17 Jul 2023
 | 17 Jul 2023
Status: this preprint is currently under review for the journal WES.

Hybrid-Lambda: A low specific rating rotor concept for offshore wind turbines

Daniel Ribnitzky, Frederik Berger, Vlaho Petrovic, and Martin Kühn

Abstract. We introduce an aerodynamic rotor concept for an offshore wind turbine which is tailored for an increased power feed-in at low wind speeds by a substantial increase of the rotor diameter while maintaining the rated power. The main objective of the conceptual design is to limit the quasi-steady loads (blade flapwise root bending moment (RBM) and thrust) to the maximum values of a reference turbine. The outer part of the blade (i.e. outer 30 % span) is designed for a higher design tip speed ratio (TSR) and a lower axial induction than the inner part. By operating at the high TSR in light winds, the slender outer part fully contributes to the increased power capture. In stronger winds the TSR is reduced and the torque generation is shifted to the inner section of the rotor. Moreover, the blade design efficiently reduces the power losses when the flapwise RBM is limited through peak shaving, below rated wind speed. This is of high importance, given the wind speed distribution at offshore sites. The characteristics of the rotor are first investigated with stationary blade element momentum simulations and further analyzed with aeroelastic simulations, considering the flexibility of blades and tower to show that a structural design is feasible even for a blade of this size and complexity. The economic revenue and the cost of valued energy of the turbine is estimated and compared to the IEA 15 MW offshore reference turbine, considering a fictitious wind speed-dependent feed-in price. Our results for the turbine concept with an increase of rotor diameter by 36 % show that the revenue can be increased by 30 % and the cost of valued energy can be reduced by 16 % compared to the reference turbine.

Daniel Ribnitzky et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wes-2023-72', Anonymous Referee #1, 01 Sep 2023
  • RC2: 'Comment on wes-2023-72', Anonymous Referee #2, 14 Sep 2023

Daniel Ribnitzky et al.

Daniel Ribnitzky et al.


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Short summary
This paper provides an innovative blade design methodology for offshore wind turbines with very large rotors compared to their rated power, which are tailored for an increased power feed-in at low wind speeds. Rather than designing the blade for one single optimized operational point, we include the application of peak-shaving in the design process and introduce a design for two TSRs. We describe how the enlargement of the rotor diameter can be realized to improve the value of wind power.