Assessing Wind Farm Impact Potential on Radar Observations and the Development of Effective Mitigation Measures

As an evolving industry, and the fastest growing segment of the energy sector, wind power is poised to make significant contributions in future energy generation requirements. However, the development of efficient wind energy production involves challenges in technology and interoperability with other systems critical to the national mission. Objects in the path of an electromagnetic wave affect its propagation characteristics. This includes actual blockage of wave propagation by large individual objects and interference in wave continuity due to diffraction of the beam by individual or multiple objects. Wind turbines impact radar measurements as a result of their large reflectivity cross section as well as though the Doppler phase shift of their rotating blades. Wind farms can interfere with operational radar in multiple contexts, with degradation impacts on: weather detection such as tornado location, wind shear, and precipitation monitoring; tracking of airplanes where air traffic control software can lose the tracks of aircraft; and in identification of other low flying targets where a wind farm located close to a border might create a dead zone for detecting intruding objects. As a result, a number of potential wind power locations have been contested on the basis of radar line of site which is dependent on local topography, and varies with atmospheric refractive index through weather and geographic conditions. Radar line of site is commonly assessed using a standard atmosphere assumption; however, the atmospheric index of refraction and refractive gradient may depart substantially from these conditions, especially in critical weather conditions. Moreover, as wind energy development looks to offshore locations where super-refractive conditions are common, the use of site specific radar line of site determination is necessary to provide the optimal balance between future energy development and radar requirements. Additionally, the development of mitigation strategies can benefit from knowing local atmospheric conditions. In order to help meet public, commercial and governmental goals for increasing renewable energy capacity, local atmospheric conditions affecting radar line of site are investigated to develop comprehensive strategies for designing wind turbine locations that are mutually beneficial to both the wind industry that is dependent on production, and radar sites which the nation relies on. There are currently a number of wind farms that are within line of site of existing Doppler weather radars. These wind farms will provide a quantitative assessment of wind turbine impacts under varying conditions, and allow the development of strategies used to mitigate their effects.