Evaluating the cost effectiveness of logistic strategies for onshore monopile handling in marshalling ports

Abstract

The global ever growing energy demand, quest for renewable alternatives for fossil fuels and desire to reduce dependency on single countries has driven the increasing demand for offshore wind energy production. The advancing technologies that enable offshore wind turbines to gain efficiency go hand in hand with increasing sizes of components and foundations. Deeper waters can be entered, but the accompanied size and weight increase poses various challenges. Fixed-bottom structures such as monopiles reach diameters of 10m and lengths up to 110m, which complicates the onshore handling of those monopiles in marshalling ports. This study identified a gap in the existing literature regarding marshalling ports and their role in supporting offshore wind farm construction.

By applying a discrete event simulation (DES) to a case study regarding the construction of an offshore wind farm in the Baltic Sea, different scenarios have been evaluated and assessed in their resilience and performance in response to schedule changes. The findings highlight the importance of a compressed project schedule in achieving cost reductions. A strategy with approximately 75% overlap between load-in and load-out schedules was identified as the most cost-efficient approach. With this approach, cost savings are not only achieved by reducing operational expenses such as personnel and equipment rental, but most substantially by the decreased amount of demanded storage area spaces. With less storage spaces needed, both the construction costs for storage bunds and the area rental costs decrease. The analysis of the experiment on schedule overlap revealed that a scenario with only one support for load-out and zero supports for the load-in exhibited higher average waiting times and total maximum fines. However, this scenario still performed best in terms of total costs, as the waiting times for ships did not outweigh the expenses associated with additional supports. The study also examined the timing of arrivals and found that when a barge arrives the day after the installation vessel departs, the waiting time for unloading significantly decreases.

Collaboration among stakeholders is emphasized as a key recommendation stemming from the study. Involving all relevant actors in offshore wind projects from an early stage can yield extensive mutual benefits. By establishing an overarching supply chain management, coordinated by the project developer, overall construction costs can be reduced without harming any particular party.

The developed discrete event simulation might be applied to other projects to extend the research, under the requirement that the included assumptions are structurally evaluated. Investigating different project sizes, schedule variations and load-out methods could improve the overall understanding of the system dynamics and parameters. In combination with a discrete event simulation, a mathematical layout optimization might enable decision makers to make choices regarding the location and priority of placing wind turbine components in marshalling port, based on the installation variability. This could eventually lead to a decision-making tool suitable for cost-optimizing marshalling activities and installation strategies for wind farm constructions globally, contributing to the acceleration of the energy transition.