]
Farmers and graziers often lease land to companies building wind farms. In the U.S., farmers may receive annual lease payments of two thousand to five thousand dollars per turbine,[23] and wind farms may also provide additional community payments "...to reward residents who have made no financial gains [directly] from wind energy development, but whose views of... [the] landscape now include a panorama of turbines".[24]
The land can still be used for farming and cattle grazing. Livestock are unaffected by the presence of wind farms. International experience shows that livestock will "graze right up to the base of wind turbines and often use them as rubbing posts or for shade".[22]
Wind-energy advocates contend that less than 1% of the land would be used for foundations and access roads, the other 99% could still be used for farming.[25] Critics point out that the clearing of trees around tower bases may be necessary for installation sites on mountain ridges, such as in the northeastern U.S.[26]
Turbines are not generally installed in urban areas. Buildings interfere with wind, turbines must be sited a safe distance ("setback") from residences in case of failure, and the value of land is high. There are a few notable exceptions to this. Toronto Hydro has built a lake shore demonstration project, and Steel Winds is a 20 MW urban project south of Buffalo, New York. Both of these projects are in urban locations, but benefit from being on uninhabited lake shore property.
In the UK there has also been concern about the damage caused to peat bogs,[5][27] with one Scottish MEP campaigning for a moratorium on wind developments on peatlands saying that "Damaging the peat causes the release of more carbon dioxide than wind farms save".[28]
Offshore locations use no land and avoid shipping channels.
Environmental assessments are routinely carried out for wind farm proposals, and potential impacts on the local environment (e.g. plants, animals, soils) are evaluated.[22] Turbine locations and operations are often modified as part of the approval process to avoid or minimise impacts on threatened species and their habitats. Any unavoidable impacts can be offset with conservation improvements of similar ecosystems which are unaffected by the proposal.[22]
Projects such as the Black Law Wind Farm have received wide recognition for its contribution to environmental objectives, including praise from the Royal Society for the Protection of Birds, who describe the scheme as both improving the landscape of a derelict opencast mining site and also benefiting a range of wildlife in the area, with an extensive habitat management projects covering over 14 square kilometres.[29]
A research agenda from a coalition of researchers from universities, industry, and government, supported by the Atkinson Center for a Sustainable Future, suggests modeling the spatiotemporal patterns of migratory and residential wildlife with respect to geographic features and weather, to provide a basis for science-based decisions about where to site new wind projects. More specifically, it suggests:
A study[31] estimates that wind farms are responsible for 0.3 to 0.4 fatalities per gigawatt-hour (GWh) of electricity while fossil-fueled power stations are responsible for about 5.2 fatalities per GWh. The study therefore states that fossil fuel based electricity causes about 10 times more fatalities than wind farm based electricity, primarily due to habitat alteration from pollution and mountain-top removal for coal mining. In Denmark, where wind turbines generate 9% of electricity, wind turbines kill about 30,000 birds per year.[32] In the United States, the U.S. Fish and Wildlife Service estimated in 2009, that turbines kill 440,000 birds per year, though mortality is expected to increase significantly as wind power generation expands by 2030 to levels about 12 times higher than 2009 levels. In comparison, 80,000 birds are killed by aircraft,[33] and 500 million killed by cats every year. Even greater numbers of bird deaths are attributed to collisions with buildings.[33][34] Other studies have stated that 57 million are killed by cars, 97.5 million killed by collisions with plate glass,[35] and hundreds of millions killed by cats.[36] An article in Nature stated that each wind turbine kills an average of 4.27 birds per year.[37]
In the UK, the Royal Society for the Protection of Birds (RSPB) concluded that "The available evidence suggests that appropriately positioned wind farms do not pose a significant hazard for birds."[4] It notes that climate change poses a much more significant threat to wildlife, and therefore supports wind farms and other forms of renewable energy. In 2009 the RSPB warned that "numbers of several breeding birds of high conservation concern are reduced close to wind turbines," probably because "birds may use areas close to the turbines less often than would be expected, potentially reducing the carrying capacity of an area."[38] The National Audubon Society in the U.S. takes a similar position, broadly supporting wind power to help mitigate global warming, while cautioning against siting wind farms in areas especially important to birds and other affected wildlife.[39]
Concerns have been expressed that wind turbines at Smøla in Norway are having a deleterious effect on the population of White-tailed Eagles, Europe's largest bird of prey. They have been the subject of an extensive re-introduction programme in Scotland, which could be jeopardised by the expansion of wind turbines.[40]
The Peñascal Wind Power Project in Texas is located in the middle of a major bird migration route, and the wind farm uses avian radar originally developed for NASA and the United States Air Force to detect birds as far as four miles away. If the system determines that the birds are in danger of running into the rotating blades, it shuts down the turbines. The system automatically restarts the turbines when the birds have passed.[41]
At the Altamont Pass Wind Farm in California, a settlement has been reached between the Audubon Society, Californians for Renewable Energy and NextEra Energy Resources (who operate some 5,000 turbines in the area). Nearly half of the smaller turbines will be replaced by newer, more bird-friendly models. The project is expected to be complete by 2015 and includes $2.5 million for raptor habitat restoration.[42]
Some paths of bird migration, particularly for birds that fly by night, are unknown. A study suggests that migrating birds may avoid the large turbines,[43] at least in the low-wind non-twilight conditions studied. A Danish 2005 (Biology Letters 2005:336) study showed that radio tagged migrating birds traveled around offshore wind farms. Less than 1% of migrating birds passing an offshore wind farm in Rønde, Denmark, got close to collision, though the site was studied only during low-wind non-twilight conditions.
Bats may be injured by direct impact with turbine blades, towers, or transmission lines. Recent research shows that bats may also be killed when suddenly passing through a low air pressure region surrounding the turbine blade tips.[45]
The numbers of bats killed by existing onshore and near-shore facilities has troubled bat enthusiasts.[46] A study in 2004 estimated that over 2,200 bats were killed by 63 onshore turbines in just six weeks at two sites in the eastern U.S.[47] This study suggests some onshore and near-shore sites may be particularly hazardous to local bat populations and more research is needed. Migratory bat species appear to be particularly at risk, especially during key movement periods (spring and more importantly in fall). Lasiurines such as the hoary bat, red bat, and the silver-haired bat appear to be most vulnerable at North American sites. Almost nothing is known about current populations of these species and the impact on bat numbers as a result of mortality at windpower locations. It has been suggested that bats are attracted to these structures in search of roosts.[48] Offshore wind sites 10 km (6 mi) or more from shore do not interact with bat populations.
Scientists at the U.S. Geological Survey have already conducted research using stable isotope analysis to track migration among terrestrial mammals. USGS scientists are currently applying this technique in their efforts to figure out the geographic origins of bats killed by wind turbines.[49]
In April 2009 the Bats and Wind Energy Cooperative released initial study results showing a 73% drop in bat fatalities when wind farm operations are stopped during low wind conditions, when bats are most active.[50]
Bats avoid radar transmitters, and placing microwave transmitters on wind turbine towers may reduce the number of bat collisions.[51][52]
Wind farms may affect weather in their immediate vicinity. Spinning wind turbine rotors generate a lot of turbulence in their wakes like the wake of a boat. This turbulence increases vertical mixing of heat and water vapor that affects the meteorological conditions downwind. Overall, wind farms lead to a warming at night and cooling during the day time. This effect can be reduced by using more efficient rotors or placing wind farms in regions with high natural turbulence. Warming at night could "benefit agriculture by decreasing frost damage and extending the growing season. Many farmers already do this with air circulators".[53][54][55]
A number of studies have used climate models to study the effect of extremely large wind farms. One study reports simulations that show detectable changes in global climate for very high wind farm usage, on the order of 10% of the world's land area. Wind power has a negligible effect on global mean surface temperature, and it would deliver "enormous global benefits by reducing emissions of CO2 and air pollutants".[56] Another study published in Atmospheric Chemistry and Physics suggested that using wind turbines to meet 10 percent of global energy demand in 2100 could actually have a warming effect, causing temperatures to rise by 1 °C (1.80 °F) in the regions on land where the wind farms are installed, including a smaller increase in areas beyond those regions. This is due to the effect of wind turbines on both horizontal and vertical atmospheric circulation. Whilst turbines installed in water would have a cooling effect, the net impact on global surface temperatures would be an increase of 0.15 °C (0.270 °F). Author Ron Prinn cautioned against interpreting the study "as an argument against wind power, urging that it be used to guide future research". "We’re not pessimistic about wind," he said. "We haven’t absolutely proven this effect, and we’d rather see that people do further research".[57]
Operation of any utility-scale energy conversion system presents safety hazards. Wind turbines do not consume fuel or produce pollution during normal operation, but still have hazards associated with their construction, operation and maintenance.
With the installation of industrial sized wind turbines numbering in the thousands, there have been at least 40 fatalities of workers due to the construction, operation, and maintenance of wind turbines, and other injuries and deaths attributed to the wind power life cycle.[58][59][60] Most worker deaths involve falls or becoming caught in machinery while performing maintenance inside turbine housings.
If a turbine's brake fails, the turbine can spin freely until it disintegrates or catches fire. Often turbine fires cannot be extinguished because of the height, and are left to burn themselves out. In the process, they generate toxic fumes and can scatter flaming debris over a wide area, starting secondary fires below. Several turbine-ignited fires have burned hundreds of acres of vegetation each, and one burned 800 square kilometres (200,000 acres) of Australian National Park.[58][61][62][63]
During winter ice may form on turbine blades and subsequently be thrown off during operation. This is a potential safety hazard,[64] and has led to localised shut-downs of turbines.[65]. Modern turbines can detect ice formation, and shut down.
Electronic controllers and safety sub-systems monitor many different aspects of the turbine, generator, tower, and environment to determine if the turbine is operating in a safe manner within prescribed limits. These systems can temporarily shut down the turbine due to high wind, ice, electrical load imbalance, vibration, and other problems. Recurring or significant problems cause a system lockout and notify an engineer for inspection and repair. In addition, most systems include multiple passive safety systems that stop operation even if the electronic controller fails.
In his book Wind Energy Comes of Age, Paul Gipe estimated that the mortality rate for wind power from 1980–1994 was 0.4 deaths per terawatt-hour.[66][67] Paul Gipe's estimate as of end 2000 was 0.15 deaths per TWh, a decline attributed to greater total cumulative generation.
Newer wind farms have larger, more widely spaced turbines, and have a less cluttered appearance than older installations. Wind farms are often built on land that has already been impacted by land clearing and they coexist easily with other land uses (e.g. grazing, crops). They have a smaller footprint than other forms of energy generation such as coal and gas plants.[68] Wind farms may be close to scenic or otherwise undeveloped areas, and aesthetic issues are important for onshore and near-shore locations.
Aesthetic issues are subjective and some people find wind farms pleasant and optimistic, or symbols of energy independence and local prosperity.[69] While some tourism officials predict wind farms will damage tourism,[70] some wind farms have themselves become tourist attractions,[71][72][73] with several having visitor centers at ground level or even observation decks atop turbine towers.
Residents near turbines may complain of "shadow flicker" on nearby residences caused by rotating turbine blades, when the sun passes behind the turbine. This can easily be avoided by locating the wind farm to avoid unacceptable shadow flicker, or by turning the turbine off for the few minutes of the day when the sun is at the angle that causes flicker.[68]
Wind towers require aircraft warning lights, which may create light pollution. Complaints about these lights have caused the FAA to consider allowing fewer lights per turbine in certain areas.[74]
Modern wind turbines produce significantly less noise than older designs. Turbine designers work to minimise noise, as noise reflects lost energy and output. Noise levels at nearby residences may be managed through the siting of turbines, the approvals process for wind farms, and operational management of the wind farm.[75]
Renewable UK, a wind energy trade organization, has said that the noise measured 305 metres (1,000 ft) from a wind farm is less than that from normal road traffic or in an office;[76] some physicians and acoustic engineers have reported problems from wind turbine noise, including sleep deprivation, headaches, dizziness, anxiety, and vertigo.[77][78][79]
Nina Pierpont, a New York pediatrician and wife of an anti-wind energy activist,[80][81] states that noise can be an important disadvantage of wind turbines, especially when building the wind turbines very close to urban environments. The controversy around Pierpont's work centers around her statements made in a self-published, non-peer-reviewed book that ultra-low frequency sounds affect human health, which are based on a very small sample of self-selected subjects with no control group for comparison. She asserts that wind turbines affect the mood of people and may cause physiological problems such as insomnia, headaches, tinnitus, vertigo and nausea.[82][83]
Simon Chapman, a professor of public health, has said that "wind turbine syndrome" is not recognised by any international disease classification system and does not appear in any title or abstract in the massive US National Library of Medicine's PubMed database. He says that the term appears to be spread by the vector of anti-wind farm activist groups.[84]
In December 2006, a Texas jury denied a noise pollution suit against FPL Energy, after the company demonstrated that noise readings were not excessive. The highest reading was 44 decibels, which was characterized as about the same level as a 10 miles per hour (16 km/h) wind. The nearest residence among the plaintiffs was 1,700 feet (520 m) from one of the turbines.[85] More recent lawsuits have been brought in Missouri,[86] Pennsylvania,[87] and Maine.[88]
In Ontario, Canada, the Ministry of the Environment created noise guidelines to limit wind turbine noise levels 30 metres away from a dwelling or campsite to 40 dB(A).[89] These regulations also set a minimum distance of 550 metres (1,800 ft) for a group of up to five relatively quiet [102 dB(A)] turbines within a 3-kilometre (1.9 mi) radius, rising to 1,500 metres (4,900 ft) for a group of 11 to 25 noisier (106-107 dB(A)) turbines. Larger facilities and noisier turbines would require a noise study.[90][91][6]
Also in Ontario, wind farms near residential homes have attracted various protests[92] and lawsuits from homeowners up to $1.5 million[93] over health claims and damage to property values. A moratorium on offshore wind farms in Lake Ontario has also led to a lawsuit from Trillium Wind Power for $2.25 billion.[94]
In a 2009 report about "Rural Wind Farms", a Standing Committee of the Parliament of New South Wales, Australia, recommended a minimum setback of two kilometres between wind turbines and neighbouring houses (which can be waived by the affected neighbour) as a precautionary approach.[95] In July 2010, Australia's National Health and Medical Research Council reported that "there is no published scientific evidence to support adverse effects of wind turbines on health".[96]
A 2008 guest editorial in Environmental Health Perspectives published by the National Institute of Environmental Health Sciences, the U.S. National Institutes of Health, stated: "Even seemingly clean sources of energy can have implications on human health. Wind energy will undoubtedly create noise, which increases stress, which in turn increases the risk of cardiovascular disease and cancer."[97]
The Japanese Environment Ministry will begin a "major study into the influence of sounds of wind turbines on people's health" in April 2010, because "people living near wind power facilities are increasingly complaining of health problems". They plan a four-year examination of all 1,517 wind turbines in the country.[98]
A 2007 report by the U.S. National Research Council noted that noise produced by wind turbines is generally not a major concern for humans beyond a half-mile or so. Low-frequency vibration and its effects on humans are not well understood and sensitivity to such vibration resulting from wind-turbine noise is highly variable among humans. There are opposing views on this subject, and more research needs to be done on the effects of low-frequency noise on humans.[99]
Research by Stefan Oerlemans for the University of Twente and the Dutch National Aerospace Laboratory suggests that noise from existing wind turbines may be reducible by up to half by adding "saw teeth" to the trailing edges of the blades, although research is not complete.[100]
A 2009 expert panel review, described as being the most comprehensive to date, delved into the possible adverse health effects of those living close to wind turbines. Their report findings concluded that wind turbines do not directly make people ill.[6][7]
The 85-page study was sponsored by the Canadian Wind Energy Association and American Wind Energy Association. The academic and medical experts who conducted the study stated that they reached their conclusions independent of their sponsors. "We were not told to find anything," said panel expert David Colby, a public health officer in Chatham-Kent and a Professor of Medicine at the University of Western Ontario. "It was completely open ended."[6]
The study did allow that some people could experience stress or irritation caused by the swishing sounds wind turbines produce. "A small minority of those exposed report annoyance and stress associated with noise perception..." [however] "Annoyance is not a disease." The study group pointed out that similar irritations are produced by local and highway vehicles, as well as from industrial operations and aircraft.[6]
The report found, amongst other things, that:[6]
The study panel members included: Robert Dobie, a doctor and clinical professor at the University of Texas, Geoff Leventhall, a noise vibration and acoustics expert in the United Kingdom, Bo Sondergaard, with Danish Electronics Light and Acoustics, Michael Seilo, a professor of audiology at Western Washington University, and Robert McCunney, a biological engineering scientist at the Massachusetts Institute of Technology. McCunney contested statements that infrasounds from wind turbines could create vibrations causing ill health: "It doesn't really have much credence, at least based on the literature out there" he stated.[6]
In 2011, the British Acoustics Bulletin published what is now the 10th independent review of the evidence on wind farms causing annoyance and ill health in people. And for the 10th time it has emphasised that "annoyance has far more to do with social and psychological factors in those complaining than any direct effect from sound or inaudible infrasound emanating from wind turbines".[84]
Two factors repeatedly came up. "The first is being able to see wind turbines, which increases annoyance particularly in those who dislike or fear them. The second factor is whether people derive income from hosting turbines, which miraculously appears to be a highly effective antidote to feelings of annoyance and symptoms".[84]
Many offshore wind farms are being built in UK waters. In January 2009, a comprehensive government environmental study of coastal waters in the United Kingdom concluded that there is scope for between 5,000 and 7,000 offshore wind turbines to be installed without an adverse impact on the marine environment. The study – which forms part of the Department of Energy and Climate Change's Offshore Energy Strategic Environmental Assessment – is based on more than a year's research. It included analysis of seabed geology, as well as surveys of sea birds and marine mammals.[101][102]
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