Infield Cable Topology Optimization of Offshore Wind Farms

Abstract

As part of the effort to reduce the cost of offshore wind energy, this thesis addresses the problem of the design of the infield cable topology for offshore wind farms. The final outcome of the project is a tool that can be implemented in a more general optimization platform for offshore wind farm design. Therefore, the main objective is to approximate the optimal inter-array cable connections in affordable computation times. A review of the state of the art collection system designs indicates the radial and branched designs as the designs with the highest potential among the conceptual designs. The key target of the optimization procedure is the minimization of cable cost. Regarding the design constraints, cable capacities are respected and inter-array cable crossings are strictly avoided. The literature review of the related research reveals the complexity of the problem and pinpoints the use of heuristic methods. Planar Open Savings (POS) [1] and Esau-Williams (EW) [2] heuristics are chosen to treat the single cable radial and branched designs respectively. Both algorithms are saving heuristic methods, starting from a star design. At each iteration, the merging of two routes is considered that could yield to the maximum cost saving. After the implementation of the algorithms is validated, a methodology is proposed to allow the possibility for multiple cable types. The behaviour of the heuristics is evaluated both cost and time-wise in a wide range of instances. The results show that the parameters that differentiate their behaviour are the use of single or multiple cable types and the position of the substation, which can be located either centrally or outside the area of the farm. Moreover, a hybrid approach between POS and EW is developed that improves the performance of EW for multiple cable types. Finally, specific recommendations are made regarding the use of the best algorithm for each case. The practicality of the developed tool is enhanced by including the possibility to choose the switchgear configuration and by eliminating the crossings between inter-array cables and transmission lines. Last, modifications allow the minimization of crossings with pipelines/cables that are possibly laid on the seabed. Throughout the report, the comparison of results provided by the tool with the actually installed layouts shows the prospects of inter-array cable cost reductions.