Summary, Conclusion, and Outlook - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 142

Chapter 7
Summary, Conclusion, and Outlook

With the objective of the evaluation of the influences that offshore wind farms can
possibly have on the atmosphere and the ocean, this study deals with the analysis of
the physical OWF effect. At this juncture, model simulations were consulted and set
in relation to measurements. Thereby, one focus is the physical, theoretical cover-
age of the OWF effect, and the other aim is the determination of, especially, oceanic
changes in the future of the North Sea within the German Bight due to politically
planned OWF expansion.
The theoretical analysis of the OWF effect on the atmosphere shows that wind
turbines produce a wind wake downstream of wind farms. Depending on wind
speed, the amount of turbines, their arrangement, and spanned area, the wind wake
consists of a maximal simulated wind speed reduction of 70 % as stronger wind is as
intensive as the wake. The wake s maximum is located within the wind farms, and

behind the wind farms wind again increases with distance to OWF center. A change
from the operating mode to nonoperating mode of the wind turbines result in
advection of the provoked wind wake by the mean wind. Depending on atmospheric
conditions and surface fluxes, an OWF can cool or warm an atmospheric boundary
by 1 K, which also affects humidity. The dimension of the wake tail counts more
than 120 km downstream of the OWF, and the wake dimension orthogonal to wind
direction is determined by OWF configurations.
The description used here of the wake is based on two approaches: the approach
by Brostr¨m and the wind turbine parameterization of atmospheric model
METRAS. METRAS leads to more realistic results when it comes to satellite
data compared to the Brostr¨m approach and has more advantages in matters of
turbine types and atmospheric simulations. Hence, results of the OWF effect on the
atmosphere are based on METRAS simulations. A technical simplification of the
wake description can be the use of statistical description and analysis of the OWF
induced variations of the atmosphere, like the example analysis of the impact of
wind direction on the wake over the German Bight, placed in Chap. 6 . Only model

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