Economic and Social Benefits of Aquavoltaics: A Case Study from Jiangsu, China

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Mrs. Wang, dear authors, 

 

Thank you for your work and contribution to the application of PV systems in China. I chose your paper to review because I am interested in how China is deploying RE systems. 

 

But I have some general remarks about your article: 

 

1.) The power and efficiency of a PV system depends primarily on the location, or solar irradiance - not on the applicaion. This should be clear from the beginning. Then there may be limitations due to agrivoltaics and aquavoltaics, shading, orientation, or other influences. Keep this in mind when conducting your study.

 

2.) You talk about "symbiotic" effects between PV and aquaculture. What is the mechanism behind this? This question remains unanswered. Or is it just land use? Perhaps the temperature coefficient of PV? 

 

3.) You have analyzed a lot of data. But please make sure it is properly cited, there are some things missing and the sources are not always clear. If you use formulas, make sure they are spelled correctly. You also need to respect the sources when you calculate something. 

 

4.) All your work is rather "descriptive", i.e. you present the data and the analysis. But I am missing the interpretation and derivation of findings. Example: I would expect the CAPEX of aquavoltaics to be higher compared to land-based systems. Why? the systems need to be "waterproof" and corrosion resistant. This requires more investment in electrical installation and better materials. Am I right or not? Can your data support this? 

 

Finally, questions such as the efficiency compared to agrivoltaics and land-based systems remain unanswered. What is the OPEX? How often do modules need to be replaced? What are the reasons? What about power reliability? Short-circuits? Failures? Fire hazard? What happens, if there are heavy weathers like floods, storms...? 

 

I hope you can improve your paper, your data is worth publishing. Please also see my comments in the document. 

 

Good luck and best regards! 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

 

Please take care the correct tenses, should be mostly present. 

Author Response

Response to Reviewer 1 Comments

 

Thank you very much for providing detailed and valuable suggestions for our article.

 

Firstly, we have made revisions based on your annotations. Among all 62 annotations, the last 60 are specific annotations to the article. We have made individual revisions to these 60 annotations (highlighted with a yellow background), as follows:

 

1 Introduction

（1）We have made revisions based on your feedback. Please refer to line 32 of the article.

（2）Generally, agrivoltaics refers to crop cultivation under photovoltaic panels, while aquavoltaics refers to aquaculture under photovoltaic panels. So, the two modes are similar.

（3）We agree with your viewpoint.

（4）We have made revisions based on your feedback. Please refer to line 71 of the article.

2 Literature review

（5）We have made revisions based on your feedback. Please refer to line 82 of the article.

（6）This is a type of aquavoltaics. But in China, more aquavoltaic systems are designed by installing photovoltaic panels above the water surface.

（7）We have made revisions based on your feedback. Please refer to lines 124-128 of the article.

（8）Using the same piece of land only represents coexistence, while symbiosis goes further, implying mutual influence and synergistic effects between the coexisting parties. This concept originated from the research of other scholars. Please refer to the first line of the second paragraph of Elamri’s article. (Elamri, Y.; Cheviron, B.; Lopez, J.-M.; Dejean, C.; Belaud, G. Water budget and crop modelling for agrivoltaic systems: 557 Application to irrigated lettuces. Agricultural Water Management 2018, 208, 440-453.)

3 Development status of aquavoltaics in China

3.1

（9）We have made revisions based on your feedback. Please refer to line 173 of the article.

（10）In China, major events related to national economy and people's livelihood, such as the development of the new energy industry, will formulate five-year plans. The period from 2016 to 2020 is the 13th Five Year Plan period, and the period from 2021 to 2025 is the 14th Five Year Plan period. Generally, industrial development will be more rapid in the early to mid stages of the five-year plan.

3.2

3.2.1

（11）We have made revisions based on your feedback. Please refer to line 190 of the article.

（12）We have made revisions based on your feedback. Please refer to line 195 of the article.

（13）We have made revisions based on your feedback. Please refer to line 198 of the article.

（14）Due to the fact that only one or a few provinces in China initially developed aquavoltaics, the CR_n basically shows a gradually decreasing trend.

（15）We have collected data on the newly added installed capacity of aquavoltaic power stations in various provinces of China from 2011 to 2023, and compiled the cumulative installed capacity data for each province each year during this period. Based on cumulative installed capacity data (S_i), we calculated the CR_n.

（16）The data in the table can tell us the clustering situation and clustering areas of China's aquavoltaics.

（17）These are two provinces in China.

（18）Thank you very much. We have made the corresponding revisions.

3.2.2

（19）We have made revisions based on your feedback. Please refer to line 232 of the article.

4 Materials and methods

4.1

（20）Nanjing is the location of the case project in this article, so a brief introduction has been provided. As for latitude and longitude data, as they are important factors affecting solar radiation, we also need to introduce them here.

（21）The development of fishery photovoltaic complementary projects relies on fishery resources, and the abundance of fishery resources largely depends on the number and area of rivers.

4.3

（22）We have made revisions based on your feedback. Please refer to Figure 2 (line 281) of the article.

4.3.1

（23）We are very sorry, we didn't understand what you meant.

（24）We have made revisions based on your feedback. Please refer to lines 300-301 of the article.

4.3.2

（25）We are very sorry, we didn't understand what you meant.

4.3.3

（26）We are very sorry, we didn't understand what you meant.

（27）We have made revisions based on your feedback. Please refer to line 318 of the article.

5 Results and Discussion

5.1

（28）We have made revisions based on your feedback. Please refer to Figure 2 (line 281) of the article.

（29）Thank you, we have made the revision. Please refer to the sections marked with yellow background in Table 4.

（30）Thank you for your suggestion. We have also considered this issue, but it is very difficult to choose a reasonable exchange rate as the investment is carried out in stages.

（31）We have made revisions based on your feedback. Please refer to Figure 4 (line 345) of the article.

（32）Thank you, we completely agree with your point of view.

（33）We have made revisions based on your feedback. Please refer to the sections marked with yellow background in Table 5.

5.2

（34）Thank you, we have made the revision. Please refer to line 352 of the article.

（35）This table is necessary. Because the cash flow values vary from year to year.

（36）Yes, this is CAPEX.

（37）No, it is the part of the OPEX that needs to be prepaid in advance.

（38）Yes, the main reasons for the attenuation of photovoltaic power generation include temperature effects, lighting conditions, transistor aging, initial photo induced attenuation, and other factors such as dark current and component defects.

（39）We have made revisions based on your feedback. Please refer to line 363 of the article.

（40）We have made revisions based on your feedback. Please refer to lines 367-368 of the article.

（41）Yes, but in the field of aquavoltaic projects, this result is within a reasonable range.

（42）We have made revisions based on your feedback. Please refer to lines 370-371 of the article.

5.3

（43）We have made revisions based on your feedback. Please refer to line 376 of the article.

（44）We have made revisions based on your feedback. Please refer to line 378 of the article.

（45）We have made revisions based on your feedback. Please refer to line 380 of the article.

（46）We completely agree with your point of view, this is just a conversion.

（47）We have made revisions based on your feedback. Please refer to line 383 of the article.

（48）Based on the consumption data of each kilowatt of thermal power generation mentioned above and the total power generation of the case project, this result is calculated.

（49）We agree with your viewpoint.

（50）We have made revisions based on your feedback. Please refer to line 396 of the article.

（51）We have made revisions based on your feedback. Please refer to line 409 of the article.

6 Conclusions and suggestions

（52）This conclusion is based on the calculation results of location quotient in 3.2.2.

（53）We are so sorry, but this is presented in the form of a conclusion, which is necessary for the format of a paper.

（54）There are currently no significant obstacles affecting the smooth implementation of the project.

（55）We are very sorry. Due to the completion time of the case project being 6 years away from now, the power generation efficiency of photovoltaic modules has been improved during this period. The technological efficiency gap we mentioned here is mainly caused by technological development.

（56）Yes, we talked from "symbiosis" before. But it mainly refers to the “symbiosis” between photovoltaic power generation and fishery aquaculture. And algae can be seen here as a part of the symbiotic environment between the two.

（57）If it affects biodiversity, we believe it is not good for aquavoltaics.

（58）Thank you for your suggestion, but we believe it should be capitalized here.

（59）We agree with your viewpoint.

（60）Please see the explanation of (8).

 

Secondly, based on your overall feedback on the article, we have provided the following responses:

 

Point 1: The power and efficiency of a PV system depends primarily on the location, or solar irradiance - not on the applicaion. This should be clear from the beginning. Then there may be limitations due to agrivoltaics and aquavoltaics, shading, orientation, or other influences. Keep this in mind when conducting your study.

 

Response 1: We fully agree with the point you raised. On the one hand, the latitude and longitude of lines 266-267 in the article can reflect the radiation situation of the project location. On the other hand, in the revised article, we have added Figure 2 to show the river conditions around the project.

 

Point 2: You talk about "symbiotic" effects between PV and aquaculture. What is the mechanism behind this? This question remains unanswered. Or is it just land use? Perhaps the temperature coefficient of PV?

 

Response 2: We are so sorry about this. The “symbiosis” here is not just land use. It refers to the mutual influence and synergistic effect between photovoltaic power generation and fishery aquaculture. The temperature coefficient of PV can be considered as one of them.

 

Point 3: You have analyzed a lot of data. But please make sure it is properly cited, there are some things missing and the sources are not always clear. If you use formulas, make sure they are spelled correctly. You also need to respect the sources when you calculate something.

 

Response 3: Thank you for your suggestion. We have made corresponding revisions in sections 4.3 and 5.3.

 

Point 4: All your work is rather "descriptive", i.e. you present the data and the analysis. But I am missing the interpretation and derivation of findings. Example: I would expect the CAPEX of aquavoltaics to be higher compared to land-based systems. Why? the systems need to be "waterproof" and corrosion resistant. This requires more investment in electrical installation and better materials. Am I right or not? Can your data support this?

 

Response 4: Thank you for this suggestion. You are right. But our article mainly analyzes aquaviltaics and does not involve a comparison between aquaviltaics and land-based photovoltaics.

 

Point 5: Questions such as the efficiency compared to agrivoltaics and land-based systems remain unanswered. What is the OPEX? How often do modules need to be replaced? What are the reasons? What about power reliability? Short-circuits? Failures? Fire hazard? What happens, if there are heavy weathers like floods, storms...? 

 

Response 5: As mentioned in the previous response, this article does not involve a comparison between aquaviltaics and land-based photovoltaics. As for the OPEX, you can refer to Table 4 and Figure 4 in the revised manuscript. This article considers the attenuation of component power generation without considering its replacement. We are very sorry that we did not take these factors into consideration. Regarding this point, we have provided additional explanations on this point in lines 357-359 of the revised manuscript. Please review.

Reviewer 2 Report

Comments and Suggestions for Authors

The work studies a case of Aquavoltaics in China, the work presents a review of the state of this technology applied to fish production systems related to agrovoltaic technology.

 

The work is relevant to the topic, however it is suggested to clarify some aspects and make some changes:

 

·        All tables must increase font size

·        In the materials and methods section, justify the use of the models for the payback period, NPV and IRR and include a reference.

·        Some strategies to improve the economic efficiency of the project over time are not explored nor are detailed long term projections presented in scenarios of uncertainty or changes in energy policy.

·        The economic analysis is limited and does not include sufficient regarding possible improvements or alternative scenarios that could make the project more robust to changes in the market or technological advances.

·        Although the study mentions that the environmental impact of installing photovoltaic panels on bodies of water is low, it does not provide sufficient evidence or long term analysis on the effects on aquatic biodiversity or local ecosystems. Furthermore, the article recognizes the decrease in photosynthesis of algal organisms, but does not offer concrete solutions or proposals to mitigate this problem.

·        The environmental analysis is insufficient, since the impacts on biodiversity and the health of the aquatic ecosystem are not addressed in the necessary depth. It would be important for the study to propose mechanisms or technologies to mitigate the ecological impact.

Author Response

Point 1: All tables must increase font size.

 

Response 1: Thank you for this suggestion. The font size in all tables has been adjusted to the maximum, and continuing to adjust it will affect the aesthetics of the tables.

 

Point 2: In the materials and methods section, justify the use of the models for the payback period, NPV and IRR and include a reference.

 

Response 2: We have made revisions based on your feedback. Please refer to section 4.3 in the revised manuscript.

 

Point 3: Some strategies to improve the economic efficiency of the project over time are not explored nor are detailed long term projections presented in scenarios of uncertainty or changes in energy policy.

 

Response 3: Regarding the strategies to improve the economic efficiency of the project over time, we have covered it in the suggestion section. Please refer to the suggestions (3) and (4). Due to the uncertainty of photovoltaic subsidy policies in the long run, improving the economic benefits of aquavoltaic projects should mainly focus on fishery aquaculture and perfecting business modes. As for the detailed long-term projections presented in scenarios of uncertainty or changes in energy policy, please refer to the section on changes in feed-in tariff of Table 7 that we have added the revised manuscript.

 

Point 4: The economic analysis is limited and does not include sufficient regarding possible improvements or alternative scenarios that could make the project more robust to changes in the market or technological advances.

 

Response 4: Thank you for this suggestion. To make the project more robust to changes in the market, we have made corresponding revisions. Please refer to lines 376-384 of the revised manuscript.

 

Point 5: Although the study mentions that the environmental impact of installing photovoltaic panels on bodies of water is low, it does not provide sufficient evidence or long-term analysis on the effects on aquatic biodiversity or local ecosystems. Furthermore, the article recognizes the decrease in photosynthesis of algal organisms, but does not offer concrete solutions or proposals to mitigate this problem.

 

Response 5: Thank you for your suggestion. We are very sorry that we were unable to collect enough data for long-term analysis. So, we reflect environmental impact as a part of social benefits. Regarding the decrease in photosynthesis of algal organisms, we mentioned it in the second point of the suggestion. The main purpose is to draw everyone's attention to this issue. As for how to solve this problem, it requires long-term observation and analysis of the ecological impact of aquavoltaics, which is not the problem that this article can solve.

 

Point 6: The environmental analysis is insufficient, since the impacts on biodiversity and the health of the aquatic ecosystem are not addressed in the necessary depth. It would be important for the study to propose mechanisms or technologies to mitigate the ecological impact.

 

Response 6: Regarding this point, we mentioned in the Response 5 that we were indeed unable to collect enough data for in-depth analysis. For this issue, we have rewritten the second suggestion based on the references to make it more precise. And we have added suggestions on the installation ratio of photovoltaic panels to reduce the ecological impact of aquavoltaics. Please refer to the section highlighted with a yellow background in Suggestion (2) of the revised manuscript.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors, 

 

thank you for the revised manuscript and you explanations. There are still some minor points which I need to stress on again. Please see my comments in the text, correct it and submit. I promise I will not complain again. 

 

One last point, which I forgot last time: please do us the favor and reformulate the abstract, it is hard to read and to understand. The abstract is always the first what the readers see and it should be written in very good English. 

 

Thank you and best regards! 

 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Except from the abstract, the English is readable and OK. 

Author Response

Thank you very much for providing detailed and valuable suggestions for our article again.

 

we have made revisions based on your annotations. Among all 9 annotations, the last 8 are specific annotations to the article. We have made individual revisions to these 8 annotations (highlighted with a yellow background), as follows:

 

Abstract

（1）Thank you for the advice. We have reformulated the abstract from DeepL Write. Please refer to the abstract section in the revised manuscript.

 

3 Development status of aquavoltaics in China

3.1

（2）We have made revisions based on your feedback. Please refer to lines 179-184 of the revised manuscript.

 

4 Materials and methods

4.1

（3）We have made revisions based on your feedback. Please refer to line 273 of the revised manuscript.

4.3

4.3.1

（4）We have made revisions based on your feedback. Please refer to lines 301, 310, 319 of the revised manuscript.

（5）Thank you very much for raising this question again. We have rechecked the formula and found no issues. However, it should be noted that PP represents time here, and since C_t is the net cash flow for year t, it has both positive and negative values. Specifically, C_t is generally negative in the first year of the project because there is initial investment in that year. During the project operation phase, C is generally positive. In this way, when the project reaches a certain stage of operation, the net cash flow of all periods adds up to 0, and this time is PP.

 

5 Results and Discussion

5.1

（6）We have made revisions based on your feedback. Please refer to sections 5 and 6 of the revised manuscript.

（7）We have made revisions based on your feedback. Please refer to Table 5 of the revised manuscript.

（8）We have made revisions based on your feedback. Please refer to line 351 of the revised manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The article was reviewed and the authors included enough information to give it robustness and a basis for their methods. Due to the above, I recommend it for publication.

Author Response

Thank you very much for your recommendation.