Feasibility of up-tower repair concepts for pultruded carbon spar cap planks in wind turbine blades

Rosemeier, Malo; Saathoff, Matthias; Kolsch, Johannes; Buriticá, Pablo; Petersen, Enno; Beer, Christopher

doi:10.5194/wes-11-1-2026

Articles | Volume 11, issue 1

https://doi.org/10.5194/wes-11-1-2026

© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/wes-11-1-2026

© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 11, issue 1

Research article

|

06 Jan 2026

Research article |

| 06 Jan 2026

Feasibility of up-tower repair concepts for pultruded carbon spar cap planks in wind turbine blades

Malo Rosemeier, Matthias Saathoff, Johannes Kolsch, Pablo Buriticá, Enno Petersen, and Christopher Beer

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Final revised paper (published on 06 Jan 2026)
Preprint (discussion started on 19 May 2025)

Interactive discussion

Status: closed

CC1:
'Comment on wes-2025-56', Wolfgang Holstein, 22 May 2025

Besten Dank Malo für die Möglichkeit an der Diskussion zur Veröffentlichung teilzunehmen.
Die Erfahrung aus meiner Praxis zeigt, daß Reparaturentscheidungen aufgrund mehrdimensionaler Kriterien erfolgen, die nicht alleine technischer Natur sind. Die Verfügbarkeit von Ersatzteilen, Material und geeignetem Personal, sowie meteorologische Bedingungen spielen hier mit eine Schlüsselrolle.
Gleichwohl zeigt das Verbundprojekt die Leistungsfähigkeit der Simulation und ingeniöse Kreativität durch versteifende Komforten als Exosketett oder Endoprthese die erforderliche Positionierung der Fügepartner herzustellen. Welch ein Aufwand am hängenden Blatt diese Hilfsvorrichtungen ohne Kran aus der Bühne oder dem Seil anzubringen.
Soviel zu dem ersten Eindruck, den ich weiter vertiefen möchte. Ich bin gespannt auf Kommentare, die ich ebenfalls zu sehen bekomme.
Wolfgang Holstein

Disclaimer: this community comment is written by an individual and does not necessarily reflect the opinion of their employer.

Citation: https://doi.org/10.5194/wes-2025-56-CC1
- AC1: 'Reply on CC1', Malo Rosemeier, 19 Sep 2025
  
  Dear Wolfgang,
  
  Thank you for your practice-based contribution. We fully agree that repair decisions are multi‑criteria and not purely technical.
  
  Your remarks on the considerable effort to install stiffening aids as an exoskeleton or endoprosthesis without a crane - from a platform or on ropes - highlight the operational challenges. Likewise, the choice between up‑tower and down‑tower repair is strongly context‑dependent: offshore it hinges on the availability, mobilization time, and day rates of jack‑up vessels, as well as suitable metocean windows; onshore it is shaped by the accessibility of remote sites (road and crane access, crane logistics, permits, seasonal constraints).
  
  Your input is very valuable and will be carefully considered in our revision.
  
  Kind regards,
  
  The Authors
  
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  Citation: https://doi.org/10.5194/wes-2025-56-AC1
RC1:
'Comment on wes-2025-56', Anonymous Referee #1, 06 Aug 2025

The comment was uploaded in the form of a supplement: https://wes.copernicus.org/preprints/wes-2025-56/wes-2025-56-RC1-supplement.pdf

Citation: https://doi.org/10.5194/wes-2025-56-RC1
- AC2: 'Reply on RC1', Malo Rosemeier, 19 Sep 2025
  
  Dear Anonymous Referee #1,
  
  Thank you for your constructive assessment. We understand your main concern is the clarity of novelty. Our manuscript’s intent is to contribute a structural feasibility assessment rather than to claim new field procedures or cost benefits. Specifically, we investigate feasibility via (i) simulations and (ii) practical considerations: an FE model of an 81.6 m commercial blade for a 7 MW offshore turbine under a maintenance load case, with loads from aeroelastic simulations, evaluating the weakened structure (step‑wise increased repair zone) for buckling, cyclic strains, and permissible wind speeds for conducting the repair.
  We confirm that the support‑structure content reflects brainstorming-concept proposals to enable up‑tower repairs, not mature designs. These proposals should be developed further and validated in more detail.
  We also agree that cost and asset availability drive the decision, and we do not present proof of O&M cost reduction; as you note, no such evidence is provided or claimed.
  Regarding Section 4.2, our intent is to keep it as part of the discussion because it documents the proposal space (and is only an excerpt of the related patent application), which helps contextualize the feasibility analysis. We will consider your recommendation to streamline it in a revision. We may also consider modifying the title to better reflect a conceptual, structural feasibility assessment.
  Regarding Section 2.1 “the proposed repair concept,” our focus is not to claim novelty for individual repair steps - which are already performed by repair companies (as cited in Fig. 2) - but to combine established practices into a coherent up‑tower sequence and assess its structural feasibility (limits) for pultruded CFRP spar caps under maintenance loads. We appreciate your detailed points on FE modeling; all relevant aspects will be considered in a revision.
  
  Thank you again for your valuable input.
  
  Best regards,
  
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  Citation: https://doi.org/10.5194/wes-2025-56-AC2
RC2:
'Comment on wes-2025-56', Anonymous Referee #2, 14 Aug 2025

Dear Authors,
Thank you for this interesting submission that already has decent quality.
The submitted manuscript addresses an interesting question with regard to feasibility of up-tower repairs for wind turbine rotor blades. Most of my comments address minor revisions in the manuscript. However, one major problem of the underlying technical challenge has not been addressed.
Please revise according to my comments in the attached *.pdf.
Best regards.

Citation: https://doi.org/10.5194/wes-2025-56-RC2
- AC3: 'Reply on RC2', Malo Rosemeier, 19 Sep 2025
  
  Dear Anonymous Referee #2,
  
  Thank you for highlighting this major point. We agree that a permissible cyclic strain (or stress) level is required for the structural validation. Our current results quantify cyclic strain/stress amplitudes under a maintenance load case, but the permissible level of cyclic loading during curing of the matrix along with movement of fibers for safe up‑tower repair must be derived experimentally.
  
  We will consider stating this explicitly in the outlook and framing our current cyclic assessment as indicative pending experimental verification.
  
  Best regards,
  
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  Citation: https://doi.org/10.5194/wes-2025-56-AC3

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

AR by Malo Rosemeier on behalf of the Authors (11 Nov 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (20 Nov 2025) by Julie Teuwen

RR by Anonymous Referee #1 (25 Nov 2025)

ED: Publish as is (08 Dec 2025) by Julie Teuwen

ED: Publish as is (10 Dec 2025) by Carlo L. Bottasso (Chief editor)

AR by Malo Rosemeier on behalf of the Authors (10 Dec 2025)

Short summary

This research explores a method for repairing wind turbine blades made from carbon fiber while they remain installed, eliminating costly disassembly. It addresses the challenges of repairing damaged blades and proposes a practical solution to improve repair efficiency. Through structural analysis, we found that this approach can ensure safety during repairs, providing significant benefits to the wind energy industry.