07 Dec 2023
 | 07 Dec 2023
Status: a revised version of this preprint is currently under review for the journal WES.

Operations and Maintenance Cost Comparison Between 15 MW Direct-Drive and Medium-Speed Offshore Wind Turbines

Orla Donnelly, Fraser Anderson, and James Carroll

Abstract. Determining offshore wind energy operational expenditures relies on acquiring reliability data, particularly as turbine power ratings increase. The uncertainty surrounding operational costs and optimal drive train configurations for larger turbines persists. While previous research addressed reliability data for 3 MW offshore wind turbines, this study reviews and collates updated failure data for 15 MW turbines, comparing direct drive and medium-speed configurations. It employs an Operations and Maintenance (O&M) modeling tool to calculate total operational costs. The study concurs with existing literature, showing that direct drive turbines have lower operational costs than medium-speed turbines in three case studies. However, the cost and availability differences between configurations are smaller than previously suggested. For 15 MW turbines, the analysis reveals that the cost disparity between direct drive and medium-speed turbines is significantly smaller than for smaller-rated turbines, with percentages of 1.59 %, 1.58 %, and 5.78 % for the three ScotWind sites selected. Previously, the absolute % difference in cost between direct drive and medium speed turbines was estimated at 29.79 %. Sensitivity analyses explore the influence of three factors—failure rates, accessibility limits, and major replacement times—on total operational costs. These analyses demonstrate that medium-speed configurations exhibit more significant cost fluctuations, and the cost gap between configurations is reduced if failure rates are lowered at the same rate for each configuration, accessibility increases or the major replacement time is reduced for the larger wind turbine components.

Orla Donnelly, Fraser Anderson, and James Carroll

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-2023-156', Anonymous Referee #1, 21 Dec 2023
    • AC1: 'Reply on RC1', Orla Donnelly, 22 Jan 2024
  • RC2: 'Comment on wes-2023-156', Davide Astolfi, 02 Jan 2024
    • AC2: 'Reply on RC2', Orla Donnelly, 22 Jan 2024
Orla Donnelly, Fraser Anderson, and James Carroll
Orla Donnelly, Fraser Anderson, and James Carroll


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Short summary
We collate the latest reliability data in operations and maintenance (O&M) for offshore wind turbines, specifically large turbines of 15 MW. We use this data to model O&M of an offshore wind farm at 3 different sites. We compare two industry dominant drive train configurations in terms of O&M cost for 15 MW turbines and determine if previous results for smaller turbines still holds true. Comparisons between drive trains is topical within industry and here, we produce cost comparisons for them.