Assessing the Techno-Economic Impact of Derating Factors on Optimally Tilted Grid-Tied Photovoltaic Systems

Round 1

Reviewer 1 Report

Dear authors,

Although I found this paper strikingly interesting and outstanding, I have a few comments about the research you properly conducted, so everyone of the following suggestions is aimed to enhance even more the quality of your paper, these are:

1. Re-write the tittle including “A case study…”
2. The Figure 1 is portrayed but not mentioned or used in the whole paper.
3. You should clearly state the difference of your paper with REFERENCE 8, otherwise your research droop sharply because both are very aligned.
4. Please standardize the titles of figures as well as tables when you cite/reference them because in some cases you use capital letters and later lowercase, f.i. line 150.
5. Make bigger table 2.
6. I highly recommend you include this reference (DOI: 10.1016/j.jclepro.2019.118870) because is very aligned to your RELATED Works and match perfectly in this section and in the cost analysis.
7. The claim makes me wonder how do you achieve the aims of this research of selling/trading the surpluses to the main grid (f.i. line 204), do you mind explaining this a bit more?
8. Please use the sameness to all your figures, f.i. Figure 8 differ widely from all others, additionally you did not include the axis names.
9. Why do not you consider Air Mass, I mean you are conducting a research about derating parameters of PV systems, so this is highly important since air mass is a key factor.
10. As far as I can see at the Figure 10 you do not have an important difference in terms of the investment, f.i. “VAC vs NT” I would like why you did not consider VAC so as to boost the PV generation along the year and reduce the PAYBACK period?
11. Lines 452-453 which aspects are you meaning here?
12. Please rewrite the conclusion adding more values, f.i. 450-451.
13. Please use the correct symbol for Celsius degree.
14. Please read this paper and consider adding to your research so it matches with rural areas and also with sizing methodologies for renewables facilities. DOI: 10.1016/j.rser.2019.109691

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Reviewer comment

The article deals with the influence of degradation factors of PV plants on the economics of their operation. Within the analysis, 6 variants of the combination of three degradation factors and two lifetimes for the selected PV system were investigated.

The article presents the results that are expected, thus confirming the known and assumed facts about the operation of PV systems.

The article is theoretical, for its wider use in practice it is necessary to explicitly define all degradation factors for a particular PV system, a specific location and specific economic conditions.

Since PV systems belong to the group of so-called unpredictable energy sources, it is very difficult to design in detail and calculate their operation from a long-term perspective.

No need to be corrected:

Line 181 - I do not understand the sentence "Simultaneously, this would be lessen the stress from the grid." Connecting PV plants to the grid, on the other hand, increases the requirements for quality and management of the grid from the point of view of the primary source of electricity.

A lot of numbers are found directly in the text, which makes the content confusing. (lines 365-382, 408-416)

Some paragraphs are unnecessary in the article, such as Chapter 3.2 and Chapter 3.5, which describe the theoretical aspects of the HOMER procedures used in the output calculations. The effect of the data in Chapter 3.7 on the results of the analyzes is also not described.

It is necessary to correct:

In the abstract it should be noted that the simulations and their results are based on average values of degradation factors.

Lines 5-7 state "However, the available literature does not explicitly concentrate on the techno-economics of the derating factors within the PV system", and lines 77-79 state "Numerous articles have studied the techno-economics of hybrid renewable energy systems ... ". It is appropriate to rephrase the sentence to reflect the explicit meaning.

There are certainly a number of scientific publications devoted to research into the degradation of PV panels, such as „Investigation of Operating Parameters and Degradation of Photovoltaic Panels in a Photovoltaic Power Plant“ and others.

Line 146 - Derating factor is given without dimension, ie 0.88. If the % unit is used, it is an efficiency.

Table 7 and Chapter 4.6 deal with the emissions of the individual configurations of the PV systems. How do these systems produce emissions? Are these emissions needed to produce PV systems, or are the emissions saved? It is necessary to explicitly define the source of emissions, or to state that it is a saving compared to a specific source of electricity (for example, a coal-fired power plant, etc.).

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Abstract: It needs to be more concise. The first 7 lines are introductory.Try to be straight to the point.

Abstract: "The PV module adopts an optimal tilt angle developed by a simple mathematical model." First, this does not belong in the abstract; perhaps in the methodology. Second, what does it supposed to mean anyway that is worth mentioning?

Abstract: "Simulation results show that PV power generation would vary around 12%". What does it mean? On a daily basis? Monthly? Annually? It does not make any sense.

Abstract: The last sentence basically says that the conclusion of this paper is that the higher the losses the lower the financial gains. Is this not common sense? What kind of reaction would you expect from the Reviewer?

Introduction is not an introduction to this work. It is an introduction to climate change etc. Please delete and rewrite or just make 1.1 and 1.2. as your 1. Introduction.

Problem statement: This is not a postgraduate dissertation. It is a journal article. Please merge sections 1 and 2 in one and please be more concise.

Table 1 is in the wrong order (figures that are mentioned later show up earlier). Also, Table 1 should have a reference.

1.1. Why is PV tracking a "derate factor"?

Figure 2 shoes up in page 3, but the authors introduce it in page 4. Actually, Figure 3 is mentioned in the text before Figure 2. Please revise.

Figure 2 has a source for an "author". Which author?

Introduction is poor. Jumping from one topic to another. What do hybrid systems have to do here? Just mention the studies on linear, nonlinear degradation, soiling, snow, thermal effects etc. and state your contribution. I disagree that this is the first one that includes technoeconomics, but I would accept the fact that it is probably the first one in the region.

Please use the degree sign. Not superscript of 0.

Rd is a common metric for degradation rate, not diffuse solar radiation. It is confusing, especially in a paper focusing on derate phenomena.

The methodology is too simplistic. Still trying to figure out what the novelty is here.

If you abbreviate something in the abstract, you have to abbreviate it again in the manuscript, e.g., IoT.

Still trying to figure out where the IoT concept is.

Line 386-388: it is not 0.5%/year. If the max is 20% loss over 20 years then the Rd could be up to 1%/year.

The figures should appear after they have been mentioned. Not the other way around.

Figure 17a is confusing. The labels on y axes should be the other way around. Caption "Annuan" should be "Annual".

I did not perform a detailed review because I spotted significant flaws from the first few pages. I understand if this a paper written by a junior researcher but the authorlist is long including senior researchers who I hope they will contribute and advise in order to bring this manuscript to a journal's standards. For now, I am very sorry but I cannot recommend it for publication.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Thank you for revising your manuscript.

Performance loss effects such as degradation, soiling, snow, etc have been extensively analyzed in the literature including financial aspects based on LCOE, NPV etc. Please enhance your introduction, and remove irrelevant citations. Include the state of the art, for example:

Linear and non-linear degradation and LCOE:

https://doi.org/10.1016/j.renene.2016.10.052

10.1002/pip.2744

10.1109/JPHOTOV.2020.2992432

Soiling and LCOE:

https://doi.org/10.1016/j.renene.2017.12.076

https://doi.org/10.1016/j.apenergy.2018.07.020

https://doi.org/10.1016/j.joule.2019.08.019

https://doi.org/10.1016/j.renene.2020.11.044

https://doi.org/10.1016/j.energy.2020.119018

Snow:

https://doi.org/10.1016/j.solener.2013.02.014

Although the list could go on with thermal, shading, LETID, LID, and other losses, the aforementioned are the main ones that would help enhance your introduction.

Other comments:

1) "Solar-powered photovoltaic" does not make any sense. Please delete "solar-powered".

2) Table 1. Be more explicit in your descriptions. You could say: "An example of typical values commonly assumed for PV system losses [1]; the values may vary according to the climatic conditions."

3) Again, Tables and figures should appear AFTER they have been mentioned in the manuscript NOT before.

4) Line 29: You could say that some derate factors are reversible (e.g., soiling can be reversed by cleaning the modules) or irreversible (e.g., material degradation can rarely be reversed).

5) Line 38/39 should not be a paragraph. Keep going with soiling including the references I have suggested. Use google scholar to find more, just type some keywords e.g., soiling photovoltaics LCOE

6) Line 52 onwards: add the references above and talk about LCOE impacts instead of generic references. For example, you cannot say "PV modules degraded non-linearly at an annual rate of 1.54%...". If it is non linear then the rate should not be fixed.

7) I am still unsure what the hybrid systems have to do here. I understand HOMER is commonly used for hybrids, but you are not comparing softwares here. You are performing a techno economic analysis for PV by quantifying the losses financially. Just try to be more concise, review the relevant literature and then make your case. Introduction does not have to be long, but it has to be straight to the point.

8) Line 114-119: Revise after including the aforementioned references. You can reduce the tone of your statements that "this is the first ever" work. Just say that it has not been extensively analyzed in the literature, especially for the region in Bangladesh.

9) Line 120-121. This is not "a contribution"; please delete.

10) Line 122-123. Same as above, nothing new here. Please delete.

11) I assume you are referring to a self consumption system? Clarify this.

12) You do not have to say "Solar PV". "PV" is fine.

13) Usually, prosumers do not get FiT. The concept of self consumption is different than FiT. I am not aware of Bangladesh policies.

14) Why is this an HRES system? Am I missing something? I thought it was connected to the grid and did not have any batteries.

15) HOMER was not developed by NREL.

16) HOMER is not the most popular tool, especially among PVSyst which is the most bankable software. Please read your manuscript carefully and if you are unsure or not have an appropriate reference do not make such bold statements which are incorrect.

17) Line 160-161: Which manufacturer claims 12% power loss for factors that are beyond PV module? E.g., snow, shading, mismatch, wiring etc.?

18) a-Si not a-si.

19) Not sure why the authors insist in talking about hybrids and standalone systems. Your case study is related to an on-grid system.

20) What do you mean by "glossier aesthetics"? PV modules should not be "glossy", because this indicates reflection losses!

21) Please add the Koppen Geiger climate index for Hatiya.

22) Line 192. This is redundant and common knowledge. Please delete.

23) Line 194. I do not understand the IoT comment here. It is irrelevant to this work, please delete.

24) Section 2.3. So what is the optimum angle? Do you assume that the modules change position every month? If yes, this is not realistic.

25) Line 281. Tilt and azimuth angles are not dependent on weather. They depend on location.

26) Line 253. Why do you keep repeating the batteries? I thought you are not using battery storage (line 137). Please also remove HRES; your system is not HRES.

27) Line 268: What emission penalties are you referring to?

28) Section 3.1. Why is this a result? Looks like an overview or theory to me.

29) Line 295. The authors mention Figure 7 after it appears in the manuscript and then they jump in Figure 9 leaving Figure 8 behind.

30) This study does not quantify the costs of individual derate factors. It only takes them at a fixed percentage: 2%, 12% and 22%.

31) The authors seems to have ignored my comments about the figures. e.g. Fig. 9

32) Try to use normalized parameters, for example kWh/kWp instead of just kWh. It makes it easier to generalize your findings.

33) Line 346: "most costlier" should be most expensive but I do not understand what you mean with that sentence. Why is the grid more expensive? And why is the converter cheaper? Among what? 1 module Vs 1 inverter? or 10 modules vs 1 inverter?

34) I might have missed it, but what size is your system?

35) PV system degradation of 0.5%/year is too low. It should be OK for PV modules but the sentence in Line 369 states 10% system degradation over 20 years.

Author Response

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Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

Thank you for your corrections.

I think that the article has been improved enough to recommend for publication. However, I still do not understand Section 3.5. It is like saying that soiling, which is an environmental parameter, affects the environment. There is no mechanical system that works with 100% efficiency. Derating is expected in any system. So, because PVs derate, it does not mean that they cause emissions because they are backed up by the grid. If that is the case, then add more PV modules to cover your losses. My recommendation would be to delete the whole section 3.5 and Table 6 before publishing this manuscript.

Furthermore, Line 406, just delete the sentence starting with"Moreover, CSP...". It is irrelevant.

Author Response

Thank you for the review. We have deleted section 3.5, Table 6, and the mentioned sentence.  Please see the attachment.

Author Response File: Author Response.pdf