Combining Hydrodynamic Modelling and Solar Potential Assessment to Evaluate the Effects of FPV Systems on Mihăilești Reservoir, Romania

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Report on hydrology-3647291

Concerns the MS, it discussed the floating photovoltaic (FPV) is a new green technology raising lately, having the indisputable advantage of not covering agricultural land, but water surface of lakes or reservoirs. Being a new technology, even if the number of studies is significant, few reliable results are available. The paper presents the possible influence of a FPV farm installed on the surface of reservoir in Romania for four scenarios for the surface covered with photovoltaic panels.

In general, it discussed an important subject on combining hydrodynamics and presented interesting results, but needs some major modifications before considering for publication as follows:

-In title "Effects" must modify to "Effect".

-Abstract must modify to reflects the important of the phenomenon and the new obtained results comparing with the previous investigation.

-Keywords: hydrodynamic and water quality modelling, floating photovoltaic systems, dsnot meet the keywords format "Word" not "Phrase", it must be modify.

 -Figure 3, doesn't appear, so, it needs resolution increasing and more discussion needed.

-All tables must be cited.

-In page 4, the authors must cleat Why studied in 2002-2023 only, "The mean energy for the 2002–2023 period was 23.845".

-All symbols must put in nomenclature.

-The authors must make simulation or present overview about the results obtained.

-Figure 7. presents a Solar path for FPV system Mihăilești using Global Solar Atlas, authors can make comparison with another investigation?

-Eqs. 1-3 must be proof or cited.

-Table 3. Calibrated constants in the model, must be cited.

-Figures 11 and 12 presented the variation of total phosphorus or total Nitrogen, the authors must discussed the differences between the obtained results and the parameters due to the variation? depth physical meaning request.

-Conclusion if put in points is worth to show the impact of the new effect on the phenomenon.

-Refs. 19 and 24 must be deleted, it not agree with the scientific journals template. 

Sincerely

Comments on the Quality of English Language

Must be revised.

Author Response

Report on hydrology-3647291

The authors are grateful to the reviewers for their commitment and observations, helping us to build an improved version of the paper to be suitable for Hydrology!

Further on we respond to all inquiries of the reviewers.

 

R1

Concerns the MS, it discussed the floating photovoltaic (FPV) is a new green technology raising lately, having the indisputable advantage of not covering agricultural land, but water surface of lakes or reservoirs. Being a new technology, even if the number of studies is significant, few reliable results are available. The paper presents the possible influence of a FPV farm installed on the surface of reservoir in Romania for four scenarios for the surface covered with photovoltaic panels.

In general, it discussed an important subject on combining hydrodynamics and presented interesting results, but needs some major modifications before considering for publication as follows:

-In title "Effects" must modify to "Effect".

Thank you for your observation! Done!

-Abstract must modify to reflects the important of the phenomenon and the new obtained results comparing with the previous investigation.

Thank you for your observation! Done! Completed with method and most important results. Lines 15 to 21.

-Keywords: hydrodynamic and water quality modelling, floating photovoltaic systems, dsnot meet the keywords format "Word" not "Phrase", it must be modify.

Thank you for your observation! Done! Line 23.

-Figure 3, doesn't appear, so, it needs resolution increasing and more discussion needed.

Thank you for your observation! We increased the resolution and expanded the discussion! Lines 133 to 135.

-All tables must be cited.

Thank you for your observation! The tables are cited.

-In page 4, the authors must cleat Why studied in 2002-2023 only, "The mean energy for the 2002–2023 period was 23.845".

Thank you for your question! At the beginning of the study we had only for this period, 2002-2023, complete data!

-All symbols must put in nomenclature.

Thank you for your observation! Abbreviations and symbols are presented in a table before the References section! Line 508.

-The authors must make simulation or present overview about the results obtained.

Thank you for your observation! We will expand the discussion of the results! Lines 355 to 371, 375 to 385 and 391 to 404.

-Figure 7. presents a Solar path for FPV system Mihăilești using Global Solar Atlas, authors can make comparison with another investigation?

Thank you for your observation! We did also investigations with PVsyst  (what we achieved with PVSys is reproduced below) and we obtained the same results. For this reason, we considered not to mention it.

-Eqs. 1-3 must be proof or cited.

Thank you for your observation! We added the references! For eqs(1) see line 239 and for (2) and (3) line 274.

-Table 3. Calibrated constants in the model, must be cited.

Thank you for your observation! We added references and citing in table 3.

-Figures 11 and 12 presented the variation of total phosphorus or total Nitrogen, the authors must discussed the differences between the obtained results and the parameters due to the variation? depth physical meaning request

Thank you for your observation! We added comments related to the figures in Lines 232 to 235, 245 to 251 and 354 to 370.

-Conclusion if put in points is worth to show the impact of the new effect on the phenomenon.

Thank you for your observation! Done! The description of the impact is presented on Lines 462 to 482.

-Refs. 19 and 24 must be deleted, it not agree with the scientific journals template. 

Thank you for your observation! We adapted the references to the journal template!

Sincerely

Thank you for your observations! Hoping we answered to all your inquiries!

Reviewer 2 Report

Comments and Suggestions for Authors

The insights provided in this paper offer valuable guidance to stakeholders interested in the development and application of FPV, paving the way for their strategic implementation in the global renewable energy landscape. As technology advances, costs decrease, and strategic implementation unfolds, FPV are poised to play a transformative role in the global transition to clean energy and become attractive options for energy producers and consumers.

I suggest that authors supplement their work with responses to the following questions and comments:

1. Introduction Line 9

 What is the main research question addressed?

• Literature review/state of the art
• Research question and objective
• Main scientific contribution and novelty statement

2. Materials and methods Line 73

 Do you believe the research topic is original or relevant to the field?

• Floating solar energy on standing water

 Does the research address a specific gap in this area? Please explain why this is/is not the case.

• Existing research has mainly focused on the technical feasibility and economic viability of floating solar panel projects. Numerous studies have examined the performance of floating solar panels in different environmental conditions, and some have assessed the economic competitiveness of FPV compared to traditional land-mounted systems. However, comprehensive comparative analyses of FPV on land and in the ocean, taking into account a wider range of factors that go beyond technical and economic considerations, remain relatively unexplored. Despite promising advances in floating solar panel technology, a critical knowledge gap remains regarding the comparative advantages and challenges between land-based and ocean-based installations, which requires detailed research to inform strategic decision-making in renewable energy development. In contrast to previous studies that have primarily focused on the technical and economic aspects of FPV.

3. Results and Discussion Line 244

 What does it add to the research area compared to other published material?

• Comparison of floating solar systems on land and ocean
• Analysis of different parameters for floating solar systems
• Contribution of floating solar energy on land and ocean to sustainable development goals

4. Conclusion Line 343

 Are the conclusions of the study consistent with the main question posed? Please explain why this is/is not the case.
• Onshore PV systems offer ease of implementation, potentially lower environmental impact in freshwater environments, and water-saving benefits. However, their scalability is limited by the available water surface area. Onshore PV systems, on the other hand, have enormous potential for large-scale energy production and potential synergy with offshore wind farms. However, they face the obstacles of complex and expensive construction, limited access to maintenance, and the need for rigorous environmental impact assessments. Onshore PV systems are ideal for regions with adequate freshwater resources and the need for efficient land-use solutions that are compatible with social acceptance. Ocean PV systems are prime candidates for countries with extensive coastlines and ambitions for large-scale clean energy production.

Author Response

Report on hydrology-3647291

The authors are grateful to the reviewers for their commitment and observations, helping us to build an improved version of the paper to be suitable for Hydrology!

Further on we respond to all inquiries of the reviewers.

R2

The insights provided in this paper offer valuable guidance to stakeholders interested in the development and application of FPV, paving the way for their strategic implementation in the global renewable energy landscape. As technology advances, costs decrease, and strategic implementation unfolds, FPV are poised to play a transformative role in the global transition to clean energy and become attractive options for energy producers and consumers.

I suggest that authors supplement their work with responses to the following questions and comments:

1. Introduction Line 9

Ø What is the main research question addressed?

• Literature review/state of the art
  • Research question and objective
  • Main scientific contribution and novelty statement

Thank you for your observation! Done! We added paragraphs and the response is presented on Lines 65 to 79.

2. Materials and methods Line 73

Ø Do you believe the research topic is original or relevant to the field?

Thank you for your observation! The answer is yes, the research topic is relevant as is an emerging field of interest, PV on water surface, and in Romania there are only two small applications, and the potential is very high. As the influence of FPV panels is not very well known, we consider this study useful and relevant.

• Floating solar energy on standing water

Ø Does the research address a specific gap in this area? Please explain why this is/is not the case.

• Main scientific contribution and novelty statement

Thank you for your observation! Done! We added paragraphs and the response is presented on Lines 65 to 79.

• Existing research has mainly focused on the technical feasibility and economic viability of floating solar panel projects. Numerous studies have examined the performance of floating solar panels in different environmental conditions, and some have assessed the economic competitiveness of FPV compared to traditional land-mounted systems. However, comprehensive comparative analyses of FPV on land and in the ocean, taking into account a wider range of factors that go beyond technical and economic considerations, remain relatively unexplored. Despite promising advances in floating solar panel technology, a critical knowledge gap remains regarding the comparative advantages and challenges between land-based and ocean-based installations, which requires detailed research to inform strategic decision-making in renewable energy development. In contrast to previous studies that have primarily focused on the technical and economic aspects of FPV.

Thank you for your observation! The object of the study wasn’t a comparative analysis. Nevertheless, we underlined the advantages of FPV related to classical onshore PV. See lines 36 to 38.

3. Results and Discussion Line 244

Ø What does it add to the research area compared to other published material?

• Comparison of floating solar systems on land and ocean
  • Analysis of different parameters for floating solar systems
  • Contribution of floating solar energy on land and ocean to sustainable development goals

Thank you for your observation! Done! We mentioned this.

4. Conclusion Line 343

Ø Are the conclusions of the study consistent with the main question posed? Please explain why this is/is not the case.
• Onshore PV systems offer ease of implementation, potentially lower environmental impact in freshwater environments, and water-saving benefits. However, their scalability is limited by the available water surface area. Onshore PV systems, on the other hand, have enormous potential for large-scale energy production and potential synergy with offshore wind farms. However, they face the obstacles of complex and expensive construction, limited access to maintenance, and the need for rigorous environmental impact assessments. Onshore PV systems are ideal for regions with adequate freshwater resources and the need for efficient land-use solutions that are compatible with social acceptance. Ocean PV systems are prime candidates for countries with extensive coastlines and ambitions for large-scale clean energy production.

Thank you for your observation! It was not the subject of our study. However, the conclusions have been modified and will hopefully be much clearer.

Reviewer 3 Report

Comments and Suggestions for Authors

This paper presents a hydrodynamic model to evaluate the effects of FPV on a reservoir in Romania. Several major concerns were raised during the review of the model, which led to the reviewer's recommendation against accepting the paper. 

1) The primary objective of an energy system model is to predict the system's energy generation capacity, typically in terms of output energy or power. In the presented model, however, the calculated results are temperature, cross-sectional area, and the concentrations of TN and TP. These outputs are less relevant to the core purpose of an energy model, and it is unclear how the tabulated power density values were obtained, which causes confusions for the reviewer.

2) The model includes numerous coefficients that require collaboration before use, yet the calibration process is not disclosed. Moreover, it is unclear whether the model is designed specifically for this reservoir or if it is applicable to other reservoirs or water bodies in the region. If it is the former, the model's applicability is too narrow, limiting its value. If it is the latter, then more examples are needed to validate the model's broader utility.

3) According to the authors' description, the model's coefficients must be calibrated using data from the specific reservoir via curve fitting. This suggests that the model was essentially fitted to the data for the same reservoir it is used to predict. As a result, it is unsurprising that the numerical results align closely with the measured data. However, it remains unclear how the model would perform in predicting the power conversion capacity of FPV systems in other water bodies. 

Other minor issues:

1) In Table 1, what does the unit "Mm" represent? Please clarify its meaning.

2) The formulations mentioned in lines 216 - 217 should be listed and explained in context.

3) In line 250, how was the optimal angle beta = 10-degree determined?

4) Figs. 9 to 12 should be discussed individually. What specific observations or conclusions can be drawn from those figures?

5) Lines 322 - 323: the ranges should be corrected to 2 to 10% and 13 to 51%.

Author Response

Report on hydrology-3647291

The authors are grateful to the reviewers for their commitment and observations, helping us to build an improved version of the paper to be suitable for Hydrology!

Further on we respond to all inquiries of the reviewers.

R3

This paper presents a hydrodynamic model to evaluate the effects of FPV on a reservoir in Romania. Several major concerns were raised during the review of the model, which led to the reviewer's recommendation against accepting the paper. 

1) The primary objective of an energy system model is to predict the system's energy generation capacity, typically in terms of output energy or power. In the presented model, however, the calculated results are temperature, cross-sectional area, and the concentrations of TN and TP. These outputs are less relevant to the core purpose of an energy model, and it is unclear how the tabulated power density values were obtained, which causes confusions for the reviewer.

Thank you for your observation! Phytoplanktonic biomass symbol is A. We calculated these outputs being in line with the objective of the paper announced in the title. We explained how power density is determined at line 310. We added from line 245 to 251 and also the abbreviations and symbols are presented in a table before the References section at line 508.

2) The model includes numerous coefficients that require collaboration before use, yet the calibration process is not disclosed. Moreover, it is unclear whether the model is designed specifically for this reservoir or if it is applicable to other reservoirs or water bodies in the region. If it is the former, the model's applicability is too narrow, limiting its value. If it is the latter, then more examples are needed to validate the model's broader utility.

Thank you for your observation! The model is based on climatology in Romania, and it has been used for assessing also other lakes in Romania. We give as examples 3 previous papers presenting the previous application of the model, lines 337 to 346.

[1. Dumitran G.E., Liana - Ioana Vuţă,: Study on Lake Izvorul Muntelui rehabilitation, Simulation Modelling Practice and Theory, WOS:000289184600016, ISSN 1569-190X, Vol. 19, pp. 1235-1242,  2011, 2.Dumitran G.E., Liana - Ioana Vuţă, Damian R.: Eutrophication modelling of Golesti reservoir in Romania, Environmental Engineering and Management Journal, WOS:000303276000017, ISSN 1582-9596, Vol.11, No. 2, pp: 1821-1829, ,  2012. 3. Dumitran G.E., Liana Ioana Vuţă., Panaitescu V.A: The eutrophication model and its application to Roşu Lake- Romania, in Advances Environmental and Geological Science and Engineering: Proceedings of the 3rd International Conference on Environmental and Geological Science and Engineering (EG’ 10), WOS:000302000200016, Constanta, Romania, 3-5 September, pp. 73 – 80, ISSN: 1792-4685, ISBN 978-960-474-221-9, 2010]

3) According to the authors' description, the model's coefficients must be calibrated using data from the specific reservoir via curve fitting. This suggests that the model was essentially fitted to the data for the same reservoir it is used to predict. As a result, it is unsurprising that the numerical results align closely with the measured data. However, it remains unclear how the model would perform in predicting the power conversion capacity of FPV systems in other water bodies. 

Thank you for your observation! We added an explanation from line 337 to 346 and line 352 to 354.

Other minor issues:

1) In Table 1, what does the unit "Mm" represent? Please clarify its meaning.

Thank you for your observation! We explicitly written 10⁶ m³.

2) The formulations mentioned in lines 216 - 217 should be listed and explained in context.

Thank you for your observation! Text from lines 216 through 217 have been reworded with clearer explanations for each term of equation 1, see lines 260 to 265.

3) In line 250, how was the optimal angle beta = 10-degree determined?

Thank you for your observation! For Romania, the optimal angle for FPV is between 8 and 15. Most of the studies referring to that are using 10 so we adopted this value. We added an explanation from line 181 to 195.

4) Figs. 9 to 12 should be discussed individually. What specific observations or conclusions can be drawn from those figures?

Thank you for your observation! We discussed and drawn specific observations related to all the figures. We added comments related to the figures in Lines 232 to 235, 245 to 251 and 354 to 370.

5) Lines 322 - 323: the ranges should be corrected to 2 to 10% and 13 to 51%.

Thank you for your observation! Done!

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I recommended it for publication in its current form.

Author Response

We thank the reviewers for their interest in improving this work. We appreciate the suggestions and advice to modify certain parts of the paper and hope that at this stage the paper is much better than the initial version.

Reviewer 3 Report

Comments and Suggestions for Authors

The reviewer thanks the authors for their time and effort in revising the manuscript. After reviewing the revised version, the reviewer agrees that all issues raised during the first round of review have been adequately addressed.

However, upon further evaluation of the current version, another concern has arisen: Why does the study focus on exploring solar energy from the reservoir and other water bodies instead of leveraging the significant potential of hydrokinetic energy? It is natural to assume that a water body such as a reservoir could be ideal for producing hydrokinetic energy. As demonstrated in previous studies [1, 2], hydrokinetic energy—such as wave energy—is a clean and sustainable form of energy with strong economic viability (e.g., reasonable capital investment and short return-on-investment periods).

Therefore, the reviewer suggests the authors clarify why the Mihailesti Reservoir is more suitable for floating photovoltaic (FPV) technology rather than wave energy conversion (WEC) systems. Is it possible to explore both forms of energy simultaneously in the reservoir? The authors are encouraged to review reference and discuss whether there are compelling advantages to prioritizing solar energy development over wave energy potential in this context.

K. L. Guiberteau, et al., "Investigation of developing wave energy technology in the Gulf of Mexico", Distributed Generation and Alternative Energy Journal, 27(4), 2012, 36-52.

Author Response

The authors are grateful to the reviewer for his commitment and observations!

At this moment, in Romania, there is a huge interest in developing FPV. Hidroelectrica, the operator of around 6400 MW in hydropower plants, intend to develop in the next years more than 1500 MW in FPV. Mihailesti reservoir, the case study reservoir in our paper, is an excellent example of interior lake, without any kinetic energy and / or waves, as on the reservoir free surface there are waves only when strong winds arise. We totally agree that both hydrokinetic and waves are as described by the reviewer, but for this reservoir none of them has a real potential.

We hope that we clarified why our subject is FPV.

More than that, we studied the indicated reference. In any case we cannot compare waves on a reservoir in a calm temperate-continental climate, 22 m depth, 8 km length and a maximum width of 3 km, with waves in the Gulf of Mexico. In Romania it is considered that even on the Black Sea the wave energy isn’t considered as having a real potential. Wave energy as well as tidal energy are not even mentioned in the law establishing the support scheme for energy produced from RES.

We hope that we addressed all reviewer inquiries and clarify that the subject of our research is as announced in the title and that is on a huge interest in that very moment in our country.

We thank the reviewers and the editor for their interest in improving this work. We appreciate the suggestions and advice to modify certain parts of the paper and hope that at this stage the paper is much better than the initial version. We also appreciate the fact that some inadvertences related to the English language were pointed out. Also in this respect, the paper has been very carefully revised by an authorised proofreader and in the re-uploaded paper we have kept the green underlined text, where we have made corrections related to the English language.

Round 3

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have addressed the reviewer’s comments thoroughly. They are encouraged to incorporate their responses into the manuscript. Once revised accordingly, the manuscript can be accepted. 

Author Response

Thank you very much for your comments.

At this stage, the revised form of the article contains the comments requested by reviewer no. 3 (see lines 79 - 85) and the changes related to the English wording.

We hope that the current form is clear and satisfactory to all.