Information AboutWind Energy |
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Wind power refers to the extraction of useful energy from the Wind . In 2005, worldwide capacity of wind-powered generators was 58,982 MW, their production making up less than 1% of world-wide electricity use. Although still a relatively minor source of electricity for most countries, wind power generation more than quadrupled between 1999 and 2005. Most modern wind power is generated in the form of electricity by converting the rotation of Turbine blades into electrical current by means of an Electrical Generator . In Windmill s (a much older technology) wind energy is used to turn mechanical machinery to do physical work, like crushing grain or pumping water. Wind power is used in large scale Wind Farms for national electrical grids as well as in small individual turbines for providing electricity in isolated locations. Wind energy is abundant, inexhaustible, widely distributed, clean, and Mitigates the Greenhouse Effect . ECONOMICS In recent years, the cost of wind-generated electric power has dropped substantially, and is now lower than the cost of fuel-generated electric power, even without taking Externalities into account.1 Since 2004, wind power has been the least expensive form of new power generation.2 (Internet Archive version)3 Wind power is growing quickly, at about 38%,4 up from 25% growth in 2002. In the United States, as of 2003, wind power was the fastest growing form of electricity generation on a percentage basis.5 In 2005, wind energy cost one-fifth as much as it did in the late 1990s, and that downward trend is expected to continue as larger multi-megawatt Turbines are mass-produced.6 WIND ENERGY See Also: Wind An estimated 1 to 3 % of energy from the Sun that hits the earth is Converted into wind energy. This is about 50 to 100 times more energy than is converted into biomass by all the plants on earth through Photosynthesis . Most of this wind energy can be found at high altitudes where continuous wind speeds of over 160 km/h (100 mph) occur. Eventually, the wind energy is converted through friction into diffuse heat all through the earth's surface and atmosphere. The origin of wind is simple. The earth is unevenly heated by the sun resulting in the Pole s receiving less energy from the sun than the Equator does. Also the dry land heats up (and cools down) more quickly than the seas do. The differential heating powers a global Atmospheric Convection system reaching from the earth's surface to the Stratosphere which acts as a virtual ceiling. The change of seasons, change of day and night, the Coriolis Effect , the irregular Albedo (reflectivity) of land and water, humidity, and the friction of wind over different terrain are some of the factors which complicate the flow of wind over the surface. Wind variability and turbine power The power in the wind can be extracted by allowing it to blow past moving wings that exert torque on a rotor. The amount of power transferred depends on the wind speed (cubed), the swept area (linearly), and the density of the air (linearly). The Mass Flow of air that travels through the swept area of a wind turbine varies with the wind speed and air density. As an example, on a cool 15°C (59°F) day at sea level, air density is about 1.22 kilograms per cubic metre (it gets less dense with higher humidity). An 8 m/s breeze blowing through a 100 meter diameter rotor would move about 76,000 kilograms of air per second through the swept area. The Kinetic Energy of a given mass varies with the square of its velocity. Because the mass flow increases linearly with the wind speed, the wind energy available to a wind turbine increases as the cube of the wind speed. The power of the example breeze above through the example rotor would be about 2.5 megawatts. As the wind turbine extracts energy from the air flow, the air is slowed down, which causes it to spread out and diverts it around the wind turbine to some extent. A German physicist, Albert Betz, determined in 1919 that a wind turbine can extract at most 59% of the energy that would otherwise flow through the turbine's cross section. The Betz limit applies regardless of the design of the turbine. More recent work by Gorlov shows a theoretical limit of about 30% for propeller-type turbines.7 Actual efficiencies range from 10% to 20% for propeller-type turbines, and are as high as 35% for three-dimensional vertical-axis turbines like Darrieus or Gorlov turbines. s.]] Windiness varies, and an average value for a given location does not alone indicate the amount of energy a wind turbine could produce there. To assess the climatology of wind speeds at a particular location, a probability distribution function is often fit to the observed data. Different locations will have different wind speed distributions. The distribution model most frequently used to model wind speed climatology is a two-parameter Weibull Distribution because it is able to conform to a wide variety of distribution shapes, from gaussian to exponential. The Rayleigh model, an example of which is plotted to the right against an actual measured dataset, is a specific form of the Weibull function in which the shape parameter equals 2, and very closely mirrors the actual distribution of hourly wind speeds at many locations. Because so much power is generated by higher windspeed, much of the average power available to a windmill comes in short bursts. The 2002 Lee Ranch sample is telling: half of the energy available arrived in just 15% of the operating time. The consequence of this is that wind energy is not dispatchable as for fuel-fired power plants; additional output cannot be supplied in response to load demand. Since wind speed is not constant, a wind generator's annual energy production is never as much as its nameplate rating multiplied by the total hours in a year. The ratio of actual productivity in a year to this theoretical maximum is called the capacity factor. A well-sited wind generator will have a capacity factor of as much as 35%. When comparing the size of wind turbine plants to fueled Power Plant s, it is important to note that 1000 kW of wind-turbine potential power would be expected to produce as much energy in a year as approximately 350 kW of fuel-fired generation. Though the short-term (hours or days) output of a wind-plant is not completely predictable, the annual output of energy tends to vary only a few percent points between years. When storage, such as with Pumped Hydroelectric Storage , or other forms of generation are used to "shape" wind power (by assuring constant delivery reliability), commercial delivery represents a cost increase of about 25%, yielding viable commercial performance. Wind power density classes Wind maps in the United States and Europe classify areas into seven classes of wind power density, which give an indication of the quality of wind power resource in the area. Each class is a range of power densities, so that an area rated as class 4, for example, would have an average power density from 200 to 250 W/m2 at 10 m above ground. Generally, economic development of wind power for electricity generation takes place in areas rated Class 3 or higher.
TURBINE SITING As a general rule, wind generators are practical where the average wind speed is greater than 20 km/h (5.5 m/s or 12.5 mph). Obviously, Meteorology plays an important part in determining possible locations for wind parks, though it has great accuracy limitations. Meteorological wind data is not usually sufficient for accurate siting of a large wind power project. An 'ideal' location would have a near constant flow of non-turbulent wind throughout the year and would not suffer too many sudden powerful bursts of wind. The wind blows faster at higher altitudes because of the reduced influence of drag of the surface (sea or land) and the reduced viscosity of the air. The increase in velocity with altitude is most dramatic near the surface and is affected by topography, surface roughness, and upwind obstacles such as trees or buildings. Typically, the increase of wind speeds with increasing height follows a logarithmic profile that can be reasonably approximated by the Wind Profile Power Law , using an exponent of 1/7th, which predicts that wind speed rises proportionally to the seventh root of altitude. Doubling the altitude of a turbine, then, increases the expected wind speeds by 10% and the expected power by 34%. Wind farms or wind parks often have many turbines installed. Since each turbine extracts some of the energy of the wind, it is important to provide adequate spacing between turbines to avoid excess energy loss. Where land area is sufficient, turbines are spaced three to five rotor diameters apart perpendicular to the prevailing wind, and five to ten rotor diameters apart in the direction of the prevailing wind, to minimize efficiency loss. The "wind park effect" loss can be as low as 2% of the combined ''nameplate'' rating of the turbines. Utility-scale wind turbine generators have low temperature operating limits which restrict the application in areas that routinely experience temperatures less than −20 °C. Wind turbines must be protected from ice accumulation, which can make Anemometer readings inaccurate and which can cause high structure loads and damage. Some turbine manufacturers offer low-temperature packages at a few percent extra cost, which include internal heaters, different lubricants, and different alloys for structural elements, to make it possible to operate the turbines at lower temperatures. If the low-temperature interval is combined with a low-wind condition, the wind turbine will require station service power, equivalent to a few percent of its output rating, to maintain internal temperatures during the cold snap. For example, the St. Leon, Manitoba project has a total rating of 99 MW and is estimated to need up to 3 MW (around 3% of capacity) of station service power a few days a year for temperatures down to −30 °C. This factor affects the economics of wind turbine operation in cold climates. {Link without Title} Rural communities are thought to welcome wind farms because they provide income to farmers and ranchers, skilled jobs, cheap electricity and additional tax revenue to upgrade schools and maintain roads. Onshore in Washington ]] Onshore turbine installations tend to be along mountain ridges or passes, or at the top of cliff faces. The change in ground elevation causes the wind velocities to be generally higher in these areas, although there may be variation over short distances (a difference of 30 m can sometimes mean a doubling in output). Local winds are often monitored for a year or more with Anemometers and detailed wind maps constructed before wind generators are installed. For smaller installations where such data collection is too expensive or time consuming, the normal way of Prospecting for wind-power sites is to directly look for trees or vegetation that are permanently "cast" or deformed by the prevailing winds. Another way is to use a wind-speed survey map, or historical data from a nearby meteorological station, although these methods are less reliable. Sea shores also tend to be windy areas and good sites for turbine installation, because a primary source of wind is convection from the differential heating and cooling of land and sea over the course of day and night. Winds at sea level carry somewhat more energy than winds of the same speed in mountainous areas because the air at sea level is more dense. Unfortunately, windy areas tend to be picturesque, and so there is sometimes opposition to the installation of wind turbines on what would otherwise be ideal sites. Offshore Offshore wind turbines are considered to be less unsightly (they can be invisible from shore), and because the winds are usually more potent offshore, such turbines don´t need to reach quite as high into the air. However, offshore conditions are harsh, abrasive, and corrosive, and it is often difficult to repair a broken down turbine in open waters. In stormy areas with extended shallow continental shelves and sand banks (such as Denmark ), turbines are reasonably easy to install, and give good service. At the site shown, the wind is not especially strong but is very consistent. The largest offshore wind turbines in the world are 3.6MW rated machines that are installed in a small group of seven turbines off the east coast of Ireland about 60km south of Dublin. The turbines are located on a sandbank approximately 10km from the coast that has the potential for the installation of 500MW of generation capacity. As Of 2006 , the largest offshore wind farm is Horns Rev which is located 15km west off the West coast of Jutland , Denmark .9 Airborne See Also: Airborne wind turbine It has been suggested that wind turbines might be flown in high speed winds at high altitude. No such systems currently exist in the marketplace. An Ontario company, Magenn Power, Inc., is attempting to commercialize tethered aerial turbines suspended with helium. UTILIZATION Large scale There are many thousands of wind turbines operating, with a total capacity of 58,982 MW of which Europe accounts for 69% (2005). It was the most rapidly-growing means of alternative electricity generation at the turn of the century and provides a valuable complement to large-scale base-load power stations. World wind generation capacity more than quadrupled between 1999 and 2005. 90% of wind power installations are in the US and Europe, but the share of the top five countries in terms of new installations fell from 71 % in 2004 to 55 % in 2005. By 2010, World Wind Energy Association expects 120,000 MW to be installed worldwide. Germany , Spain , the United States , India and Denmark have made the largest investments in wind generated electricity. Denmark is prominent in the manufacturing and use of wind turbines, with a commitment made in the 1970s to eventually produce half of the country's power by wind. Denmark generates over 20% of its electricity with wind turbines, the highest percentage of any country and is fifth in the world in total power generation. The Danes and Germans are leading exporters of large turbines (each generating 0.66 to 5.0 megawatt). Wind accounts for 1% of the total electricity production on a global scale (2005). Germany is the leading producer of wind power with 32% of the total world capacity in 2005 (6% of German electricity); the official target is that by 2010, renewable energy will meet 12.5% of German electricity needs - it can be expected that this target will be reached even earlier. Germany has 16,000 wind turbines, mostly in the north of the country - including three of the biggest in the world, constructed by the companies Enercon (4.5 MW), Multibrid (5 MW) and Repower (5 MW). Germany's Schleswig-Holstein province generates 25% of its power with wind turbines. Spain and the United States are next in terms of installed capacity. In 2005, the government of Spain approved a new national goal for installed wind power capacity of 20,000 MW by 2012. According to the American Wind Energy Association , wind generated enough electricity to power 0.4% (1.6 million households) of total electricity in US, up from less than 0.1% in 1999. In 2005, both Germany and Spain have produced more electricity from wind power than from Hydropower plants. US Department of Energy studies have concluded wind harvested in just three of the fifty U.S. states could provide enough electricity to power the entire nation, and that offshore wind farms could do the same job. Wind power could grow by 50% in the U.S. in 2006.11 India ranks 4th in the world with a total wind power capacity of 4,430 MW. Wind power generates 3% of all electricity produced in India. The World Wind Energy Conference in New Delhi in November 2006 will give additional impetus to the Indian wind industry. In December 2003, General Electric installed the world's largest offshore wind turbines in Ireland, and plans are being made for more such installations on the west coast, including the possible the use of floating turbines. On August 15 , 2005 , China announced it would build a 1000-megawatt wind farm in Hebei for completion in 2020 . China reportedly has set a generating target of 20,000 MW by 2020 from renewable energy sources - it says indigenous wind power could generate up to 253,000 MW.12 Following the World Wind Energy Conference in November 2004, organised by the Chinese and the World Wind Energy Association, a Chinese renewable energy law was adopted. In late 2005, the Chinese government increased the official wind energy target for the year 2020 from 20 GW to 30 GW. Another growing market is Brazil, with a wind potential of 143 GW.13 The federal government has created an incentive program, called Proinfa ,14 to build production capacity of 3300 MW of renewable energy for 2008, of which 1422 MW through wind energy. The program seeks to produce 10% of Brazillian electricity through renewable sources. Brazil produced 320 TWh in 2004. Recently, Canada has experienced rapid growth of wind capacity - moving from a total installed capacity of 137MW to 943MW in under 6 years, showing a growth rate of 38% from 2000-2005, and rising.15 This growth has been fed by provincial measures, including installation targets, economic incentives and political support. For example, the government of the Canadian province of Ontario announced on 21 March 2006 that it will introduce a feed-in tariff for wind power, referred to as 'Standard Offer Contracts', which may boost the wind industry across the entire country.16 In the Canadian province of Quebec , the state-owned hydroelectric utility plans to generate 2000 MW from wind farms by 2013.17 Small scale and runs various 12 volt appliances within the building on which it is installed.]] Wind turbines have been used for household electricity generation in conjunction with battery storage over many decades in remote areas. Household generator units of more than 1 kW are now functioning in several countries. To compensate for the varying power output, grid-connected wind turbines may utilise some sort of Grid Energy Storage . Off-grid systems either adapt to intermittent power or use Photovoltaic or Diesel systems to supplement the wind turbine. Wind turbines range from small four hundred watt generators for residential use to several megawatt machines for wind farms and offshore. The small ones have direct drive generators, Direct Current output, Aeroelastic Blades , lifetime bearings and use a vane to point into the wind; while the larger ones generally have geared power trains, alternating current output, flaps and are actively pointed into the wind. Direct drive generators and aeroelastic blades for large wind turbines are being researched and direct current generators are sometimes used. In urban locations, where it is difficult to obtain large amounts of wind energy, smaller systems may still be used to run low power equipment. Distributed Power from rooftop mounted wind turbines can also alleviate power distribution problems, as well as provide resilience to power failures. Equipment such as parking meters or wireless internet gateways may be powered by a wind turbine that charges a small battery, replacing the need for a connection to the power grid and/or maintaining service despite possible power grid failures. Small scale turbines are available that are approximately 7 feet (2 m) in diameter and produce 900 watts. Units are lightweight, e.g. 16 kg (35 pounds), allowing rapid respond to wind gusts typical of urban settings and easy mounting much like a television antenna. It is claimed that they are inaudible even a few feet under the turbine. Dynamic Braking regulates the speed by dumping excess energy, so that the turbine continues to produce electricity even in high winds. The dynamic braking resistor may be installed inside the building to provide heat (during high winds when more heat is lost by the building, while more heat is also produced by the braking resistor). The proximal location makes low voltage (12 volt, or the like) energy distribution practical. An additional benefit is that owners become more aware of electricity consumption, possibly reducing their consumption down to the average level that the turbine can produce. According to the World Wind Energy Association, it is difficult to assess the total number or capacity of small-scaled wind turbines, but in China alone, there are roughly 300,000 small-scale wind turbines generating electricity. CONTROVERSY Arguments for and against wind power are listed below. Arguments of opponents , in California. Developed during a period of tax incentives in the 1980s, this wind farm has more turbines than any other in the United States. These turbines are only a few tens of kilowatts each. They cost several times more per kWh and spin much more quickly than modern megawatt turbines, endangering birds and making noise.]] Economics
Yield
CO2 Emissions
Ecological footprint
, Reading , England ]]
Scalability
Aesthetics
Arguments of supporters E70-4]] Supporters of wind energy state that: Pollution
Long-term potential
Coping with intermittency
, Australia . Energy-intensive process like this could utilize burst electricity from wind.]]
Ecology
Economic feasibility
Aesthetics s at La Mancha , Spain .]]
SEE ALSO Power Generation Green Energy
REFERENCES SOURCES Technical
Political
Wind power projects
Academic Institutions EXTERNAL LINKS
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