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.

Despite this successful example, rooftop wind turbines were slow to catch on. Over time, however, the materials and designs improved, and people became increasingly aware of the environmental benefits of renewable energy. As a result, there has been as much as a 25 percent growth in small wind energy projects over the last 15 years, according to the American Wind Energy Association. This demand is helping the industry expand.

“We want competition,” Becker says. “There are 3.5 billion urban customers out there and there’s no way we can meet the needs for all of them.”

Other companies vying for urban clients include the British company Quiet Revolution, Cleanfield Energy in Ontario, and PacWind in California. “We can’t make the turbines fast enough,” says Philippa Rogers, spokesperson for Quiet Revolution. PacWind just allied with a company to help manufacture turbines on a large scale. Right now many of them are sprinkled throughout the U.S., but company president Phil Watkins estimates that more than 40,000 turbines will be distributed by this time next year.

Each design comes at a different price depending on its size and energy-generating capacity. PacWind offers a turbine for residential homes for about $3,000 (without installation) that can produce 2,160 kilowatt-hours of electricity.

At the other end of the cost spectrum, one of Quiet Revolution’s turbines designed for commercial buildings sells for about $50,000 without installation and generates up to 9,600 kilowatt-hours of electricity a year—about ten percent of the energy needed to power a 6,500-square-foot office building. (The cost of installation varies, but typically increases the total price tag by about 35 percent.)

Some skeptics

Still, not everyone is convinced that rooftop wind turbines are the best way to generate renewable energy. “Small windmills on rooftops are an unfortunate distraction from the real work of building a renewable energy society,” says Paul Gipe, who has written numerous books and studied wind energy for 30 years. Instead, Gipe says, we should focus on promoting solar panels and wind farms made up of large turbines and owned by cooperatives and municipal utility companies.

Aside from the fact that rooftop systems can still be expensive to build and install—mainly because there aren’t many companies supplying materials yet—there is also no certification process in place for small wind turbines that would verify their safety and performance. The American Wind Energy Association is currently working to develop standards that will allow “turbines to be compared apples to apples,” says Ron Stimmel, an association spokesperson.

Though the certification process won’t be finalized for at least another year, wind energy advocates say that the industry will continue to grow in the meantime. That, in part, is because the benefits of creating renewable energy in cities outweigh the drawbacks, according to Watkins of PacWind. “We get the power here where we need it instead of spending huge amounts of money building grid systems and infrastructure,” he says.

Becker says he’d like to see city buildings become mini power plants. His company is one of those working on ways to further improve urban wind technology by designing buildings that accelerate wind through a turbine to generate more electricity. Becker predicts that “the most prevalent renewable energy form in the next 50 years will be wind-capturing devices.”

A mighty wind: Why rooftop wind turbines are gaining popularity
Rooftop wind turbines are an increasingly popular way to generate electricity in cities.