Optimization Configuration of Electric–Hydrogen Hybrid Energy Storage System Considering Power Grid Voltage Stability

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper focuses on the economic and stable operation of the IES, aiming to minimize the configuration costs of hybrid energy storage systems, system voltage deviations, and net load fluctuations. The paper is generally well-written and technically sound, but I have few comments that could improve the quality of the paper:

1) What are the specific advantages of the proposed optimisation method compared to existing approaches? As the scenario under study is not novel, a comparison with at least one representative baseline method should be included to highlight the contributions.

2) To support the optimisation study, mathematical models, Eqs (7) and (8), for the electrolyzer, hydrogen tank, and fuel cell, including power–hydrogen conversion, mass balance, and system power flow, should be provided.

Author Response

Dear Reviewer,

Thank you very much for your time and effort in reviewing our manuscript.
We have carefully addressed all the comments and suggestions, and detailed point-by-point responses are provided in the attached PDF file.

We sincerely hope that our revisions meet your expectations and would greatly appreciate your further consideration.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper addresses a critical challenge in renewable energy integration—voltage stability and load fluctuations—by proposing a hybrid electric-hydrogen energy storage system (ESS). This aligns well with global efforts to decarbonize energy systems and enhance grid flexibility.

However, I have some comments for the authors:

1. The paper does not detail the scalability or energy density limitations of hydrogen storage (e.g., tank size, pressure requirements). Addressing these would strengthen the feasibility discussion.
2. While the complementary roles between BESS-HESS are highlighted, the control strategy for seamless switching between BESS (fast response) and HESS (long-term storage) is not elaborated. A flowchart or pseudocode could clarify this.
3. Equation 10 lacks granularity. A table comparing capital and operational costs of BESS vs. HESS would help readers assess cost trade-offs.
4. Hydrogen equipment (e.g., electrolyzers, fuel cells) typically has shorter lifespans than batteries. The replacement cost (Equation 12) should explicitly account for this.
5. Sensitivity analysis (e.g., varying renewable penetration rates or load profiles) would demonstrate robustness under different grid conditions.
6. While MOAHA is described as effective, a brief comparison with other multi-objective algorithms (e.g., NSGA-II, MOPSO) in terms of convergence speed or solution quality would bolster the methodological choice.
7. Regarding to Real-World Applicability:

• Safety and Regulations: Hydrogen storage poses safety challenges (e.g., leakage, flammability). A discussion on safety protocols or regulatory constraints would enhance practical relevance.
• Geographic Scalability: The case study focuses on a specific test system. Generalizing findings to larger or rural grids would broaden impact.

 

 

Author Response

Dear Reviewer,

Thank you very much for your time and effort in reviewing our manuscript.
We have carefully addressed all the comments and suggestions, and detailed point-by-point responses are provided in the attached PDF file.

We sincerely hope that our revisions meet your expectations and would greatly appreciate your further consideration.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The topic is of high interest to current research in the area of electricity-hydrogen system. However, i would suggest some improvements in the manuscript.

1. The abstract covers many technical terms (e.g., “Multi-Objective Artificial Hummingbird Algorithm”) without briefly explaining their significance. Could the authors add a sentence clarifying why this algorithm is chosen over more common ones like NSGA-II or MOEA/D?
2. While the introduction covers recent literature well, the research gap is implied rather than explicitly stated. Could the authors more clearly state what specific problem in the literature they are addressing (e.g., voltage stability not being integrated into hybrid ESS planning)?
3. The introduction could benefit from a clearer link to real-world applications, challenges and strategies. For example, are there regions or systems where this model could be applied directly? It is recommended to take a look at (https://doi.org/10.1016/j.ijhydene.2025.03.112) to get relevant ideas.
4. The model assumes specific component efficiencies and fixed behavior profiles. How sensitive are the outcomes to variations in these parameters (e.g. hydrogen tank efficiency, electrolyzer conversion efficiency)?
5. The model structure for load demand and renewable variability seems deterministic. Have the authors considered stochastic modeling to reflect uncertainty in PV and wind output? Please mention it in the manuscript if considered in present Or future work.
6. Equations for CHP, BESS, and HESS models are thorough, but the notation is difficult. A table summarizing all variables and units used would greatly help readability.
7. Three objective functions are introduced: cost, voltage deviation, and net load fluctuation. Could the authors elaborate on why these three were chosen and how they balance economic vs. technical performance?
8. The paper includes bounds on voltage and power capacities, but it’s unclear if these are industry-standard or arbitrarily chosen. Are these constraints based on a national grid code or test system specification?
9. While MOAHA is novel, the paper would benefit from a brief comparison with more traditional metaheuristics (e.g., PSO, GA, NSGA-II). Why is MOAHA superior for this problem? If it is in the scope of future exploration, authors can simply answer what they would expect in comparative analysis.
10. What metrics are used to determine convergence of the algorithm, and how is the solution robustness verified across multiple runs?
11. Only two scenarios are tested (with/without hybrid ESS). Could more granular comparisons e.g., BESS only vs. HESS only vs. hybrid , provide insight into the complementary nature of the storage types? Is it under future scope of your work?
12. The results are promising, but validation is limited to simulation. Is there a benchmark or real data validation (e.g., historical voltage profiles) that could support these findings?
13. The results depend on specific configurations of storage sizes and locations. Have the authors performed sensitivity analysis on cost weights, load variability, or initial conditions to test robustness?
14. The conclusion claims "superiority in practical engineering applications." This may be overstated given that the study is simulation-based and lacks field data validation.
15. it is noted that Node 1 does not show any voltage improvement after integrating the hybrid ESS, while all other nodes do. The paper does not explain this exception. Since Node 1 is typically the slack bus in the IEEE-33 system, could the authors briefly clarify why this node behaves differently and why it's excluded from improvement trends?
16. In Equation (12), the replacement cost formula includes both a discount rate `r` and a cost reduction rate `θ`, but their values are never mentioned in the case study or assumptions. Since these two parameters can significantly influence the long-term cost analysis, it would be helpful if the authors specify the values used and justify them.
17. In Equation (6), the SOC update equations assume perfect tracking of the charging/discharging power without accounting for degradation or thermal limits of the battery. In practice, SOC dynamics are also affected by aging and temperature. Could the authors comment on how such practical aspects might influence the model or be incorporated in future work?

Author Response

Dear Reviewer,

Thank you very much for your time and effort in reviewing our manuscript.
We have carefully addressed all the comments and suggestions, and detailed point-by-point responses are provided in the attached PDF file.

We sincerely hope that our revisions meet your expectations and would greatly appreciate your further consideration.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

My comments have been addressed. I have no additional comments.

Reviewer 2 Report

Comments and Suggestions for Authors

no comments

Reviewer 3 Report

Comments and Suggestions for Authors

Authors have addressed all the comments satisfactorily. I have no further comments.