Preliminary Techno-Economic Study of Optimized Floating Offshore Wind Turbine Substructure

Abstract

Abstract. Wild fires and excessive floodings have been seasonal climatic changes across the globe in the past decade. The need for clean energy to fight against the climate changes observed as a result of excessive green-house emission over the years is driving the development of the offshore wind sector. This drive is pushing the exploitation of rich wind resources in deep waters with water depth greater than 60 metres requiring a deviation from the commercialized fixed bottom foundation offshore wind technology. Resolving the issue of exploiting rich wind resources requires the use of floating foundation offshore wind technology satisfying stability and durability requirement in any environmental condition. Floating offshore wind turbines (FOWTs) are still in the pre-commercial stage and although different concepts of FOWTS are being developed, cost is a main barrier to commercializing the FOWT system. This is evidence in the comparison of the CAPEX (capital expenditure) for a fixed bottom platform and a floating platform with the fixed bottom foundation CAPEX representing 13.5 % of the total CAPEX of the system while the floating platform CAPEX represents about 29 % of the total CAPEX of the system leading to an increasing cost. This article aims to use a shape parameterization technique within a multidisciplinary design analysis and optimization framework to alter the shape of the FOWT platform with the objective of reducing cost. This cost reduction is then implemented in a 30 MW floating offshore wind farm (FOWF) designed based on the static pitch angle constraints (5 degrees, 7 degrees and 10 degrees) used within the optimization framework to estimate the reduction in the levelized cost of energy (LCOE) in comparison to a FOWT platform without any shape alteration – OC3 spar platform design. The optimal platform design variants and the OC3 platform are also deployed in a scaled up 60 MW farm to see the impact of platform geometric shape optimization in a scaled-up scenario. Key finding in this work shows that an optimal shape alteration of the platform design that satisfies the design requirements, objectives and constraints set within the MDAO framework contributes to significantly reducing the CAPEX cost and the LCOE in the 30 MW floating wind farm. This is due to the reduction in the required platform mass for hydrostatic stability when the static pitch angle is increased. The FOWF designed with a 10 degrees static pitch angle constraint provided the lowest LCOE value while the FOWF designed with a 5 degrees static pitch angle constraint provided the largest LCOE value barring the FOWT designed with the OC3 dimension which is over designed and over dimensioned. The total cost and LCOE is further reduced in a scaled up 60 MW farm for each design assessed. This further reduction is due to combination of the geometric shape parameterization and optimization of the platform with the economics of scale of the wind farm.