Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study employs a combined approach of Life Cycle Assessment (LCA) and normalized cost of energy storage (LCOS) to conduct cross-dimensional comparisons of three mainstream stationary energy storage technologies: lithium-ion batteries, lead-acid batteries, and hydrogen systems. The analysis covers the entire lifecycle from raw material extraction to end-of-life recycling, with standardized comparisons across heterogeneous technologies achieved through a functional unit of "delivering 1MWh of electricity within 20 years." While the research framework complies with standards, several issues require clarification.

1. The LCA methodology focuses solely on six core indicators including Global Warming Potential (GWP) and CED, while neglecting critical factors like human toxicity and land use. Moreover, it fails to analyze environmental differences among various hydrogen storage methods (compression, liquefaction, solid-state hydrogen compounds), resulting in insufficient evaluation depth.
2. The LCOS calculations are based on the EU's 2025 average electricity price and discount rate, without considering variations in electricity prices across EU member states, dynamic pricing mechanisms, or subsidy policies. Additionally, the methodology excludes secondary utilization value of energy storage technologies (e.g., cascade utilization of retired batteries), leading to incomplete consideration of lifecycle economic efficiency.
3. Although the study clearly illustrates key results such as LCOS sensitivity and GWP decomposition through charts, the analysis of the underlying mechanism behind "cost convergence in hydrogen systems with over 12-hour energy storage duration" (e.g., fixed cost allocation effects) remains superficial, lacking concrete engineering case studies for validation.

Author Response

First, I would like to thank you for your thorough review of our paper „Comparative Technoeconomic and Environmental Assessment of Stationary Energy Storage Systems: Lithium-Ion, Lead-Acid, and Hydrogen“, (batteries-3888337) and helpful comments to improve it.

 

Reviewer 1

Comments to the Authors
This study employs a combined approach of Life Cycle Assessment (LCA) and normalized cost of energy storage (LCOS) to conduct cross-dimensional comparisons of three mainstream stationary energy storage technologies: lithium-ion batteries, lead-acid batteries, and hydrogen systems. The analysis covers the entire lifecycle from raw material extraction to end-of-life recycling, with standardized comparisons across heterogeneous technologies achieved through a functional unit of "delivering 1MWh of electricity within 20 years." While the research framework complies with standards, several issues require clarification.

 

• The LCA methodology focuses solely on six core indicators including Global Warming Potential (GWP) and CED, while neglecting critical factors like human toxicity and land use. Moreover, it fails to analyze environmental differences among various hydrogen storage methods (compression, liquefaction, solid-state hydrogen compounds), resulting in insufficient evaluation depth.
• The LCOS calculations are based on the EU's 2025 average electricity price and discount rate, without considering variations in electricity prices across EU member states, dynamic pricing mechanisms, or subsidy policies. Additionally, the methodology excludes secondary utilization value of energy storage technologies (e.g., cascade utilization of retired batteries), leading to incomplete consideration of lifecycle economic efficiency.
• Although the study clearly illustrates key results such as LCOS sensitivity and GWP decomposition through charts, the analysis of the underlying mechanism behind "cost convergence in hydrogen systems with over 12-hour energy storage duration" (e.g., fixed cost allocation effects) remains superficial, lacking concrete engineering case studies for validation.

 

 

To Reviewer 1:

            Thank you very much for your review and valuable remarks.

 

1. The LCA methodology focuses solely on six core indicators including Global Warming Potential (GWP) and CED, while neglecting critical factors like human toxicity and land use. Moreover, it fails to analyze environmental differences among various hydrogen storage methods (compression, liquefaction, solid-state hydrogen compounds), resulting in insufficient evaluation depth.

 - We thank the reviewer for this valuable observation. In the revised manuscript, we have added a dedicated paragraph in the Discussion section addressing the limitations of focusing solely on the six core LCA indicators. In this new text, we explicitly acknowledge the importance of additional impact categories such as human toxicity and land use, and we outline how their inclusion could further refine the sustainability assessment. Furthermore, we have extended the discussion to highlight the environmental differences among hydrogen storage methods (compressed gas, liquefied hydrogen, and solid-state hydrides), noting their distinct implications for efficiency, cost, and ecological footprint. Finally, we point out that future research will incorporate these broader indicators and storage options to provide an even more comprehensive assessment.

2. The LCOS calculations are based on the EU's 2025 average electricity price and discount rate, without considering variations in electricity prices across EU member states, dynamic pricing mechanisms, or subsidy policies. Additionally, the methodology excludes secondary utilization value of energy storage technologies (e.g., cascade utilization of retired batteries), leading to incomplete consideration of lifecycle economic efficiency.

- We sincerely thank the reviewer for this very constructive remark. In the revised manuscript, we have expanded the Economic Indicators (Section 5) and Discussion (Section 7) to explicitly address the limitations of using average EU-2025 electricity prices and discount rates. We now comment on the importance of regional variations across EU member states, the role of dynamic pricing mechanisms, and the influence of subsidy policies on LCOS results. In addition, we have included a discussion of the secondary utilization value of energy storage technologies, such as the cascade use of retired lithium-ion batteries from electric vehicles, noting their potential to reduce both LCOS and environmental impacts. Finally, we indicate that future work will extend the analysis with scenario-based modeling across different EU countries and policy frameworks, in order to further refine the economic and sustainability assessment.

3. Although the study clearly illustrates key results such as LCOS sensitivity and GWP decomposition through charts, the analysis of the underlying mechanism behind "cost convergence in hydrogen systems with over 12-hour energy storage duration" (e.g., fixed cost allocation effects) remains superficial, lacking concrete engineering case studies for validation.

- We thank the reviewer for this insightful comment. In the revised manuscript, we have added a dedicated paragraph at the end of Section 6 to provide a more detailed explanation of the underlying mechanism behind the observed cost convergence in hydrogen systems with storage durations exceeding 12 hours. Specifically, we elaborate on the role of fixed cost allocation (electrolyzer, fuel cell, and control systems) versus variable tank costs, and how this structural difference leads to improved LCOS performance at longer durations. We also clarify that, while concrete engineering case studies are not yet included, we have strengthened the analysis through scenario-based sensitivity modeling, which provides an intermediate validation step. Future work will extend this by incorporating real engineering case studies for empirical confirmation.

 

We sincerely thank the reviewers for their valuable remarks and comments. Their feedback has been very helpful in refining the manuscript, emphasizing its main contributions, and ensuring that the new and unique elements are clearly highlighted for the readers.

Reviewer 2 Report

Comments and Suggestions for Authors

This article provides a comprehensive comparative analysis of three stationary energy storage technologies: Li-ion batteries, lead-acid batteries, and hydrogen systems. It integrates Life Cycle Assessment and Levelized Cost of Storage to evaluate the environmental and economic performance of these technologies over a 20-year operational horizon and at various cycling number and duration scenarios. The study highlights the complementary roles of these technologies in energy storage systems and provides some summarised conclusions: 1) Lithium-ion batteries dominate in short-term applications, while hydrogen systems are better suited for long-term energy storage. 2) Policy measures, such as tariff design and decarbonization of the electricity supply chain, are critical to optimising cost and environmental impact.

It is worth emphasising the strengths, weaknesses, and significance of this study.

The strengths of the study are: 1) The study takes a holistic approach, combining both economic and environmental metrics, which gives a balanced picture beyond cost alone; 2) It clearly differentiates the role of each analysed technology: Li-ion for short/medium storage, Pb-acid for cost-sensitive backup, and hydrogen for long-term/seasonal use; 3) Practical guidance is offered for policymakers and investors, linking technical results with real-world decision-making.

The weaknesses of the study are: 1) The analysis relies on assumptions about future costs and efficiencies, especially for hydrogen, so the conclusions may shift as technology evolves; 2) Some social and supply chain impacts, e.g., mining and recycling risks of critical elements (Li, Co, Ni, Pb) in poorly regulated regions, are noted but not deeply explored; 3) Results are presented mainly in a European context, which may limit global generalisation.

The significance: In summary, the paper is valuable as a comparative benchmark for energy storage choices in the energy transition. It reinforces the dominance of Li-ion batteries today, highlights the enduring recyclability of lead-acid batteries, and frames hydrogen production by electrolysis and its "burning" in fuel cells as a long-term strategic solution despite current limitations.

Regarding the structure of the article, it is well-structured, providing detailed technical, environmental, and economic analyses. It uses robust methodologies and validated data sources, making the findings reliable and potentially valuable for policymakers, investors, and industry stakeholders. However, future research could explore dynamic tariffs, second-life applications, and hybrid storage systems to refine the conclusions further.

In my opinion, the paper would be completely eligible for publication in the journal MDPI Batteries if the authors considered the following comments to improve the quality of the presented information.

1) It would be valuable if the authors provided comments (perhaps in the introduction) about the most widely studied, commercialised, and implemented in practice on different scales redox flow batteries (eg. All-Vanadium, Zinc-Bromine) and their current place in the context of energy storage technologies, and also provided arguments why they did not include this type of batteries in their study.

2) It would be great if the full terms were introduced before their abbreviations. The current version of the article lacks explanations of these abbreviations when they appear in text for the first time: DoD (line 399), O&M (line 388), and CAPEX (in the abstract, line 21). In general, I think it would be worth expanding the table of abbreviations (on page 27) by including all abbreviations. This way, it would be convenient for the reader to use such a table without having to memorise and look up the abbreviation and its meaning when it first appears.

3) In the titles of Figures 2, 3, and 4, it should be clarified what 4 h means. Does this indicate the duration of charging or discharging (or the total duration of both processes) per day?

4) The unit of measurement for the Y axis in Figures 9, 10, 11, and 13 should be clarified. What does the square mean?

5) Figures 15 and 16 should show the name of the primary Y axis (most likely SoC) with the unit of measurement (most likely kWh), and the legend should be moved to the left, to an empty area of the graph, so as not to obscure the curves.

Author Response

First, I would like to thank you for your thorough review of our paper „Comparative Technoeconomic and Environmental Assessment of Stationary Energy Storage Systems: Lithium-Ion, Lead-Acid, and Hydrogen“, (batteries-3888337) and helpful comments to improve it.

 

Reviewer 2

Comments to the Authors
This article provides a comprehensive comparative analysis of three stationary energy storage technologies: Li-ion batteries, lead-acid batteries, and hydrogen systems. It integrates Life Cycle Assessment and Levelized Cost of Storage to evaluate the environmental and economic performance of these technologies over a 20-year operational horizon and at various cycling number and duration scenarios. The study highlights the complementary roles of these technologies in energy storage systems and provides some summarised conclusions: 1) Lithium-ion batteries dominate in short-term applications, while hydrogen systems are better suited for long-term energy storage. 2) Policy measures, such as tariff design and decarbonization of the electricity supply chain, are critical to optimising cost and environmental impact.

 

It is worth emphasising the strengths, weaknesses, and significance of this study.

 

The strengths of the study are: 1) The study takes a holistic approach, combining both economic and environmental metrics, which gives a balanced picture beyond cost alone; 2) It clearly differentiates the role of each analysed technology: Li-ion for short/medium storage, Pb-acid for cost-sensitive backup, and hydrogen for long-term/seasonal use; 3) Practical guidance is offered for policymakers and investors, linking technical results with real-world decision-making.

 

The weaknesses of the study are: 1) The analysis relies on assumptions about future costs and efficiencies, especially for hydrogen, so the conclusions may shift as technology evolves; 2) Some social and supply chain impacts, e.g., mining and recycling risks of critical elements (Li, Co, Ni, Pb) in poorly regulated regions, are noted but not deeply explored; 3) Results are presented mainly in a European context, which may limit global generalisation.

 

The significance: In summary, the paper is valuable as a comparative benchmark for energy storage choices in the energy transition. It reinforces the dominance of Li-ion batteries today, highlights the enduring recyclability of lead-acid batteries, and frames hydrogen production by electrolysis and its "burning" in fuel cells as a long-term strategic solution despite current limitations.

 

Regarding the structure of the article, it is well-structured, providing detailed technical, environmental, and economic analyses. It uses robust methodologies and validated data sources, making the findings reliable and potentially valuable for policymakers, investors, and industry stakeholders. However, future research could explore dynamic tariffs, second-life applications, and hybrid storage systems to refine the conclusions further.

 

In my opinion, the paper would be completely eligible for publication in the journal MDPI Batteries if the authors considered the following comments to improve the quality of the presented information.

 

1) It would be valuable if the authors provided comments (perhaps in the introduction) about the most widely studied, commercialised, and implemented in practice on different scales redox flow batteries (eg. All-Vanadium, Zinc-Bromine) and their current place in the context of energy storage technologies, and also provided arguments why they did not include this type of batteries in their study.

 

2) It would be great if the full terms were introduced before their abbreviations. The current version of the article lacks explanations of these abbreviations when they appear in text for the first time: DoD (line 399), O&M (line 388), and CAPEX (in the abstract, line 21). In general, I think it would be worth expanding the table of abbreviations (on page 27) by including all abbreviations. This way, it would be convenient for the reader to use such a table without having to memorise and look up the abbreviation and its meaning when it first appears.

 

3) In the titles of Figures 2, 3, and 4, it should be clarified what 4 h means. Does this indicate the duration of charging or discharging (or the total duration of both processes) per day?

 

4) The unit of measurement for the Y axis in Figures 9, 10, 11, and 13 should be clarified. What does the square mean?

 

5) Figures 15 and 16 should show the name of the primary Y axis (most likely SoC) with the unit of measurement (most likely kWh), and the legend should be moved to the left, to an empty area of the graph, so as not to obscure the curves.

 

 

 

To Reviewer 2:

            Thank you very much for your review and valuable remarks.

 

1. It would be valuable if the authors provided comments (perhaps in the introduction) about the most widely studied, commercialised, and implemented in practice on different scales redox flow batteries (eg. All-Vanadium, Zinc-Bromine) and their current place in the context of energy storage technologies, and also provided arguments why they did not include this type of batteries in their study.?

- We thank the reviewer for this constructive suggestion. In the revised manuscript, we have added a new paragraph in the Introduction and further comments in the Discussion section regarding redox flow batteries (e.g., all-vanadium and zinc-bromine systems). We briefly outline their current level of commercialization, main advantages (e.g., high cyclic stability, modularity, and safety), and limitations (e.g., limited large-scale deployment in Europe by 2025 and high variability in industrial configurations). We also clarify the rationale for not including them in the present comparison, emphasizing that their exclusion is due to the lack of consolidated LCOS and LCA data rather than their technological irrelevance. Finally, we note that future extensions of this study will incorporate redox flow batteries once more homogeneous and comprehensive datasets become available, in order to provide an even broader and more robust comparison.

2. It would be great if the full terms were introduced before their abbreviations. The current version of the article lacks explanations of these abbreviations when they appear in text for the first time: DoD (line 399), O&M (line 388), and CAPEX (in the abstract, line 21). In general, I think it would be worth expanding the table of abbreviations (on page 27) by including all abbreviations. This way, it would be convenient for the reader to use such a table without having to memorise and look up the abbreviation and its meaning when it first appears.

- We thank the reviewer for this helpful remark. In the revised manuscript, we have introduced the full terms before their abbreviations at the first occurrence (e.g., Depth of Discharge (DoD), Operation and Maintenance (O&M), Capital Expenditures (CAPEX)). In addition, the table of abbreviations at the end of the manuscript has been expanded to include all acronyms used, making it more convenient for the reader to follow the text without having to look them up separately.

3. In the titles of Figures 2, 3, and 4, it should be clarified what 4 h means. Does this indicate the duration of charging or discharging (or the total duration of both processes) per day?

- We thank the reviewer for pointing out this ambiguity. In the revised manuscript, we have corrected the titles of Figures 2, 3, and 4 and edited the corresponding figure descriptions in the text to clarify the meaning of 4 h. It now clearly states that this value refers to the daily discharge duration assumed in the scenarios, with charging adjusted accordingly. These revisions improve the clarity and consistency of the results presentation.

4. 4. The unit of measurement for the Y axis in Figures 9, 10, 11, and 13 should be clarified. What does the square mean?

- We appreciate the reviewer’s careful observation. In the revised manuscript, the Y-axis units in Figures 9, 10, 11, and 13 have been corrected to display the proper dimensions, and the use of the squared term has been clarified. The captions were also revised accordingly to ensure consistency and avoid ambiguity.

5. 5. Figures 15 and 16 should show the name of the primary Y axis (most likely SoC) with the unit of measurement (most likely kWh), and the legend should be moved to the left, to an empty area of the graph, so as not to obscure the curves.

- We thank the reviewer for this helpful suggestion. In the revised manuscript, new versions of Figures 15 and 16 have been generated and replaced. The primary Y-axis is now clearly labeled as State of Charge (SoC) [kWh], and the legends have been repositioned to the left in empty areas of the graphs to ensure that the curves are not obscured. These improvements enhance the readability and clarity of the figures.

 

 

 

 We sincerely thank the reviewer for the constructive feedback. The comments and suggestions were very helpful in improving the clarity, accuracy, and overall quality of the manuscript.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

all questions are well responsed.