SAR-WAKE: Offshore wake effect study from Earth Observation Synthetic Aperture Radar

    Project Details


    The SAR-WAKE project runs in years 2003 and 2004 with funding from the Danish Technical Research Council (STVF) at the Danish Research Agency.


    One of the environmental effects of a large offshore wind farm is that it causes changes in the local wind climate. From theoretical work the effect of a large offshore wind farm is calculated to reach of the order of 5 to 15 km downstream. The wake effect is the shadowing (lee-effect) from one wind turbine to the next and much further downstream. It is known that the wind speed directly downwind of a turbine is decreased (up to 30 %) and the turbulence intensity is increased. A turbine placed downwind of another turbine produces less energy, typically 10-20 % less but in the worst cases where turbines are closely spaced up to 60% less. So far only very few meteorological observations behind single or few wind turbines in a row have been collected offshore. Wake effects at larger scales are poorly understood despite the possibility that higher turbine generated turbulence may impact air-sea interactions.


    The goal of the project is to quantify the horizontal extent and intensity of the wake effect through analysis of Earth Observation (EO) data from Synthetic Aperture Radar (SAR).

    Earth Observation data and study site

    Observations from the ERS-2 SAR satellite and the ENVISAT ASAR satellite of the European Space Agency (ESA) and airborne ESAR data from German Aerospace Research Establishment (DLR) are collected at the Horns Rev site in the North. Here the world’s largest offshore wind farm consisting of 80 wind turbines covering an area of 20 km2 in the North Sea is in operation since 12 December 2002. The wind farm is positioned in a trapezoid-grid at a distance more than 16 km from the coastline.


    Risø National Laboratory, Wind Energy Department Charlotte Bay Hasager (coordinator), Rebecca Barthelmie, Merete Christiansen, Jørgen Højstrup

    Ørsted -Denmark Technical University: Henning Skriver, Jørgen Dall

    Elsam Engineering: Paul Sørensen

    Visiting Post.doc. at Risø: Birgitte Furevik from NERSC
    Effective start/end date01/02/200301/04/2006


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