A European Assessment of the Solar Energy Cost: Key Factors and Optimal Technology

Round 1

Reviewer 1 Report

The article under consideration has a relevant topic of calculating the economic efficiency of solar photovoltaic stations geographically located in European countries. In general, the article makes a positive impression and will be of interest to specialists and researchers in this area of ​​knowledge and can be recommended for publication. However, authors should pay attention to the following points when preparing the final version of the article:

1. The presence of different colors of the text is not clear - are there any additions according to the comments?
2.  Perhaps the authors should avoid abbreviations in the title of the article - an initial decoding of all abbreviations is required, including in keywords.
3.  The authors should consider the economic issues of payback of solar power plants with a service life of 40-50 years of photovoltaic modules, which are gradually coming to the market and compare with the economics of standard laminated modules (Panchenko V., Izmailov A., Kharchenko V., Lobachevskiy Ya. (2020). Photovoltaic Solar Modules of Different Types and Designs for Energy Supply. International Journal of Energy Optimization and Engineering, V 9, I 2, 74-94, DOI:10.4018/IJEOE.2020040106).
4.  Also interesting are the economic calculations of solar hybrid (photovoltaic thermal) solar stations, the efficiency of which is much higher than standard photovoltaic systems (Kharchenko V., Panchenko V., Tikhonov P., Vasant P. (2018). Cogenerative PV Thermal Modules of Different Design for Autonomous Heat and Electricity Supply. Handbook of Research on Renewable Energy and Electric Resources for Sustainable Rural Development, 86-119, DOI:10.4018/978-1-5225-3867-7.ch004).
5.  Authors should consider payback options depending on the efficiency of photovoltaic plants, when the efficiency of photovoltaic converters reaches more than 20-25%.
6.  The recommendations specified in paragraphs 3-5 are optional and can be directions for further research by the authors (which should be supplemented to the subsection of the article), since they are promising areas.
7.  Table 1, which takes two pages, can be described in a literary review or in the background more compactly (no more than one page), but in a more familiar format, while retaining all its information content.
8.  Authors should indicate the electrical efficiency of the considered solar power plants in different countries or indicate its fixed value if it is the same for all power plants, since this is a very important parameter.
9.  Figures 1, 2 and 3 should be grouped more compactly according to the order in which the content of the article is presented.
10.  The data obtained in Table 11 are interesting, but the authors should describe in more detail the conclusions drawn from it with the practical point of view.
11.  Authors should shorten the appendixes a little and leave only the most important and relevant information, and indicate the secondary information in the links to the sources.
12.  Perhaps the authors should indicate the sources of the appendix (their formatting should be treated more carefully) (page 23) in brackets in the text of the appendix or in the general list of References.

Subject to the above remarks, the article edited by the authors may be published in the journal Sustainability. 

Author Response

 

Comments and Suggestions for Authors

The article under consideration has a relevant topic of calculating the economic efficiency of solar photovoltaic stations geographically located in European countries. In general, the article makes a positive impression and will be of interest to specialists and researchers in this area of ​​knowledge and can be recommended for publication. However, authors should pay attention to the following points when preparing the final version of the article: 

The authors would like to thank the reviewer for the kind words. We clarify the remaining questions/comments below in blue:

1. The presence of different colors of the text is not clear - are there any additions according to the comments? 

 

The color of the whole text has been homogenized in black. In the case of Table 10, where color indicated the best and worst option regarding PV tracking systems LCOE-wise, the color encoding has been replaced by a binary code: (b) instead of green-filled cells indicates the best configuration and (w) instead of red-filled cells indicates the worst. This change has been made for the sake of clarity, in order to avoid problems when printing in black and white color.

 

1.  Perhaps the authors should avoid abbreviations in the title of the article - an initial decoding of all abbreviations is required, including in keywords. 

 

All abbreviations and acronyms in the title as well as in the keywords have been replaced.

The title now reads: “A European assessment of the solar energy cost: Key factors and optimal technology.”

The corrected keywords are as follows: “Solar Power; Levelized costs of energy; Economic assessment; European countries; PVGIS; Photovoltaic energy; Econometric model”

 

1.  The authors should consider the economic issues of payback of solar power plants with a service life of 40-50 years of photovoltaic modules, which are gradually coming to the market and compare with the economics of standard laminated modules (Panchenko V., Izmailov A., Kharchenko V., Lobachevskiy Ya. (2020). Photovoltaic Solar Modules of Different Types and Designs for Energy Supply. International Journal of Energy Optimization and Engineering, V 9, I 2, 74-94, DOI:10.4018/IJEOE.2020040106). 

 

1.  Also interesting are the economic calculations of solar hybrid (photovoltaic thermal) solar stations, the efficiency of which is much higher than standard photovoltaic systems (Kharchenko V., Panchenko V., Tikhonov P., Vasant P. (2018). Cogenerative PV Thermal Modules of Different Design for Autonomous Heat and Electricity Supply. Handbook of Research on Renewable Energy and Electric Resources for Sustainable Rural Development, 86-119, DOI:10.4018/978-1-5225-3867-7.ch004). 

 

 

1.  Authors should consider payback options depending on the efficiency of photovoltaic plants, when the efficiency of photovoltaic converters reaches more than 20-25%. 

 

1.  The recommendations specified in paragraphs 3-5 are optional and can be directions for further research by the authors (which should be supplemented to the subsection of the article), since they are promising areas. 

 

These topics have indeed potential to be studied in order to assess how efficiency and payback varies according to technological advances. They have been included and referenced accordingly in the last paragraph of section 5, along with other possible future lines of research. Starting at line 459, The added section reads as follows: “The introduction of new models of photovoltaic modules, which increase the service life of PV systems to 40-50 years, as well as their consequences on payback of solar power plants, is also a topic to be considered; specially when compared to standard laminated modules [50]. Solar hybrid is also a promising field of study, which could provide higher efficiencies and a positive effect in the payback of the project [51]. A sensitive analysis could be applied with regard to the efficiency, in the aforementioned scenarios, in order to assess the effect of technological advances in this variable.”

 

1.  Table 1, which takes two pages, can be described in a literary review or in the background more compactly (no more than one page), but in a more familiar format, while retaining all its information content. 

Table 1 has been summarized and spaces have been trimmed when possible, in order to fit it in a single page, this way the information is conveyed in a more compact way. No relevant information to the present study has been omitted in the table.

 

1.  Authors should indicate the electrical efficiency of the considered solar power plants in different countries or indicate its fixed value if it is the same for all power plants, since this is a very important parameter. 

The efficiency of the system is implicit in the parameter system loss, for which a value of 14 % has been selected and already defined in Table 6 along with rest of the characteristics of the standard solar PV system selected. This is the default value proposed by PVGIS and, since the materials and installation of the PV facilities are considered equal for every country in the study, it has been defined as a constant. A clarification has been added to the main text, starting at line 274 of the new paper version: “Regarding the efficiency of the system, a constant value of system loss of 14 % has been selected for the present research, since this is the default value proposed by the PVGIS tool. It is also taken into consideration the hypothesis of same installation conditions and materials for every country; hence, this parameter remains constant for all cases. In Table 6 a summary of the specific values to simulate the PV installation is displayed. A more detailed definition of these variables is found in appendix A..”

 

1.  Figures 1, 2 and 3 should be grouped more compactly according to the order in which the content of the article is presented. 

 

Figures 1,2 and 3 have been placed sequentially right after they are introduced in section 3.4. Now starting at line 325 of the new paper version.

 

1.  The data obtained in Table 11 are interesting, but the authors should describe in more detail the conclusions drawn from it with the practical point of view. 

 

The following paragraph have been added to the conclusions. Starting at line 448 of the new paper version, it: “The econometric model offers an interesting interpretation from a practical point of view. Assuming that climatic conditions are pre-established within each country, and that wage and maintenance costs will remain stable in the coming years in each country, we can see the model as a predictive tool about the effect that technological change (with increasingly cheaper facilities) may have on the LCOE indicator in the next years.”

 

1.  Authors should shorten the appendixes a little and leave only the most important and relevant information and indicate the secondary information in the links to the sources. 

Appendix A regarding PVGIS, which was the longest of them, has been summarized and reduced to almost a half of its original size. Additional information can be found in the official documentation of the tool. The essential information that connects directly with the main text has remained unaltered, for the sake of clarity.

 

1.  Perhaps the authors should indicate the sources of the appendix (their formatting should be treated more carefully) (page 23) in brackets in the text of the appendix or in the general list of References.

 

The references of the appendix B have been formatted according to the references of the main text, in order to avoid misalignments between both.

Subject to the above remarks, the article edited by the authors may be published in the journal Sustainability. 

Thank you very much for your feedback

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

General comment:

This work presents results from different methodologies for assessing profitability along with economic parameters and a comparison of four PV configurations in different countries of Europe, under the title “A European assessment of the PV LCOE: Key factors and optimal technology”. The paper is well prepared, the results from PVGIS are interesting and useful and these of LCOE are innovative and explained clearly. Some minor comments are following below.

 

Names of authors

L 4: Since all authors have the same affiliation, remove the numbers 1,2,3.

 

1. Introduction

L 50-51: Please provide also values for cost and energy efficiency progress in the last decade, if available.

L 53: I suggest placing reference [11] at the end of the sentence (likewise in the rest of the manuscript in similar cases):

E.g.: A method of creating a suitability map for solar power generation, in the European Union (EU) geographical area, is proposed [11].

Or just state the names and add the reference afterwards,

E.g.: A method of creating a suitability map for solar power generation, in the European Union (EU) geographical area, is proposed by Perpiña-Castillo et al. [11].

 

4. Discussion

L 393: “with two axes…”.

Author Response

General comment:

This work presents results from different methodologies for assessing profitability along with economic parameters and a comparison of four PV configurations in different countries of Europe, under the title “A European assessment of the PV LCOE: Key factors and optimal technology”. The paper is well prepared, the results from PVGIS are interesting and useful and these of LCOE are innovative and explained clearly. Some minor comments are following below.

The authors would like to thank the reviewer for the kind words. We clarify the remaining questions/comments below in blue:

Names of authors

L 4: Since all authors have the same affiliation, remove the numbers 1,2,3.

The numbers have been removed in order to avoid redundancy.

1. Introduction

L 50-51: Please provide also values for cost and energy efficiency progress in the last decade, if available.

The second paragraph of section 1 (Introduction) has been expanded. Specific numbers regarding the evolution of total installation costs for PV facilities, as well as module efficiency have been included.

The modified extract now reads as follows: “The global capacity weighted-average total installed cost, for solar photovoltaic projects commissioned in 2019, was 995 $/kW, 79 % less when compared to 2010 data. The average module efficiency of crystalline modules has also increased; from 14.7% in 2010 to 19.2% in 2019”

L 53: I suggest placing reference [11] at the end of the sentence (likewise in the rest of the manuscript in similar cases):

E.g.: A method of creating a suitability map for solar power generation, in the European Union (EU) geographical area, is proposed [11]. 

Or just state the names and add the reference afterwards,

E.g.: A method of creating a suitability map for solar power generation, in the European Union (EU) geographical area, is proposed by Perpiña-Castillo et al. [11].

Every reference number have been moved to the end of the corresponding sentence. The name of the reference has been also stated when applicable, as recommended.

1. Discussion 

L 393: “with two axes…”.

This sentence has been corrected and now reads: “Thus, using panels with vertical or inclined axis, instead of a two-axis configuration, reduces the LCOE by approximately 21% {= exp(–0.235) – 1}, while the reduction is 18.6% {= exp(–0.206) – 1} if the fixed axis is used”

 

 

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The article presents an interesting economic evaluation of the solar photovoltaic potential within a European context. The indicator used in the evaluation is adequate as it takes into account the variation of costs and revenues during the system operational life cycle. Although the results are interesting and valuable to both researchers and practitioners in the PV electricity generation sector, the articles still has some questions and issues that need to be addressed before the article is deemed adequate for publication.

After reading it, I have some general comments/questions concerning it.

• The abstract focus to much on describing the work relevance, and does not enough information concerning what was done and the main results of the work. It should be improved to be more objective and to give a proper assessment of what was done.
• Some statements should be supported, as for example the growth of PV in the period between 2010 and 2019. Please better support many statements given in the article.
• In the introduction a more complete description of the European situation was expected. Please improve it giving an account of the European situation and how PV fits in current strategic plans.
• Table 1 is not referred in the text. Also, it looks like is a combination of the references you consider in the text. Please refer it in the text and adjusted description of the references.
• Not completely sure if Appendix A is really necessary, as PVGIS is an open-source tool and a description can be found online.
• Why you consider carbon costs in the calculations? How you can include them in the calculations, and from where you may get the data needed?
• Concerning the city selection, it is clear you select capital cities, but did not mentioned it in the article and justified it. Do you believe the sample is representative of the European climatic zones? For example, semi-arid and warm Mediterranean climates that are found in Spain (https://en.wikipedia.org/wiki/K%C3%B6ppen_climate_classification), seem to be missing from the sample.
• The study is for standalone PV generation of for domestic generation, or is valid for both? Not clear in which conditions result are valid.
• Concerning Table 6, it is unclear how you determined the values of the discount rates, in particular where you get the data and how they were calculated. Please give more information.
• Figures 1 to 3 are especially relevant, and probably can be removed. They are all similar. Also, in particular in countries with large variations in climatic conditions, as is the case of Spain, do you believe they can be valid for the whole country?
• Concerning the econometric model, more information must be given, in particular: what is the model, how the parameters were calculated, referring the software used if any was used, and other information is necessary.
• Conclusions are too large, they need to be shorten.

Bellow I list of some more specific comments and questions concerning the article.

• The quality of the English is goof, yet the style is rather informal and not very scientific in some parts of the article. Please improve the article style to ensure is more scientific. Also, some expressions are rather odd, as for example in line 172 “powered by”, better “supported by” in my opinion.
• References are not uniform, and some are missing. Please check the references to make them uniform. Also do that for tables and figures, MDPI may not check of references are consistent in the article.
• PV are changing, in which direction?
• Sun hours? Maybe is better solar insolation.
• At the end of the introduction there are some duplications of text, and it is confused. Please check it, from lines 130 to 152 it should be rephrased and simplified.
• It seems you confound metric/indicator with index, a combinations of indicators or indices. Please be careful.
• OPEX and CAPEX need to be defined explicitly.
• Do OPEX include costs of maintenance? Please be more objective.
• What are connection costs? I think this are costs of connecting initially to the network right? You should explain it better, as a renting cost for the connection may exist in some European countries, as for example in mine.
• Why you give the average minimum and maximum temperatures for the cities? Better give the climatic classification, is more important.

I believe that in the current form the paper should be subjected to Major Revisions probably needing an additional revision. The questions/observations considered above should be considered to improve the quality and readability of the study.

Author Response

Response to Reviewer 1 Comments

Paper sustainability-965089:

A European assessment of the PV LCOE: Key factors and optimal technology.

The authors sincerely acknowledge the reviewer's contribution to the improvement and delimitation of the scope of the paper. We are confident that the current status of the paper clarifies all the reviewer's concerns. We have included our answers in blue below to each of the points raised by the reviewer, and marked up in red all changes made to the paper.

The article presents an interesting economic evaluation of the solar photovoltaic potential within a European context. The indicator used in the evaluation is adequate as it takes into account the variation of costs and revenues during the system operational life cycle. Although the results are interesting and valuable to both researchers and practitioners in the PV electricity generation sector, the articles still has some questions and issues that need to be addressed before the article is deemed adequate for publication.

Answer:

Thanks for your kind words. We have made our best efforts to improve the paper and make it easier to understand. We have incorporated all your comments that we think will improve the quality and academic level of the paper.

After reading it, I have some general comments/questions concerning it.

1. The abstract focus to much on describing the work relevance, and does not enough information concerning what was done and the main results of the work. It should be improved to be more objective and to give a proper assessment of what was done.

Answer:

The abstract has been modified, including a better description of the process and results obtained. All expressions that could be considered subjective have been removed from this section.

Regarding the results, the following statements have been included at the end of the abstract: " The results show that one-axis tracking systems are the best option in all countries, reducing LCOE by more than 30 % when compared to two-axis tracking system. The impact of wages is also signifcant. In higher latitudes, in most cases, wages also increase, hence the LCOE are higher and consequently less interesting for a potential investor.”

2. Some statements should be supported, as for example the growth of PV in the period between 2010 and 2019. Please better support many statements given in the article.

Answer:

The abstract and the introduction have been completely overhauled and rewritten. All general statements are now supported by references and objective data. Displayed below some examples from the introduction, including the one commented in the present question:

 

“Between 2010 and 2019, solar PV electricity generation capacity has increased from 1.9 GW to over 133 GW. In order to reduce greenhouse gas (GHG) emission by 55 % in 2030, between 325 and 375 GWDC of PV capacity are required to be installed in Europe in the timeframe 2020 to 2030 [6].”

 

“Europe is demonstrating a strong commitment, providing an opportunity to further improve the environmental performance of clean energy solutions. As a matter of fact, more new capacity was installed for solar than any other power generation technology in the EU in 2019 [1]. This commitment is also illustrated with the approval by the European Commission of a legislative package called “Clean Energy for all Europeans”, finally completed in 2019”

3. In the introduction a more complete description of the European situation was expected. Please improve it giving an account of the European situation and how PV fits in current strategic plans.

Answer:

 

As commented in the previous question, the introduction has been rewritten almost entirely. The situation on the European Union has been expanded with new information, commenting how important is PV in the European Union, with more capacity installed of solar PV than any other generation technology in 2019. The legislative package called “Clean Energy for all Europeans” shows that a legal framework has already been stablished.

 

Table 1 is not referred in the text. Also, it looks like is a combination of the references you consider in the text. Please refer it in the text and adjusted description of the references.

 

Answer:

 

A reference to table 1 has been included in the introduction. The mentioned paragraph reads as follows: “It must be highlighted the importance of the literature in the current research. In Table 1, the main contributions of individual references cited in this paper, with respect to the present study, are outlined and grouped by topic. It is also indicated the geographical region in which each contribution applies and the year of publishing.”

4. Not completely sure if Appendix A is really necessary, as PVGIS is an open-source tool and a description can be found online.

Answer:

The authors agree with this assessment. The appendix is not completely necessary given that PVGIS is a widely used tool available for free. We leave the final decision of removing this section to the edior.

5. Why you consider carbon costs in the calculations? How you can include them in the calculations, and from where you may get the data needed?

Answer:

 

Carbon costs are mentioned as part of the general definition of the LCOE which applies to every type of energy generation technology. For solar PV, carbon costs do not apply and are considered zero. The final expression for LCOE considered in this text for PV facilities is expressed in equation (5), which considers and initial investment and operation and maintenance costs.

6. Concerning the city selection, it is clear you select capital cities, but did not mentioned it in the article and justified it. Do you believe the sample is representative of the European climatic zones? For example, semi-arid and warm Mediterranean climates that are found in Spain (https://en.wikipedia.org/wiki/K%C3%B6ppen_climate_classification), seem to be missing from the sample.

Answer:

The authors completely agree with the reviewer’s assessment, since in countries with a large surface area (or length), such as Spain, there can be a wide variation between the values obtained in different locations (in the case of Spain, up to 30% of differences in irradiation between Seville and La Coruña). However, in those cases with a higher dispersion (Spain and Italy), the capital is in the centres of the countries, so there are facilities above and below, and this can be a representative average value. It would have been more accurate, instead of the capitals of the countries, to use the geographical centre, but we did not have available climatological data from these geographical points, which led us to use the capitals' data as a first approach.

We have included the climatic zone for each capital city in table 2, this parameter is later commented in the results in section 3.4: “With respect to the climatic zone of the most optimal countries LCOE wise, there is not a unique value, with best options corresponding to oceanic, Mediterranean and Humid continental climates. Even though Mediterranean climates often comes with higher solar insolation, the effect of wages outweight this effect in some specific cases like Bulgaria and Romania.”

 

7. The study is for standalone PV generation of for domestic generation, or is valid for both? Not clear in which conditions result are valid.

Answer:

The study is performed for utility scale PV solar generation facilities, since costs could vary between both types of installations. This work could be adapted for  domestic generation, but costs would need to be recalculated. In any case, the value of costs are parametric and could be modified in future research.

8. Concerning Table 6, it is unclear how you determined the values of the discount rates, in particular where you get the data and how they were calculated. Please give more information.

Answer:

The method for estimating the discount rates for  different countries is described in the reference [41] in the main text. Since this reference comes from an unpublished manuscript, it has been made available online to be read in the following link: http://arxiv.org/abs/2010.11912

This methodology is based on the WACC method with two main two hypotheses: 1) there is a unicity of capital goods, technology and capital markets in the European Union,

2) there are country-specific characteristics in terms of taxation and business risks.

After these two hypothesis, the general method for calculating WACC is detailed. The complete mathematical demonstration can be consulted in the aforementioned reference as well as the final values. Some comments regarding the main hypothesis are commented in the main text.

9. Figures 1 to 3 are especially relevant, and probably can be removed. They are all similar. Also, in particular in countries with large variations in climatic conditions, as is the case of Spain, do you believe they can be valid for the whole country?

The authors completely agree with the reviewer’s assessment, since in countries with a large surface area (or length), such as Spain, there can be a wide variation between the values obtained in different locations (in the case of Spain, up to 30% of differences in irradiation between Seville and La Coruña). However, in those cases with a higher dispersion (Spain and Italy), the capital is in the centres of the countries, so there are facilities above and below, and this can be a representative average value. It would have been more accurate, instead of the capitals of the countries, to use the geographical centre, but we did not have available climatological data from these geographical points, which led us to use the capitals' data as a first approach.

 

10. Concerning the econometric model, more information must be given, in particular: what is the model, how the parameters were calculated, referring the software used if any was used, and other information is necessary.

Answer:

Answer:

The next paragraph has been introduced in the discussion section:

“In order to quantify the effect on the LCOE of the different determinants considered in this study, we propose to estimate a two-level mixed regression model for the dependent variable LCOEic (in logarithm); the subscript ‘i’ represents a particular PV configuration and ‘c’ represents the country where it takes place –the estimation has been made with the statistical software STATA 15.0. The multilevel regression model can be seen as a generalization of the linear regression model which allows the inclusion of random deviations other than those associated with the overall error term of the model –for multilevel analysis details, see for example [45, 46].

 

Level 1 model:

        

 

Level 2 model:

;  

 

The fixed part of the model has the following explanatory variables: the global average of the endogenous variable, , for all the countries ; the dummy variables {, , } which control for the tracking system of the PV panel (the two axis system is the reference configuration in the estimation); the dummy variables {} which respectively control for  changes in the hardware cost (being the actual hardware cost the reference value in the estimated model); the O&M costs and the solar irradiation (kWh per m2), both depending on country and PV configuration; and those explanatory variables which collect idiosyncratic information from each country, such as the wage costs (in logarithm) and the maximum and minimum temperatures –the discount rate for each coutry is not statistically significant in the estimated model, probably due to its low variance. For its part, the random part of the model has the two following purely random effects: , which control for the specificity (level 2 random intercept) of every particular country; and , which represents the overall or level 1 error term. The results of the estimation are represented in Table 10.”

 

 

 

11. Conclusions are too large, they need to be shorten.

Answer:

 

The conclusion section has been reduced by a 25 % of total words of the original manuscript. The first two paragraphs of this section have been combined and trimmed to be more concise and clear, in order to focus the conclusions in the results obtained.

12. Bellow I list of some more specific comments and questions concerning the article.
13. The quality of the English is goof, yet the style is rather informal and not very scientific in some parts of the article. Please improve the article style to ensure is more scientific. Also, some expressions are rather odd, as for example in line 172 “powered by”, better “supported by” in my opinion.

Answer:

 

A grammar review has been performed in the whole text to ensure the quality of style used. Expressions that could be considered subjective, informal or overly complicated have been removed or replaced. Specific changes can be identified in red in the new version of the manuscript.

14. References are not uniform, and some are missing. Please check the references to make them uniform. Also do that for tables and figures, MDPI may not check of references are consistent in the article.

Answer:

 

The bibliography has been cited according to the MDPI style. References have been checked again to be uniform. All reference errors in the text regarding tables and figures have been corrected.

 

PV are changing, in which direction?

Answer:

 

Ambiguous expressions like this one have removed as part of the overhaul performed in the abstract and introduction section. This sentence is particular is not present anymore.

15. Sun hours? Maybe is better solar insolation.

Answer:

Sun hours is an equivalent measure of solar insolation. For the sake of clarity in the text, all ocurrences of sun hours have been replaced with solar insolation

16. At the end of the introduction there are some duplications of text, and it is confused. Please check it, from lines 130 to 152 it should be rephrased and simplified.

Answer:

 

The last paragraphs of the introduction has been rewritten to ensure the clarity of the text and to avoid duplication. The paragraph describing the contribution of this text now reads:

 “The contribution of this paper is to provide an assessment of different utility scale PV system configurations in 20 European locations (representing countries or group of countries), by calculating lifecycle produced energy and lifecycle costs for each of these locations and each of the four sun-tracking system considered (fixed, vertical one-axis, inclined one-axis and two axis tracking system). This allows to compute the total cost of energy production through the LCOE calculation measure, obtaining the profitability of the optimal system in every country. Every PV configuration has the same size, measured by the concept of installed peak power, with 1kWp each. As one of the main hypotheses of the study, the cost of materials is assumed to be constant among countries. However, labor costs present a significant degree of heterogeneity. Hence, they are addressed as one of the main variables to be estimated in this research. Afterwards, an econometric analysis for main variables involved in the analysis is performed; with the goal of quantifying their effect on the final result, in order to understand how strong the correlation between specific variables and the final result is.”

17. It seems you confound metric/indicator with index, a combinations of indicators or indices. Please be careful.

Answer:

 

The authors agree with this comment and apologize for the confusion. The definitions of LCOE and discount rate are now referred as measurements instead of metrics in order to avoid any confusion and to ensure clarity.

18. OPEX and CAPEX need to be defined explicitly.

Answer:

 

CAPEX refers to capital expenditures. They esentially include all costs associated to the initial investment (including costs of material and labor costs which are specially significant in the current case study). OPEX refers to Operational expenditures. They include recurring costs such as utilization, maintenance or taxes. The previous sentences have been included in section 2.2 to ensure clarity.

19. Do OPEX include costs of maintenance? Please be more objective.

Answer:

 

OPEX do include maintenance costs. As stated in the answer to the previous question, these clarifications have been added to section 2.2. The sentences added read as follows: “Capital expenditures include costs associated to the initial investment (including costs of material and labor costs which are specially significant in the current case study) while Operational expenditures include costs such as utilization, maintenance or taxes”

20. What are connection costs? I think this are costs of connecting initially to the network right? You should explain it better, as a renting cost for the connection may exist in some European countries, as for example in mine.

Answer:

The general definition of connection costs include both: the initial costs of connecting to the grid and possible renting costs that could ocurr in some specific regions. A comment has been added in section 2.2  in order to clarify this.

21. Why you give the average minimum and maximum temperatures for the cities? Better give the climatic classification, is more important.

Answer:

 

Average minimum and maximum temperatures are part of the econometric analysis. That is the main reason to keep these values. The authors completely agree with the importance of climatic zones and have been included in table 2 as well as some comments regarding their effect on the results.

22. I believe that in the current form the paper should be subjected to Major Revisions probably needing an additional revision. The questions/observations considered above should be considered to improve the quality and readability of the study.

Answer:

 

The authors would like to thank the reviewer for his/her valuable comments and complete review. We sincerely hope that the answers provided and changes made can help in clarifying all points raised.

Author Response File: Author Response.pdf

Reviewer 2 Report

I cannot verify the details of the analysis. In working through the assumptions in section 2, I looked into multiple references to validate the assumptions, and in each case, I found that the cited reference did not contain the information implied in the manuscript. In some cases, the material in the reference was close to the topic but fell short of supporting the specific detail used in the manuscript. In other cases, the reference appeared to have no material bearing on the point under discussion. This is most troubling in the analysis sections, however I also found an example in the introduction where the numbers in the manuscript are completely different from those in the reference. Finally, there are multiple places in the manuscript where the reference is simply missing (lines 229 and 313), perhaps due to errors in the citation management software.

Until these errors are corrected and the references in the manuscript actually support and refer to the material they are being cited to support, this manuscript cannot be published, as it would misrepresent the cited literature.

I am including the comments I had made up to the point where I gave up, in case they are useful to the authors as they make corrections.

At present this manuscript is overly long and organized in a somewhat confusing fashion. The introduction could be shortened significantly and focused on the material that begins on line 61. The four paragraphs following from line 61 give an overview of existing analysis on (1): PV generation potential in Europe and factors governing LCOE for systems of various sizes, modes (rooftop vs ground), countries and electricity compensation schemes; (2) Solar radiation estimation, single-site or single country case studies of PV profitability and sensitivity to subsidy or compensation regime (such as feed-in tariffs); (3) the challenge of estimating the discount rate for LCOE calculations; and (4) the impact of tracking (single or dual-axis) on the electricity generation and cost of a PV array.  While all of the material referenced in these paragraphs was no-doubt useful to the authors in the development of their analyses, much of it is of limited relevance to the work presented.  In particular, many of the references dwell on the impact of subsidy and electricity compensation schemes, compare rooftop and ground mounted PV installations (which have different installation cost and soft cost structures), and/or compare PV costs by installation size.  None of those variations are represented or compared in the LCOE model presented in section 2, and if the authors want to introduce a lot of background material on these areas, they also need to include some discussion that clarifies what particular value this study offers and what knowledge gap it addresses. The paragraphs starting on line 130 do this to a minimal extent, but additional explanation is necessary, even if only to say that the study examines country-level variation in solar resource, labor costs and discount rate for four types of ground mount installation of arbitrary size.

In section 2. The authors include a list of variables after sequences of equations and derivation are developed. I suggest either defining the variables as they appear in the text below each equation, or placing the variable names before the equations for clarity.

In section 2.3.2, the modeling assumptions that determine the investment cost inputs to the model are not sufficiently clear. Line 244 – It’s reasonable to assume a fixed hardware cost across the different countries, however this assumption is inconsistent with the statement that it is ~50% of total investment in the context of varying labor costs. Reference [29] does not make any statement about the relative contribution of hardware and soft costs to the total capital investment.

Line 251 - Reference [39] does not at all discuss the relative costs of fixed and tracking PV systems, nor does it make a hypothesis that supports the cost structure in Table 2.

Line 255  - the authors give no reference for the value of T or how it varies with the tracking scheme. As this parameter is intended to capture installation and soft costs when scaled by the wage adjustment, this is a large gap in the cost model! The authors should include a reference and explanation and also add this parameter to Table 2.

 

 “Between 2010 and 2019 solar PV electricity generation increased…” – this should be generation capacity or alternatively report the number of GW-hrs/year generated in the respective years.

 

Line 46: “…leading to an installed capacity of 825 GW.” – This sentence does not make sense in combination with the previous one. If capacity is 133 GW in 2019, that would imply 692 GW must be installed to meet the 825 GW target, not “between 75 and 350 GW”.  Furthermore, reference [6] states that in order to achieve a 55% reduction in GHG emission by 2030, between 325 and 375 GWdc of PV must be installed between 2020 and 2030, leading to a cumulative capacity of 455-605 GW. None of the numbers in the reference match the ones in the manuscript.

 

Figure 1 – please include a color scale and/or increase the font size on the labels. The map could be truncated near 38 degrees East to provide space on the page for a color scale without losing resolution in the area of interest.  This applies to all subsequent map figures.

Author Response

Response to Reviewer 2 Comments

Paper sustainability-965089:

A European assessment of the PV LCOE: Key factors and optimal technology.

The authors sincerely acknowledge the reviewer's contribution to the improvement and delimitation of the scope of the paper. We are confident that the current status of the paper clarifies all the reviewer's concerns. We have included our answers in blue below to each of the points raised by the reviewer, and marked up in red all changes made to the paper.

I cannot verify the details of the analysis. In working through the assumptions in section 2, I looked into multiple references to validate the assumptions, and in each case, I found that the cited reference did not contain the information implied in the manuscript. In some cases, the material in the reference was close to the topic but fell short of supporting the specific detail used in the manuscript. In other cases, the reference appeared to have no material bearing on the point under discussion. This is most troubling in the analysis sections, however I also found an example in the introduction where the numbers in the manuscript are completely different from those in the reference. Finally, there are multiple places in the manuscript where the reference is simply missing (lines 229 and 313), perhaps due to errors in the citation management software.

Until these errors are corrected and the references in the manuscript actually support and refer to the material they are being cited to support, this manuscript cannot be published, as it would misrepresent the cited literature.

I am including the comments I had made up to the point where I gave up, in case they are useful to the authors as they make corrections.

1. At present this manuscript is overly long and organized in a somewhat confusing fashion. The introduction could be shortened significantly and focused on the material that begins on line 61. The four paragraphs following from line 61 give an overview of existing analysis on (1): PV generation potential in Europe and factors governing LCOE for systems of various sizes, modes (rooftop vs ground), countries and electricity compensation schemes; (2) Solar radiation estimation, single-site or single country case studies of PV profitability and sensitivity to subsidy or compensation regime (such as feed-in tariffs); (3) the challenge of estimating the discount rate for LCOE calculations; and (4) the impact of tracking (single or dual-axis) on the electricity generation and cost of a PV array.  While all of the material referenced in these paragraphs was no-doubt useful to the authors in the development of their analyses, much of it is of limited relevance to the work presented.  In particular, many of the references dwell on the impact of subsidy and electricity compensation schemes, compare rooftop and ground mounted PV installations (which have different installation cost and soft cost structures), and/or compare PV costs by installation size.  None of those variations are represented or compared in the LCOE model presented in section 2, and if the authors want to introduce a lot of background material on these areas, they also need to include some discussion that clarifies what particular value this study offers and what knowledge gap it addresses. The paragraphs starting on line 130 do this to a minimal extent, but additional explanation is necessary, even if only to say that the study examines country-level variation in solar resource, labor costs and discount rate for four types of ground mount installation of arbitrary size.

Answer:

 

The introduction has been overhauled and rewritten. The first two paragraphs in this section, which describes current status regarding the European Union commitment to solar PV, have been reduced and corrected to be more concise and clear. Regarding the rest of the paragraphs which detail different studies in the literature, even though the general structure of the text has been kept, a lesser weight has been given to those researches not directly related to the present study. With these changes, the introduction size is lower than 15 % over the total number of words of the whole document.

 

It has been included in the text a reference to table 1. In this table, contributions of every research are outlined, in order to provide a more comprehensive view of the current state of the art without expanding and repeating the same information in the main text unnecessarily.

 

For those topics not directly related to the present study, they have been highlighted in section 5 as future lines of research, since some of them are interesting to be included in the future analysis for LCOE computing, such as feed-in-tariffs and subsidies. These variables would allow the creation of even more complex optimal LCOE maps.

 

The last part of the introduction, from line 130 in the original manuscript, has also been improved, describing with more detail the research performed and conveying the ideas in a more concise manner.

2. In section 2. The authors include a list of variables after sequences of equations and derivation are developed. I suggest either defining the variables as they appear in the text below each equation, or placing the variable names before the equations for clarity.

Answer:

The lists of variables after all equations have been removed. The variables have been defined in the previous paragraph prior to each equation or set of equations, for the sake of clarity.

3. In section 2.3.2, the modeling assumptions that determine the investment cost inputs to the model are not sufficiently clear. Line 244 – It’s reasonable to assume a fixed hardware cost across the different countries, however this assumption is inconsistent with the statement that it is ~50% of total investment in the context of varying labor costs. Reference [29] does not make any statement about the relative contribution of hardware and soft costs to the total capital investment.

Answer:

There is a mistake in the reference, The correct reference in line 245 should read [39] not [29]. The authors sincerely apologize for this error. The source of this assumption is a combination of the source material and specific meetings with the authors of the cited reference and other industry experts. In any case, the value of this hypothesis is parametric and could be modified in future research.

4. Line 251 - Reference [39] does not at all discuss the relative costs of fixed and tracking PV systems, nor does it make a hypothesis that supports the cost structure in Table 2.

Answer:

As in the previous question, the source of these assumptions is a combination of the specific source material for this reference and specific meetings with the authors of this text and other industry experts.

5. Line 255  - the authors give no reference for the value of T or how it varies with the tracking scheme. As this parameter is intended to capture installation and soft costs when scaled by the wage adjustment, this is a large gap in the cost model! The authors should include a reference and explanation and also add this parameter to Table 2.

Answer:

 

The equation (7) of the original manuscript is displayed below:

 can also be expressed as shown below:

 

 is a 1 x 20 vector of relative weight of wage for each country.  is a 1 x 4 vector of H values for each tracking technology, as calculated in Table 3.  .  

H is a 20 x 4 matrix of hardware costs repeated for every country.  is a 20 x 4 matrix which represents the scaled costs for every country and every technology. Considering the hypothesis of 50 % of total costs corresponding to Hardware costs [39], the remaining costs are scaled for every tracking technology according the wage(as a function of H), being an approximation to the sum of soft costs and installation costs.  T is a mathematical abstraction which represents a constant scalar parameter, which leads to obtaining the same result as multiplying the transpose value of vector  for a matrix F, thus, simplifying the equation in the main text.

A footnote has been included in the main text with the following information: “T is a scalar parameter which results from computing a vector of 4 components containing the H values displayed in Table 3, for each PV configuration. This results from the hypothesis detailed in section 2.3.2. which states that 50 % of total costs correspond to Hardware costs. The remaining 50 % of costs are computed as a function of labor costs.”. The specific values of   for each tracking technology have been added to Table 4.

6. “Between 2010 and 2019 solar PV electricity generation increased…” – this should be generation capacity or alternatively report the number of GW-hrs/year generated in the respective years.

Answer:

The authors completely agree with this correction. The statistics are refered to generation capacity increase in this decade in the European Union (including the UK) according to reference [6] of the original manuscript. The text has been corrected to reflect this change. The sentence starting in line 46 of the original manuscript now reads: “Between 2010 and 2019, solar PV electricity generation capacity has increased from 1.9 GW to over 133 GW”

7. Line 46: “…leading to an installed capacity of 825 GW.” – This sentence does not make sense in combination with the previous one. If capacity is 133 GW in 2019, that would imply 692 GW must be installed to meet the 825 GW target, not “between 75 and 350 GW”.  Furthermore, reference [6] states that in order to achieve a 55% reduction in GHG emission by 2030, between 325 and 375 GWdc of PV must be installed between 2020 and 2030, leading to a cumulative capacity of 455-605 GW. None of the numbers in the reference match the ones in the manuscript.

Answer:

 

The authors agrees that the numbers are not correct and sincerely apologize for this mistake. The sentence starting at line 46 of the original manuscript has been changed and now reads as follows: “In order to reduce greenhouse gas (GHG) emission by 55 % in 2030, between 325 and 375 GW_DC of PV capacity are required to be installed in Europe in the timeframe 2020 to 2030” better reflecting the information contained in the original source, according to reference [6] of the original manuscript.

8. Figure 1 – please include a color scale and/or increase the font size on the labels. The map could be truncated near 38 degrees East to provide space on the page for a color scale without losing resolution in the area of interest.  This applies to all subsequent map figures.

Answer:

 

All maps have been rescaled. A color scale have also been added to the upper left corner of every one of them in order to improve clarity. The map have also been truncated near 38 degrees east, therefore zooming the zones of interest of the study. The map showing the LCOE results for vertical-axis tracking is displayed below as an example of the final result:

 

Figure 1 EU map LCOE (€/MWh) – vertical-axis tracking PV modules (source: own elaboration with Open StreetMap layer [42])

 

Author Response File: Author Response.pdf

Reviewer 3 Report

View attached file

 

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 3 Comments

Paper sustainability-965089:

A European assessment of the PV LCOE: Key factors and optimal technology.

The authors sincerely acknowledge the reviewer's contribution to the improvement and delimitation of the scope of the paper. We are confident that the current status of the paper clarifies all the reviewer's concerns. We have included our answers in blue below to each of the points raised by the reviewer, and marked up in red all changes made to the paper.

 

• The selection of climate data from the capital of each country as representative of that country may lead to inaccurate results. In countries such as Spain there are great climatic differences within the same country. 

 

Answer:

The authors completely agree with the reviewer’s assessment, since in countries with a large surface area (or length), such as Spain, there can be a wide variation between the values obtained in different locations (in the case of Spain, up to 30% of differences in irradiation between Seville and La Coruña). However, in those cases with a higher dispersion (Spain and Italy), the capital is in the centres of the countries, so there are facilities above and below, and this can be a representative average value.

It would have been more accurate, instead of the capitals of the countries, to use the geographical centre, but we did not have available climatological data from these geographical points, which led us to use the capitals' data as a first approach.

Regarding the text, some issues have been noted: 

 

2. In the abstract and the introduction, lines 10, 27 and 31, statements of a subjective nature are made that are not very appropriate for scientific texts. 

Answer:

The abstract and the introduction have been overhauled and rewritten from scratch. All expressions and statements that were not considered appropriate for scientific texts have been replaced, removed or supported by objective data in specific cases.

For example, general statements like “Europe is demonstrating a strong commitment…” are now supported by data and literature references. Other expressions like “it is an undeniable fact…” have been removed.

3. On lines 46 and 47, if the installed power is 133 GW and is increased by 350 GW, 850 GW is not obtained.Clarify this. 

Answer:

The authors agrees that the numbers are not correct and sincerely apologize for this mistake. The sentence starting at line 46 of the original manuscript has been changed and now reads as follows: “In order to reduce greenhouse gas (GHG) emission by 55 % in 2030, between 325 and 375 GWDC of PV capacity are required to be installed in Europe in the timeframe 2020 to 2030”

 

4. In table 2, the meaning of F is not described. Is the O&M cost annual? 

Answer:

F, in table 3, is meant to represent the value for Hardware costs for fixed angle PV facilities. This variable is used as a means to represent how the cost of the other 3 configurations are computed as a percentage increase from the fixed case. F has been replaced in table 3 by H_fixed for the sake of clarity.

O&M represented in Table 3 are annual, an annotation have been added to the title of the table and in the previous paragraph.

 

5. In section 4, an econometric analysis is presented but the model equations do not appear. There is not enough information to understand this section. 

Answer:

The next paragraph has been introduced in the discussion section:

“In order to quantify the effect on the LCOE of the different determinants considered in this study, we propose to estimate a two-level mixed regression model for the dependent variable LCOEic (in logarithm); the subscript ‘i’ represents a particular PV configuration and ‘c’ represents the country where it takes place –the estimation has been made with the statistical software STATA 15.0. The multilevel regression model can be seen as a generalization of the linear regression model which allows the inclusion of random deviations other than those associated with the overall error term of the model –for multilevel analysis details, see for example [45, 46].

 

Level 1 model:

        

 

Level 2 model:

;  

 

The fixed part of the model has the following explanatory variables: the global average of the endogenous variable, , for all the countries ; the dummy variables {, , } which control for the tracking system of the PV panel (the two axis system is the reference configuration in the estimation); the dummy variables {} which respectively control for  changes in the hardware cost (being the actual hardware cost the reference value in the estimated model); the O&M costs and the solar irradiation (kWh per m2), both depending on country and PV configuration; and those explanatory variables which collect idiosyncratic information from each country, such as the wage costs (in logarithm) and the maximum and minimum temperatures –the discount rate for each coutry is not statistically significant in the estimated model, probably due to its low variance. For its part, the random part of the model has the two following purely random effects: , which control for the specificity (level 2 random intercept) of every particular country; and , which represents the overall or level 1 error term. The results of the estimation are represented in Table 10.”

 

 

 

Author Response File: Author Response.pdf

Reviewer 4 Report

Dear Authors, Thank you for gathering detailed information and performing the data processing/studies on solar LCOE. Please see my comments below: Language: English language is fine. However, in some places it felt to be using too many complicated wording without any gain in clarity/quality. Abstract: Sets the reader expectation properly. Introduction: Literature review is well done. However, the length of the introduction may be too long. Some trimming is suggested. Few more comments: Line #32: Should refer to first package from 2008. Eqn#2: The definition of ‘r’ presented very late in line #215. Instead, it can be presented in line# 205 like: “with discount rate(r)” Table#2 may be redundant. (line #231). Line #229 has reference error: “Error! Reference source not found” There are two table#2 (line#231 & line #251). In Tabble #2 (above line 253), is is not clear what is meant by thrid columns (3),(3) & (5) like 2% Io (3). Also, what is the fundamental reason for using 10% for single axis and 25% double axis. Please clarify. In table #7: What is the significance of color fills (red and green)? We see that in line #321. However, this legend should be on top of bottom of the table for readers' convenience. The table with all 20 countries and their standing seen table #7 is the most important table in this manuscript. It is well presented Portugal, Bulgaria and Romania are good for one-axis. Authors may consider including their current situations in terms of energy generation from renewable/PV. I am assuming, the term "Own Elaboration" was used to convey the author interpreted the result for their tools? Appendix is well presented. I suggest the authors to revise this manuscript and make it a little shorter. If conveyed more efficiently and concisely, this manuscript can be an interesting read. Sincerely The Reviewer

Author Response

Response to Reviewer 4 Comments

Paper sustainability-965089:

A European assessment of the PV LCOE: Key factors and optimal technology.

The authors sincerely acknowledge the reviewer's contribution to the improvement and delimitation of the scope of the paper. We are confident that the current status of the paper clarifies all the reviewer's concerns. We have included our answers in blue below to each of the points raised by the reviewer, and marked up in red all changes made to the paper.

 

Dear Authors, Thank you for gathering detailed information and performing the data processing/studies on solar LCOE. Please see my comments below:

 

• Language: English language is fine. However, in some places it felt to be using too many complicated wording without any gain in clarity/quality.

 

Answer:

A grammar review has been performed in the whole text. Complicated expressions and wording have been removed for the sake of clarity.

 

• Abstract: Sets the reader expectation properly.

 

• Introduction: Literature review is well done. However, the length of the introduction may be too long. Some trimming is suggested.

 

Answer:

The introduction has been overhauled and rewritten. The section has been trimmed. Since the main contributions of these studies to the paper are already summarized in Table 1, in order to not repeat this information, some of them have been removed from the main text. A reference to Table 1 has also been included in this section.

 

 

• Few more comments:

 

Line #32: Should refer to first package from 2008.

 

Answer:

The reference to the climate package has been removed as part of the trimming process in the introduction.

 

The authors appreciate this comment. The first two paragraphs of the introduction has been rewritten entirely. The reference to the climate and energy package has been removed as part of the trimming process in the introduction. New data have been introduced: “In the current global context of transition from fossil fuels to cleaner energy sources, Europe is demonstrating a strong commitment, providing an opportunity to further improve the environmental performance of clean energy solutions. As a matter of fact, more new capacity was installed for solar than any other power generation technology in the EU in 2019 [1]. This commitment is also illustrated with the approval by the European Commission of a legislative package called “Clean Energy for all Europeans”, finally completed in 2019.”

 

Eqn#2: The definition of ‘r’ presented very late in line #215. Instead, it can be presented in line# 205 like: “with discount rate(r)”

 

Answer:

The authors completely agree with this comment. The definition of r has been introduced prior to equation (2) so the reader is able to identify the parameter earlier.

 

Table#2 may be redundant. (line #231).  

 

Answer:

Table 2 has been expanded with the climatic zone for each country. This information is valuable regarding some comments in the discussion of the results. Average minimum and maximum temperatures are also part of the econometric model developed.

 

Line #229 has reference error: “Error! Reference source not found”

 

Answer:

The authors sincerely apologize for this mistake. All reference errors have been corrected in the main text. The reference in Line 229 was referring in the original manuscript to Table 2.

 

There are two table#2 (line#231 & line #251). In Tabble #2 (above line 253), is is not clear what is meant by thrid columns (3),(3) & (5) like 2% Io (3). Also, what is the fundamental reason for using 10% for single axis and 25% double axis. Please clarify.

 

Answer:

The authors thank the reviewer for this correction. There is a mistake in the numbering of these two tables. The real table 2 is placed above line 231. The table starting in line 253 in the original manuscript is meant to be Table 3. The values in column 3 correspond to an early classification in a previous Draft. This numbering has been removed.

 

Hardware costs for each PV configuration have been assumed as function of costs of the fixed case with a 10 % and 25 % increment. This hypothesis is assumed as a combination of the source material of reference [39] and specific meetings with the authors of the cited reference and other industry experts. In any case, the value of this hypothesis is parametric and could be modified in future research.

 

In table #7: What is the significance of color fills (red and green)?

 

We see that in line #321. However, this legend should be on top of bottom of the table for readers' convenience.

 

Answer:

A legend has been added to Table 9 describing the meaning of each color fill to convey this information clearly. This legends reads as follows: “Green filled: Best PV configuration for each country/group of countries. Red filled: Worst PV configuration for each country/group of countries.”

 

The table with all 20 countries and their standing seen table #7 is the most important table in this manuscript. It is well presented Portugal, Bulgaria and Romania are good for one-axis. Authors may consider including their current situations in terms of energy generation from renewable/PV.

 

Answer:

A brief overview and comparison have been added at the end the of results section, in order to provide a better context. It reads as follows: “It is interesting to note that best countries LCOE wise still have an underdeveloped potential regarding solar PV; Portugal, Bulgaria and Romania had in 2019 an accumulated total installed capacitiy in solar PV facilities of under 1500 MWpeak each, while far from optimal countries LCOE wise like Germany had over 49000 MWpeaks of accumulated total installed capacitiy in solar PV facilities by the end of the same year [44]”

 

I am assuming, the term "Own Elaboration" was used to convey the author interpreted the result for their tools?

Answer:

The term own elaboration is used in this text to clarify that either a table or a figure have been built by the authors with the aid of an external source of data ,tool or map information. For example PVGIS, OpenStreetMap.

Appendix is well presented. I suggest the authors to revise this manuscript and make it a little shorter. If conveyed more efficiently and concisely, this manuscript can be an interesting read. Sincerely The Reviewer 

 

Thank you again for your kind words and your comments.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

This a review for the revised version of a previously submitted article. The comments were taken into account, and a much better improved article has resulted. Yet, there are still some issues that need to be tackled before the article is deemed adequate for publication, as considered bellow.

After reading it, I have some general comments/questions concerning it.

• The abstract is better, but still needs some improvements. The first phrase is surely badly written; it is possible to say that the locations are capital cities, and LCOE is singular not plural. Please improve it.
• You refer maps in the abstract, and they are presented in the article. Yet, in particular for large countries (e.g Spain, France) with various climatic zones consider that the all country has the same behaviour. Maybe include a discussion that the climate is not so relevant when compared to other factors, in order to justify the inclusion of the figures. As it is, one may wonder why not a heat map.
• Too much keywords were used, for example Solar PV is not necessary in my opinion.
• Concerning Table 1, the references numbers must be included in it, and a brief analysis of the information given in the references is desirable.
• The relevance of including the average minimum and maximum is more clear in the results. Yet, when you give the information, no note is given that this information will be used bellow. Can you refer that the information is used bellow, and how temperature influences the performance of PV systems.
• I have strong doubts that you refer correctly the climate zones. For example,. Sofia has a Humid Continental Climate, not Oceanic Climate (is more than 200 km from the closest sea, and more than 2000 km from the Atlantic), and even the Wikipeda states otherwise. Please check them.
• Calculation are made in a n yearly basis, but sometimes is harder to understand it. For example, some variables should include year, as for example w, wages. Please be more clear.
• A split of the main terms of LCOE will be desirable for the various capitals, it will help identify what are the main cost terms.
• It is clear you tested a lot of models. Yet, you tried what the software had in store, or was there a logic to your selection.
• In the model is clear that the average temperatures look to be more important than solar radiation, but no explanation is given. Please try to better analyse the results, is too limited.

Bellow I list of some more specific comments and questions concerning the article.

• The English is much better, but still deserves a revision. Please do it. For example, sometimes .. appear.
• A more complete discussion of the WACC is desirable, in particular what are the main terms, as for example private equity or bank loan. Please outside management are normally not aware of what WACC is. Give an example when results are presented on how a value is determined, it is unclear how you calculate the values and the references you use.
• Table legends should be before the table and nor after. Not sure what is the formatting rules of MDPI, but check them before and do the changes, not sure if MDPI will do it.
• Please format text to minimize blank spaces, in my point of view is no problem start section 2 before Table 1.
• You refer that there are two methods to estimate the LCOE. Yet, you do not refer which one you use.
• You refer that you only aggregate if the countries are smaller than 65 000 Km². Yet, you aggregate Denmark and Sweden, and Sweden is as large as Spain. Please explain why you violated your criteria.
• A list of variables and acronyms will be a good addition to the article, there are too many variables, is easy to forget them. And variables should be defined the first time they are used, in some tables they appear before they are defined.
• Concerning the reference to Seville, and the relevance of the wages, is odd that the LCOE in Seville is larger than Madrid. Capital cities normally have the largest wages in a country, many times by a massive margin. Is the opposite in Spain.
• The description of the variables and constants of the econometric model should be more complete. Please elaborate.

More questions and issues can be considered for this article, but the listed above are sufficient the paper should be subjected to Minor Revisions, probably without needing a revision after submission of the revised version. The questions/observations considered above should be considered to improve the quality and readability of the study.

Reviewer 2 Report

The manuscript is much improved, particularly in the introduction. The scope of the analysis and reference to background is much clearer.

Regarding my central question about the model, much remains unclear however. The authors make two statements that seem inconsistent. First, that hardware costs are fixed across the common market and second that hardware costs are ~50% of initial investment even though their model then analyzes widely the widely varying labor cost component of the initial investment. These two statements cannot both be correct unless the authors mean that hardware costs are ~50% on average across the common market, with labor contributing a greater and lesser fraction in different countries.  That is how I interpreted the model at first read, but some of the language in section 2.3.2 is inconsistent. If my understanding above is correct, then T is simply the hardware cost of the corresponding tracking/fixed configuration, in which case introducing a new variable/parameter is adding to the confusion. It would be much simpler to state something like, "T is the average installation and soft costs (~=H) for the common market," or something that captures the concept. As it is, the text implies an independent T value for each location, and the response to reviewer comments isn't completely clear. If this is correct, please be more explicit. Including the weighted labor costs in Table 4 is helpful. 

The other great source of uncertainty about the model is the source of the relative hardware costs in Table 3.  Again, reference [39] contains only very general discussion about the relative contribution of hardware costs to the total, no discussion of the relative hardware costs of different tracking configurations, and in fact no discussion of how cost scenarios vary across the countries of Europe or any geographic basis. Further, the cost scenarios in the reference do not themselves refer to any supporting documentation, and appear to be included mainly as model inputs to a further analysis of PV/storage systems. No doubt the discussion of econometric concepts was very useful to the authors' development of the present analysis, and the authors of [39] may have a great deal of generalized expertise on the subject, but there is no substance in the reference to support the claims in the manuscript that refer to it.

The ability of the model to correctly identify the optimal PV configuration will depend greatly on the accuracy of the hardware costs assigned in Table 3. If the relative cost of single or dual axis tracking is higher or lower, it will be reflected in the I₀ component of the LCOE calculation - both directly through the hardware cost and indirectly through the assumed labor costs. If the authors lack a concrete source for these relative values, that doesn't eliminate the value of the manuscript and the model developed, but they must be more explicit about how the relative weights are obtained and whether they trace to anything more concrete than reference [39].

I must note that reference [39] is a thesis focused on analysis of economic payback and LCOE for PV systems in combination with storage under different consumption and compensation schemes. This material is far afield of the subject of this manuscript, and the thesis presents no data on PV system costs. Using this source to support concrete claims about relative costs is misleading, in my opinion.

As I stated in my previous review, given the uncertainty of the sourcing of these fundamental claims, I cannot truly validate the work here and therefore cannot recommend publication.

I suggest the authors consider other references and check their input values. Here is a possible place to start:

Rodríguez-Gallegos, Carlos D., et al. "Global Techno-Economic Performance of Bifacial and Tracking Photovoltaic Systems." Joule (2020).

Reviewer 4 Report

Dear Authors:

The revised version addressed some of the weaknesses in the earlier submission. 

The image quality/resolutions should be fixed in final published version.

Sincerely
The Reviewer