Analysis of different means of transport in the operation and maintenance strategy for the reference DOWEC offshore wind farm

The DOWEC project aims at implementation of large wind turbines in large-scale offshore farms. A baseline wind farm has been determined consisting out of 80 wind turbines of 6 MW each and is located 43 km off the Dutch coast. The following access systems for O&M crew have been investigated in the paper: a rubber boat (zodiac), the offshore access system and a helicopter. For these access systems the operational limits, expressed as maximum mean wind speed and significant wave height, have been established. On the basis of the NEXT database the statistics of the corresponding weather windows are been determined. These statistics together with the failure statistics and the regular maintenance demand of the wind turbines and the other offshore wind farm components determine its availability at the specific site. Estimates of the availability of the offshore wind farm have been obtained with a sophisticated Monte Carlo simulation model of the operations within the wind farm. The simulations show that use should be made of access systems with an accessibility of at least 82%; this rules out simple options as a rubber boat in order to maintain a farm availability of above 90%.