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The Article
Pictures from the energy companies show slim towers rising cleanly from the landscape or hovering faintly in the distant haze, their presence modulated by soft clouds behind them. But a 200- to 300-foot tower supporting a turbine housing the size of a bus and three 100- to 150-foot rotor blades sweeping over an acre of air at more than 100 mph requires, for a start, a large and solid foundation. On a GE 1.5-MW tower, the turbine housing, or nacelle, weighs over 56 tons, the blade assembly weighs over 36 tons, and the whole tower assembly totals over 163 tons. [Click here for a perspective on their size. Click here for the specs of popular models.]
As FPL (Florida Power & Light) Energy says, "a typical turbine site takes about a 42×42-foot-square graveled area." Each tower (and a site needs at least 15-20 towers to make investment worthwhile) requires a huge hole filled with steel rebar–reinforced concrete (e.g., 1,250 tons in each foundation at the facility in Lamar, Colo.). According to Country Guardian, the hole is large enough to fit three double-decker buses. At the 89-turbine Top of Iowa facility, the foundation of each 323-foot assembly is a 7-feet-deep 42-feet-diameter octagon filled with 25,713 pounds of reinforced steel and 181 cubic yards of concrete. The foundations at the Wild Horse project in Washington are 30 feet deep. At Buffalo Mountain in Tennessee, too, each foundation is at least 30 feet deep and may contain more than 3,500 cubic yards of concrete (production of which is a major source of CO2). On Cefn Croes in Wales the developer built a complete concrete factory on the site, which is not unusual, as well as opened quarries to provide rock for new roads -- neither of which activities were part of the original planning application [click here for photos of the abhorrent destruction on Cefn Croes].
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Each tower should be at least 5-10 times the rotor diameter from neighboring towers and trees for optimal performance. For a tower with 35-meter rotors, that is 1,200-2,400 feet, a quarter to a half of a mile. A site on a forested ridge would require clearing 45-90 acres per tower to operate optimally (although only 4-6 acres of clearance per tower, the towers spaced every 500-1,000 feet, is typical, making them almost useless when the wind is not a perfect crosswind). The Danish grid operator Eltra has found that a turbine can decrease the production of another turbine 5 kilometers (3.1 miles) away. The proposed 45-square-mile facility on the Scottish island of Lewis represents 50 acres for each megawatt of rated capacity. FPL Energy says it requires 40 acres per installed megawatt, and the U.S. Environmental Protection Agency (EPA) says 60 acres is likely. Facilities worldwide generally use 30-70 acres per megawatt, i.e., about 120-280 acres for every megawatt of likely average output (25% capacity factor). [Click here for a list of the areas of some facilities.]
GE boasts that the span of their rotor blades is larger than the wingspan of a Boeing 747 jumbo jet. The typical 1.5-MW assembly is two stories higher than the Statue of Liberty, including its base and pedestal.
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