Mathematical Analysis and Design of a Low Power Gravity-Based Energy Storage System and Comparison with Battery Storage Systems
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
This article experimentally investigates a gravity-based energy storage system by evaluating its input–output characteristics, energy conversion efficiency, cost scalability, and performance under varying load conditions. The study also compares the gravity energy storage approach with conventional battery systems in terms of operational life, economics, and scalability potential.
The topic is relevant to renewable and sustainable energy research, and the experimental work provides valuable insight into mechanical-to-electrical energy conversion. However, the current version of the manuscript requires substantial improvement in terms of theoretical justification, quantitative efficiency analysis, and discussion of system limitations.
The manuscript is suitable for publication following major revisions.
The following comments may be useful for the authors’ consideration.
- The manuscript could benefit from a clearer articulation of the specific research gap and novelty. While the study introduces and experimentally validates a gravity-based energy storage concept, it might be helpful to clarify which aspect of the system is being emphasized or advanced (e.g., efficiency improvement, design optimization, drivetrain control, or cost analysis).
- Section 2 provides a general description of energy storage systems, do you think adding a specific theoretical model or schematic of the proposed gravity storage setup will be better?
- Could you provide a quantitative evaluation of system efficiency or energy conversion？Without efficiency data, it is difficult to assess how “efficient” or “economical” the system truly is.
- Tables 5–7 compare gravity and battery systems, but the comparison is not normalized by lifetime, efficiency, or capacity. Therefore, the statement that “gravity storage is more economical” is not scientifically supported.
- A thorough revision of the paper for grammar and English style is needed.
Author Response
Reviewer 1
Comment: 1
The manuscript could benefit from a clearer articulation of the specific research gap and novelty. While the study introduces and experimentally validates a gravity-based energy storage concept, it might be helpful to clarify which aspect of the system is being emphasized or advanced (e.g., efficiency improvement, design optimization, drivetrain control, or cost analysis).
Response:
We acknowledge the reviewer’s concern regarding the articulation of novelty. The energy storage concepts are updated and incorporated in section 1.3
Comment:2
Section 2 provides a general description of energy storage systems, do you think adding a specific theoretical model or schematic of the proposed gravity storage setup will be better?
Response:
We sincerely thank the reviewer for the specific theoretical model. As per the suggestion the detailed energy storage system model updated in figure 3, figure 4 and a revised described is incorporated in section 2.3.1.
Comment:3
Could you provide a quantitative evaluation of system efficiency or energy conversion？Without efficiency data, it is difficult to assess how “efficient” or “economical” the system truly is.
Response:
We acknowledge the reviewer’s concern regarding the need for a quantitative efficiency assessment. The quantitative energy consumption data improved and addressed in section 3
Comment:4
Tables 5–7 compare gravity and battery systems, but the comparison is not normalized by lifetime, efficiency, or capacity. Therefore, the statement that “gravity storage is more economical” is not scientifically supported.
Response:
We appreciate the reviewer’s observation regarding the need to normalize the comparison by lifetime, efficiency, and storage capacity. The revised description is updated and all the comparison are addressed in section 3.5. Although a full normalization by lifecycle efficiency and capacity is another part of research work. It will be included in our future publication work.
Comment:5
A thorough revision of the paper for grammar and English style is needed.
Response:
We sincerely thank the reviewer for the feedback and regret the lack of clarity and linguistic quality in the earlier version. The paper was completely revised with native language correction and all the grammar and language were verified and updated in our revised version.
Reviewer 2 Report
Comments and Suggestions for Authors
The manuscript is incomprehensible - at this point, I cannot be sure if the authors used AI to generate the text, or decided to throw random words at google translate.
Comments on the Quality of English Language
The manuscript is incomprehensible - at this point, I cannot be sure if the authors used AI to generate the text, or decided to throw random words at google translate.
Author Response
Comment:1
The manuscript is incomprehensible - at this point, I cannot be sure if the authors used AI to generate the text, or decided to throw random words at google translate.
Response:
We sincerely thank the reviewer for the feedback. The author declares there is no AI generated text or random words are used in our manuscript.
Reviewer 3 Report
Comments and Suggestions for Authors
This research introduces a novel drive drain model to validate the feasibility of gravity energy storage, which involves storing potential energy by elevating stack weight using solar photovoltaic input and subsequently releasing the weight to generate electrical energy using gravitational field.
1. The topic lacking clarity: at present the research addresses a very broad aim; the authors should concentrate on a more clearly defined core sub-topic to enable deeper investigation.
2. While relationships among multiple variables are proposed, the theoretical framework does not yet show a complete logic or mechanism chain; the authors are advised to include a model diagram to enhance clarity.
3. The definitions of the independent and dependent variables remain vague, and some operationalizations are not sufficiently clear; it is recommended to detail measurement indicators and variable boundaries in the methods section.
4. The selection of control variables appears inadequate: the current set may not fully eliminate potential confounders, so consider adding key controls or explaining their omission.
5. The discussion of sample representativeness and bias risks is currently insufficient: the authors should clarify how the sample was selected, and assess possible selection or non-response bias and its impact on the findings.
6. There may be endogeneity issues in the model specification—such as reverse causality, omitted variables or common‐method bias; if these risks are present, the authors should adopt instrumental variables, fixed‐effects or other robust methods to test.
7. Although some results have been presented, the robustness checks are still weak: relying on a single model reduces confidence in the conclusions; consider subsample analyses, tests with alternative variables, or sensitivity analyses across different model settings.
8. The interpretation of results tends to lean toward inferring causality from correlation: the authors should make a clear distinction between “association” and “causation” in the discussion to avoid over-inference.
9. The link between empirical findings and theory is not strong enough: the empirical results show weak connection to the initial theoretical hypotheses; the authors should deepen the theoretical linkage in the discussion and validate or adjust their mechanism.
10. The conclusion and future research outlook lack depth: currently the conclusion section focuses mainly on summary; the authors should include reflections on policy or practice implications, theoretical extension opportunities, and the study’s limitations.
Author Response
Comment:1
The topic lacking clarity: at present the research addresses a very broad aim; the authors should concentrate on a more clearly defined core sub-topic to enable deeper investigation.
Response:
We appreciate the reviewer’s observation regarding the clarity of the topic. The complete research flow added in section1 and the energy storage concepts are updated and incorporated in section 1.3.
Comment:2
While relationships among multiple variables are proposed, the theoretical framework does not yet show a complete logic or mechanism chain; the authors are advised to include a model diagram to enhance clarity.
Response:
We sincerely thank the reviewer for the clarity of the proposed system. As per the reviewer suggestion the detailed conceptual model diagram incorporated in figure 3 and figure 4 and updated the description in our revised version in section 2.3.1.
Comment:3
The definitions of the independent and dependent variables remain vague, and some operationalizations are not sufficiently clear; it is recommended to detail measurement indicators and variable boundaries in the methods section.
Response:
We appreciate the reviewer’s observation regarding the variables Know we are clearly defined the measurement indicators and variable boundaries in detail in section 2.4.5 and added in our revised version.
Comment:4
The selection of control variables appears inadequate: the current set may not fully eliminate potential confounders, so consider adding key controls or explaining their omission.
Response:
We sincerely thank the reviewer for the control variables The proposed control variable is sufficient to describing the rotation system, as per your suggestion we have updated the description in our revised version in section 2.4.5. A more complete nonlinear and electromechanical model including additional state variables will be developed in future work to extend the present baseline description.
Comment:5
The discussion of sample representativeness and bias risks is currently insufficient: the authors should clarify how the sample was selected, and assess possible selection or non-response bias and its impact on the findings.
Response:
We sincerely thank the reviewer for the impact of finding. The samples for this study were selected using a systematic approach to ensure representativeness of the operating conditions typically encountered in electromechanical energy conversion systems. Specifically, multiple measurement sets were collected under controlled no-load and loaded conditions, including LED. We have updated the findings in the revised version. It will be included in our future publication work.
Comment:6
There may be endogeneity issues in the model specification—such as reverse causality, omitted variables or common‐method bias; if these risks are present, the authors should adopt instrumental variables, fixed‐effects or other robust methods to test.
Response:
We appreciate the reviewer’s observation regarding the endogeneity model specification. The novel energy storage in terms of gravitational power of earth is proposed and the workability of system is verified with the prototype. The experiment results of gravity system for different load setup to validate the system operation. The instrumental variables and risk analysis are future part of research work and these inputs are update in our revised version section 3.2.
Comment:7
Although some results have been presented, the robustness checks are still weak: relying on a single model reduces confidence in the conclusions; consider subsample analyses, tests with alternative variables, or sensitivity analyses across different model settings.
Response:
We thank the reviewer for highlighting the importance of robustness checks. As a part of my research work single and double stack model test are concluded in this paper, the sentivity analyses for different model setting is a different part of work. It will be included in our future publication work.
Comment:8
The interpretation of results tends to lean toward inferring causality from correlation: the authors should make a clear distinction between “association” and “causation” in the discussion to avoid over-inference.
Response:
We thank the reviewer for highlighting this point. We have carefully revised the discussion to clearly distinguish between association and causation, ensuring that our interpretations are presented as correlations rather than implying causal relationships. This clarification strengthens the scientific rigor and accuracy of our conclusions. The corrections are updated in our revised version in section 4
Comment:9
The link between empirical findings and theory is not strong enough: the empirical results show weak connection to the initial theoretical hypotheses; the authors should deepen the theoretical linkage in the discussion and validate or adjust their mechanism.
Response:
We appreciate the reviewer’s suggestion regarding the connection between empirical findings and theory. The corrections are updated in our revised version in session 3.3, 3.4 and 3.5.
Since this work introduces a novel energy storage system, the primary goal was to experimentally demonstrate the feasibility and workability of the system. Nevertheless, we have now strengthened the discussion to more explicitly link our experimental results to the theoretical framework, clarifying how the observations support or refine the proposed mechanism. This enhances the conceptual grounding of our study while highlighting the practical validation of the new system. It will be incorporated in another part of research work.
Comment:10
The conclusion and future research outlook lack depth: currently the conclusion section focuses mainly on summary; the authors should include reflections on policy or practice implications, theoretical extension opportunities, and the study’s limitations.
Response:
We thank the reviewer for this insightful suggestion. As per suggestion the conclusion was updated and improved in our revised version in section 4 and 5
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors
The authors have carefully revised the manuscript according to the reviewers’ previous comments. The revised version has significantly improved in terms of clarity, structure, and technical presentation. All the major concerns raised in the initial review have been properly addressed.
I am satisfied with the current version and have no further suggestions.
Reviewer 2 Report
Comments and Suggestions for Authors
The comment was not about using AI, but about the lack of clarity in expression. At this point, I have to ignore it and comment only on the science.
Reviewer 3 Report
Comments and Suggestions for Authors
Accept
