Aero-Structural Analysis and Dimensional Optimization of a Prototype Hybrid Wind–Photovoltaic Rotor with 12 Pivoting Flat Blades and a Peripheral Stiffening Ring

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This article covers the fields of mechanical engineering and renewable energy, with particular emphasis on the aero-structural analysis and design optimization of a hybrid wind-photovoltaic rotor. The authors claim that this article presents the first aero-structural analysis of a 3-meter-diameter hybrid wind-photovoltaic rotor with flat blades stiffened by a peripheral ring. Due to the lack of previous data, the authors developed a consistent, preliminary set of data on loads and performance. The conclusions from the numerical studies provide new knowledge on the performance and loads of this type of structure, particularly in the context of its application in rural microgrids and autonomous agricultural units. This allows the article to be considered innovative.

The authors clearly state the research objective in the abstract and introduction, and the methods used are appropriate for this type of preliminary analysis. The data analysis is logical and consistent with the methodology. The authors present the results of BEM, CFD, and FEM simulations step by step. They verify their assumptions by comparing BEM results with CFD results, and then calibrate the FEM models based on aerodynamic data. Multiple iterations and comparison with literature data confirm the consistency of the approach. The conclusions are directly based on the simulation results and are consistent with the numerical data and visualizations presented in tables and graphs. The article demonstrates a good understanding of the current state of research and appropriately references existing literature, which is up-to-date. The article follows the standard, logical structure of a scientific paper, making it easy to follow. The content is clear, and each section is well-organized. The use of tables and graphs in the results section aids in the visualization and understanding of the data, although many of them are of poor quality.

Critical comments and suggestions:
The study's greatest limitation is the lack of experimental validation. Although the authors declare that the work provides a basis for future testing, the inclusion of even preliminary results from simple wind tunnel tests could significantly strengthen the validity of the presented simulations. Although the authors mention fatigue control in the "Materials and Methods" section, their results focus primarily on static stresses. A more detailed analysis of cyclic loading and its impact on the structure's service life, especially at critical points, would be a valuable addition.
The article deliberately omits considerations of the generator, brake, and drives. While this is justified by the simplification of the model, a more comprehensive study could consider the impact of these elements on overall performance and dynamics.
The final conclusions are quite categorical ("the structure is sufficiently stiff"), but there is no clear indication of the limitations of the research – for example, the lack of tests in real-world conditions, simplifications of the PV geometry, or the impact of material aging. There is also no reference to the influence of the mass and inertia of the stiffening ring on the system's dynamics.
Most of the figures are very unclear and therefore difficult to interpret, and they are very blurry when enlarged – this should be corrected.

Author Response

Dear Reviewer,

Please find attached the document containing the requirements and comments regarding the paper entitled “Aero-Structural Analysis and Dimensional Optimization of a Prototype Hybrid Wind–Photovoltaic Rotor with 12 Pivoting Flat Blades and a Peripheral Stiffening Ring”.

We sincerely thank you for your time and valuable feedback.

Best regards,
Alexis Negrea

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents the design and evaluation of a low-cost modular hybrid wind–photovoltaic rotor, which employs flat blades stiffened by a peripheral ring and passive pitch control, suitable for rural microgrids or autonomous agricultural units. The prototype can operate safely under variable wind conditions and allows integration with commercial actuators, generators, and tracking systems without the need for structural redesign. For this reason, it is considered that the subject addressed in this article covers relevant aspects within the field of study, particularly in the area of energy generation through hybrid (wind–photovoltaic) rotors.

The main contributions of this work, in comparison with other published materials, are as follows: A) Design and evaluation of a novel prototype consisting of a rotor with flat blades stiffened by a peripheral ring at a scale of 3 m, for which no direct precedents exist. B) According to the results, this prototype is positioned within the segment of surface wind turbines (≤10 kW), suitable for rooftops or isolated stations. The annular reinforcement reduces noise levels by eliminating the free blade tip, thus meeting urban acoustic standards. C) Hybrid photovoltaic integration. In feathered position (β = 90°), the rotor allows ~90% of solar irradiance to pass through, a key advantage for agrivoltaic configurations, where shading of <15% is considered acceptable.D) Simplified control strategy. The simulations presented indicate only three critical pitch positions: 20° (automatic start-up), 10° (nominal), and 90° (protection). This allows for a mechanical stop and bevel gear mechanism, more reliable and economical than continuous servo systems.

After reviewing the manuscript, the following observations are issued:

• In general, the methodology of the work is unclear. It is necessary to describe in detail the methodology of the study, outlining each of its phases or stages to achieve the stated objectives, addressing the subject matter in a clear and comprehensible manner, and supporting the information with pertinent and up-to-date references.
• The incorporation of an introductory paragraph is required for the following sections: 2. Materials and Methods; 3. Results; 4. Discussion.
• It is necessary to highlight the contributions of this research, which may be included in the Introduction section.
• It is necessary to present the article organisation, which may also be incorporated into the Introduction section.
• The format of each section and subsection title should be standardised throughout the manuscript (in some cases italics, bold, etc. are used).
• The information presented in Section 2. Materials and Methods appears disorganised. It is important to organise the content more effectively in order to provide greater clarity. Multiple titles and subtitles are presented within each subsection, revealing a lack of coherence in the information structure.
• In line 156, the acronym HAWT is introduced; however, its meaning is not explained (nor does it appear in the abbreviations section). All acronyms and abbreviations should be revised throughout the manuscript.
• The content presented in Section 3. Results is highly disorganised. It is essential to restructure this section in order to enhance clarity and coherence. A wide variety of titles, subtitles, bullet points, and numbering systems are employed inconsistently. Several subsections are titled as Partial conclusions, Comparison, Observations, Scenario 1, among many others, resulting in significant disorganisation in this section overall.
• The Figures are excessively blurred and must be replaced with higher quality versions.
• Figures 3, 4, and 6 require a greater number of plotted points, as they lack precision regarding the variables presented.
• Several Figures are neither mentioned nor described in the text (Figures: 1, 2, 11, 12, 13, 17, 19, 20, 21).
• Several Tables are neither mentioned nor described in the text (Tables: 3, 4, 12, 13, 14).
• In Figures 3 and 4, the meaning of the values (legends) shown on the right should be explained.
• The text refers to a Figure 18; however, this figure is not provided.
• The format of Table titles should be revised (in some cases they appear centred, in others not); the same applies to Figures.
• The acronym URES (line 1182) appears with subscripts, whereas in the manuscript it is presented in uppercase. This detail must be corrected. Similar inconsistencies in acronyms should be revised throughout the manuscript.
• The text within the first cell of Table 11 should be expanded.
• In Section 4. Discussion, the use of bullet points and numbering should be standardised.
• The conclusions are consistent with the evidence and arguments presented and clearly address the main research question; however, it is necessary to strengthen the section regarding future perspectives (derived from the subject matter developed throughout the manuscript).
• The references presented in the manuscript are considered pertinent and up to date, adequately supporting the discussion.

Author Response

Dear Reviewer,

Please find attached the document containing the requirements and comments regarding the paper entitled “Aero-Structural Analysis and Dimensional Optimization of a Prototype Hybrid Wind–Photovoltaic Rotor with 12 Pivoting Flat Blades and a Peripheral Stiffening Ring”.

We sincerely thank you for your time and valuable feedback.

Best regards,
Alexis Negrea

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors responded to my comments extensively and made numerous changes. The quality of the figures remains questionable, but I'll leave the decision to the editors. In my opinion, they should be improved because they're still "blurry." I have no further comments and recommend the article for publication.

Author Response

Dear Reviewer,

Please find attached the document with our detailed, point-by-point responses to the comments and requirements concerning the manuscript entitled “Aero-Structural Analysis and Dimensional Optimization of a Prototype Hybrid Wind–Photovoltaic Rotor with 12 Pivoting Flat Blades and a Peripheral Stiffening Ring.”

We sincerely appreciate your time, effort, and valuable feedback, which have helped us to further improve the clarity and quality of the paper.

Best regards,
Alexis Negrea

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

In this new version of the manuscript, it is considered that some of the observations identified in the first version of the manuscript have been addressed. The methodology has been favourably adjusted, approaching the subject matter with greater clarity and comprehensibility; likewise, the information is supported by reliable and pertinent sources. The information presented in Sections 2 and 3 has been reorganised, thereby improving its clarity. The following details should be taken into account:

Several figures appear very blurred (1, 2, 7–24).
Two Figures 18 are shown.
Several parts of the manuscript appear overcrowded; it is recommended to insert spaces between titles, subtitles, figures, tables, section headings, and figure and table captions in order to improve the clarity of the manuscript.
The formatting of the text throughout the manuscript should be verified (some figure captions are presented in bold type and others not; the font type of the title of Section 5 appears different from that used in the rest of the manuscript).
The formatting of the bullet points should be verified and standardised.
The conclusions are considered consistent with the evidence and arguments presented, and the main research question posed is clearly addressed; however, it is necessary to strengthen the writing regarding future perspectives (derived from the subject matter addressed throughout the manuscript) in the conclusions section.

Author Response

Dear Reviewer,

Please find attached our detailed responses to the comments and suggestions regarding the manuscript entitled “Aero-Structural Analysis and Dimensional Optimization of a Prototype Hybrid Wind–Photovoltaic Rotor with 12 Pivoting Flat Blades and a Peripheral Stiffening Ring.”

We sincerely thank you for your valuable feedback, which has been very helpful in further improving the manuscript.

Best regards,
Alexis Negrea

Author Response File: Author Response.docx

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

In this new version of the manuscript, it is considered that the observations identified in the previous version have been addressed. The conclusions have been strengthened, clearly presenting the future perspectives derived from the subject matter addressed throughout the manuscript.

Concerns remain regarding the low clarity of Figures 1, 2, and 7–25; it is hoped that the visibility of these images can be improved.

Author Response

Dear Reviewer,

Thank you once again for your valuable feedback. We have carefully revised the figures as suggested, improving their resolution and clarity, and we also provide the images separately to ensure the best quality in the final version.

Best regards, 

Alexis Negrea

Author Response File: Author Response.docx