Offshore Electricity Infrastructure in Europe - European Wind Energy ...

4. Case-independent model
During the course of the study it became apparent that
the appropriate wind farm connection design is very
sensitive to the specific cases under investigation:
distances to shore, wind farm capacities, price profile
differences between the countries, etc. The results of
the specific cases are useful but general conclusions
are necessary for the optimal offshore grid design and
also for clear recommendations, which is one central
goals of the OffshoreGrid study. A case-independent
model was therefore developed with inputs from the
infrastructure model and the power system model. It
allows developing general offshore grid design rules,
which are then validated with the results of the specific
cases of the model.
In the following sections, the key features of each of
the mentioned models are described.
C.I Wind power time series
model
Since on- and offshore wind power production is a crucial
element in designing an offshore grid, OffshoreGrid
builds on high-resolution time series of wind speed
and power output of onshore- and offshore wind farms
which served as input for the modelling power flows
and power markets. For all single offshore wind farm
locations of the input scenario, synchronous hourly
time series of historical wind speed were calculated
with a high-resolution weather model. These are then
transformed into wind power production time series by
using special power curves.
The applied Weather Research and Forecasting Model
WRF [1] is a meso-scale numerical weather prediction
model, able to simulate the atmospheric conditions
across a wide range of horizontal resolutions from
100 km down to 1 km. The data input for WRF is
provided by 6-hourly global weather analysis data 59 .
The WRF-simulations dynamically downscale the
weather analysis data from six-hourly resolution on
a horizontal grid of 1° by 1° to one-hourly data on a
9x9 km² grid 60 .
59 In this case: FNL Final Analysis from the United States’ National Centre for Environmental Prediction (NCEP).
60 In geographical coordinates, 1° corresponds approximately to 50-111 km.
OffshoreGrid – Final Report
FiGuRe 12.2: GeOGRaphical dOmains FOR the wRFsimulatiOn
as used in the OFFshOReGRid pROject
The region of the Northern European waters is
modelled with a higher spatial resolution than the
remainder of Europe (see Figure 12.2):
• Europe north of the Alps: 9 x 9 km² (including
offshore regions in focus)
• Europe south of latitude 48°N: 27 x 27 km²
The wind speed time series were calculated for all
relevant hub heights of turbines in today’s and future
offshore and onshore wind farms. Special attention
was paid to the vertical wind speed profiles in different
thermal stratifications of the local atmospheric flow,
which were modelled with an improved, so called
MYJ-Scheme for the atmospheric Planetary Boundary
Layer (PBL) [7]. The model output is validated
with real wind speed data at different heights, i.e.
measurements from the German offshore platform
FINO-1 [6]. Previous simulations with similar model
settings were also checked with other meteorological
observations, e.g. the met mast Östergarnsholm in
the Baltic Sea. The model proved to be accurate and
robust.
After the WRF model runs were performed and
validated, the wind speed time series at more than
350 offshore sites and 16,000 onshore grid points as
defined in the scenarios and models were determined.
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