Abstract
Economic growth, elevated living standards, and a growing population are all drivers of increasing electricity demand. Along comes a rise in greenhouse gas emissions, ultimately leading to a rising global temperature. To meet the goals of the Paris agreement and the Sustainable Development Goals (SDGs) set by the United Nations (UN), mitigation strategies must be implemented. Offshore wind energy is proven to be clean, renewable, highly available, cost-competitive and efficient. However, several stakeholders have raised concerns about the effect of offshore wind farms (OWFs) on ocean variability and marine ecosystems. The main objective of this thesis is how reduced wind stress in the farm wake affects vertical mass transport and distribution of temperature and nutrients – and, in turn, how this influences near-surface sound speed and primary production in the nearby areas.
This thesis uses Regional Ocean Modeling System (ROMS) with idealized numerical setup to conduct a sensitivity analysis of the impacts of OWFs on the nearby ocean environment. The analysis is conducted with eight single-farm experiments with farm size L= 5 km and L= 10 km under four different wind stress conditions (weak wind stress, moderate wind stress, strong wind stress, and combination of strong wind stress and strong wind stress reduction), as well as two multiple overlapping-farm experiments with size L= 8 km under strong wind stress conditions. The farm wake is analytically calculated using a Gaussian function.
The results show that OWFs can create unbalanced dipoles with upwelling on one side and down- welling on the other side of the farm. The affected area increases along with L, and the magnitude of wind stress reduction is a determining factor for the magnitude of disturbance for most of the studied properties. The findings underscore that the effect of OWFs on ocean variability is complex and varies throughout the water column. The results also suggest that the presence of OWFs causes a slight net reduction in sound speed near the surface and a net increased primary production.
While these findings provide a solid foundation for evaluating the impact of OWFs on ocean variability and marine ecosystems, further realistic and site-specific studies are needed to assess the significance of disturbances on marine life and other stakeholders. Nonetheless, the study emphasizes the importance of including wake effects in the risk assessment of offshore wind energy projects.