Whither Wind?
(Page 2 of 7)
February/March 2007
By Charles Komanoff
What would WIND FARMS entail?
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To begin, I want to be clear that the turbines I’m talking about are huge, with blades up to 165 feet long mounted on towers rising several hundred feet. Household wind machines such as the 100-foot-high Bergey 10-kilowatt BWC Excel with 11-foot blades, the mainstay of the residential and small business wind turbine market, may embody democratic self-reliance and other “small is beautiful” virtues, but we can’t look to them to make a real dent in the big energy picture.
What dictates the supersizing of windmills are two basic laws of wind physics: A wind turbine’s energy potential is proportional to the square of the length of the blades, and to the cube of the speed at which the blades spin. I’ll spare you the math, but the difference in blade lengths, the greater wind speeds higher off the ground, and the sophisticated controls available on industrial-scale turbines all add up to a market-clinching 500-fold advantage in electricity output for a giant General Electric or Vestas wind machine.
How much land do these industrial turbines require? The answer turns on what “require” means. An industry guideline is that to maintain adequate exposure to the wind, each big turbine needs space around it of about 60 acres. Since 640 acres make a square mile, those 400,000 turbines would need 37,500 square miles, or roughly all the land in Indiana or Maine.
On the other hand, the land actually occupied by the turbines — their “footprint” — would be far, far smaller. For example, each 3.6-megawatt Cape Wind turbine proposed for Nantucket Sound will rest on a platform roughly 22 feet in diameter, implying a surface area of 380 square feet — the size of a typical one-bedroom apartment in New York City. Scaling that up by 400,000 suggests that just six square miles of land — less than the area of a single big Wyoming strip mine — could house the bases for all of the windmills needed to banish coal, oil and gas from the U.S. electricity sector.
Of course, erecting and maintaining wind turbines also can necessitate clearing land: Ridgeline installations often require a fair amount of deforestation, and then there’s the associated clearing for access roads, maintenance facilities, and the like. But there are also now a great many turbines situated on farmland, where the fields around their bases are still actively farmed. Depending, then, on both the particular terrain and how the question is understood, the land area said to be needed for wind power can vary across almost four orders of magnitude.
WIND POWER: A Fractious Debate
Similar divergences of opinion are heard about every aspect of wind power. Big wind farms kill thousands of birds and bats ... or hardly any, in comparison to avian mortality from other tall structures such as skyscrapers. Industrial wind machines are soft as a whisper from a thousand feet away, and even up close their sound level would rate as “quiet” on standard noise charts ... or they can sound like “the shrieking sound of a wild animal,” according to one unhappy neighbor of an upstate New York wind farm.
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