Can wind turbines and military radar co-exist?



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Wind power in the U.S. is growing faster than ever before. U.S. President George W. Bush recognized the value of wind energy in his Advanced Energy Initiative, announced in February this year, noting that it could contribute up to 20 percent of the U.S. electrical supply. However, a recent report to the Congressional Defense Committees by the U.S. Department of Defense (DoD) Office of the Director of Defense Research and Engineering, entitled "The Effect of Windmill Farms on Military Readiness - 2006"states that, while DoD strongly supports wind energy, wind turbines located in a radar installation's line of sight might adversely impact the unit's ability to detect threats. The study was requested by Congress under the National Defense Authorization Act (passed in 2005 and effective Jan. 1, 2006). The issue it raised subsequently held up a large number of wind farm projects, with the potential to negatively impact the wind energy industry - which is a big consumer of composite materials as well as an economic engine for rural communities. Fortunately, the U.S. Federal Aviation Admin. (FAA), which is responsible for impact mitigation on U.S. Air Traffic Control radar facilities, recently approved a number of the delayed projects, including the $630 million (USD) Twin Groves farm in Illinois, after detailed review found that no problem existed. But the potential for future delays and possible restrictions means that projects could be shut down, threatening jobs, local economic revenue and renewable energy growth - an outcome both unproductive and inappropriate.

While the American Wind Energy Assn. (AWEA) recognizes and respects the paramount importance of national security concerns, the Association believes that rapid development of domestic energy sources is vital to national security as well. The good news is that wind projects and radar systems already coexist in some locations, so we know there are solutions available.

Defining the problem

A radar system consists of a transmitter that emits radio frequency waves, an antenna, a receiver and a processor. An object in this radar beam, typically referred to as the target, will reflect some of this energy back to the receiver. Processing the radar reflection from a target of interest depends upon the strength and variability of the signal at the receiver relative to other sources. Variables include the power of the transmitter itself, the distance to the target, atmospheric effects (e.g., rain), the target's radar cross-section, intervening physical objects and antenna geometry. The radar may receive reflected radiation from buildings and other objects, as well as natural and manmade radio waves from mobile phone towers and the like.

While fiberglass blades on large, utility-scale wind turbines are nearly transparent to radar frequencies - after all, most radar antennae and military aircraft radomes are made from fiberglass - they are not completely radar transparent. Wind blades also contain a few metallic components, such as lightning strike ground wires and pitch-control devices, which can reflect radiation. Further, blades that contain carbon fiber in the central structural spar are certainly much less radar-transparent. The metallic towers and generators also contribute. When they rotate, utility-scale turbine blades can appear to be a radar target like an airplane because of their height, great length, aerodynamic shape and tip speeds.

Mitigation strategies are already available, including radar software upgrades; turbine site adjustment to accommodate the radar's line of sight; and blade design and construction modifications to reduce the amount of carbon and metal components, although the latter would have an admittedly negative impact on carbon fiber suppliers. Further, the Department of Energy (DoE) and the National Renewable Energy Laboratory (NREL) are ready and able to undertake testing to explore mitigation strategies for a variety of wind blade designs.

Most important, however, decades of experience tell us that wind turbines and radar can co-exist. The busy Logan International Airport in Boston, Mass., for example, has no difficulty with nearby turbines. Perhaps most telling is that the U.S. Air Force is the largest nonutility purchaser of "green power"in the U.S., and several active military installations have working wind turbines that provide electrical power. These include F.E. Warren Air Force Base in Wyoming and the U.S. Navy installation at Guantanamo Bay, Cuba. Since radar and wind farms coexist at these locations, AWEA is confident that acceptable solutions can be found in nearly every case. The key is to continue the case-by-case review of projects and consultation that has led to these mutually beneficial solutions.

Clearly, the wind energy industry does not want to be part of a problem, but rather wants to be perceived as a solution to energy independence. We look forward to working with the U.S. government to address this issue so that the wind industry can work for the benefit of the environment and energy security.