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ECN publication
Offshore Wind Access 2018
Published by: Publication date:
ECN Wind Energy 8-2-2018
ECN report number: Document type:
ECN-E--17-071 ECN publication
Number of pages: Full text:
46 Download PDF  

Offshore wind farms in Europe are moving further from shore in order to capture more favourable wind conditions. However, this creates additional challenges regarding their Operations & Maintenance (O&M). O&M costs contribute significantly (20-30%) to the Levelised Cost of Energy (LCOE) over the lifetime of an offshore wind farm. One of the main reasons is the relatively low accessibility to the wind farm, which increases the down-time and therefore lost energy production, especially for far-offshore wind farms. This has driven the research into innovative access systems which promise average annual accessibility of 90%.

In this second edition, an updated overview is presented of existing and future access systems for offshore wind farms. Three categories of access system are identified, based on the point of access: i) access to the boat landing, ii) access to the platform of the transition piece, and iii) access to the helideck on top of the nacelle. Besides the conventional method of access to the boat landing through Crew Transfer Vessels (CTVs), motion compensated gangways mounted on the deck of Service Operation Vessels (SOVs) have ECN-E–17-071 7 entered the market during the last decade, which moves the maintenance base offshore. The analysis in this report shows that the growth of this market is in alignment with the needs for more efficient and safer transfer of technicians and cargo. In addition, while the relatively close-to-shore locations of current offshore wind farms has driven the extensive use of CTVs, more SOVs are being deployed as wind farms move further from shore, and new designs for motion compensated gangways are being introduced.

It is important to model offshore wind farm O&M activities to fully assess the impacts of a particular access solution. By doing so, design drivers can be identified, business cases of new systems can be established and optimal decisions can be made both for defining the O&M strategy and choosing between different access solutions. This analysis is possible through ECN’s in-house developed tool ECN O&M Access, an O&M cost estimator specifically developed for designers and developers of maintenance vessels and access systems in the offshore wind industry. Using ECN O&M Access, a case study is presented, comparing simple representations of accessibility with newer sophisticated modelling of environmental conditions, vessel hydrodynamics and motion-induced human fatigue of technicians. The case study shows that the modelling of accessibility is improved by incorporating vessel hydrodynamics and motion-induced human fatigue in the transit and transfer phases.

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