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Debate for and against wind power
Arguments for and against wind power are listed below.

Arguments of supporters
Supporters of wind energy state that:

Pollution
Wind power is a renewable resource, which means using it will not deplete the earth's supply of fossil fuels. It also is a clean energy source, and operation does not produce carbon dioxide, sulfur dioxide, mercury, particulates, or any other type of air pollution, as do conventional fossil fuel power sources.

During manufacture of the wind turbine, however, steel, concrete, aluminium and other materials will have to be made and transported using energy-intensive processes, generally using fossil energy sources. Nevertheless, the energy used for manufacture of a wind turbine is earned back in four to six months of operation.

Long-term potential

 * Wind's long-term technical potential is believed five times current global energy consumption or four times current electricity demand. This would require ~13% of all land area, or that land area with Class 3 or greater potential at a height of 80 meters. It assumes a placement of six large wind turbines per square kilometer on land. Offshore resources experience mean wind speeds ~90% greater than that of land, so offshore resources could contribute about seven times more energy than land.   This number could also increase with higher altitude or airborne wind turbines.

Coping with intermittency

 * As the fraction of energy produced by wind ("penetration") increases, different technical and economic factors affect the need, if there is one, for grid energy storage facilities. Large networks, connected to multiple wind plants at widely separated geographic locations, may accept a higher penetration of wind than small networks or those without storage systems or economical methods of compensating for the variability of wind. In systems with significant amounts of existing pumped storage (e.g. UK, eastern US) this proportion may be higher. Isolated, relatively small systems with only a few wind plants may only be stable and economic with a lower fraction of wind energy (e.g. Ireland).


 * On most large power systems a moderate proportion of wind generation can be connected without the need for storage. For larger proportions, storage may be economically attractive or even technically necessary.


 * Long-term storage of electrical energy involves substantial capital costs, space for storage facilities, and some portion of the stored power will be lost during conversion and transmission. The percentage retrievable from stored power is called the "efficiency of storage."  The cost incurred to "shape" intermittent wind power for reliable delivery is about a 20% premium for most wind applications on large grids, but approaches 50% of the cost of generation when wind comprises more than 70% of the local grid's input power. See: Grid energy storage


 * Electricity demand is variable but generally very predictable on larger grids; errors in demand forecasting are typically no more than 2%. Because conventional powerplants can drop off the grid within a few seconds, for example due to equipment failures, in most systems the output of some coal or gas powerplants is intentionally part-loaded to follow demand and to replace rapidly lost generation. The ability to follow demand (by maintaining constant frequency) is termed "response." The ability to quickly replace lost generation, typically within timescales of 30 seconds to 30 minutes, is termed "spinning reserve." Nuclear power plants in contrast are not very flexible and are not intentionally part-loaded. A power plant that operates in a steady fashion, usually for many days continuously, is termed a "base load" plant.


 * What happens in practice therefore is that as the power output from wind varies, part-loaded conventional plants, which must be there anyway to provide response (due to continuously changing demand) and reserve, adjust their output to compensate; they do this in response to small changes in the frequency (nominally 50 or 60 Hz) of the grid. In this sense wind acts like "negative" load or demand.


 * The maximum proportion of wind power allowable in a power system will thus depend on many factors, including the size of the system, the attainable geographical diversity of wind, the conventional plant mix (coal, gas, nuclear) and seasonal load factors (heating in winter, air-conditioning in summer) and their statistical correlation with wind output. For most large systems the allowable penetration fraction  (wind nameplate rating divided by system peak demand) is thus at least 15% without the need for any energy storage whatsoever. Note that the interconnected electrical system may be much larger than the particular country or state (e.g. Denmark, California) being considered.


 * It should also be borne in mind that wind output, especially from large numbers of turbines/farms can be predicted with a fair degree of confidence many hours ahead using weather forecasts.


 * The allowable penetration may of course be further increased by increasing the amount of part-loaded generation available, or by using energy storage facilities, although if purpose-built for wind energy these may significantly increase the overall cost of wind power.


 * Existing European hydroelectric power plants can store enough energy to supply one month's worth of European electricity consumption. Improvement of the international grid would allow using this in the relatively short term at low cost, as a matching variable complementary source to wind power. Excess wind power could even be used to pump water up into collection basins for later use.


 * Energy Demand Management or Demand-Side Management refers to the use of communication and switching devices which can release deferrable loads quickly to correct supply/demand imbalances. Incentives can be created for the use of these systems, such as favorable rates or capital cost assistance, encouraging consumers with large loads to take advantage of renewable energy by adjusting their loads to coincide with resource availability. For example, pumping water to pressurize municipal water systems is an electricity intensive application that can be performed when electricity is available. Real-time variable electricity pricing can encourage all users to reduce usage when the renewable sources happen to be at low production.


 * In energy schemes with a high penetration of wind energy, secondary loads, such as desalination plants and electric boilers may be encouraged because their output (water and heat) can be stored. The utilization of "burst electricity", where excess electricity is used on windy days for opportunistic purposes greatly improves the economic efficiency of wind turbine schemes. An ice storage device has been invented which allows cooling energy to be consumed during resource availability, and dispatched as air conditioning during peak hours.


 * Multiple wind farms spread over a wide geographic area and gridded together produce power much more constantly.


 * Electricity produced from solar energy could be a counter balance to the fluctuating supplies generated from wind. It tends to be windier at night and during cloudy or stormy weather, so there is likely to be more sunshine when there is less wind.

Ecology

 * Because it uses energy already present in the atmosphere, and can displace fossil-fuel generated electricity (with its accompanying carbon dioxide emissions), wind power mitigates global warming. If the entire world's nameplate electrical demand expected in 2010 were served from wind power alone, the amount of energy extracted from the atmosphere would be less than the increase added by radiative forcing by additional carbon dioxide at 2000 levels above those of the year 1500, before fossil fuel consumption became significant.


 * Energy payback ratio (ratio of energy produced compared to energy expended in construction and operation)for wind turbines is between 17 and 39 (i.e. over it's life-time a wind turbine produces 17-39 times as much energy as is needed for its manufacture, construction, operation and decomissioning). This is to be compared with 11 for coal power plants and 16 for nuclear power plants.


 * The energy consumption for production, installation, operation and decommissioning of a wind turbine is usually earned back within 3 months of operation.


 * Unlike fossil or nuclear power stations, which circulate large amounts of water for cooling, wind turbines do not need water to generate electricity.


 * Studies show that the number of birds killed by wind turbines is negligible compared to the amount that die as a result of other human activities such as traffic, hunting, power lines and high-rise buildings and especially the environmental impacts of using non-clean power sources. For example, in the UK, where there are a few hundred turbines, about one bird is killed per turbine per year; 10 million per year are killed by cars alone. In the United States, turbines kill 70,000 birds per year, compared to 57 million killed by cars and 97.5 million killed by collisions with plate glass. Another study suggests that migrating birds adapt to obstacles; those birds which don't modify their route and continue to fly through a wind farm are capable of avoiding windmills, at least in the low-wind non-twilight conditions studied. 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." It notes that climate change poses a much more significant threat to wildlife, and therefore supports wind farms and other forms of renewable energy.


 * Clearing of wooded areas is often unnecessary, as the practice of farmers leasing their land out to companies building wind farms is common. Farmers receive annual lease payments of two thousand to five thousand dollars per turbine. The land can still be used for farming and cattle grazing.


 * The ecological and environmental costs of wind plants are paid by those using the power produced, with no long-term effects on climate or local environment left for future generations.


 * Less than 1% of the land would be used for foundations and access roads, the other 99% could still be used for farming. Turbines can be sited on land unused in techniques such as center-pivot irrigation.


 * After decommissioning wind turbines, even the foundations are removed.

Economic feasibility

 * Conventional and nuclear power plants receive massive amounts of direct and indirect governmental subsidies. If a comparison is made on real production costs, wind energy is competitive in many cases. If the full costs (environmental, health, etc.) are taken into account, wind energy is competitive in most cases. Furthermore, wind energy costs are continuously decreasing due to technology development and scale enlargement.
 * Nuclear power plants receive special immunity from the disasters they may cause, which prevents victims from recovering the cost of their continued health care from those responsible, even in the case of criminal malfeasance.
 * Conventional and nuclear plants also have sudden unpredictable outages (see above). Statistical analysis shows that 1000 MW of wind power can replace 300 MW of conventional power.

Aesthetics

 * Improvements in blade design and gearing have quietened modern turbines to the point where a normal conversation can be held underneath one
 * Newer wind farms have more widely spaced turbines due to the greater power of the individual wind turbines, and so look less cluttered


 * Wind turbines can be positioned alongside motorways, significantly reducing aesthetic concerns


 * The aesthetics of wind turbines have been compared favourably to those of pylons from conventional power stations


 * Areas under windfarms can be used for farming, and are protected from development


 * Offshore sites have on average a higher energy yield than onshore sites, and often cannot be seen from the shore.

Economics

 * To compete with traditional sources of energy, wind power often receives financial incentives. In the United States, wind power receives a tax credit of 1.9 cents per kilowatt-hour produced, with a yearly inflationary adjustment. However, in 2004 when the U.S. production tax credit had lapsed for nine months, wind power was still a rapidly growing form of electrical generation, calling into question the value of these production tax credits. Another tax benefit is accelerated depreciation. Many American states also provide incentives, such as exemption from property tax, mandated purchases, and additional markets for "green credits." Countries such as Canada and Germany also provide tax credits and other incentives for wind turbine construction.


 * Many potential sites for wind farms are far from demand centers, requiring substantially more money to construct new transmission lines and substations.

Yield

 * The goals of renewable energy development are reduction of reliance on fossil and nuclear fuels, reduction of greenhouse gas and other emissions, and establishment of more sustainable sources of energy. Some critics question wind energy's ability to significantly move society towards these goals. They point out that 25-30% annual load factor is typical for wind facilities. The intermittent and non-dispatchable nature of wind turbine power requires that "spinning reserves" are kept burning for supply security. The fluctuation in wind power requires more frequent load ramping of such plants to maintain grid system frequency. This can force operators to run conventional plants below optimal thermal efficiency resulting in greater emissions. A recent European Nuclear Society study estimates that the equivalent of one third of energy saved from wind generation is lost to these inefficiencies.

CO2 Emissions

 * Electric power production is only part (about 39% in the USA ) of a country's energy use, so wind power alone does little to mitigate the larger part of the effects of energy use. For example, despite more than doubling the installed wind power capacity in the U.K. from 2002 to 2004, wind power contributed less than 1% of the national electricity supply, and that country's CO2 emissions continued to rise in 2002 and 2003 (Department of Trade and Industry).  Six of the U.K.'s nuclear reactors were closed in this period.


 * Groups such as the UN's Intergovernmental Panel on Climate Change state that the desired mitigation goals can be achieved at lower cost and to a greater degree by continued improvements in general efficiency — in building, manufacturing, and transport — than by wind power. Such statements, however, do not take into account long-term costs and calculations, like drastically increasing prices for oil, gas, uranium etc. Also once an investment in a wind turbine is made, the electricity produced by that turbine is fixed for a period of 20 years.

Ecological footprint

 * The clearing of trees may be necessary since obstructions reduce yield.


 * Wind turbines should idealy be placed about ten times their diameter apart in the direction of prevailing winds and five times their diameter apart in the perpendicular direction for minimal losses due to wind park effects. As a result, wind turbines require roughly 0.1 square kilometres of unobstructed land per megawatt of nameplate capacity. A wind farm that produces the energy equivalent of a conventional power plant might have turbines spread out over an area of approximately 200 square kilometres. A nuclear plant of comparable capacity would be surrounded of a 100 square kilometre exclusion zone, and strip mines supplying coal power plants claim large tracts of land. Though restrictions in land use possibilities are different in the three cases, the area needed for wind farming is not excessive compared to conventional power.




 * Windmills kill birds, especially birds of prey. Siting generally takes into account known bird flight patterns, but most paths of bird migration, particularly for birds that fly by night, are unknown. Although a Danish survey in 2005 (Biology Letters 2005:336) showed that less than 1% of migrating birds passing a wind farm in Rønde, Denmark, got close to collision, the site was studied only during low-wind non-twilight conditions. A survey at Altamont Pass, California conducted by a California Energy Commission in 2004 showed that turbines killed 4,700 birds annually (1,300 of which are birds of prey). Radar studies of proposed sites in the eastern U.S. have shown that migrating songbirds fly well within the reach of large modern turbines. Many more birds are killed by cars, and this is a widely accepted cost.

A wind farm in Norway's Smøla islands is reported to have destroyed a colony of sea eagles according to the British Royal Society for the Protection of Birds. The society said turbine blades killed nine of the birds in a 10 month period, including all three of the chicks that fledged that year. Norway is regarded as the most important place for white-tailed eagles.

In 1989, Smøla was designated as having one of the highest densities of white-tailed eagles in the world. But the society now fears the 100 or so more wind farms planned in the rest of Norway could have a similar impact.

"Smøla is demonstrating the damage that can be caused by a wind farm in the wrong location. The RSPB strongly supports renewable energies including wind, but the deaths of adult birds and the three young born last year make the prospects for white-tailed eagles on the island look bleak," said Dr. Rowan Langston, senior research biologist at the RSPB.


 * The numbers of bats killed by existing facilities has troubled even industry personnel. A six-week study in 2004 estimated that over 2200 bats were killed by 63 turbines at two sites in the Eastern US. This study suggests some site locations may be particularly hazardous to local bat populations, and that more research is urgently 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 (Lasiurus cinereus), and red bat (Lasiurus borealis) along with semi-migratory silver-haired bats (Lasionycteris noctivagans) 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.

Scalability

 * To meet the energy demands worldwide in the future in a sustainable way, a much larger number of turbines than we have today will be required. Naturally this will affect more people and wildlife habitat.

Aesthetics

 * Perceptions that wind turbines are noisy and contribute to "visual pollution" creates resistance to the establishment of land-based wind farms in some places. Moving the turbines offshore mitigates the problem, but offshore wind farms are more expensive to maintain and there is an increase in transmission loss due to longer distances of power lines. One solution to such objections is the early and close involvement of the local population, as recommended in the sustainability guidelines of the World Wind Energy Association - in the ideal case through community/citizen ownership of wind farms.


 * Some residents near windmills complain of "shadow flicker," which is the alternating pattern of sun and shade caused by a rotating windmill casting a shadow over residences. Efforts are made when siting turbines to avoid this problem.