Offshore wake effect study from Earth Observation Synthetic Aperture Radar.

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 (PI), 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

1. Christiansen, M.B.; Hasager, C.B., Wake effects of large offshore wind farms identified from satellite SAR. Remote Sens. Environ. (2005) 98 , 251-268 Abstract/full text

2. Hasager, C.B., Christiansen, M.B., Astrup, P., Nielsen, R., Barthelmie, R. 2005 Using satellite data for mapping offshore wind resources and wakes. Oral presentation at the Copenhagen Offshore Winds, 26-28 October 2005, Copenhagen, Denmark. Slides. Proceedings paper in press.

3. Christiansen, M.B.; Hasager, C.B., Wake studies around a large offshore wind farm using satellite and airborne SAR. In: Proceedings (CD-ROM). 31. International symposium on remote sensing of environment: Global monitoring for sustainability and security, St. Petersburg (RU), 20-24 Jun 2005. (Nansen International Environmental and Remote Sensing Centre, St. Petersburg, 2005) 4 p.

4. Hasager, C.B.; Christiansen, M.B., SAR-WAKE results: On wake effects at large offshore wind farms mapped by satellite and airborne images. EGU General Assembly 2005, Vienna (AT), 24-29 Apr 2005. Geophys. Res. Abstr. (CD-ROM) (2005) 7

5. Christiansen, M.B., Wind energy studies offshore using satellite remote sensing. 19. World energy congress 2004, Sydney (AU), 5-9 Sep 2004. Unpublished. Paper available Full text version

6. Christiansen, M.B.; Hasager, C.B., Detection of wind wakes offshore from satellite sar. In: Abstracts (CD-ROM). 35. COSPAR scientific assembly 2004, Paris (FR), 18-25 Jul 2004. (CNES, Paris, 2004) 1 p.

7. Christiansen, M.B.; Hasager, C.B., Offshore wake effect study from earth observation SAR. 2004 Envisat and ERS symposium, Salzburg (AT), 6-10 Sep 2004. Abstract available.

Satellite scenes are kindly granted at research cost through the ESA EO-1356 project.

Charlotte Bay Hasager is the PI.



Charlotte Bay Hasager
DTU Wind
+45 46 77 50 14