Offshore Wind Farm Clusters Wakes Observed from Satellite SAR and Wake Model Results
Hasager, Charlotte1; Mouche, Alexis2; Badger, Merete1; Badger, Jake1; Volker, Patrick1
1DTU Wind Energy, DENMARK; 2CLS, FRANCE

The EU project EERA DTOC (European Energy Research Alliance - Design Tools for Offshore Wind Farm Clusters, www.eera-dtoc.eu) from 2012 to 2015 is led by DTU Wind Energy and there are 10 science partners, 11 wind industry partners and one satellite expert partner (CLS) involved. One of the major aims of the project is to increase knowledge on the influence of very large offshore wind farms to the atmospheric flow downwind of the wind farms. This information is useful for strategic planning and development of new wind farms. At the moment more than 4 GW offshore wind power capacity is installed and grid connected in the Northern European Seas with around 35.000 people employed directly and indirectly. According to the European Wind Energy Association (www.ewea.eu) the offshore capacity is expected to increase to 40 GW in 2020 and 150 GW in 2030. It has earlier been shown that for specific atmospheric conditions the wind farm wake behind the Horns Rev 1 offshore wind farm in the North Sea in Denmark persisted more than 20 km downstream. This may be an exceptional case as most other investigated ERS and Envisat SAR images showed somewhat shorter downstream wakes (Christiansen and Hasager 2005). Since this early study of the first large offshore wind farm in the world that started operation in December 2000, many new large offshore winds have been constructed. CLS has collected a database of Envisat and Radarsat SAR images covering 10 large offshore wind farms. These include Horns Rev 1 (21 km2), Horns Rev 2 (33 km2), Nysted 1 (26 km2), Rodsand 2 (34 km2), BARD Offshore 1, Scroby Sands, Robin Rigg, and Thanet (35 km2). The surface area for some of the wind farms are listed in brackets. For the Horns Rev 1 and Horns Rev 2 in the North Sea and for the Nysted 1 and Rodsand 2 in the Baltic Sea the wind farms are relatively close, as twin wind farms, and there will for certain wind directions be a wake effect between the wind farms. This is particularly interesting to investigate as in the future many more large offshore wind farms will be located in relatively close proximity. See e.g. http://www.4coffshore.com/offshorewind/ The presentation will provide insight to the satellite SAR scenes at some wind farms and the observed wake. Furthermore, the presentation will include selected model results from coupled use of meso-scale and micro-scale models for offshore wind farm wake quantification. Reference: Christiansen MB, Hasager C. Wake effects of large offshore wind farms identified from satellite SAR. Remote Sens Environ 2005; 98: 25168. We acknowledge satellite data from ESA Envisat ASAR image the access has been granted to CLS the context of contract n°4000103095/11/I-LG SAR Ocean Wind-Waves and Currents: Upgrade of the SOPRANO Web-service and Copyright ''RADARSAT-2 Data and Products © MacDONALD, DETTWILER AND ASSOCIATES LTD. (year of acquisition) All Rights Reserved''. Funding from the EU EERA DTOC is FP7-ENERGY-2011-1/ n°282797 is acknowledged.