by Jack E. Dell

The new Freedom Tower’s wind turbines will provide 20% of the building’s electricity (artist’s rendering, Battle McCarthy) This 3000-watt rated turbine powering a home in Quintana Roo, Mexico, delivers in excess of 500 kwh per month in a 12 mph wind. The blades are 6 feet long.

he planned redevelopment of Ground Zero in lower Manhattan may become the latest feather in the cap of urban wind power enthusiasts. Environmental designers for the new Freedom Tower, the Londonbased Consulting Engineering & Landscape Architecture firm Battle McCarthy, say the new structure will include "the world's first urban wind farm," with as many as 30 turbines located 1,200 feet above the base of the tower, generating up to 2.6 million kilowatt hours of electricity annually- 20 percent of the building's anticipated energy needs.

Many wind-power promoters see rooftop generation as the key battlefield for the future of renewable energy, with fossilfuels dwindling down and becoming more expensive, and with customers seeking independence from an electrical power grid with a tendency to collapse on occasion. And then there are the dreaded greenhouse gasses. But some industry voices are expressing doubt as to the viability of urban wind power, and are uncertain that the finished Freedom Tower will indeed feature wind turbines.

Today most of the action in wind generation is still taking place in rural areas or offshore, where the wind blows on average three times stronger than in cities. Those wind farms use giant turbines, with 60-180 foot long rotating blades, each producing as much as 5 megawatts, or the energy consumption of a good size office building.

Everyone in the field is keeping their eyes trained on the city of Toronto, where WindShare, a project developed by the Toronto Renewable Energy Co-operative (TREC), is providing an opportunity for citizens to generate renewable power in Ontario's new deregulated electricity marketplace. They are building two power generating wind turbines on the Toronto waterfront, the first utility scale, 30-story tall turbines, capable of powering up to 250 houses. The two turbines will generate emissions-free electricity, to be distributed through the city’s hydro electric grid.

And while rural wind farms are often opposed by locals, who say they ruin their view, Toronto’s turbines have received an enthusiastic support from the community, which raised 50% of the installation costs.

The first of the two turbines has already been built at Exhibition Place, southwest of the city, and started generating power early in 2003. The second turbine will be built on the grounds of the Ashbridges Bay Treatment Plant on the east end of the city.

Smaller wind turbines in big cities are not problem free. The blades weigh hundreds of pounds and speeds can exceed 50 MPH. Should a blade break, an escaping fragment could cause serious damage in urban canyons. Worse, a rooftop-mounted turbine can cause nasty surprises, as an owner in upstate New York learned one stormy night when his Air turbine destroyed itself—then plunged through his roof.

But proponents of green energy say modern turbines come with safety features like speed control and blades designed to turn edge-on into the wind during storms. The turbines' noise, however, is a more realistic source for concern.

Any slight imbalance in the blades will be amplified by centrifugal forces, causing the whole apparatus to vibrate and shake. No rotating machinery can remain perfectly balanced, and any imbalance will show up once every revolution. The noise this will produce may vary from an annoying thump to a maddening rumble. And once the turbine speed matches the harmonic resonance frequency of a supporting beam within the building’s structure, the building itself will begin to vibrate and amplify the noise.

If the turbine is indigenous to the original design, as may be the case with our own Freedom Tower, the builders can dampen the vibrations. But Several renewable energy companies have reportedly decided not to bid on the Freedom Tower project, unable to come up with a reasonable cost for a construction which would effectively dampen the turbines’ vibrations. This is the main reason why many experts doubt there will ever be turbines on the tower. Are there wind turbines in our own future on the Lower East Side? We probably shouldn't expect to erect whole wind farms on our rooftops any time soon. But wind power need not be the only answer, and turbines for high-riser use need not be enormous to offer some benefit, essentially for free.

Last May, the first rooftop turbines were installed at each of five primary schools in Fife, Scotland. The revolutionary Swift turbine was developed by Renewable Devices Limited, in Edinburgh. These small turbines can be installed on roofs in urban or rural environments and directly power the building with no need to feed into the grid. Each turbine is expected to generate up to 4000 kw hours of electricity each year (the average annual requirement per building is 10,000 kw hours), saving up to 3800 Lbs. of carbon dioxide, the main greenhouse gas, and cutting the school's energy bill by up to $1,000. The turbine arms are only 6 feet long and generate minimal vibration. Do you think we could fit a few of those on each one of our high risers? They cost approximately $3,000 each. You do the math...