July 2002

Wind Power for Pennies

Continued from page 2

By Peter Fairley

Wind Shadows

These upgrades will make big, heavy turbines more reliable, but they don't add up to a fundamental shift in the economics of wind power. Nations like Denmark and Germany are prepared to pay for wind power partly because fossil fuels are so much more costly in Europe, where higher taxes cover environmental and health costs associated with burning them. (About 20 percent of Denmark's power comes from wind.) But for wind power to be truly cost competitive with fossil fuels in the United States, the technology must change.

What makes Wind Turbine's Rocky Flats design such a departure is not only its hinged blades, but also their downwind orientation. The Danish design faces the blades into the wind and makes the blades heavy so they won't bend back and slam into the tower. The Wind Turbine design can't face the wind-the hinged blades would hit the tower-so the rotor is positioned downwind. Finally, it uses two blades, rather than the three in the traditional design, to further reduce weight.

Advances in the computer modeling of such dangerous forces as vibration helped the design's development. Flexible blades add an extra dimension to the machine's motion; so does the fact that the whole machine can freely swivel with the wind. (Traditional designs are driven to face the wind, then locked in place.) Predicting, detecting and preventing disasters-like rapidly shifting winds that swing a rotor upwind and send its flexible blades into the tower-are control challenges even with the best design. "If you don't get that right, the machine can literally beat itself to death," says Ken Deering, Wind Turbine's vice president of engineering.

Two years ago, when Wind Turbine's prototype was erected at Rocky Flats, there were worries that this machine, too, would beat itself to death. Thresher says some of his staff feared that the machine, like its 1980s predecessors, would not long escape the scrap heap. Today, despite some minor setbacks, those doubts are fading.

Emboldened by its early success, Wind Turbine has installed, near Lancaster, CA, a second prototype, with a larger, 48-meter blade span. By the end of this year, the company expects to boost blade length on this machine to 60 meters-full commercial size. What's more, this new prototype has a thinner tower, aimed at reducing the noisy thump-known as a "wind shadow"-that can occur each time a blade whips through the area of turbulent air behind the tower. And with its lighter weight, the turbine could be mounted atop higher towers, reaching up to faster winds.