There is growing public and private sector interest in generating electrical power using wind energy. According to the Department of Energy, over 60,000 megawatts of wind power capacity is in operation worldwide with over 10,000 megawatts installed in the United States. These systems are largely comprised of installations of up to several hundred wind turbines with rotating blades reaching to heights of up to 500 feet. The numbers, height and rotation of these wind turbines present technical challenges to the effectiveness of radar systems that must be carefully evaluated on a case-by-case basis to ensure acceptable military readiness is maintained. For many cases, processes are in place to allow responsible federal authorities to complete determination of acceptability of wind turbine impacts on military readiness. However, since wind energy use in the United States is dramatically increasing, research and interagency coordination is warranted to enhance capability for completing timely determinations and developing measures for mitigating readiness impacts. This report focuses on the effects of wind farms on air defense and missile warning radars and the resulting potential impact on military readiness. Its scope is limited to these specific subjects and is based on the current level of understanding regarding interactions between such defense systems and state-of-the-art wind turbines.
The report begins with a brief introduction of the key principles of radar systems, describes in what circumstances wind farms might cause problems for the Department and under what circumstances such wind farms would not cause problems. Radar test results from multiple flight trials near wind farms performed by the United Kingdom Ministry of Defence are discussed. The results from those flight trials documented that state-of-the-art utility-class wind turbines can have a significant impact on the operational capabilities of military air defense radar systems. The results demonstrated that the large radar cross section of a wind turbine combined with the Doppler frequency shift produced by its rotating blades can impact the ability of a radar to discriminate the wind turbine from an aircraft. Those tests also demonstrated that the wind farms have the potential to degrade target tracking capabilities as a result of shadowing and clutter effects.