Wake studies around a large offshore wind farm using satellite and airborne SAR

2. STUDY SITES Abstract A method is presented for the mapping of wind speed over the ocean using satellite (ERS-2 SAR, ENVISAT ASAR) and airborne (E-SAR) synthetic aperture radars. Impacts of a large offshore wind farm on the local wind climate are described quantitatively from the radar measurements. Of particular interest is the magnitude and extent of wakes (i.e. regions of reduced wind speed and high turbulence intensity). Results indicate that wind speed reductions in the order of 1 m s occur and that wind speed recovers to match the free stream velocity over a downstream distance of ~10 km. This is the minimum spacing that should be recommended between large offshore wind farms in order to limit shadowing and reduced power production. An array of 80 wind turbines are operating at Horns Rev in the North Sea, Denmark (http://www.hornsrev.dk/). The spacing between individual turbines is 560 m and the distance to shore is 16-20 km. Another wind farm consisting of 72 turbines is located at Nysted in the Baltic where turbines are spaced with 867 m in the east-west direction and 481 m in the north-south direction. The distance to shore is 10-13 km. All turbines have a total height of 110 m above mean sea level.