Development of Obstruction Lighting Standards for Wind Turbine Farms

The U.S. Department of Energy has mandated that renewable energy sources, such as wind turbines, will provide 5 percent of the nation’s electricity by the year 2020. As a result, wind turbine farms are sprouting all over the USA; farms having over 200 turbines spread over mountain ranges up to 20 miles long are not uncommon. Standing at heights up to 442 feet, these structures are considered obstructions to air navigation. As such, these obstructions must be illuminated so the aircraft can easily identify and avoid them, while at the same time, minimizing any impact of the illumination on surrounding communities. The Federal Aviation Administration visited 11 wind turbine sites, each containing numerous turbines, to investigate their existing lighting installations, their appearance from the air in day- and nighttime, and how these lights affected the surrounding communities. Each investigation included documentation flights, still and video photographs, and interviews with both the local wind turbine developer and the local community. Considering the lighting concepts currently used for illuminating radio towers and long-span bridges, which states that obstructions near to each other should be treated as if they were one large obstruction, a similar lighting concept was adopted for illuminating the wind turbine farms. The lighting concept for wind turbine farms includes the use of red, simultaneously flashing lights positioned on the outer perimeter of the wind turbine farm, each spaced no more than one-half statute mile from each other, and requires only one fixture per turbine. As long as the wind turbines are painted white in color, daytime illumination is not required. A test site was established in Lawton, Oklahoma, to validate the new lighting concept. Research personnel conducted repeated evaluation flights of the test site, and confirmed that the proposed lighting concept provided approaching aircraft ample warning that the wind turbine farm was a single, very large obstruction that should be avoided.