One of the world's largest clusters of energy-producing wind turbines sites here on Buffalo Ridge, several miles from the South Dakota border and just high enough to catch the full force of gales that sweep back and forth across the prairies from Hudson Bay to the Gulf of Mexico. There are 403 dazzling white machines, strung for 30 miles along the crest of the ridge. They vary in height from 120 to 250 feet making them incongruous skyscrapers that almost comically dwarf the barns and dilos of neighbouring farms. Denmark gets 15 percent of its energy from windpower.