Offshore wind turbines are normally designed for a nominal service life of 20 to 25 years; however, with a significant number of units approaching the second half of their service life, the discussion on selecting the most appropriate end of life scenario becomes ever more relevant. Scenarios to be investigated mainly include decommissioning, repowering or service life extension, while such decisions depend on a number of criteria which should be taken into account and should ultimately inform a techno-economic and risk assessment. This paper performs an initial comparative assessment between two of these scenarios, repowering and decommissioning, through a purpose developed techno-economic analysis model which calculates relevant key performance indicators. The economic model of risk aversion is further adopted to calculate the certainty equivalent of LCoE (Levelized Cost of Energy) based on each of the examined end of life scenarios and a stochastic expansion of the deterministic model. An application to a typical, hypothetical offshore wind farm, qualifies the full repowering scenario as the prevailing option, under the assumptions considered, with a lower amount of risk premium (1.136 £/MWh) and certainty equivalent (69.821 £/MWh) in comparison to other scenarios, reducing LCoE by nearly 35% compared to partial decommissioning and 36.5% compared to full decommissioning.

With many offshore wind turbines (OWTs) approaching the end of their estimated service life, there is an increasing demand for developing and evaluating end-of-life strategies that can maximize these assets' value while at the same time satisfying the requirements of the stakeholders involved. This study aims to perform a detailed review and develop a framework that will consider multiple criteria in the decision-making process, presenting and discussing available technologies and strategies, as well as influencing factors such as schedule, cost and environmental impact. Service life extension, repowering and decommissioning are included in this review as the main end-of-life strategies considered by asset owners, and these are translated into four processes that are applicable to offshore wind farms through a generic decision tree. A SWOT analysis is also conducted which aims to compare the different characteristics of the proposed processes. The factors contributing to the uncertainty of the processes as well as lessons learnt from the oil & gas industry are also discussed.