Flexibility Value of Multimodal Hydrogen Energy Utilization in Electric–Hydrogen–Thermal Systems
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn this article, the authors presented an analysis of the Electric-Hydrogen- Thermal integrated energy systems and focused on the production, storage, and utilization of hydrogen energy. The authors have done very good research, however these articles need comprehensive improvement. Here are my suggestions
1. The title should be modified, in its present form, it does not show the core of this paper. The title must be short, simple, and precise.
2. In the introduction section line 33, Currently, the majority of this energy is derived from……. From where (fossil fuels), please complete this sentence.
3. Please use correct English words, such as line 54, solar energy, and can release both electrical and thermal energy, instead of releasing the produce or generating electrical and thermal energy.
4. The introduction section lists the methods of H2 production, please give some details of electrolyzers, AEM, PEM SOFC, etc….
5. Please also give details regarding to the H2 storage, and/or its transportation. How do we maintain a constant temperature for storage?
6. In the introduction section I did not find what are the research gap/research question this paper is going to fulfill. There are 1000s of paper on H2 production, storage, and utilization. In the last section of interdiction please describe the research question/gap.
7. All four contributions which are presented in this article are already widely presented. What is new?
8. Section 2.1. I strongly suggest authors include one of the most important electrolyzers AEM.
9. What is the efficiency of the H2 storage system?
10. Please explain Figure 2 in section 3.1 shortly, and I would suggest shortening section 3.2 Advantage, too many words and information are given. A manuscript must be to the point.
11. Section 4.1. The author said the Model of Electrolyzer, which electrolyzer? AEM, PEM, or what? Secondly how the author mentioned/reported the efficiency of the electrolyzer is between 65% to 70%... If this is true, please give the reference.
12. The same thing applies to the rest of the sections 4.1.2, 4.1.3…. Please clearly explain all these models with references. I also did not identify the references to these models in the introduction section.
13. Section 5.2, results of simulation. Instead of mentioning from m 1:00 to 6:00, and 7 to 9…… please add tables and describe the results once. Too many unnecessary details are presented.
14. Again, please remain to the point, the conclusion section is too long. The details are already presented in the above section. Please shorten the conclusion section.
15. The whole paper needs to be very carefully revised and polished, there are numerous grammatical mistakes.
Comments on the Quality of English LanguageEnglish must be improve
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe paper analyzes the flexibility of hydrogen energy systems: production of hydrogen by electrolysis of water using wind energy; hydrogen storage; the use of hydrogen to produce electricity and heat (fuel cells, gas turbine, gas boiler). The authors propose a model for optimizing the use of hydrogen by minimizing the operating costs and maximizing the integration of wind energy.
The manuscript needs to be improved, clarifications and additions are necessary.
The abstract should be concise and inform the readers of background, research question, hypothesis, methodology, the main results and conclusions of research presented. The main results obtained must be highlighted in the abstract.
The case studies (scenarios) are not clearly presented and compared.
Line 460: Please correct "Ô‘ = 0.19 Nm3(kWh, ηEH = 70%."
Lines 483, 485: Figure 3 must be renumbered.
Lines 484, 534: The unit of measure on the vertical axes is missing.
Line 592, Table 4: How were they obtained/ what is the source of the values "Consumption/kW"? It is specified in the title "Cost comparison between ..."
The conclusions should be rewritten and more focused on the results obtained and not just general discussion.
Comments on the Quality of English LanguageMinor editing of English language required.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe author’s study focuses on the efficient utilization of clean renewable energy through a multimodal hydrogen production and utilization system. An electric-hydrogen-thermal integrated energy system (EHT-IES) is proposed as a flexible energy system utilizing hydrogen energy to mitigate the variability in renewable energy supply and electricity markets. The authors present a novel process in the form of EHT-IES to achieve power system flexibility and demonstrate the framework through a detailed case study. The following comments need to be addressed before this manuscript can be accepted for publication.
1. The authors need to clarify how the economic feasibility of the system is influenced by the sizing of the system components and the associated investment cost. The proposed model does not include the system design and investment costs. Specifically, components such as the electrolyzer and fuel cells will have significant investment costs based on the system size, which will affect the economic feasibility. To make the model more robust and accurately capture the system flexibility, the sizing needs to be considered.
2. How does the model account for the power consumed and the electricity costs associated with compression of hydrogen for storage? These costs are expected to be significant considering the high pressure of hydrogen storage.
3. The model is a mixed integer linear programming model and the authors have assumed linear mechanisms of the system dynamics for all the system components. However, the various equipment such as electrolyzer, fuel cells and gas turbines have nonlinear operational dynamics. Considering linear dynamics for all equipment seems to be an oversimplification and would lead to loss of accuracy. The authors need to provide basis and good justification for the consideration of the linear dynamics and the fixed efficiencies assumed.
4. The sizes of the hydrogen production and storage system are assumed to be fixed numbers. This would likely lead to suboptimal solutions especially when diverse load and wind generation profiles are considered.
5. The authors need to comment on the safety considerations of hydrogen storage in the long-term as compared to storage using batteries. Also, battery storage systems are highly efficient and more suited for short to medium-term energy storage compared to hydrogen energy storage. Battery storage systems are also more mature and can be easily integrated with existing renewable energy systems. For the current application which requires short duration energy storage, the economies of scale might not be favorable to bring down the cost of hydrogen storage systems. Since the system requires short-term energy storage as compared to long-term seasonal storage, a battery system might be more suitable for this application. Please clarify.
6. The authors have considered one specific day-ahead profile for load and wind power output. The authors need to apply the proposed framework for a variety of load and wind power generation profiles and demonstrate the results. This will help demonstrate the model’s robustness and input sensitivity.
Minor comments
1. Page 1, line 33: the sentence is incomplete.
2. Page 1, line 41 seems a repetition of line 39. Please update.
Author Response
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Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for Authors1. In Chapter 4, there are a total of 35 equations. How to use them? In the subsequent analysis and simulation process, I cannot understand how to apply the equations. Please explain in detail.
2. What is the source of the simulation and analysis data in this study? Is it real data or virtual data? It should be explained in detail.
3. Please give an example of how the statistics in Figure 3-10 are calculated and simulated.
4. There are two Figure 3 in this article, please correct them.
5. The reference format is inconsistent. Please correct it according to the format specified by the journal.
6. What is the unit of the Y-axis in Figure 3? And in Figure 5. The unit of the Y-axis is not marked clearly, please correct them.
7. What is SOC in Figure 9, please provide additional explanation.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors responded to all my requests and improved the presentation of their manuscript accordingly.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have satisfactorily addressed my comments and I recommend the manuscript for publication.
Reviewer 4 Report
Comments and Suggestions for AuthorsI agree this paper can be accepted in its present form
