“You’re seeing the birth of a movement,” said Jared Blumenfeld, director of the San Francisco Department of Environment, who hopes to put a turbine on his own home. “Ten years from now, you could probably see 2,000 to 3,000 rooftops with wind.”
But many experts caution that rooftops, while abundant, are usually poor places to harness the breeze. Not only are cities less windy than the countryside, but the air is choppier because of trees and the variation in heights in buildings. Turbulence can wear down a turbine and make it operate less efficiently. This is particularly problematic for houses with pitched roofs.
“In an urban environment, more times than not you’re better off with a solar panel,” said Mr. Stimmel, of the wind industry association.
A recent British study of wind on home roofs found that turbines generate less power than installers projected because of lower-than-expected wind speeds. Ian Woofenden, a senior editor at Home Power magazine who teaches wind workshops, estimates that electricity from rooftop turbines may cost $1.50 a kilowatt hour or more. (That is enough electricity to run a hair dryer for an hour, roughly.)
By comparison, he said, power from a well-sited, tower-mounted turbine would cost 10 to 50 cents a kilowatt hour, and power from utility-scale wind farms costs less than 10 cents a kilowatt hour.
“Rooftop wind economics are abysmal, since the resource just isn’t there,” he said in an e-mail message.
Rooftop wind advocates argue that output will turn out to be healthy in windy areas, and they also think that prices for small turbines will come down as the market grows, altering the economics.
The most established company selling rooftop turbines is AeroVironment, a California company better known for making unmanned aerial vehicles. It has installed demonstration projects on about a dozen commercial rooftops, including those at Logan airport and the Brooklyn Navy Yard.
According to Paul Glenney, director of the company’s clean energy technology center, the edge of a long, flat roof (above, say, a big-box store or warehouse) can experience up to 40 percent extra wind, much like the stiff breeze at the edge of a cliff.
Demand for AeroVironment’s rooftop turbines, which it sells for about $6,500 each, is strong, he said. “We’ve hidden our Web site very carefully, and yet people find us,” Mr. Glenney said.
AeroVironment officials say that rooftop turbines at windy sites in states with costly electricity could pay for themselves in four to eight years, but acknowledge that in places with low power prices, the turbines may never recoup their costs.
In May and June, the 20 Logan turbines combined produced just 1,430 kilowatt hours — less than the average home would use over that time. Airport authorities said, however, that the Boston winds pick up in the fall and winter. Mr. Leno thinks his turbine has generated about 725 kilowatt hours in six months of operation.
“You can say, ‘That’s not a lot,’ or ‘Every bit helps,’ ” Mr. Leno said.
British studies have recently suggested that making and transporting turbines for cities may lead to more carbon dioxide emissions than the turbines save.
A special challenge of urban turbine manufacturers is to make machines with minimal noise and vibration. At Logan, the only complaint has come from a person with an office right under a turbine.
“Basically he said it just sounds like he’s in a Stephen King movie — that howling when there’s a lot of wind,” said Sam Sleiman, director of capital programs at Massport, the agency overseeing the airport project.
But the more common reaction to these small turbines is envy. Reino Niemela, a San Franciscan, has a direct view of Mr. Beaudoin’s turbines from his backyard.
“I was thinking of doing something like that myself,” he said.