The Impact of Offshore Wind Farms on Sea State Demonstrated by Airborne LiDAR Measurements

Abstract

The increasing number of wind farms installed in the North Sea has an impact on the downstream wind speed. This has been hypothesized as well for sea state properties. Wave effects can be expected in particular in fetch-limited conditions with offshore wind directions. With systematic flights deploying an airborne laser scanner, these impacts are shown directly for the first time. The flights were conducted perpendicular to the main wind direction upstream and downstream of the cluster of the offshore wind parks Amrumbank West, Nordsee Ost, and Meerwind Süd/Ost. The flight legs covered the area potentially influenced by the wind parks and the undisturbed area next to the wind parks. The analysis of the spectral energy distribution shows a re-distribution of the wave energy in the downstream area with enhanced energy at smaller wavelengths. The effect is still clearly visible at a distance of 55 km. As the sea surface constitutes the link between the atmosphere and the ocean, it is very likely that wind parks modify the properties of the water column as well.

Climatic Impacts of Wind-Wave-Wake Interactions in Offshore Wind Farms

“…More in-depth analysis on how wind farms impact other parameters beside significant wave height (e.g., wave period and peak direction) should be performed in the future, follow up on Christensen et al (2013) conclusions that wind farms have little effect on wave periods. Furthermore, wave spectra could be analysed to investigate the impact of wind farms on other parts of the spectrum following up on Bärfuss et al (2021). A better understanding on the wave impact is necessary, since energy input though waves affects the ocean mixing and thus life in the sea (Jenkins et al, 2012;Carpenter et al, 2016).…”

“…The interaction of wakes and waves also influence the wave field. Bärfuss et al (2021) analysed airborne laser scanner measurements up-and downwind of a wind farm under fetch-limited conditions in the German Bight and found a redistribution of wave energy from larger to smaller wave length in the wake up to at least 55 km downstream. From a theoretical point of view wind turbines influence waves in two ways: 1) through the interaction with the wind turbine pole due to reflection, diffraction and drag dissipation and 2) though a reduced wind stress as a consequence of the kinetic energy extraction by the turbines (Christensen et al, 2013).…”

Fit-for-Purpose Information for Offshore Wind Farming Applications—Part-II: Gap Analysis and Recommendations

“…Regular measurement campaigns are performed with ships (e.g., Ludwig Prandtl), e.g., including scanfish measurements. Dedicated airborne campaigns to analyze the OWF impacts on sea state were conducted by the University of Braunschweig [37,38].…”