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Analytical Prediction Using a
Computer Model
The modelling tool used transfers the wind resource of a known site to the actual site taking into account the terrain conditions at both sites. The current modelling tools provide reliable results for flat terrain but are not sufficient when the terrain becomes hilly and complex with levels of roughness. In this case, direct measurements on the site are necessary. Inspection of both potential and reference sites is necessary to use a modelling tool. The orography (terrain conditions), roughness and all obstacles must be assessed and entered as input data in the modelling program.
With long term wind resource data and the terrain description of the reference site A (as shown in the diagram above), the undisturbed flow conditions on this site is determined .These undisturbed flow conditions are therefore not influenced by the terrain conditions at site A anymore and can be transferred to the actual site B. Terrain conditions at site B are then taken into account to determine the long term wind resource of the actual site. What can be obtained from this simulation are the wind direction distribution at different heights and the Weibull distribution. Once the wind resource of the site has been obtained, it is possible to calculate the annual energy production of the planned wind turbine, knowing the type of turbine used. If more than one wind turbine is planned, it is also important to take into account the wake effect of each wind turbine on the others in the park. The energy production of the whole farm, the losses generated by the wake effect and the overall wind farm efficiency can then be presented. Depending on the results, the layout of the park can be optimised to increase the overall efficiency by sitting the different wind turbines trying to minimise the wake effect. Problems Obviously, these predictions of the wind resource and the energy production are subjects to uncertainties. The transfer of the wind conditions from the reference site to the actual site can generate errors, mainly due to the difficulty to perfectly assess the terrain conditions. Moreover, the uncertainty associated with the effect of each turbine on the others can distort the calculation of the wind farm efficiency or the optimal position of each turbine. In order to minimise these uncertainties, the best solution is to carry out a verification of the results. Comparing the predicted results to the real results of close existing wind turbines (using the same methodology) enables to improve the simulation model in order to get the same results.
The current modelling tools provide reliable results for flat terrain but are not sufficient when the terrain becomes complex with high levels of roughness. In this case, direct measurements on the site are necessary.
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