A Mighty Wind

Rooftop wind turbines are an increasingly popular way to generate electricity in cities

By Susan Cosier

Aerotecture International’s turbines twirl on a rooftop in Chicago. Credit: Kurt Holtz at Lucid Dream Productions

The wind turbines that engineer Bil Becker installed on top of a Chicago apartment building last year probably don’t resemble the structures that pop into your head when you think “windmill.” Instead of propellers mounted on soaring poles, these turbines are made primarily with curved, galvanized steel shaped like the double helix of DNA. This special design means that they can generate renewable electricity in the densely-built urban environment, unlike their counterparts found twirling in the boonies.

Becker’s Chicago company, Aerotecture International, is just one of a growing number that is developing rooftop wind turbine technology. Unlike the towering, free-standing commercial variety, these vertical-axis wind turbines extend from buildings, capturing winds blowing from any direction. Some can generate electricity in conditions running the gamut from 8-mile-per-hour breezes to 100-mile-per-hour gusts—a range nearly three times that of conventional, horizontal-axis turbines. New rooftop wind turbines don’t have the same problems as their predecessors: They’re safer for wildlife, quieter, and don’t vibrate violently in howling winds. And, at as little as $3,000, they’re increasingly affordable. Obstacles to widespread implementation remain, but the number of buildings crowned with spinning turbines climbs every year.

“People love the way they seem to dance,” says Becker, a professor emeritus of engineering at the University of Illinois, Chicago who founded Aerotecture International two years ago. The structures aren’t just aesthetically appealing, he adds. “We learned to make them safe, lightweight, and quiet.”

Rooftop systems aren’t entirely new. In 1976, owners of a co-op in New York City installed the first urban rooftop windmill that contributed energy to the northeastern power grid. The turbine generated 200 kilowatt-hours of electricity each month, meeting 110 percent of their common-use energy needs, such as lighting hallways and heating water.

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