Data analysis and wake modelling ofthe Lillgrund wind farm

Abstract: This work consists of two parts: the analysis of the operating data collected at Lillgrund between December 2007 and March 2018, and the implementation and evaluation of three wake models. Operational and meteorological data from the Lillgrund wind farm have been analyzed to assess the aerodynamic efficiency and general performance of the farm. Power output, wake losses and array efficiency have been calculated in order to further characterize phenomena related to clustering of wind turbine and garther a database for future model validations. The results of the analysis quantify the intensity of the wake effect at Lillgrund and the power losses due to both wake effect and unavailability of turbines. Moreover, it is found that the array efficiency did not vary through the years. Additionally, effects of atmospheric stratification are evaluated by showing diurnal and seasonal variations of the array efficiency: results are opposite of what was expected, with the wind farm being more efficient at night and during winter. Furthermore, three wake models have been implemented and validated using the developed database: the Jensen model, the Ainslie model and the Gaussian model developed by Bastankhah & Porté-Agel (2014). The objective of the wake effect and power output that is reachable at a very low computational cost for offshore cases. By comparing the results with those of prior works, it can be stated that there is not a substantial diffference in the accuracy of wake models and CFD simulations for the case of Lillgrund.