Abstract
Offshore wind farms are central to the global energy transition, especially as larger turbines and new substructures enable deployment at greater depths. While cost and energy yield are typically the main drivers of design, integrating environmental impacts into the design process is becoming increasingly important. This thesis develops a framework in which life cycle greenhouse gas (GHG) emissions are quantified and expressed through the global warming potential (GWP) in grams of CO₂-equivalent per kWh, thereby creating a metric that can be directly compared with the levelized cost of energy (LCOE). In doing so, GWP becomes a design-relevant parameter for optimizing offshore wind farms not only for economics, but also for sustainability.
The study investigates wind farms ranging from 400 MW to 1000 MW, with turbine ratings of 5 MW, 10 MW, 15 MW, and 22 MW. Three foundation types are considered: monopile (fixed-bottom), semi-submersible (floating), and spar buoy (floating). A bottom-up life cycle assessment (LCA) was applied, covering material production, manufacturing, transport, installation, operation, and decommissioning. The assessment incorporates a logistics model for marine operations and farm-level scaling to ensure realistic representation of installation demands and component quantities. Results were normalized by the annual energy production (AEP) of each configuration, enabling fair comparison across technologies and site conditions.
Findings show that increasing turbine size consistently reduces GWP, as fewer units are needed to achieve a given farm capacity, lowering both material requirements and installation activities. In a 400 MW farm, semi-submersible turbines achieve GWP reductions of 50.50%, 65.28%, and 73.96% when scaling from 5 MW to 10 MW, 15 MW, and 22 MW, respectively. Spar buoy turbines show similar reductions of 50.91%, 67.29%, and 75.93%. For monopile foundations, also considered at shallower depths, larger turbines likewise reduce environmental impacts per kWh. Expanding farm capacity from 400 MW to 1000 MW further enhances performance, as economies of scale amplify both environmental and economic benefits.
Economic analysis reveals parallel trends. LCOE decreases with turbine scaling for all foundation types, although monopiles remain most competitive in shallow waters, while spar buoys gain advantage in deeper sites. Semi-submersibles bridge the intermediate depths but also benefit significantly from turbine upscaling. The alignment between GWP and LCOE trends indicates that design decisions favoring cost reductions also contribute to environmental sustainability. However, the marginal reduction in GWP diminishes at very high turbine ratings, suggesting that beyond a threshold, other factors such as LCOE, reliability and system integration may dominate design trade-offs.
In conclusion, this thesis demonstrates that by quantifying environmental impacts into a comparable metric, sustainability can be incorporated into wind farm design. Across farm scales, turbine ratings, and foundation types, results consistently show that larger turbines on monopile, semi-submersible, and spar foundations deliver lower GWP and improved LCOE, confirming that technology scaling serves both economic and environmental objectives in offshore wind development.