Talking About Green

Q. Why is it that nearly every time I see a wind farm, like the one at Altamont Pass, so few of the turbines are spinning, even in a stiff breeze?

A. The wind farm at Altamont Pass in California is one of the oldest in the country, and technology has marched on.

The performance and reliability of older wind turbines from the 1970s and 1980s era, of which there are quite a few in California, is analogous to an older computer,” said Mark Rodgers, communications director of Cape Wind, the developer of an offshore wind farm in Nantucket Sound in Massachusetts. “It would be like offices still using Apple II’s or Commodores from 1978.”

“With modern wind farms,” he said, “it is possible that an individual turbine could be down for maintenance. Or if the winds were light, it could be right on the edge where some turbines are getting just enough wind to operate, others slightly less.”

Wind direction is not a big issue. In the old days, Mr. Rodgers said, the turbines were generally set in the direction of the prevailing wind, and the operators hoped for the best. With modern wind turbines, the nacelle, the boxy part at the top, can rotate 360 degrees, he said, and the blades can feather — that is, shift their position. Wind sensors gauge speed and direction, and the turbines can orient themselves accordingly. C. CLAIBORNE RAY

By C. CLAIBORNE RAY