Blade switch: Composites built into this 44-meter blade installed on a U.K. wind turbine can absorb microwave signals, reducing radar signatures that can disrupt air-traffic safety control systems.
Appleton says that the stealth technology should be suitable for any type of wind turbine, and that “any cost increase will prove acceptable to our customers.” What is less clear is what proportion of blocked wind farms could be freed up by the stealth technology. “Each site is different and needs assessing to see what the problem is and whether our technology will help,” says Appleton. Crucial factors include the type of radar in use, distance from radar towers, and type and distribution of wind turbines.
The JASON report concluded that stealth technology showed “considerable” potential to deal with short-wave radar but is not suitable for reducing interference for long-wavelength L-band radars employed by U.S. air security–a critique that Appleton rejects. “We have already demonstrated an L-band absorber,” he claims.
Nevertheless, the U.K. is financing development of Raytheon’s alternative solution: using signal-processing algorithms to distinguish stationary targets such as wind turbines and erasing them from air-traffic control radar screens. Brian Smith, Raytheon Canada’s general manager, says the key is teaching the systems to recognize wind turbines as false targets, despite their spinning blades. “As the radar spins, it sends out scans every few seconds,” Smith says. “Our solution will use an algorithm in tracker software to say this can’t really be a plane, because it’s standing still.”
Smith projects that by 2011 Raytheon will have algorithms in place for both short and long-range radar systems, and will have demonstrated not only that they can erase wind farms from radar screens but also that they can retain valid stationary targets such as hot-air or weather balloons. He estimates that it will take another year to add the algorithms to any of the 250 Raytheon radar systems operating worldwide–about 40 percent of the market.
The JASON report proposed one more approach to addressing radar interference problems: replacing aging analog radar stations with modern digital equipment that is amenable to upgrades such as Raytheon’s. “Current circumstances provide an interesting opportunity for improving the aging radar infrastructure of the United States, by replacing radar that inhibits the growth of wind farms with new, more flexible and more capable systems, especially digital radar hardware and modern computing power. Such improvements could significantly increase the security of U.S. airspace.”
The FAA has proposed precisely that as a means of allowing the Cape Wind offshore wind farm to be built. It says that adding digital radar at Otis Air Force Base on Cape Cod, one of three radar stations expected to be affected by the project, would help the region’s air-traffic controllers see through the anticipated signal clutter. Negotiations between the FAA and Cape Wind are said to be nearing completion. But the price tag, according to the FAA, could be $1.5 million to $15 million.