Net energy gain[edit]

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. According to a meta study, in which all existing studies from 1977 to 2007 were reviewed, the EROI for wind ranges from 5 to 35,^[20] with the most common turbines in the range of 2 MW nameplate capacity-rotor diameters of 66 meters, on average the EROI is 16.^[22][20] EROI is strongly proportional to turbine size, and larger late-generation turbines average at the high end of this range, are by one study, approximately 35.^[23]

Wind turbine manufacturer Vestas claims that initial energy "pay back" is within about 7–9 months of operation for a 1.65-2.0MW wind turbine under low wind conditions,^[24][25] whereas Siemens Wind Power calculates 5–10 months depending on circumstances.^[24]

Pollution & effects on the grid[edit]

Pollution costs[edit]

Wind power consumes no water^[26] for continuing operation, and has near negligible emissions directly related to its electricity production. Wind turbines when isolated from the electric grid produce negligible amounts of carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen dioxide, mercury and radioactive waste when in operation, unlike fossil fuel sources and nuclear energy station fuel production, respectively.

With the construction phase largely to blame, wind turbines emit slightly more particulate matter (PM), a form of air pollution, at an "exception" rate higher per unit of energy generated(kWh) than a fossil gas electricity station("NGCC"),^[23][27] and also emit more heavy metals and PM than nuclear stations, per unit of energy generated.^[28][29] As far as total pollution costs in economic terms, in a comprehensive 2006 European study, alpine Hydropower was found to exhibit the lowest external pollution, or externality, costs of all electricity generating systems, below 0.05 c€/kWh. Wind power externality costs were found to be 0.09 - 0.12c€/kW, while nuclear energy had a 0.19 c€/kWh value and fossil fuels generated 1.6 - 5.8 c€/kWh of downstream costs.^[30] With the exception of the latter fossil fuels, these are negligible costs in comparison to the cost of electricity production, which is approximately 10 c€/kWh in European countries.

Findings when connected to the grid[edit]

The Vattenfall utility company study found Hydroelectric, nuclear stations and wind turbines to have far less greenhouse emissions than other sources represented.

A typical study of a wind farm's Life cycle assessment, when not connected to the electric grid, usually results in similar findings as the following 2006 analysis of 3 installations in the US Midwest, where the carbon dioxide (CO
2) emissions of wind power ranged from 14 to 33 tonnes (15 to 36 short tons) per GWh (14–33 gCO
2/kWh) of energy produced, with most of the CO
2 emission intensity coming from producing the concrete for wind-turbine foundations.^[31] By combining similar data from numerous individual studies in a meta-analysis, the median global warming potential for wind power was found to be 11–12 g CO₂/kWh and unlikely to change significantly.^[32][33][34]

However these relatively low pollution values begin to increase as greater and greater wind energy is added to the grid, or wind power 'electric grid penetration' levels are reached. Due to the effects of attempting to balance out the energy demands on the grid, from Intermittent power sources e.g. wind power (sources which have low capacity factors due to the weather), this either requires the construction of large energy storage projects, which have their own emission intensity which must be added to wind power's system-wide pollution effects, or it requires more frequent reliance on fossil fuels than the spinning reserve requirements necessary to back up more dependable sources. With the latter combination presently being the more common.^[35][36][37]

This higher dependence on back-up/Load following power plants to ensure a steady power grid output has the knock-on-effect of more frequent inefficient (in CO
2e g/kWh) throttling up and down of these other power sources in the grid to facilitate the intermittent power source's variable output. When one includes the total effect of intermittent sources on other power sources in the grid system, that is, including these inefficient start up emissions of backup power sources to cater for wind energy, into wind energy's total system wide life cycle, this results in a higher real-world wind energy emission intensity. Higher than the direct g/kWh value that is determined from looking at the power source in isolation and thus ignores all down-stream detrimental/inefficiency effects it has on the grid. This higher dependence on back-up/Load following power plants to ensure a steady power grid output forces fossil power plants to operate in less efficient states. In a 2012 paper that appeared in the Journal of Industrial Ecology it states.^[38]

The thermal efficiency of fossil-based power plants is reduced when operated at fluctuating and suboptimal loads to supplement wind power, which may degrade, to a certain extent, the GHG(Greenhouse gas) benefits resulting from the addition of wind to the grid. A study conducted by Pehnt and colleagues (2008)^[39] reports that a moderate level of [grid] wind penetration (12%) would result in efficiency penalties of 3% to 8%, depending on the type of conventional power plant considered. Gross and colleagues (2006) report similar results, with efficiency penalties ranging from nearly 0% to 7% for up to 20% [of grid] wind penetration. Pehnt and colleagues (2008) conclude that the results of adding offshore wind power in Germany on the background power systems maintaining a level supply to the grid and providing enough reserve capacity amount to adding between 20 and 80 g CO₂-eq/kWh to the life cycle GHG emissions profile of wind power.

In comparison to other low carbon power sources Wind turbines, when assessed in isolation, have a median life cycle emission value of between 11 and 12 (gCO
2eq/kWh). The more dependable alpine Hydropower and nuclear stations have median total life cycle emission values of 24 and 12 g CO₂-eq/kWh respectively.^[40][41]

While an increase in emissions due to the practical issues of load balancing is an issue, Pehnt et al. still conclude that these 20 and 80 g CO₂-eq/kWh added penalties still result in wind being roughly ten times less polluting than fossil gas and coal which emit ~400 and 900 g CO₂-eq/kWh respectively.^[41]

As these losses occur due to cycling of fossil power plants, they may at some point become smaller when more than 20–30% of wind energy is added to the power grid, as fossil power plants are replaced, however this has yet to occur in practice.^{[42][better source needed]}

Rare-earth use[edit]

The production of permanent magnets used in some wind turbines makes use of neodymium.^[43][43] Primarily exported by China, pollution concerns associated with the extraction of this rare-earth element have prompted government action in recent years,^[20][38] and international research attempts to refine the extraction process.^[44] Research is underway on turbine and generator designs which reduce the need for neodymium, or eliminate the use of rare-earth metals altogether.^[20] Additionally, the large wind turbine manufacturer Enercon GmbH chose very early not to use permanent magnets for its direct drive turbines, in order to avoid responsibility for the adverse environmental impact of rare-earth mining.^[45]

Land use[edit]

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.^[46]

A study by the US National Renewable Energy Laboratory of US wind farms built between 2000 and 2009 found that, on average, only 1.1 percent of the total wind farm area suffered surface disturbance, and only 0.43 percent was permanently disturbed by wind power installations. On average, there were 63 hectares (156 acres) of total wind farm area per MW of capacity, but only 0.27 hectares (0.67 acres) of permanently disturbed area per MW of wind power capacity.^[47]

In the UK many prime wind farm sites - locations with the best average wind speeds - are in upland areas which are frequently covered by blanket bog. This type of habitat exists in areas of relatively high rainfall where large areas of land remain permanently sodden. Construction work may create a risk of disruption to peatland hydrology which could cause localised areas of peat within the area of a wind farm to dry out, disintegrate, and so release their stored carbon. At the same time, the warming climate which renewable energy schemes seek to mitigate could itself pose an existential threat to peatlands throughout the UK.^[48][48] A Scottish MEP campaigned for a moratorium on wind developments on peatlands saying that "Damaging the peat causes the release of more carbon dioxide than wind farms save".^[15] A 2014 report for the Northern Ireland Environment Agency noted that siting wind turbines on peatland could release considerable carbon dioxide from the peat, and also damage the peatland contributions to flood control and water quality: "The potential knock-on effects of using the peatland resource for wind turbines are considerable and it is arguable that the impacts on this facet of biodiversity will have the most noticeable and greatest financial implications for Northern Ireland."^[49]

Wind-energy advocates contend that less than 1% of the land is used for foundations and access roads, the other 99% can still be used for farming.^[50] A wind turbine needs about 200–400 m² for the foundation. A (small) 500-kW-turbine with an annual production of 1.4 GWh produces 11.7 MWh/m², which is comparable with coal-fired plants (about 15-20 MWh/m²), coal-mining not included. With increasing size of the wind turbine the relative size of the foundation decreases.^[51] Critics point out that on some locations in forests the clearing of trees around tower bases may be necessary for installation sites on mountain ridges, such as in the northeastern U.S.^[52] This usually takes the clearing of 5,000 m² per wind turbine.^[53]

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. The WindShare ExPlace wind turbine was erected in December 2002, on the grounds of Exhibition Place, in Toronto, Ontario, Canada. It was the first wind turbine installed in a major North American urban city centre.^[54] Steel Winds also has 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.

Livestock[edit]

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".^[55]

In 2014, a first of its kind Veterinary study attempted to determine the effects of rearing livestock near a wind turbine, the study compared the health effects of a wind turbine on the development of two groups of growing geese, preliminary results found that geese raised within 50 meters of a wind turbine gained less weight and had a higher concentration of the stress hormone cortisol in their blood than geese at a distance of 500 meters.^[56]

Semi-domestic reindeer avoid the construction activity,^[56] but seem unaffected when the turbines are operating.^[56][57]

Impact on wildlife[edit]

Environmental assessments are routinely carried out for wind farm proposals, and potential impacts on the local environment (e.g. plants, animals, soils) are evaluated.^[58] 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.^[56]

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:

• Use existing data on migratory and other movements of wildlife to develop predictive models of risk.
• Use new and emerging technologies, including radar, acoustics, and thermal imaging, to fill gaps in knowledge of wildlife movements.
• Identify specific species or sets of species most at risk in areas of high potential wind resources.^[59]

Birds[edit]

The impact of wind energy on birds, which can fly into turbines directly, or indirectly have their habitats degraded by wind development, is complex. 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.^[81]

The preliminary data,^[82] from the above table during 2013, 'Causes of avian mortality in the United States, annual', shown as a bar graph, inclusive of a high nuclear-fission bird mortality figure that the author later recognized was due to a major error on their part.^[82]

The meta-analysis on avian mortality by Benjamin K. Sovacool led him to suggest that there were a number of deficiencies in other researchers' methodologies.^[83] Among them, he stated were a focus on bird deaths, but not on the reductions in bird births: for example, mining activities for fossil fuels and pollution from fossil fuel plants have led to significant toxic deposits and acid rain that have damaged or poisoned many nesting and feeding grounds, leading to reductions in births. The large cumulated footprint of wind turbines, which reduces the area available to wildlife or agriculture, is also missing from all studies including Sovacool's. Many of the studies also made no mention of avian deaths per unit of electricity produced, which excluded meaningful comparisons between different energy sources. More importantly, it concluded, the most visible impacts of a technology, as measured by media exposure, are not necessarily the most flagrant ones.^[84]

Sovacool estimated that in the United States wind turbines kill between 20,000 and 573,000 birds per year, and has stated he regards either figure as minimal compared to bird deaths from other causes. He uses the lower 20,000 figure in his study and table (see Causes of avian mortality table) to arrive at a direct mortality rate per unit of energy generated figure of 0.269 per GWh for wind power. Fossil-fueled power plants, which wind turbines generally require to make up for their weather dependent intermittency, kill almost 20 times as many birds per gigawatt hour (GWh) of electricity according to Sovacool. Bird deaths due to other human activities and cats total between 797 million and 5.29 billion per year in the U.S. Additionally, while many studies concentrate on the analysis of bird deaths, few have been conducted on the reductions of bird births, which are the additional consequences of the various pollution sources that wind power partially mitigates.^[85]

Of the bird deaths Sovacool attributed to fossil-fuel power plants, 96 percent were due to the effects of climate change. While the study did not assess bat mortality due to various forms of energy, he considered it not unreasonable to assume a similar ratio of mortality.^[86][86] The Sovacool study has provoked controversy because of its treatment of data.^[86][82] In a series of replies, Sovacool acknowledged a number of large errors, particularly those that relate to his earlier "0.33 to 0.416" fatalities overestimate for the number of bird deaths per GWh of nuclear power, and cautioned that "the study already tells you the numbers are very rough estimates that need to be improved."^[87]

A 2013 meta-analysis by Smallwood identified a number of factors which result in serious under-reporting of bird and bat deaths by wind turbines. These include inefficient searches, inadequate search radius, and carcass removal by predators. To adjust the results of different studies, he applied correction factors from hundreds of carcass placement trials. His meta-analysis concluded that in 2012 in the United States, wind turbines resulted in the deaths of 888,000 bats and 573,000 birds, including 83,000 birds of prey.^[86]

Also in 2013, a meta-analysis by Scott Loss and others in the journal Biological Conservation found that the likely mean number of birds killed annually in the U.S by monopole tower wind turbines was 234,000. The authors acknowledged the larger number reported by Smallwood, but noted that Smallwood's meta-analysis did not distinguish between types of wind turbine towers. The monopole towers used almost exclusively for new wind installations have mortality rates that "increase with increasing height of monopole turbines", but as of yet, it remains to be determined if increasingly taller monopole towers result in lower mortality per GWh.^[88][89]

Bird mortality at wind energy facilities can vary greatly depending on the location, construction, and height, with some facilities reporting zero bird fatalities, and others as high as 9.33 birds per turbine per year.^[90] A 2007 article in the journal Nature stated that each wind turbine in the U.S. kills an average of 0.03 birds per year, and recommends that more research needs to be done.^[91][92]

A comprehensive study of wind turbine bird deaths by the Canadian Wildlife Service in 2013 analyzed reports from 43 out of the 135 wind farms operating across Canada as of December 2011. After adjusting for search inefficiencies, the study found an average of 8.2 bird deaths per tower per year, from which they arrived at a total of 23,000 per year for Canada at that time. Actual habitat loss averaged 1.23 hectares per turbine, which involved the direct loss of, on average, 1.9 nesting sites per turbine. The effective habitat loss, which was not quantified, was observed to be highly variable between species: some species avoided nesting within 100 to 200 m from turbines, while other species were observed feeding on the ground directly under the blades. The study concluded that, overall, the combined effect on birds was "relatively small" compared to other causes of bird mortality, but noted that mitigation measures might be required in some situations to protect at-risk species.^[89]

While studies show that other sources, such as cats, cars, buildings, power lines, and transmission towers kill far more birds than wind turbines, many studies and conservation groups have noted that wind turbines disproportionately kill large migratory birds and birds of prey, and are more likely to kill birds threatened with extinction.^[93][94] Wind facilities have attracted the most attention for impacts on iconic raptor species, including golden eagles. The Pine Tree Wind energy project near Tehachapi, California has one of the highest raptor mortality rates in the country; by 2012 at least eight golden eagles had been killed according to the U.S. Fish and Wildlife Service (USFWS).^[91] Biologists have noted that it is more important to avoid losses of large birds as they have lower breeding rates and can be more severely impacted by wind turbines in certain areas.

Large numbers of bird deaths are also attributed to collisions with buildings.^[89] An estimated 1 to 9 million birds are killed every year by tall buildings in Toronto, Ontario, Canada alone, according to the wildlife conservation organization Fatal Light Awareness Program.^[92][92] Other studies have stated that 57 million are killed by cars, and some 365 to 988 million are killed by collisions with buildings and plate glass in the United States alone.^[95][96][97] Promotional event lightbeams as well as ceilometers used at airport weather offices can be particularly deadly for birds,^[98] as birds become caught in their lightbeams and suffer exhaustion and collisions with other birds. In the worst recorded ceilometer lightbeam kill-off during one night in 1954, approximately 50,000 birds from 53 different species died at the Warner Robins Air Force Base in the United States.^[99]

Arctic terns and a wind turbine at the Eider Barrage in Germany.

In the United Kingdom, 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."^[100] It notes that climate change poses a much more significant threat to wildlife, and therefore supports wind farms and other forms of renewable energy as a way to mitigate future damage. 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 wildlife carrying capacity of an area.^[101]

Concerns have been expressed that wind turbines at Smøla, 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.^[102]

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 4 miles (6.4 km) away. If the system determines that the birds are in danger of running into the rotating blades, the turbines shut down and are restarted when the birds have passed.^[103] A 2005 Danish study used surveillance radar to track migrating birds traveling around and through an offshore wind farm. Less than 1% of migrating birds passing through an offshore wind farm in Rønde, Denmark, got close enough to be at risk of collision, though the site was studied only during low-wind conditions. The study suggests that migrating birds may avoid large turbines, at least in the low-wind conditions the research was conducted in.^[104][105] Furthermore, it is not thought that nocturnal migrants are at higher risk to collision than diurnally active species.^[106]

Old style wind turbines at Altamont Pass in California, which are being replaced by more "bird-friendly designs". While newer designs are taller, there is as yet, no definitive evidence that they are "friendlier". A recent study suggests that they might not be safer to wildlife,^[107] and are not a "simple fix", according to Oklahoma State University ecologist Scott Loss.^[108]

In 2012, researchers reported that, based on their four-year radar tracking study of birds after construction of an offshore wind farm near Lincolnshire, that pink-footed geese migrating to the U.K. to overwinter altered their flight path to avoid the turbines.^[109]

At the Altamont Pass Wind Farm in California, a settlement between the Audubon Society, Californians for Renewable Energy and NextEra Energy Resources who operate some 5,000 turbines in the area requires the latter to replace nearly half of the smaller turbines with newer, more bird-friendly models by 2015 and provide $2.5 million for raptor habitat restoration.^[110] The proposed Chokecherry and Sierra Madre Wind Energy Project in Wyoming is allowed by the Bureau of Land Management (BLM) to "take" up to 16 eagles per year as predicted by the Fish and Wildlife Service, while making powerlines less damaging.^[111][112] A 2012 BLM study estimated nearly 5,400 birds each year, including over 150 raptors.^{[113][clarification needed]} Some sites are required to watch for birds.^[112] In 2016, the Obama administration finalized a rule that granted 30-year licenses to wind-energy companies that operate high-speed turbines permitting them to kill or injure up to 4,200 golden eagles and bald eagles, four times the existing limit, before facing penalties.^[114] There are 143,000 bald eagles and 40,000 golden eagles in the United States.^[115]

Bats[edit]

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.^[116]

The numbers of bats killed by existing onshore and near-shore facilities have troubled bat enthusiasts.^[117]

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.^[118] Bats avoid radar transmitters, and placing microwave transmitters on wind turbine towers may reduce the number of bat collisions.^[119][120]

A 2013 study produced an estimate that wind turbines killed more than 600,000 bats in the U.S. the previous year, with the greatest mortality occurring in the Appalachian Mountains. Some earlier studies had produced estimates of between 33,000 and 888,000 bat deaths per year.^[120]

Weather and climate change[edit]

Wind farms may affect weather in their immediate vicinity. This turbulence from spinning wind turbine rotors increases vertical mixing of heat and water vapor that affects the meteorological conditions downwind, including rainfall.^[121] Overall, wind farms lead to a slight warming at night and a slight 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".^{[121][122][123]}

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 CO
2 and air pollutants".^[124] Another peer-reviewed study 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 (1.8 °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 (0.27 °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".^[125]

Aesthetics[edit]

The surroundings of Mont Saint-Michel at low tide. While windy coasts are good locations for wind farms, aesthetic considerations may preclude such developments in order to preserve historic views of cultural sites.

Aesthetic considerations of wind power stations have often a significant role in their evaluation process.^[126] To some, the perceived aesthetic aspects of wind power stations may conflict with the protection of historical sites.^[127] Wind power stations are less likely to be perceived negatively in urbanized and industrial regions.^[128] Aesthetic issues are subjective and some people find wind farms pleasant or see them as symbols of energy independence and local prosperity.^[129] While studies in Scotland predict wind farms will damage tourism,^[130] in other countries some wind farms have themselves become tourist attractions,^{[131][132][133]} with several having visitor centers at ground level or even observation decks atop turbine towers.

In the 1980s, wind energy was being discussed as part of a soft energy path.^[134] Renewable energy commercialization led to an increasing industrial image of wind power, which is being criticized by various stakeholders in the planning process, including nature protection associations.^[135] 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.

Coastal areas and areas of higher altitude such as ridgelines are considered prime for wind farms, due to constant wind speeds. However, both locations tend to be areas of high visual impact and can be a contributing factor in local communities' resistance to some projects. Both the proximity to densely populated areas and the necessary wind speeds make coastal locations ideal for wind farms.^[1]

Loreley rock in Rhineland-Palatinate, part of UNESCO World heritage site Rhine Gorge

Wind power stations can impact on important sight relations which are a key part of culturally important landscapes, such as in the Rhine Gorge or Moselle valley.^[2] Conflicts between heritage status of certain areas and wind power projects have arisen in various countries. In 2011 UNESCO raised concerns regarding a proposed wind farm 17 kilometres away from the French island abbey of Mont-Saint-Michel.^[2] In Germany, the impact of wind farms on valuable cultural landscapes has implications on zoning and land-use planning.^[3][4] For example, sensitive parts of the Moselle valley and the background of the Hambach Castle, according to the plans of the state government, will be kept free of wind turbines.^[4]

Wind turbines require aircraft warning lights, which may create light pollution. Complaints about these lights have caused the US FAA to consider allowing fewer lights per turbine in certain areas.^[5] Residents near turbines may complain of "shadow flicker" caused by rotating turbine blades, when the sun passes behind the turbine. This can be avoided by locating the wind farm to avoid unacceptable shadow flicker, or by turning the turbine off for the time of the day when the sun is at the angle that causes flicker. If a turbine is poorly sited and adjacent to many homes, the duration of shadow flicker on a neighbourhood can last hours.^[6]

Wind turbine syndrome[edit]

Wind turbine syndrome is a psychosomatic disorder largely caused by anxiety about wind farms and not by the turbines themselves. There is limited evidence of anxiety effects caused by low level noise in the close vicinity of the turbines.^[7]

Safety[edit]

Some turbine nacelle fires cannot be extinguished because of their height, and are sometimes left to burn themselves out. In such cases they generate toxic fumes and can cause secondary fires below.^[8] Newer wind turbines, however, are built with automatic fire extinguishing systems similar to those provided for jet aircraft engines. These autonomous systems, which can be retrofitted to older wind turbines, automatically detect a fire, shut down the turbine unit, and extinguish the fires.^{[9][10][11][12][13]}

During winter, ice may form on turbine blades and subsequently be thrown off during operation. This is a potential safety hazard, and has led to localised shut-downs of turbines.^[14] A 2007 study noted that no insurance claims had been filed, either in Europe or the US, for injuries from ice falling from wind towers, and that while some fatal accidents have occurred to industry workers, only one wind-tower related fatality was known to occur to a non-industry person: a parachutist.^[1]

Given the increasing size of production wind turbines, blade failures are increasingly relevant when assessing public safety risks from wind turbines. The most common failure is the loss of a blade or part thereof^[15]

Many offshore wind farms have contributed to electricity needs in Europe and Asia for years, and as of 2014 the first offshore wind farms are under development in U.S. waters. While the offshore wind industry has grown dramatically over the last several decades, especially in Europe, there is still some uncertainty associated with how the construction and operation of these wind farms affect marine animals and the marine environment.^[16]

Traditional offshore wind turbines are attached to the seabed in shallower waters within the near-shore marine environment. As offshore wind technologies become more advanced, floating structures have begun to be used in deeper waters where more wind resources exist.

Common environmental concerns associated with offshore wind developments include:^[17]

• The risk to seabirds being struck by wind turbine blades or being displaced from critical habitats;
• Underwater noise associated with the installation process of monopile turbines;
• The physical presence of offshore wind farms altering the behavior of marine mammals, fish, and seabirds by reasons of either attraction or avoidance;
• Potential disruption of the near-field and far-field marine environments from large offshore wind projects.

Germany restricts underwater noise during pile driving to less than 160 dB.^[18]

Due to the landscape protection status of large areas of the Wadden Sea, a major World Heritage Site with various national parks (e.g. Lower Saxon Wadden Sea National Park) German offshore installations are mostly restricted on areas outside the territorial waters.^[1] Offshore capacity in Germany is therefore way behind the British or Danish near coast installments, which face much lower restrictions.

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.^[1][1] There does not seem to have been much consideration however of the likely impact of displacement of fishing activities from traditional fishing grounds.^[2]

A study published in 2014 suggests that some seals prefer to hunt near turbines, likely due to the laid stones functioning as artificial reefs which attract invertebrates and fish.^[3]

• Environmental movement
• Environmental concerns with electricity generation
• Environmental effects of coal
• Environmental effects of nuclear power
• Environmental issues with energy
• Health effects from noise
• Renewable energy debate

• Robert Gasch, Jochen Twele (ed.), Wind power plants. Fundamentals, design, construction and operation, Springer 2012 ISBN 978-3-642-22937-4.
• Erich Hau, Wind turbines: fundamentals, technologies, application, economics Springer, 2013 ISBN 978-3-642-27150-2 (preview on Google Books)
• Alois Schaffarczyk (ed.), Understanding wind power technology, Wiley & Sons 2014, ISBN 978-1-118-64751-6.
• Hermann-Josef Wagner, Jyotirmay Mathur, Introduction to wind energy systems. Basics, technology and operation. Springer 2013, ISBN 978-3-642-32975-3.

• NWCC. National Wind Coordinating Collaborative website, facilitated by the American Wind and Wildlife Institute, includes its updated summaries of wind-wildlife interactions from 2010.