Determining the Optimal Vessel Fleet for Maintenance of Offshore Wind Farms

Today the offshore wind energy industry needs financial support to be profitable.For offshore wind farms to be more competitive against other energy sources, thecosts must be reduced, and this may be achieved by increasing the efficiency ofoperation and maintenance. In this thesis operations research is used to developboth a deterministic and stochastic strategic model to determine the optimal fleetsize and mix for doing maintenance, by taking stepwise development into account.The results show that the deterministic model can solve problems of realisticsize for a planning horizon of 25 years in less than 23 minutes. The stochastic modeltakes uncertainties in number of failures and weather conditions into account. Thecomputational study shows that a stepwise development of wind farms influencethe optimal fleet and is therefore important to take into consideration. The valueof the stochastic solution is significant and there is a benefit of having a stochasticmodel compared to a deterministic one. The problem solver uses the Branch& Bound method as solution strategy to solve the mixed integer programmingproblem, and the Branch & Bound tree grows rapidly in size. An integer solutionis found fast, but it takes some time to prove that the optimal solution is found,due to a flat solution landscape