Wind energy is the conversion of wind energy into a useful form of energy, such as using
wind turbines to make electrical power,
windmills for mechanical power,
wind pumps for water pumping or drainage,
sails to propel ships.
Large wind farms consist of hundreds of individual wind turbines which are connected to the electric power transmission network. Offshore wind farms can harness more frequent and powerful winds than are available to land-based installations and have less visual impact on the landscape but construction costs are considerably higher. Small onshore wind facilities are used to provide electricity to isolated locations and utility companies increasingly buy surplus electricity produced by small domestic wind turbines.[1]
Wind power, as an alternative to fossil fuels, is plentiful, renewable, widely distributed, clean, produces no greenhouse gas emissions during operation and uses little land.[2] Any effects on the environment are generally less problematic than those from other power sources. As of 2011, Denmark is generating more than a quarter of its electricity from wind. 83 countries around the world are using wind power on a commercial basis.[3] In 2010 wind energy production was over 2.5% of total worldwide electricity usage, and growing rapidly at more than 25% per annum. The monetary cost per unit of energy produced is similar to the cost for new coal and natural gas installations.[4] Although wind power is a popular form of energy generation, the construction of wind farms is not universally welcomed due to aesthetics.[5][6][7][8][9][10][11]
Wind power is very consistent from year to year but has significant variation over shorter time scales. The intermittency of wind seldom creates problems when used to supply up to 20% of total electricity demand,[12] but as the proportion increases, a need to upgrade the grid, and a lowered ability to supplant conventional production can occur.[13] Power management techniques such as having excess capacity storage, geographically distributed turbines, dispatchable backing sources, storage such as pumped-storage hydroelectricity, exporting and importing power to neighboring areas or reducing demand when wind production is low, can greatly mitigate these problems.[14] In addition, weather forecasting permits the electricity network to be readied for the predictable variations in production that occur.[15][16]
Wind energy
Wind energy is the kinetic energy of air in motion, also called wind. Total wind energy flowing through an imaginary area A during the time t is:
(33)
where ρ is the density of air; v is the wind speed; Avt is the volume of air passing through A (which is considered perpendicular to the direction of the wind); Avtρ is therefore the mass m passing per unit time. Note that ½ ρv2 is the kinetic energy of the moving air per unit volume.
Power is energy per unit time, so the wind power incident on A (e.g. equal to the rotor area of a wind turbine) is:
(34)
Wind power in an open air stream is thus proportional to the third power of the wind speed; the available power increases eightfold when the wind speed doubles. Wind turbines for grid electricity therefore need to be especially efficient at greater wind speeds.
Wind is the movement of air across the surface of the Earth, affected by areas of high pressure and of low pressure.[34] The surface of the Earth is heated unevenly by the Sun, depending on factors such as the angle of incidence of the sun's rays at the surface (which differs with latitude and time of day) and whether the land is open or covered with vegetation. Also, large bodies of water, such as the oceans, heat up and cool down slower than the land. The heat energy absorbed at the Earth's surface is transferred to the air directly above it and, as warmer air is less dense than cooler air, it rises above the cool air to form areas of high pressure and thus pressure differentials. The rotation of the Earth drags the atmosphere around with it causing turbulence. These effects combine to cause a constantly varying pattern of winds across the surface of the Earth.[34]
The total amount of economically extractable power available from the wind is considerably more than present human power use from all sources.[35] Axel Kleidon of the Max Planck Institute in Germany, carried out a "top down" calculation on how much wind energy there is, starting with the incoming solar radiation that drives the winds by creating temperature differences in the atmosphere. He concluded that somewhere between 18 TW and 68 TW could be extracted.[36] Cristina Archer and Mark Z. Jacobson presented a "bottom-up" estimate, which unlike Kleidon's are based on actual measurements of wind speeds, and found that there is 1700 TW of wind power at an altitude of 100 metres over land and sea. Of this, "between 72 and 170 TW could be extracted in a practical and cost-competitive manner".[36]
Distribution of wind speed
The strength of wind 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 frequency 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 Weibull model closely mirrors the actual distribution of hourly wind speeds at many locations. The Weibull factor is often close to 2 and therefore a Rayleigh distribution can be used as a less accurate, but simpler model.[37]
Wind farms
A wind farm is a group of wind turbines in the same location used for production of electricity. A large wind farm may consist of several hundred individual wind turbines, and cover an extended area of hundreds of square miles, but the land between the turbines may be used for agricultural or other purposes. A wind farm may also be located offshore.
Almost all large wind turbines have the same design — a horizontal axis wind turbine having an upwind rotor with three blades, attached to a nacelle on top of a tall tubular tower. In a wind farm, individual turbines are interconnected with a medium voltage (often 34.5 kV), power collection system and communications network. At a substation, this medium-voltage electric current is increased in voltage with a transformer for connection to the high voltage electric power transmission system.
Many of the largest operational onshore wind farms are located in the US. As of 2012, the Alta Wind Energy Center is the largest onshore wind farm in the world at 1020 MW, followed by the Shepherds Flat Wind Farm (845 MW), and the Roscoe Wind Farm (781.5 MW). As of September 2012, the Sheringham Shoal Offshore Wind Farm and the Thanet Wind Farm in the UK are the largest offshore wind farms in the world at 317 MW and 300 MW, followed by Horns Rev II (209 MW) in Denmark.
There are many large wind farms under construction including; The London Array (offshore) (1000 MW), BARD Offshore 1 (400 MW), Sheringham Shoal Offshore Wind Farm (317 MW), Lincs Wind Farm (offshore), Clyde Wind Farm (548 MW), Greater Gabbard wind farm (500 MW), Macarthur Wind Farm (420 MW), Lower Snake River Wind Project (343 MW) and Walney Wind Farm (367 MW).
Feeding into grid
Induction generators, often used for wind power, require reactive power for excitation so substations used in wind-power collection systems include substantial capacitor banks for power factor correction.[39] Different types of wind turbine generators behave differently during transmission grid disturbances, so extensive modelling of the dynamic electromechanical characteristics of a new wind farm is required by transmission system operators to ensure predictable stable behaviour during system faults (see: Low voltage ride through). In particular, induction generators cannot support the system voltage during faults, unlike steam or hydro turbine-driven synchronous generators. Doubly fed machines generally have more desirable properties for grid interconnection.[40][41] Transmission systems operators will supply a wind farm developer with a grid code to specify the requirements for interconnection to the transmission grid. This will include power factor, constancy of frequency and dynamic behavior of the wind farm turbines during a system fault.[42][43]
Literature:
1.Gipe, Paul. The Wind Industry's Experience with Aesthetic Criticism. Leonardo. JSTOR 1575818.
2.doi:10.1016/j.rser.2008.09.017
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3. REN21 (2011). Renewables 2011: Global Status Report.
4. International Energy Outlook. Energy Information Administration (2006).
5.Why Australia needs wind power (PDF). Retrieved on 7 January 2012.
6.Carbon footprint of electricity generation. UK Parliamentary Office of Science and Technology (October 2006). Retrieved on 7 April 2012.
7.Wind Energy and the Environment (PDF). Retrieved on 17 January 2012.
8.A Summary of Opinion Surveys on Wind Power (PDF). Retrieved on 17 January 2012.
9.Public attitudes to wind farms. Eon-uk.com (28 February 2008). Retrieved on 17 January 2012.
10.The Social Acceptance of Wind Energy. European Commission.
11.Energy. Retrieved on 31 October 2012.
12.Hannele Holttinen, et al. (September 2006). "Design and Operation of Power Systems with Large Amounts of Wind Power", IEA Wind Summary Paper (PDF). Global Wind Power Conference 18–21 September 2006, Adelaide, Australia.
13.Jo Abbess (28 August 2009). Claverton-Energy.com. Claverton-Energy.com. Retrieved on 29 August 2010.
14.Impact of Wind Power Generation in Ireland on the Operation of Conventional Plant and the Economic Implications. eirgrid.com (February 2004). Retrieved on 22 November 2010.
15.Wind power delivers too much to ignore Reg Platt New Scientist 21 January 2013
16.Beyond the Bluster why Wind Power is an Effective Technology - Institute for Public Policy Research August 2012
17.Dietrich Lohrmann, "Von der östlichen zur westlichen Windmühle", Archiv für Kulturgeschichte, Vol. 77, Issue 1 (1995), pp.1–30 (10f.)
18.A.G. Drachmann, "Heron's Windmill", Centaurus, 7 (1961), pp. 145–151
19.Ahmad Y Hassan, Donald Routledge Hill (1986). Islamic Technology: An illustrated history, p. 54. Cambridge University Press. ISBN 0-521-42239-6.
20.Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific American, May 1991, p. 64-69. (cf. Donald Routledge Hill, Mechanical Engineering)
21.Mark Kurlansky, Salt: a world history,Penguin Books, London 2002 ISBN 0-14-200161-9, pg. 419
22.Baker, T. Lindsay. Brief History of Windmills in the New World. Windmillers' Gazette. Retrieved on 31 October 2012.
23.Quirky old-style contraptions make water from wind on the mesas of West Texas. Mysanantonio.com (23 September 2007). Archived from the original on 16 September 2010. Retrieved on 29 August 2010.
24.Windmills in Rural America. Greenenergyohio.org. Retrieved on 2013-01-11.
25.World Energy Timeline. Danielyergin.com (21 September 2011). Retrieved on 2013-01-11.
26.A surprising history. Environmentalhistory.org (29 October 2012). Retrieved on 2013-01-11.
27.Hardy, Chris (6 July 2010). Renewable energy and role of Marykirk's James Blyth. The Courier. D. C. Thomson & Co. Ltd.. Archived from the original on 14 March 2012. Retrieved on 12 December 2010.
28.Price, Trevor J (3 May 2005). "James Blyth – Britain's first modern wind power engineer". Wind Engineering 29 (3): 191–200. doi:10.1260/030952405774354921.
29.29.0 29.1 29.2 NIxon, Niki (17 October 2008). Timeline: The history of wind power. The Guardian. Guardian News and Media Limited. Retrieved on 10 April 2012.
30.Dodge, Darrell M.. Part 2 – 20th Century Developments. Illustrated history of wind power development. TelosNet Web Development. Retrieved on 10 April 2012.
31.Anon. The historical development of the wind turbine. NTNU environmental studies: Wind power. NTNU. Retrieved on 7 January 2013.
32.Enercon E-126 7.5MW still world's biggest. Windpowermonthly.com (1 August 2012). Retrieved on 2013-01-11.
33.Harvesting the Wind: The Physics of Wind Turbines (PDF). Retrieved on 2013-01-11.
34.Anon (2010). What is wind?. Renewable UK: Education and careers. Renewable UK. Retrieved on 9 April 2012.
35.Hurley, Brian. How Much Wind Energy is there? – Brian Hurley – Wind Site Evaluation Ltd. Claverton Group. Retrieved on 8 April 2012.
36.Anil Ananthaswamy and Michael Le Page (30 January 2012). Power paradox: Clean might not be green forever. New Scientist.
37.Wind statistics and the Weibull distribution. Wind-power-program.com. Retrieved on 2013-01-11.
38.by bruce stutz. High-Altitude Wind Energy: Huge Potential — And Hurdles. E360.yale.edu. Retrieved on 2013-01-11.
39.Wind Generation Technical Characteristics p.17
40.Lamb, John (2009). The Greening of IT: How Companies Can Make a Difference for the Environment. p. 261. ISBN ISBN 978-0-13-715083-0.
41.Castellano, Robert (2012). Alternative Energy Technologies. p. 26. ISBN ISBN 978-2813000767.
42.Demeo, E.A.; Grant, W.; Milligan, M.R.; Schuerger, M.J. (2005). "Wind plant integration". Power and Energy Magazine, IEEE 3 (6): 38–46. doi:10.1109/MPAE.2005.1524619. http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1524619
43. Zavadil, R.; Miller, N.; Ellis, A.; Muljadi, E. (2005). "Making connections". Power and Energy Magazine, IEEE 3 (6): 26–37. doi:10.1109/MPAE.2005.1524618. http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1524618