Major Component Replacement on Floating Wind Turbines

Abstract: Among the challenges that floating offshore wind (FOW) energy faces today, operation and maintenanc ecosts, and especially major component replacements (MCR), are an important cost reduction lever. MCRs are defined as any failure on a wind turbine requiring the change of an entire main component of the turbine, such as a gearbox, generator, blade, nacelle, etc.. The method of performing MCRs for floating wind turbines needs to be completely rethought compared to bottom-fixed offshore wind (BFOW) turbines because the high ocean depth does not allow jack-up vessels, as typically used in BFOW, to rise above the water to perform the repair in a stable manner. The literature review brings to light that the current MCR reference method for floating wind turbines is the tow-to-port (TTP) method, which consists of unhooking the turbine from its mooring system and then towing it to a port where it will be attached to perform the repair in a stable environment (mooring system and no wave effects). Although this is the reference method, it has many disadvantages: long duration compared to BFOW turbines and therefore large losses of electricity production, and problems related to the availability of equipment (cranes, etc.) capable of performing the repair in ports near the windfarms. Thus, alternative methods are under development in order to avoid these disadvantages. Among these methods, the use of self-hoisting cranes (SHC) seems promising. Already used onshore, this method consists in placing on the wind turbine a crane device able to perform the replacement itself. This study aims at comparing from a techno-economic point of view these two methods of realization ofan MCR. The analysis is based on a case study of a wind farm off the French Atlantic coast in a first step. As the outcome of the study is very project-specific, an important sensitivity analysis is carried out in order to determine if it is possible to draw general conclusions on the superiority of one method over another. All the scenarios covered by this analysis show a certain trend: the SHC method is the most advantageous financially, but also the most risky one because it is much more sensitive to weather conditions than the TTP method