Publishers version - DTU Orbit

Figure 190: Envisat ASAR wind field from Iceland observed on 24 September 2005 at 11:30
UTC. The wind is flowing from the northwest. Along the eastern and southern coastline a
pattern of lee effects and speed up from valleys is seen.
In the on-going FP7 (2012-2015) European Energy Research Alliance Design Tool for
Offshore Wind Farm Clusters (EERA DTOC) project the wake effect of clusters of wind
farms is being addressed. One project task is to analyze high-resolution SAR wind fields to
quantify the wind farm wake field near large wind farms in operation. Figure 192 shows a
RADARSAT-1 scene covering the Horns Rev -1 and -2 offshore wind farms and a very long
wind farm wake, around 10 km wide and 88 km long. TerraSAR-X wind fields observed near
the Alpha Ventus offshore wind farm also show wind farm wake effects (Li and Lehner, 2012).
15.9 Wind resources from SAR
Planningawind farm includesthe identificationofthe wind resource at the site. Thepotential
wind power production is closely related to the prevailing wind climate. Wind observations
from offshore meteorologicalmasts may be used but due to high cost only few are established
and mainly by private wind farm developers. If meteorological observations of wind speed and
winddirectionfromaleastoneyearfromanoffshoremastareavailable,thewindresourcemay
be assessed using the de facto standard software, the Wind Atlas Analysis and Applications
Program (WAsP, www.wasp.dk) (Mortensen et al., 2005).
The usual procedure in a WAsP analysis is to divide the data into twelve bins for 30 degree
wind direction sectors and determine the Weibull wind-speed distribution for each of these.
The method is described in the European Wind Atlas (Troen & Petersen, 1989). For land
and offshore coastal sites the local scale maps of topography, roughness of the terrain and
obstacles should be used. Wind resource assessment in the offshore coastal zone - where most
offshore wind farms are located or are in development - is challenging as coastal wind systems
DTU Wind Energy-E-Report-0029(EN) 285