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4/22/20141The University of Iowa Intelligent Systems LaboratoryWind Turbine SitingAndrew KusiakIntelligent Systems Laboratory2139 Seamans CenterThe University of Iowa Iowa City, Iowa 52242 - [email protected]: 319-335-5934 Fax: 319-335-5669http://www.icaen.uiowa.edu/~ankusiakThe University of Iowa Intelligent Systems LaboratoryOutline Terrain roughness  Escarpments Wind shear The roughness rose Variable winds Turbulence Wind obstacles Wind shade The park effect The hill effect Turbine siting Offshore winds Wind mapsThe University of Iowa Intelligent Systems LaboratoryWind Farm Designhttp://awsopenwind.organdwww.firstlook.3tier.com(best use www.3tier.com)Download this freeware The University of Iowa Intelligent Systems LaboratoryRoughness  At high altitudes, the wind is hardly influenced by the surface of the earth At the lower layers of the atmosphere the wind speed is affected by the friction against the surface of the earth  In the wind industry one distinguishes between the influence from the terrain roughness, obstacles, and the terrain contours (referred to as the orographyof the area)  Let’s explore orography while investigating so called speed up effects, i.e., tunnel effects and hill effectsIntroduction4/22/20142The University of Iowa Intelligent Systems LaboratoryRoughness In general, the more rough the earth's surface is, the morethe wind slows down  Forests and large cities slow down the wind considerably, while concrete runways in airports slow the wind a little  Water surfaces are smoother than concrete runways andbarely impact the wind speed Long grass, shrubs, and bushes slow down the wind to some degreeThe University of Iowa Intelligent Systems LaboratoryRoughness Classes (Lengths) E. Hau (2006), p. 463The University of Iowa Intelligent Systems LaboratoryRoughness Classes (Lengths)  Roughness classes or lengths, are usually used to evaluate wind conditions at a landscape A high roughness class of 3 to 4 refers to landscapes with many trees and buildings, while a sea surface is in roughness class 0 Concrete runways in airports are in roughnessclass 0.5. The same applies to the flat and open landscape The University of Iowa Intelligent Systems LaboratoryWind Shear  This graph shows how the wind speed varies in roughness class 2(agricultural land with some houses and sheltering hedge rows atsome 500 m intervals), assuming the wind speed of 10 m/s at a height of 100 meters Wind shear (wind gradient), is a difference in wind speed and direction over a relatively short distance in the atmosphere Wind shear can be broken down into vertical and horizontal components4/22/20143The University of Iowa Intelligent Systems LaboratoryWind Shear  Wind shear is an important factor in the design of wind turbines  Consider a wind turbine with a hub height of 40 meters and a rotor diameter of 40 meters (blade length = 20 m)  The wind blows at 9.3 m/s when the tip of the blade is in its uppermost position, and only 7.7 m/s when the tip is in the bottom position  This means that the forces acting on the rotor blade when it is in its top position are larger than when it is in its bottom positionThe University of Iowa Intelligent Systems LaboratoryDirectional vs Speed ShearSpeed shear: the wind speed increases with the heightDirectional shear: a change in the wind directionwith the heighthttp://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/modl_shear.rxmlThe University of Iowa Intelligent Systems LaboratoryWind Shear and Escarpments  It is not correct to assume that the height of a cliff compensates for the height of the wind turbine tower, at least when the wind is coming from the sea The cliff creates turbulence and brakes the wind before it reaches the cliff This most likely reduces the turbine lifetime, duewear and tear caused by the turbulent airThe University of Iowa Intelligent Systems LaboratoryWind Shear and Escarpments  If one had a choice, one would select a rounded hill in the direction facing the sea, rather than the escarpment seen in the picture A speed up effect may occur at a rounded hill© Copyright 1997-2003 Danish WindIndustry Association4/22/20144The University of Iowa Intelligent Systems LaboratoryWindMain sources of wind data for wind farm siting Wind map data Computational modeling Site specific data collection Neighborhood wind farmsThe University of Iowa Intelligent Systems LaboratoryWind Frequency/Velocity/Energy RoseS. Mathew (2006)Spider diagramCircular histogramThe University of Iowa Intelligent Systems LaboratoryThe Roughness Rose Similar to wind rose mapping wind energy coming from different directions, a roughness rose describes the roughnessof the terrain in different directions from a prospective wind turbine site Normally, the compass is divided into 12 sectors of 30 degrees each, but other divisions are possible Rose = Spider diagramThe University of Iowa Intelligent Systems LaboratoryWind Speed Variability Short Term Variability of the Wind (second scale)  The wind speed fluctuates and sodoes the energy content of the wind  The wind variation depends both on the weather and local surfaceconditions and obstaclesThe most rapid variations are to some extent compensated by the inertia of the wind turbine rotor4/22/20145The University of Iowa Intelligent Systems LaboratoryWind Speed VariabilityDistribution of 10-second data from two different months0.002.004.006.008.0010.003.50 5.50 7.50 9.50 11.50 14.00 18.00 21.00Percentage [%]Wind speed [m/s]Data set 1 Data set 2The University of Iowa Intelligent Systems LaboratoryWind Speed Variability22.533.544.555.566.571 16 31 46 61 76 91 106 121 136 151 166 181 196 211Wind speed (m/s)10 - minute dataThe University of Iowa Intelligent Systems LaboratoryWind Speed Variability22.533.544.555.566.571 31 61 91 121 151 181 211 241 271 301 331 361 391Wind speed (m/s)10-second data024681012141 31 61 91 121 151 181 211 241 271 301 331 361 391Wind speed (m/s)10-minute dataThe University of Iowa Intelligent Systems LaboratoryWind Speed Variability Diurnal (Night and Day) Variations of the Wind  At most locations around the globe it is more windy during the daytime than at night The graph shows how the wind speed at Beldringe, Denmark in by 3 hour intervals  This variation is largely due to the fact that the temperature difference, e.g., between the sea surface and the land


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