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Methodology II: GWS® MESO by Al-Pro


GWS® MESO

Application

GWS® MESO maps provide an overview of the regional wind condition that can be expected in the region of interest. With GWS® MESO, you can strategize your search for a suitable wind farm site, saving time and money. With GWS® MESO, it is not possible to pinpoint exact locations for the installation of met masts or the erection of wind turbines. GWS® MESO should be considered as a tool to find areas which justify further detailed analysis, i.e. using GWS® MICRO modeling or high resolution potential studies.

MC2 model

The GWS® MESO simulations are performed using AnemoScope [5], software developed in Canada, which is based on the Mesoscale Compressible Community (MC2) model [6], a state-of-the-art atmospheric model used worldwide.

Meteorological
database
NCAR/NCEP

The 3D representation of the atmospheric state (i.e. a long time series - every 6 hours for 43 years from 1958 until 2000 - of the geostrophic wind vector) available at 2.5 degree resolution over the globe is known as NCAR/NCEP reanalysis [7] and is used as the meteorological data base for GWS® MESO modeling. So called climate states are defined by classifying the elements of the data base [8] using the geostrophic wind direction and wind speed at 0 m and the sign of 0-1500 m geostrophic wind shear (positive or negative). A set of climate states and their frequency of occurrence are associated to each data base grid point. This information is necessary to initialize the mesoscale simulations and to complete the post-processing.

Geophysical data
USGS topo
database and
GLC

1/60 degree resolution (~900 m at 60°N) – data from the US Geological Survey (USGS) is used to model the GWS® MESO topography. The roughness field is determined from the GLC land use database [9]. Both databases are interpolated to the GWS® MESO model resolution.

Model size and model resolution

Each GWS® MESO map covers an area of 2.5 x 2.5 degrees (approximately 200 x 300 km depending on the geographic latitude of the center of the map). The center of each GWS® MESO map is associated with the nearest grid point of the NCAR/NCEP global data base.
The GWS® MESO model size is approximately 50% larger than the tile size to eliminate boundary effects and to generate overlapping zones between adjacent maps. AnemoScope allows the computation of models with up to 256 x 256 grid cells. The targeted resolution (i.e. grid cell size) defines the extent of the model area. The Polar Stereographic grid with 2 km resolution at variant center latitude was chosen for the meso modeling. The center latitude differs from model to model depending on the latitude of the NCAR/NCEP grid point used for the model area.

Wind resource
assessment
heights

There are 28 unevenly distributed vertical levels with the two lowest model levels at 50 m and 150 m. Thus, wind calculations results can be obtained for a range of levels between 50 m and 150 m a.g.l.

Mesoscale simulation and statistical postprocessing

For each climate state, a simulation with the MC2 model is performed. This includes the initialization with the climate states data which are this way downscaled to the model resolution. A simplified physics scheme without radiation, condensation or diurnal cycles is used to accelerate model convergence to the final state. For each GWS® MESO map, the entire set of model outputs is combined using the frequencies of the climate states simulated as their weight. Results are then post-processed with a statistical model representing the dominant winds to obtain the mean wind speed, the mean wind power as well as the frequency distributions of the wind speed and wind power. Statistical post-processing prepares data to be used with a microscale model.

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