In recent years, costs in the offshore wind energy sector have risen significantly. Rising interest rates, shortage of skilled labour and a supply chain which is under pressure due to the ever increasing size of offshore wind turbines all cause costs to increase. At the same time, the pressure to realise sustainable energy continues to grow. The installation phase is one of the most expensive and resource-intensive parts of offshore wind projects. Reducing the installation duration could aid in significantly reducing the installation costs, and make offshore wind farms more economically feasible.

The Slipjoint is a novel connection method developed by Delft Offshore Turbine (DOT), that aims to reduce offshore installation time, and therefore installation cost, by removing the need for bolting or grouting connections between wind turbine parts. When coupled with a complete pre-assembly strategy, it enables installation of offshore wind turbines with a single lift.

This paper presents a Discrete-Event Simulation (DES) model that compares traditional and Slipjoint-based wind turbine installation methods in terms of time, cost, and weather sensitivity. The model gives insight into how weather, vessel characteristics, and campaign timing influence installation performance of both the standard and Slipjoint-based installation methods. A multi-year simulation is run over a range of weather datasets, to give insight into installation performance as a function of start date. The multi-year model is applied to two case studies: the Ecowende wind farm in the North Sea, and the Star of the South wind farm off the coast of mainland Australia, near Tasmania. The standard installation method is compared to the Slipjoint method. The Slipjoint method is run with two values for the capacity to investigate the impact of the capacity on performance. Results show that the Slipjoint can reduce installation duration by 30 to 60\%. Increased vessel dayrate and mobilisation costs, caused by the need for Heavy-Lift Vessels for the Slipjoint method, partially offset the economic gain from the reduction in installation time. Still, a cost reduction of 0 to 30\% can be achieved, depending on the vessel capacities which can be achieved. Furthermore, the Slipjoint methods are shown to have a higher weather workability, meaning they are less affected by bad weather conditions than the standard installation method. This enables them to have a wider envelope in which the installation campaigns can start. These results show the potential of the Slipjoint to change the way offshore wind farms are installed, in order to make offshore wind energy more economically feasible.