The Limits of the Current Consensus Regarding the Carbon Footprint of Photovoltaic Modules Manufactured in China: A Review and Case Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article reviews the LCA of modules manufactured in China with a case study based on the Ecoinvent 3.7 database. During the article, the author raises several differences in the studies developed according to the LCA methodology for photovoltaic modules and suggests increasing the standardization and reliability of the assessments.

 

The topic of LCA methodology for photovoltaic modules, particularly in the context of modules manufactured in China, is not only relevant but also crucial for the development of the field. The criticisms made in the article are pertinent and contribute to the ongoing discourse. However, it is important to note the challenges in gathering information for the databases, as this underscores the complexity and necessity of LCA studies in understanding the environmental performance of PV and comparing their carbon footprint. 

 

Some specific topics for review are:

- The methodology could mention the parameters for selecting the LCAs.  

- Tables could be previously discussed in the text, facilitating their understanding and describing the results. 

- Some phases of LCA can be explained more clearly as they are the crux of the results. For example, in lines 46 and 47, the explanation about the conversion to environmental impact data could be better structured. 

- It is essential to provide more theoretical grounding in the text. This can be achieved by incorporating citations during the introduction and paragraphs on the Current landscape and Allocation models. This will not only enhance the academic rigor of the article but also provide readers with a deeper understanding of the theoretical underpinnings of the LCA methodology for photovoltaic modules. 

- The lack of citations continues throughout the discussion as well.

- Please avoid acronyms as keywords

 

- Provide a list of acronyms used in the paper.

 

Author Response

Comment 1: The methodology could mention the parameters for selecting the LCAs.
Response 1: Thank you for pointing it out. I agree. Therefore, I have explained the criteria I used to select the documents (lines 82-86). 

Comment 2: Tables could be previously discussed in the text, facilitating their understanding and describing the results.
Response 2: Thank you for pointing it out. Agreed. Therefore, I added references to the content of the tables within the text.  (lines 173-174)

Comment 3: Some phases of LCA can be explained more clearly as they are the crux of the results. For example, in lines 46 and 47, the explanation about the conversion to environmental impact data could be better structured. 
Response 3: Thank you for pointing it out. Agreed. I have tried to explain better how the impact categories work and how they are estimated (lines 61-64, 66-69). 

Comment 4: It is essential to provide more theoretical grounding in the text. This can be achieved by incorporating citations during the introduction and paragraphs on the Current landscape and Allocation models. This will not only enhance the academic rigor of the article but also provide readers with a deeper understanding of the theoretical underpinnings of the LCA methodology for photovoltaic modules. 
Response 4: Thank you for pointing it out. Agreed. Therefore, I added 9 citations in the Introduction chapter (1-9), 29 citations in Current landscape (29 cross references) and 5 citations in Allocation models chapter (83-87). 

Comment 5: The lack of citations continues throughout the discussion as well. 
Response 5: Thank you for pointing it out. Agreed. Therefore, I added 2 citations. 

Comment 6: Please avoid acronyms as keywords
Response 6: Thank you for pointing it out. Agreed.

Comment 7: Provide a list of acronyms used in the paper.
Response 7: Thank you for pointing it out. Agreed (lines 22-35).

I have also included the revisions requested by the other reviewers. 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

In the manuscript “The limits of the current consensus regarding the carbon footprint of photovoltaic modules manufactured in China: a review and case study”, the authors review the state of current literature and highlights the difficulties in estimating the carbon footprint of photovoltaic modules manufactured in China. The review emphasizes the inherent limitations of Process-Based Life Cycle Assessment, including data collection challenges, dynamic environmental changes, and subjective methodological choices. The study underscores the need for improved transparency, standardization, and reproducibility in Life Cycle Assessments to provide more accurate and reliable environmental impact evaluations. I recommend publication of this manuscript; however the current version needed to be modified for further consideration. My comments are listed here:

1. The research targets aren’t clear, compared with similar literatures. Please clarify the main goals for better understanding.

2. Figure 1 is hazy, please modify.

3. I recommend providing more recent work focusing on development and application of low-carbon materials and composites.

4. I recommend adding the following reference to enhance your Introduction:

https://link.springer.com/article/10.1007/s10924-022-02631-x

5. Add a conclusive section, may be merged with the last section.

6. Better to rewrite the Introduction as one paragraph, not separate phrases as you present.

Author Response

Comment 1: The research targets aren’t clear, compared with similar literatures. Please clarify the main goals for better understanding.
Response 1: Thank you for pointing it out. I agree. Therefore, I have clarified the main goal of the review (lines 99-102). 

Comment 2: Figure 1 is hazy, please modify.
Comment 2. Thank you for pointing it out. I modified the image and the caption (Figure 1). 

Comment 3: I recommend providing more recent work focusing on development and application of low-carbon materials and composites.
Response 3: Thank you for pointing it out. I cannot find a section where I can introduce this topic. The use of low-carbon materials is undoubtedly a promising avenue for the photovoltaic industry, but I think this topic is beyond the scope of this review.

Comment 4: I recommend adding the following reference to enhance your Introduction: https://link.springer.com/article/10.1007/s10924-022-02631-x
Response 4: Thank you for the suggestion. See response 3

Comment 5: Add a conclusive section, may be merged with the last section.
Response 5: Thank you for pointing it out. I added a short concluding paragraph (lines 418-428) and merged it with the concluding chapter (future directions).

Comment 6: Better to rewrite the Introduction as one paragraph, not separate phrases as you present.
Response 6: Thank you for pointing it out. However, this request conflicts with those of the other reviewers, who ask me to strengthen the introduction. It is difficult to encapsulate the complexity of the topic in a single paragraph.

I have also included the revisions requested by the other reviewers. 

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

The article presents relevant points about the current limitations in assessing the carbon footprint of PV modules made in China but falls short in various critical aspects.  Major revisions are needed before reconsideration can be advised, focusing particularly on clarifying the introduction, enhancing transparency through detailed referencing, and improving the overall readability and coherence of the text.

Major Comments:

1. Lack of Clear Introduction to the Topic:

   - The introduction fails to adequately present the main theme and aim of the review. While the transition to low-carbon energy and the significance of solar energy is mentioned, there is no specific focus on why China's PV modules are the chosen model for this study. 

2. Insufficient Referencing:

   - The introduction and several other sections lack adequate references to support assertions made. For instance, lines 114-115 which state, “As a consequence of the sum of all these factors, overall the literature landscape appears chaotic, opaque and potentially misleading,” lack supporting citations.

3. Figures and Tables:

   - The article includes figures and several tables, but proper references to data sources are missing. It's crucial to attribute the sourced information correctly to enhance credibility. For instance, Figure 1 lacks a citation, making it unclear where the data originated. Also there are no mentions regarding tables and figures in the text.

4. Clarity Issues:

   - Certain sections of the text are difficult to read and understand. The flow and clarity need significant improvement. For example, in lines 191-193, the text is overly generalized with no specific information or context provided.

5. Inherent Contradictions:

   - Text discusses 5N and 9N silicon, Table 3 discusses 4N and 5N silicon, but the reference to this table in the main text is missing.

6. Misleading Statements:

   - The statement in lines 114-115 about the literature landscape being "chaotic, opaque and potentially misleading" is too vague and unsupported by evidence. The author needs to reshape this statement to be more objective and include supportive data or references.

7. Scope for Short Communication:

   - Given the current state of the article, it may be better suited for a conference proceeding or a short communication due to its narrow focus and current lack of depth and breadth expected from a full review article.

Comments on the Quality of English Language

Moderate editing of English language required

Author Response

Comment 1: Lack of Clear Introduction to the Topic: The introduction fails to adequately present the main theme and aim of the review. While the transition to low-carbon energy and the significance of solar energy is mentioned, there is no specific focus on why China's PV modules are the chosen model for this study. 
Response 1: Thank you for pointing it out. I specified why I chose to analyse the life cycle of PV modules made in China. (lines 99-102)

Comment 2: Insufficient Referencing: The introduction and several other sections lack adequate references to support assertions made. For instance, lines 114-115 which state, “As a consequence of the sum of all these factors, overall the literature landscape appears chaotic, opaque and potentially misleading,” lack supporting citations.
Response 2: Thank you for pointing it out. If necessary, I am open to removing the sentence. But I would like to understand why. Estimates of the carbon footprint in the literature range from 400 to 3000 kgCO2/kWp. Each study adopts different boundaries. Fan et al. 2021 analyse the process flow from quartzite mining to wafer production (excluding cell production and module assembly). Jia et al. 2023 only include electrical energy inputs and do not include heat/steam. The UNECE report analyses polycrystalline modules, even though they have accounted for around 5% of the global photovoltaic market for years. The studies included as sources in the AR6 even analyse modules based on biotechnology or made with Upgraded Metallurgical Grade Silicon cells. The IEA report (IEA 2022) publishes a graph in which the carbon footprint of modules made in China is estimated at around 300 kgCO2. However, on the next page, the report's authors point out that once glass and aluminium are included, the carbon footprint can double or even triple. The sources most cited in the public debate do not make explicit either the methodological choices or the inventories, while the industrial sources on which the inventories are based are confidential. Material emission factors are usually not explicitly stated. Is this not a ‘chaotic, opaque and potentially misleading’ landscape?

Comment 3: Figures and Tables: The article includes figures and several tables, but proper references to data sources are missing. It's crucial to attribute the sourced information correctly to enhance credibility. For instance, Figure 1 lacks a citation, making it unclear where the data originated. Also there are no mentions regarding tables and figures in the text.
Response 3: Thank you for pointing it out. I agree. I added a reference or explanation of the content of each image and table in the text. 

Comment 4: Clarity Issues: Certain sections of the text are difficult to read and understand. The flow and clarity need significant improvement. For example, in lines 191-193, the text is overly generalized with no specific information or context provided.
Response 4: Thank you for pointing it out. I have added context to clarify that assertion. (lines 221-224)

Comment 5: Inherent Contradictions: Text discusses 5N and 9N silicon, Table 3 discusses 4N and 5N silicon, but the reference to this table in the main text is missing.
Response 5: Thank you for pointing it out. I reworked the table and tried to improve the clarity of the text. (lines 199-200)

Comment 6: Misleading Statements: The statement in lines 114-115 about the literature landscape being "chaotic, opaque and potentially misleading" is too vague and unsupported by evidence. The author needs to reshape this statement to be more objective and include supportive data or references.
Response 6: Thank you for pointing it out. See Reponse 2. 

Comment 7: Scope for Short Communication: Given the current state of the article, it may be better suited for a conference proceeding or a short communication due to its narrow focus and current lack of depth and breadth expected from a full review article
Response 7: Thank you for pointing it out. I disagree. I think the most appropriate format is a review. See Hsu et al. 2012 https://doi.org/10.1111/j.1530-9290.2011.00439.x, Nugent and Sovacool 2014 https://doi.org/10.1016/j.enpol.2013.10.048 and Louwen et al. 2016 https://doi.org/10.1038/ncomms13728

I have also included the revisions requested by the other reviewers. 

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Author, thank you for reviewing the paper. While some improvements have been made, it's crucial to emphasize that intensive optimization is still of paramount importance. The conclusions need to be thoroughly reconsidered and reshaped, as simply adding an introductory paragraph does not sufficiently address the overall structure and content needed to enhance the paper's clarity and impact.

Additionally, there are still some objections related to the current review format. Although I have no issues with the review itself, relying solely on examples from articles dated 2012-2016 is not ideal. For instance, articles by Hsu et al. (2012), Nugent and Sovacool (2014), and Louwen et al. (2016) are somewhat outdated for a field that's rapidly evolving.

If you intend to focus your research on China, it's essential to incorporate more specific and recent references relevant to that region to better align with the current advancements in life cycle assessment (LCA) and photovoltaic (PV) technologies. In particular, the research landscape has shifted considerably in recent years. According to Scopus data, there were 285 articles published using "LCA" and "PV" as keywords in the abstract from 2010-2020, and this number increased to 301 articles in the span of just 2021-2024. This indicates rapid development and an influx of new insights that should be reflected in your references.

Comments on the Quality of English Language

Minor revision is needed

Author Response

Comment: Dear Author, thank you for reviewing the paper. While some improvements have been made, it's crucial to emphasize that intensive optimization is still of paramount importance. The conclusions need to be thoroughly reconsidered and reshaped, as simply adding an introductory paragraph does not sufficiently address the overall structure and content needed to enhance the paper's clarity and impact.

Additionally, there are still some objections related to the current review format. Although I have no issues with the review itself, relying solely on examples from articles dated 2012-2016 is not ideal. For instance, articles by Hsu et al. (2012), Nugent and Sovacool (2014), and Louwen et al. (2016) are somewhat outdated for a field that's rapidly evolving.

If you intend to focus your research on China, it's essential to incorporate more specific and recent references relevant to that region to better align with the current advancements in life cycle assessment (LCA) and photovoltaic (PV) technologies. In particular, the research landscape has shifted considerably in recent years. According to Scopus data, there were 285 articles published using "LCA" and "PV" as keywords in the abstract from 2010-2020, and this number increased to 301 articles in the span of just 2021-2024. This indicates rapid development and an influx of new insights that should be reflected in your references.

Response: Thank you for the food for thought, but I don't quite understand what you are asking for. I mentioned Hsu et al. 2012, Nugent and Sovacool 2014 and Louwen et al. 2016 to point out that review is the most common format for this kind of comparative analysis. 

However, I do not use these three publications as sources (see Table 1). In contrast, the IPCC uses these three publications as primary sources in AR5 (Hsu et al. 2012) and AR6 (Nugent and Sovacool 2014 and Louwen et al. 2016). 

In my review, the sources analysed are recent (2021-2023) and aim to reflect the current variability in the scientific, institutional and commercial literature. Indeed, although the number of LCAs is increasing, the primary sources remain the same. If you know of a study that uses primary sources other than those I have cited, please point it out.

I would need more precise requests for the introduction. I do not understand what could be improved. Please look at the introductory chapters of the reviews I cited above. I seem to have introduced the topic in much more depth than is usually done. However, if you explain what I need to add or change, I will enrich it further.

Also concerning the conclusions, I would need more precise indications.

Round 3

Reviewer 3 Report

Comments and Suggestions for Authors

The revisions made by the author are quite robust, and the article can be accepted in its current form.

Comments on the Quality of English Language

Minor editing of English language is required.