The optimal access system for future far-offshore wind farms

Operation and maintenance (Oaamp;M) of offshore wind turbines is one of the main cost drivers of offshore wind energy. One of the aspects critical for an efficient and cost-effective Oaamp;M strategy is the selection of the access system which is used to transfer technicians and, optionally, small spare parts. Currently, most offshore wind farms are located close to shore, and their size is relatively small. For these farms the typical access system consists of catamaran-like workboats, which are used to transfer both technicians and small spare parts. As wind farms move further offshore this Oaamp;M concept might no longer be cost-effective. Currently, different alternative Oaamp;M concepts are being considered for the future far-offshore sites. In this paper an extensive and holistic comparison of different Oaamp;M concepts including different access system solutions is presented. This analysis has been performed using the OMCE-Calculator, ECNs software for advanced Oaamp;M cost modelling. Different sites have been considered, which are typical for the future offshore wind farms that will be commissioned during the next five years. The results of the performed analyses indicate that when moving further offshore harbour-based Oaamp;M strategies are no longer economical, even when helicopters are added to the mix. Looking at farm-based Oaamp;M concepts a supply vessel with a compensated access gangway offers great potential. However, the calculations also indicate that its ability to transfer small spare parts, in addition to technicians, is crucial.