FOWTs: SEASONAL TECHNO-ECONOMIC REVIEW OF CORRECTIVE MAINTENANCE STRATEGIES – BASED ON HINDCAST MODEL

Maintenance in the offshore wind sector is one of the primary cost drivers, largely due to the harsh marine environment and the logistical challenges of accessing turbines located far from shore. Operations are highly dependent on weather and sea conditions, often leading to long delays and complex management. The aim of the Thesis is to develop a methodology able to evaluate, from both a technical and economic perspective, the seasonal impact associated with corrective maintenance in the context of floating offshore wind turbines (FOWTs). Although it is not possible to precisely predict when a turbine will experience a failure, the proposed approach allows for a more reliable estimation of the associated intervention costs and expected downtime.  This analysis is based on metocean data, including significant wave height (Hs) and wind speed at 100 m from the ERA5 database. These variables are vital to assess the accessibility and feasibility of maintenance in offshore environments.  One of the main challenges of floating wind power, still an emerging technology, concerns the management of maintenance activities. Although, some models are available for the Opex estimation, they often involve high computational costs and require several input parameters in order to achieve results that reflect real-world operating conditions. For this reason, the present Work aims to provide a preliminary contribution toward defining a methodological basis for future analyses and developments in the field.  The study of a representative "typical year" highlighted a marked seasonality in metocean conditions. Winter emerges as the most severe and limiting season for offshore operations, while summer offers more favourable conditions for performing interventions, particularly preventive ones. For this reason, the analysis is structured on a seasonal basis, with the goal of identifying waiting times, intervention costs, operational windows, and completed maintenance actions.  In summary, the proposed methodology represents a first step toward building a predictive model for the economic and operational management of corrective maintenance in floating offshore wind turbines.  In this work, the proposed methodology is applied specifically to the generator and the pitch system, two components that are particularly critical from a maintenance perspective. In addition, a post-processing approach is presented to define a starting point model to assess the annual Opex related to a corrective maintenance approach. Based on the seasonal average costs provided by the hindcast model, it is possible to estimate the annual Opex of each component by considering four key factors: - the chosen maintenance strategy, - the component’s annual failure rate, - the seasonal distribution of failures, - the site selections. This approach lets the assessment of the annual Opex of individual components related to corrective maintenance, with the potential to extend the analysis to the entire turbine. By applying the same methodology to major elements such as the floating platform and electrical cables, by using different corrective strategies, it is also possible to estimate the annual Opex associated with corrective maintenance for a floating offshore wind turbine, and to scale the evaluation to an entire wind farm. Although preliminary, this analysis provides an initial framework for future studies aiming to quantify the operational costs of floating offshore wind farms.