Abstract
Abstract. Rapid growth in the offshore wind energy sector means more offshore wind farms are placed closer to each other and in the lee of large land masses. Synthetic aperture radar (SAR) offers maps of the wind speed offshore with high resolution over large areas. These can be used to detect horizontal wind speed gradients close to shore and wind farm wake effects. SAR observations have become much more available with the free and open-access data from European satellite missions through Copernicus. Examples of applications and tools for using large archives of SAR wind maps to aid offshore site assessment are few. The Anholt wind farm operated by the utility company Ørsted is located in coastal waters and experiences strong spatial variations in the mean wind speed. Wind speeds derived from the Supervisory Control And Data Acquisition (SCADA) system are available at the turbine locations for comparison with winds retrieved from SAR. The correlation is good, both for free-stream and waked conditions. Spatial wind speed variations along the rows of wind turbines derived from SAR wind maps prior to the wind farm construction agree well with information gathered by the SCADA system and a numerical weather prediction model. Wind farm wakes are detected by comparisons between images before and after the wind farm construction. SAR wind maps clearly show wakes for long and constant fetches but the wake effect is less pronounced for short and varying fetches. Our results suggest that SAR wind maps can support offshore wind energy site assessment by introducing observations in the early phases of wind farm projects.
Highlights
Europe has a total installed offshore wind capacity of 15 780 MW corresponding to 4149 grid-connected wind turbines across 11 countries
We have demonstrated that wind speed maps retrieved from synthetic aperture radar (SAR) observations of radar backscatter can be used to predict the spatial wind speed variability at a potential wind farm site before construction begins
The satellitebased wind speed maps can be used for characterization of wake effects around existing wind farms and to partially determine the cumulative effects of coastal wind speed gradients and wake effects
Summary
Europe has a total installed offshore wind capacity of 15 780 MW (status as end of 2017) corresponding to 4149 grid-connected wind turbines across 11 countries. New wind farms are built in less favourable locations, e.g. in the lee of land masses or large wind farms. The lee effect of land, i.e. the horizontal wind speed gradient due to a varying distance to shore (fetch), and wind farm wakes from other wind farms both influence the wind resource. This study is motivated by this challenge and focuses on the Anholt offshore wind farm in the Kattegat Strait in Denmark. It involves analysis of satellite-based synthetic aperture radar (SAR) wind maps, wind turbine data, and simulation results from the Weather Research and Forecasting (WRF) model
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