Desalination in Spain and the Role of Solar Photovoltaic Energy
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsDear Authors,
thank you for your paper and your work on this topic. I would recommend it with some revisions for publication and I hope you can see my comments in the PDF, which I did during the reading. Please consider the following points:
1.) Desalination: I think we are talking here about reverse osmosis technology, but you did not mention this at all. Please add it in the introduction and describe at least briefly, how this works.
2.) Environmental impact: yes, desalination can help with water scarcity and everywhere new plants are being build or old plants extended. But nobody considers the effects of brine discharge to water bodies or even considers this during the planning of these plants. Did you ever see such an outfall and are you aware of the quantities of highly saline and heavily polluted water discharged? You should mention this at least, despite it is not the topic of your paper.
3.) Wording: when you are talking about energy, it is never produced! Also a PV plant does not produce solar electricity. Be aware of the 1st law of thermodynamics and use words like generated or converted. It reads much better for someone with a background in energy engineering. Also: energy is not injected to the grid; it is fed in or something like that. You are injecting a medication, not electricity.
4.) Design of PV system: this is subject to another topic and does not play any role in the framework associated of PV driven RO (esp. Fig. 5). You always would optimize solar systems to be as efficient as possible, especially to save the generation costs. It is OK to use PVGIS, but I would not put Fig. 6 – everybody can use this website easily. The benefit of Fig.7 and the 3D view on it are a nice variation, but you could also give the increase in power giving a percentage. Same with Fig. 8 – give the power increase in kWh by 1 resp. 2 axis tracking, you can put it in the figure or give a percentage.
5.) RO and PV: you are missing an important assumption, which you silently take: the electrical grid is actually not a storage system, where you simply can put excess solar electricity and take it during the night. This requires fossil fuel powered plants, which need to be there in parallel to the installed PV plant. You should clearly state that you are analyzing grid-connected desalination plants and the cost effects on the water price by PV, but with this assumption it could be erected anywhere. It is not needed to put them besides the desalination unit, where maybe land costs are high and access to the grid complicated.
6.) Economic analysis: you are assuming, that there are no financing costs in general. Mostly, such projects have to be financed by banks, which require an interest rate (for the analysis, mostly “weighted averaged capital costs” are considered). You can do so, but state it clearly and estimate, how much the impact on the analysis is. Your general results are interesting, showing the optimal capacity of PV systems, but the range is also very wide (e.g. 60-120 MW) which makes it not very specific. If you consider EU funds, the whole analysis becomes obsolete. Better you delete it (line 467), it confuses the reader.
7.) Formal aspects on Figures and Tables:
a. Tab. 1 is unreadable, please consider
i. switching lines and columns,
ii. round numbers,
iii. use the right units,
iv. format numbers always right aligned and
v. never split tables between pages! This is generally for all tables.
b. Fig. 2 is done by XLS and pasted with bad resolution to LaTex, my students do that better. Consider your diagrams by a nicer software with LaTex export, e.g. GNUplot or something more usable. Consider this for all diagrams.
c. Fig. 4: Energy is not produced!!
d. Fig. 5: trivial and not our topic here, unless you explain why.
e. Fig. 6: trivial and not necessary.
f. Fig. 9: put them separately, because this is one of your important results. I would choose the colors differently and more convenient.
g. Watch for unit spelling in Tab. 4 !
h. Fig. 10: this is the core result of your work to me, put it separately and maybe not with XLS.
8.) Conclusion: you should put another focus on your core results of the analysis, see again Fig. 10 and summarize this. Also give a possible future outlook, where research still needs to be conducted and from what PV-RO systems would benefit (i.e. island solutions for remote areas, where no electricity is available)
Summarizing, there is still some rework to do, but I am confident that your work will benefit from the improvements and the result will be a nicer paper.
Best regards and good luck!
Comments for author File: 
Comments.pdf
The English is mostly OK and understandable, sometimes there are spelling mistakes, undefined abbreviation and mistyped units. It would be minor revisions necessary.
Author Response
The authors want to express thanks to the reviewer for your valuable comments that have improved the manuscript.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors1. This article is written in quite general terms and resembles a part of an engineering thesis in which calculations were made assuming many simplifications. The topic itself is interesting, but the article is not written in a truly scientific manner (insufficient introduction to the topic, too many general assumptions and general descriptions of the desalination system/history in Spain, too little emphasis was placed on the accuracy of energy analyses performed). The conclusions written by the authors are also too general, and, in my opinion, in their current form, they do not make a significant contribution to the topic discussed. The article should be significantly revised and enriched with up-to-date relevant references. The energy analysis part should be described in more detail (more scientifically).
2. The article requires linguistic and editorial correction.
3. Abbreviations should be defined the first time they are used in the text.
4. Lines 42-43: Cite more information regarding the cases discussed, related to the cited articles.
5. Line 52: reference [14] seems a bit out of date (2016). Present current data with appropriate literature sources.
6. Lines 59-61: incomprehensible sentence. And for what purpose do the authors provide this data? (The flow of the text is inconsistent.)
7. The Introduction chapter should be edited to include more current references and to properly introduce the topic of seawater desalination while maintaining the flow of the text.
8. The authors wrote: "This paper demonstrates the viability of implementing photovoltaic systems in seawater desalination to make this resource attractive for agriculture", but they did not precede this statement with an appropriate introduction to the above-mentioned topic.
9. Improve the readability of Table 1.
10. Lines 161-166: Incomprehensible paragraph (duplication of information).
11. The chapter Cost of desalination should be rewritten so that it forms a coherent whole.
12. The methodology described by the authors in the Methodology chapter is very simplified.
13. Lines 296-297: Provide details related to horizontal one-axis solar tracking.
14. Why is the mean irradiance for 1-axis tracking lower than 2-axis tracking at 12:00 in Fig. 8?
15. Lines 323-324: “For latitudes above 40 degrees and for latitudes below 40 degrees”, therefore, for all latitudes except 40 degrees? The rest of the sentence is also not comprehensible enough.
16. Lines 342-343: “[…] GCR = 0.3, which means 3 square meters of land area occupied for each 342 useful square meter of solar facility.” is incorrect.
17. Line 354: not Fig.8.
18. Line 454: units.
Comments on the Quality of English LanguageModerate editing of English language required.
Author Response
The authors want to express thanks to the reviewer for your valuable comments that have improved the manuscript.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsDear Authors,
thanks for all your corrections! You significantly improved your paper to bring it to publication. After the final typesetting, I would be grad to receive the final version. Keep up your good work and continue with the publication of your research.
Best regards!
Reviewer 2 Report
Comments and Suggestions for Authors1. I state that the authors provided comprehensive answers to the comments presented to them and introduced the necessary changes. I have no further comments.
Comments on the Quality of English LanguageNo further comments.
