Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> An optimization framework for simultaneous design of wind turbines (WTs) and cable layout for a collection system of offshore wind farms (OWFs) is presented in this paper. The typical approach used in both research and practical design is sequential, with an initial annual energy production (AEP) maximization, followed then by the collection system design. The sequential approach is robust and effective. However it fails to exploit the synergies between optimization blocks. Intuitively, one of the strongest trade-offs is between the WTs and cable layout, as they generally compete; i.e. spreading out WTs mitigates wake losses for larger AEP but also results in longer submarine cables in the collection system and higher costs. The proposed optimization framework implements a gradient-free optimization algorithm to smartly move the WTs within the project area subject to minimum distance constraint, while a fast heuristic algorithm is called in every function evaluation in order to calculate a cost estimation of the cable layout. In a final stage, a refined cable layout design is obtained by iteratively solving a mixed integer linear programme (MILP), modelling all typical engineering constraints of this particular problem. A comprehensive performance analysis of the cost estimation from the fast heuristic algorithm with respect to the exact model is carried out. The applicability of the method is illustrated through a large-scale real-world case study. Results shows that (i) the quality of the cable layout estimation is strongly dependent on the separation between WTs, where dense WT layouts present better performance parameters in terms of error, correlation, and computing time, and (ii) the proposed simultaneous design approach provides up to 6â% of improvement on the quality of fully feasible wind farm designs, and broadly, a statistically significant enhancement is ensured in spite of the stochasticity of the optimization algorithm.
Highlights
Offshore wind currently represents one of the main drivers towards power systems fully based on renewable energies
Results shows that: (i) the quality of the cable layout estimation is strongly dependent on the separation between wind turbines (WTs), where dense WTs layouts present better performance parameters in terms of error, correlation and computing time, and (ii) the proposed simultaneous design approach 15 provides up to 6% of improvement on the quality of fully feasible wind farm designs, and broadly, a statistically significant enhancement is ensured in spite of the stochasticity of the optimization algorithm
4 Conclusions 415 The proposed method provides an approach for simultaneous design of WTs and cable layout
Summary
Offshore wind currently represents one of the main drivers towards power systems fully based on renewable energies. The projected compound annual growth rate of the global offshore wind market is of at least 8% for the starting decade, where yearly new installations are expected to surpass the figure of 20 GW (GWEC, 2020b). Apart from the WTs, the set of supporting and auxiliary 30 components of the project (balance of plant, BoP) must be sized as well. This mainly includes submarine cables, offshore transformers, converters stations in case of direct current technology (DC), foundations, structures, and protection/control equipment. WTs alone account today for around 30% of the overall levelized cost of energy (LCoE), while a similar figure is attributable to the BoP, with submarine cables representing the most expensive component with around 11% of the LCoE (ORE Catapult, 2020). Electrical integration system costs (capital expenses associated primarily to submarine cables and offshore substation) are not following the overall decreasing trend, mainly due to the lack of optimization techniques for designing this subsystem, and the need of longer and bigger submarine cables (Tennet, 2019)
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