Analysis 01: OWF Effect on the Atmosphere - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 45

Fig. 4.6 Dependence of
number (#) of wind
turbines, respectively grid
boxes, on overall wind
speed maximum and
minimum of the 10-m wind
field after 4 h of METRAS
simulation time. Outliner
occurs with 16 affected grid
boxes

These sensitivity simulations show how difficult a nonmodeled parameterization
for wind farms is, especially for wake flanks. There is not a clear linearity between
affected grid cells and wind change, but the analysis of only three cases does not
allow a final statement; for that, more cases would be necessary.
But an issue of scale becomes apparent because, as explained, the wind farm
with 12 turbines results in nearly a similar outcome as that of a wind farm of
48 wind turbines. Only on the basis of wind speed, respectively wind stress, can one
recognize a difference with a slightly expected stronger minimum in case of
48 turbines. This is explainable by the grid boxes covering the wind turbines.
That side effect of modeling hampers a detailed statement of wind farm effects
on the wind field. Hence, it is not exact to speak here of wind farms of 12, 48, or
more wind turbines. A better way would be to specify wind changes based on the
amount of turbines over an OWF district of, for example, four grid boxes. So in the
case of 12 turbine wind farm used here, the effect is a matter of 12 turbines shared
over 4 grid boxes affecting ratably an area of 6

6km 2 . The detected issue of
horizontal resolution may overestimate the affected area and has to be considered.
However, a tendency of wake intensification with an amount of wind turbines,
respectively the covered areas, can be supposed in reality. Hence, a bigger wind
farm leads to a wider and stronger wind wake with a distinctive core of low wind
speed within OWF district, and the structure of the influence will be mostly
the same.