Emerging technology can ease the problem of wind farms causing interference with air-traffic control systems. But deployment of that technology in the U.S. has been slowed by questions over authority and cost.
Since 2006, radar maker Raytheon and National Air Traffic Services, which provides air traffic control in the U.K., have been working on a project to upgrade air traffic radar so it can distinguish between aircraft and wind turbines' spinning blades. Concerns over the disturbances turbines can cause on air traffic control systems are already stunting the growth of wind power: radar and wind turbines conflicts derailed nearly as much as the total amount of installed wind power capacity in the U.S. last year.
In the test, due for completion next spring, Raytheon and NATS are seeking to certify a combination of wind turbine mitigation techniques, including upgrading radar hardware and changing signal-processing algorithms.
"When you start putting a set of turbines across an area, what it looks like to the radar is a whole great field of moving objects," said Peter Drake, Raytheon's technical director for Digital Airport Surveillance Radar, the radar system used for airport terminals. "It's a very real problem."
Even though there are technical solutions, it's not clear how quickly they will make it into the field in the U.S. because air safety touches multiple government agencies with different priorities and budgets. "There's a lot of discussion taking place between everybody, but there isn't anybody who is tagged as lead," said Drake.
Wind farms can cause interference, or "clutter," on radar systems in more than one way. Spinning blades can appear on radar screens as an airplane, creating a false "target." Or, signals from the turbines can cause legitimate targets, such as an aircraft above a farm, to suddenly jump position, Drake explained.
A few turbines near an airport may not cause serious issues, but having wind farms with hundreds or thousands of turbines is far more challenging, he said. Exacerbating the issue is that wind-rich areas are often located near landing strips.
The problem is particularly troublesome at some military bases. So far, no serious safety incidents have occurred, but concerns with radar conflict have delayed or scrapped a number of wind farm projects in the U.S.
Raytheon began investing in wind turbine mitigation technology years ago in anticipation of the issue coming to a head as governments push for more renewable energy. The same techniques used in the NATS project could be applied to airport terminal radar systems in the U.S., said Brian Smith, the general manager for Raytheon Canada.
One technique, called concurrent beam processing, allows radar systems to discriminate between objects in the air and in the ground. Another creates a more accurate map of what the terrain looks like in all directions to help screen out stationary turbines from moving objects.
Implementing these technical fixes requires upgrading the electronics in radar systems so they can process more data and changes to the software that handles the data. These capabilities could be added as part of radar upgrades done for other reasons. "We're very confident that we have good solutions to solve the problems," said Smith.
There are other mitigation strategies in addition to upgrading radar, but people should not think that one single solution is a "magic bullet" that completely solves the problem in every case, said Gary Seifert, a program manager for renewable energy technologies at the Idaho National Laboratories and an expert on wind-radar conflicts.
"Anybody who says they can solve all the problems is probably overstating," he said. "You can't just put in a magic box and have all the radar clutter disappear without impacting some performance issue."
Seifert recommends that each location be evaluated individually and that potential problems get identified early on in the process, so that wind developers' projects are not scuttled at the last moment.
Often, reducing the density of turbines can help address the issue, he said. In other cases, relatively straightforward software upgrades can greatly improve the ability of radar systems to filter out turbines.
Turbine manufacturers, including Vestas, are working on "stealth turbines" that have a material on the blades that cuts down on their reflectivity and cuts the amount of noise on radar systems.
Many other aerospace companies are working on the issue as well. Lockheed Martin, for example, has developed a long-range radar system that has more pinpoint control over radar performance near wind farms. Air traffic controllers could also use neighboring radars to improve the overall picture.
Even promising technologies, however, take many months or years to certify, whereas wind farm developers may have tight deadlines to keep costs under control. Also, there's the question of who will pay for the technical fixes: should it be taxpayer-funded agencies or wind farm developers?
The American Wind Energy Association said that there needs to be an increase in cooperation between wind developers and government agencies, such as the Federal Aviation Authority, the Department of Defense, and the Department of Homeland Security. Without it, the U.S. will not be able to meet a Department of Energy goal of getting 20 percent of electricity from wind, it said in a paper from April (click for PDF).
"I can't imagine a better example of everyone wanting to do the right thing and nobody doing it," aviation consultant and former FAA official Howard Swancy told The New York Times. "We need an infrastructure-size development plan."