The optimum range of design axial induction factors for lowest levelized-cost of energy

Abstract. The present work proposes a new fatigue, aerodynamics, and cost-scaled turbine (FACT) blade design methodology. The basis of the FACT blade design is an objective function for change in levelized-cost of energy, ΔLCOE, as a function of design axial induction factor, a, that strikes a balance between increasing (or up-scaling) blade length and annual energy production while accounting for the additional cost and loading changes associated with a longer blade. In the process of developing the ΔLCOE objective function, new insights were gained about changes in capital cost and operations and maintenance cost with rotor up-scaling. As part of the capital cost function development, new engineering approximations for rotor mass are discussed that are suitable for large-diameter offshore wind turbines, which use improved materials technologies and manufacturing processes. Additionally, a detailed operations and maintenance model is developed using available wind farm reliability data. Furthermore, a relationship between turbine failure rate and damage-equivalent loads for failure-prone turbine subsystems is proposed. FACT rotor blade design points are identified using five reference wind turbines with power ratings of 10- to 22-MW as a baseline. Projected LCOE savings with a FACT rotor blade design are on the order of 5 % for an optimum design axial induction factor in the range of a = 0.21 and 0.27, thus falling between the low-induction rotor concept (a = 0.18) and the Betz optimum for maximum C_P (a =  0.33).