The Wake Effect and Wind Farm Clustering

Abstract: The wind energy industry is growing rapidly and as offshore wind expands in the Baltic sea, more and more clusters will be observed. The purpose of this work is to better understand the impact that wakes have on the electricity production for wind farm clusters in the Southern Middle Bank region. This report aims to answer the following research questions; 1) How big of an impact do wakes have on electricity production for future wind farm clusters in the Southern Middle Bank region? 2) How do different changes made to the layout of the wind farm cluster impact the resulting electricity production change due to wakes? 3) What are the economical implications of making layout changes in order to mitigate the impact of the wake effect? In order to answer the research questions, the methodology was based on simulations done in the WindFarmer: Analyst software program (DNV GL, n.d.-a). The results of this work has shown the importance of considering the wake effect for future offshore wind farm development. For clusters containing 20 turbines (16 MW), the lost electricity production due to wakes has been shown to stand for 4.8% of the gross yield when using 7D separation distance. When the separation distance was lowered to 4D, the loss of electricity production due to wakes stood for 14.1% of the gross yield. Layout changes that were introduced in order to mitigate the impact of wakes, such as smaller rotor diameter and higher towers, showed modest improvements within the range of tenths of a percentage point. Other measures, such as sector management, resulted in a less desirable outcome. In the case of building neighbouring wind farm clusters (with a distance of ~3 km), the impact would be another 0.5 percentage points loss in electricity production relative to the gross yield. Therefore, key findings of this work are that it is most beneficial to build wind farms with larger separation distancing, both in terms of lowering the impact of wakes as well as profitability. However, this does not take into account how well the area is utilized or the total amount of electricity produced.