sperimentazione nella grande mela.

windmill.1841.jpg, image/jpeg, 184x201

A New York stanno entrando in funzione le prime turbine fluviali per la produzione di energia elettrica.

Il progetto prevede tra le 200 e 300 turbine piantate sul fondo dell'Hudson, il fiume di New York, capaci di una produzione di circa 10 megawatt, secondo l'articolo tale potenza consentirebbe l'alimentazione di circa 8.000 abitazioni.

Una goccia nel mare urbano, e ad un costo di circa un quarto superiore al costo medio dell'energia sul nercato, ma i promotori si dicono figduciosi sul futuro del sistema una volta industrializzato e diffuso.

Il sistema trasfoma il flusso del fiume per azionare le turbine e produrre energia.

l'articolo del N.Y. Times
In Search of New Power Source, City Looks Underwater
By IAN URBINA

Published: July 10, 2004

hey look like underwater windmills. And in late August, when six of them are dropped into the rapid currents of the East River alongside Roosevelt Island, these giant "tidal turbines" will begin harvesting about 150 kilowatts of electricity.

If all goes well, an entire underwater wind farm of 200 to 300 sleek 15-feet-tall turbines will discreetly spin under the surface of the river by 2006, providing about 10 megawatts of electricity, enough to power more than 8,000 homes.



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"That will make New York City one of the greenest cities in the world when it comes to locally produced clean energy," said Trey Taylor, the owner of Verdant Power, a company in Virginia that has been given permits by the city to build the submerged turbines. "It makes sense for this city to take the lead because it has extreme energy needs and unique energy potential."

That potential rests in the distinct geography of the East Channel between Queens and Roosevelt Island. As the Long Island Sound and the Atlantic Ocean squeeze their currents down the long, narrow and steep downward slope of the East Channel, the result is a water flow of about six miles per hour, one of the fastest flows of any waterway on the East Coast. "That's a lot of kinetic energy that the city could put to use," Mr. Taylor, 56, said. The East Channel is shallow enough that large commercial ships prefer to use the side of Roosevelt Island facing Manhattan, and it is also deep enough that the turbines pose no risk to recreational boats.

"We're very optimistic about these plans," said Mr. Collins, a spokesman for New York State Energy Research and Development Authority, which subsidizes promising technological projects in the state. Last year, the authority gave Verdant a $1 million grant for the project, the largest single award the agency has given to date. "The pilot tests on these structures have been incredibly positive, and things are moving forward quickly," Mr. Collins said.

The project has three stages. In December 2002, a single turbine was suspended under a barge anchored between the Queensboro Bridge and the Roosevelt Island Bridge. It operated for about 5 weeks, and the test period showed that the 8-foot propellers, which rotate only 30 revolutions per minute, were slow enough to avoid harming local aquatic life. The project's second stage starts in late August with the construction of a "six pack" of turbines that will be mounted on pilings under the water and will provide electricity to residents on Roosevelt Island, which has about 3,000 homes. The third stage, if all goes as planned, will start in the fall of 2005. For that, Verdant must get approval from the Federal Energy Regulatory Commission to build a $20 million turbine field that would stretch about a third of the way across the East Channel and would extend from the Roosevelt Island Bridge to the northern tip of Roosevelt Island.

The turbines, the tops of which are about 8 feet beneath the water's surface, swivel to face the oncoming current. The rotors, which have three blades, can swing out of the water for maintenance.

The technology for the turbines is not new. But Mr. Taylor said the project was delayed when his only prototype of the turbine was lost several years ago after being sent to Pakistan for testing. "I'm still not sure how you lose a package that large," he said during a presentation to a group of engineers and city officials at the Center for Architecture near Washington Square on Thursday. "But we are back on track now so long as we can get through the remaining layers of regulatory red tape."

Dick Lutz, the editor of Roosevelt Island's newspaper, The Main Street WIRE, said residents support the project. "We live in asthma alley, so this is a huge step in the right direction," he said, explaining that many residents complain about the effects of living downwind from KeySpan Energy Corporation's Ravenswood power plant and several 10-megawatt generators belonging to New York Power Authority in Long Island City.

"How can you go wrong?" said John Catsimatidis, chief executive of Gristedes Supermarket. The Gristedes on Roosevelt Island, like the rest of the buildings there, would use electricity from the turbines. "This is a steady harvest of energy that doesn't cough pollution back onto us."

A 10-megawatt field, Mr. Taylor said, would save the city the equivalent of about 65,000 barrels of oil each year and would reduce annual carbon dioxide emissions by about 33,000 tons.

"The beauty of the project is not just that it's clean energy, but that it's local," Mr. Taylor said.

Since the electricity would not be traveling far, it would not burden an already overstretched transmission grid. It would also help bolster the city's energy supply, which is expected to run short of demand by 2009. To avoid overdependence on outside sources of energy, New York State requires that at least 80 percent of the city's electricity be generated within the five boroughs. Mr. Taylor said that while the city used 1,000 times what the 10-megawatt turbine field would produce, it is an important start.

But challenges remain. At a price of 7 cents per kilowatt-hour, the electricity from the tidal turbines is still about 2 cents above the wholesale market rate. There is also the problem of supply shortages during the six hours a day of "slack tide," when the tides cause the water to change direction, making the current too slow to turn turbines' rotors.

Mr. Taylor expects the price of tidal energy to drop as customers sign up, and he says power dips will easily be handled by using fuel-cell technology to store energy during times when the currents produce excess electricity.

"The question here is not whether there is enough energy," Mr. Taylor said. "It's how soon can we tap into it."