Wind Power in the UK (PDF). - Sustainable Development Commission

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Wind Power in the UK (PDF). - Sustainable Development Commission

6 Landscape and environment6.4 Visual characteristics of windfarmsOnshoreThe visual characteristics of wind turbines varywith their make and model. Simple andsculptural forms of turbines using three bladesgenerally appear most appropriate, and theseare the designs that have become the industrystandard.Onshore wind developments in the UK vary insize from a one turbine to large-scaledevelopments containing over one hundredturbines. The average size of winddevelopments in the UK is around 10-20turbines.Wind developments from the early 1990s,during the early days of the UK wind industry,typically used turbines with a capacity range of300-400 kW. Over the last 10 years or so turbinetechnology has evolved, and turbines today cangenerate up to 3 MW each; a ten-foldimprovement in as many years. There arepractical limits for onshore sites, as largerturbines and towers become difficult totransport by road. This is likely to put aneventual brake on the upward trend in turbinesize.Today’s wind turbines typically have the hublocated up to 90m above the ground withturbine blades that sweep a radius of between40m and 45m, giving the total tip height fromthe ground to the tip of the vertical rotor, the‘blade tip height’, of between 60-120m. Themost recently built wind farms typically haveturbines with blade tip heights of 100m andabove. As a comparison, the height of Big Ben is100m, the Glasgow Tower 105m, and theLondon Eye 135m. Future turbine developmentsmay lead to improved performance along withincreases in height and rotor diameters. Recentwind farms have fewer, larger machines withbigger blades, operating at lower rotationalspeeds. Arrays of these larger turbines are lessdense because of the increased spacingbetween the turbines, but this extends theirvisual influence over a wider overall footprint.Although the visibility and impact of wind farmsincreases with larger turbines, it is often difficultto discern relative differences in turbine heights,especially at a distance. It is generallyconsidered better in terms of visual impact for awind farm to have a lesser number of largerturbines rather than greater numbers of smallerturbines.OffshoreOffshore wind farms are sited at sea off themainland coast, either within territorial watersor the newly created Renewable Energy Zone xx .There are less constraints on size for offshoreturbines and so larger capacities are beingdeveloped – up to 5 MW over the next decade.Typically, they share some of the same visualcharacteristics as those onshore, but they canalso include navigational markings, night-timelighting, offshore substations and onshore gridconnections. Use of these markings depends onthe variability of the coastal edge, variablevisibility with weather conditions and the effectsof curvature of the earth.xxAll current offshore wind farms are within territorial waters.sustainable development commissionWind Power in the UK 55

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