Performance of Monofacial and Bifacial Silicon Heterojunction Modules under Desert Conditions and the Impact of PV Soiling

Round 1

Reviewer 1 Report

My comments attached with

Comments for author File: Comments.pdf

The article was written in good language with some typographical errors that were clarified in the report

Author Response

May 2^nd , 2023

Manuscript ID: sustainability-2345613

Dear Reviewers,

Thank you for having the time to review our paper “Performance of monofacial and bifacial silicon heterojunction modules under desert conditions and the impact of PV soiling”. Here is our respond to your feedback including the details on the revised manuscript. Revisions to the manuscript are marked up using the “Track Changes” function.

Responses to Reviewers’ Comments – Reviewer #1

1. Abstract: No significant findings of the study were mentioned in the abstract

Since the paper aimed at comparing the performance of monofacial and bifacial silicon heterojunction technology in desert climate through indoor and outdoor testing. Paper findings were reported in the abstract as:

• Bifacial gain of 15% of silicon heterojunction technology when compared with monofacial silicon heterojunction technologyinstalled in desert climate.
• The reason of high bifacial gain is mainly due to high albedo measured in real operating conditions.
• Since soiling has a major impact on PV performance in desert climate we have reported two main findings:
  • Bifacial technology is less sensitive to soiling compared with monofacial since soiling rate on the rear side of bifacial module is insignificant.
  • The cleaning frequency of bifacial should be optimized compared with monofacial technology.

2. Please provide a statistical data about how much the percentage of bifocal PV technology represented from the total built-up PV capacity.

According to the International Technology Roadmap for Photovoltaic (ITRPV) 2022, the bifacial technology will increase form 40% in 2022 up to 85% in 2032.

This information has been added to the manuscript (Line 29).

3. Line 33-34 "Several studies have reported a bifacial gain up to 33 30% when comparing to monofacial technology", While, in line 54-55 " Our main findings showed that the bifacial module demonstrated 15% higher energy yield than the monofacial module". Why this difference, discuss?

Agree, in addition to the mentioned parameters that impact the bifacial gain (Line 35-36), in this study a lower bifacial gain has been reported mainly because of the PV soling.

A paragraph has been added to the manuscript (Line 58-60) to discuss the difference in the bifacial gain obtained in this study.

4. Line 75: " in Doha, state of Qatar" Please, add the latitude and longitude of the site

Latitude and longitude of Doha has been added to the manuscript (Line 77-78).

5. Line 76 : " tilt angle of 22° was measured" source is missing

The Plane of Array Irradiance (POA) has been measured at the Outdoor Test facility OTF (latitude 25.33° North and longitude 51.43° E) at 22°. This is the optimal tilt angle for the OTF.

6. The literature review is limited and many important relevance works are missing. The works cited in the introduction were not discussed.

From the authors view pints, the introduction has been structured according to the following paragraphs as follows:

- Latest status of the PV market and the role of bifacial technology.

- Identifying the gap in literature, particularly, desert climate regions.

- narrow the focus of the paper to the impact of temperature and soiling.

- Finally, give a brief on what will be discuss in this paper (paper outline).

Additional paragraph has been added (Line 58-60) to discuss the difference in the bifacial gain obtained in this study.

7. There is no mention to the soiling in the Material and methods section!!!

The module cleaning schedule was performed to understand the impact of soiling on PV module performance. Further, we referred to table 2 for more details on module cleaning frequency (Line 94-95).

8. Table 1; Source is missing

Source has been clarified from PV module nameplate to PV module data sheet (Line 116).

9. Line 87: How you measured the Temperature of the cells in the module, where you put the prop of the thermocouple? Please depict it in Fig. 1

Module temperature was measured using PT 1000 thermocouple attached to the rear side of the module (Line 89-91).

Figure 1 has been modified to include the thermocouple (Fig. 1, Line 109-110).

10. In this context - Fig.4 –C, depicted the average module temperature during the year 2019! I think you measured the temperature of the glass cover, because these temperatures is approximately equal to ambient temperature!

We measure the module temperature using thermocouple PT1000 as per standard procedure on the rear side of the module and not on the front glass. Ambient air temperature has been measured using Thermo Transmitter. Generally, module temperature is higher than the ambient temperature.

11. Figure 5. Please add the sky-diffuse solar irradiation to the Fig. 5.

Diffused Horizontal Irradiance (DHI) has been added (Fig. 5b).

12. What is the benefit of Fig. 5, if it is not reflected the real situation of the operation condition of the Bifacial PV module. The back side of the Bifacial PV will not receive this much of reflected solar radiation!!!! Authors should depict the global tilted solar radiation for both sides.

Figure 5 reflects the real measured solar irradiance components at the Outdoor Test Facility (OTF).

The benefit of Figure 5a shows the typical measured albedo throughout one year. Two conclusions from this Fig. one is the high measured albedo of about 40% and second is the insignificant variation of this values throughout the year.

The benefit of Fig. 5b is to represent a typical daily profile of the solar irradiance components including albedo. We have added also here the DHI as recommended by the reviewer. This figure again shows that albedo is quite constant throughout. Additionally, the ratio between the solar irradiance components are presented.

The back side of the module will receive a considerable amount of the solar irradiance. However, non-uniformity of the solar irradiance received on the module rear side is known issues and required a separate study to measure the solar irradiance at different points on the rear side of the solar module using solar cells as a sensor to measure solar irradiance.

13. For a comprehensive overview, it is advisable to add a data from the month-long to summarize the (min., max. and average monthly values) of air temperature, solar radiation, solar cell temperature and global energy generation by PV.

Average values over the testing period of the ambient air temperature, solar radiation and module temperature has been provided (Line 160-163).

14. Line 160: Typo " repectively"

Corrected (Line 163)

15. Line 196: Typo " temprature"

Corrected (Line 173)

16. Line 224: Typo " Similar studies [25]" it should be " A similar study [25] "

Corrected (Line 232)

17. The ref. [25] has no deal with bifacial PV at all !!!!!

Correct, the reference [25] reported the soiling impact not the bifacial gain. Reference has been replaced with the right one [Cuevas, A., Luque, A., Eguren, J., Alamo, J.D. 50% more output power from an albedo-collecting flat panel using bifacial solar cells. Solar Energy, 1982, 29, 419-420] (Line 401-402)

18. This study is useless if the authors do not correlate a relation for the surface temperature of the PV cell in terms of the air temperature and the solar radiation incidents on the front and back solar panels. Please refer to: https://doi.org/10.1016/j.desal.2007.04.013, which has done for desert climate

Indeed the impact of the surface temperature and the configuration of the PV module (with or without back sheet material) will impact the heat effect on PV performance. From the author’s point of view, the heat effect is additional important factor that affect PV performance and, therefore, requires a separate paper to study. The focus of this paper is limited to compare the performance of bifacial and monofacial silicon heterojunction technology and the impact of soiling in desert climate.

Recommended reference has been added (Line 387).

19. How authors treated the ground reflected solar radiation from measured data.

Albedo has been calculated based on the measured reflected solar irradiance divided by the measured incident solar irradiance. Both are measured irradiance (description was given in section 2.2 Line 77-85)

20. There are no convincing discussions to the results what is written is description not discussion! For example: Why the productivity in 2018 less than in 2019? Why the monthly productivity of monfacial higher than bifacial at some months in Dec. 2017 to March 2018

Discussion of these points has been elaborated (Line 306-319).

21. Line 201-203"Note that for the year 2017, data collection for both modules started from April 2017" While, Fig. 7 shows that the data collection started even in February 2017 for bifacial

Dates are corrected, for the monofaical technology data collection started in March 2017 and for the bifacial technology data collection started from Jan. 2017 (Line 210-211) and Fig. 7b (Line 227-228)

22. Fig. 7 (b), written years 2017-2018, while the x-axis shows three years!

Corrected, years in the x-axis has been corrected to 2017-2019 (Fig. 7b)

23. Fig. 8, the descriptions that written over the charts are not convincing at all! How can rain continue in a desert area like Qatar for most of the year? How can a sandstorm blow for several months? This statement is not convincing at all!!!!

Figure 8 can be used with the detailed data presented in table 2. The comments column in table 2 givesthedateswhen there was:

- PV module cleaning,

- An event of raining and

- An event of dust storm.

Rain events in Qatar are occasionally during winter months only.

Sand storm happen several times per year during one or two days as stated in the comments column of table 2.

24. Line 267-268: " the calculated soiling rate for the monofacial module is 0.48 %/day, 267 0.58 %/day and 0.50 %/day, respectively ". Who it measured and calculated?

The calculation of the soiling rate in %/day has been explained (Line 248-251). Measuring the drop in the energy yield during a defined period in days has been used to determine the soiling rate.  

25. There is nothing about Assumptions, Limitations of the study and Uncertainties of the obtained results. Please refer to https://doi.org/10.1007/s40243-022-00216-1

Measurement uncertaiity has been given for the indoor testing of the the PV module (Line 131).

Measurement unceetainity of the PV module has also been given (Line 176).

26. The list of references is very short!

Additional reference has been added (Line 387). Self-cited references are removed

Finally, I say: The increase in the energy yield of the bifacial is clearly expected, of course, as a result of doubling the area! The question is, is the feasibility of this technology approved, and is it necessary for use in Qatar? Therefore, an economic study must be done to demonstrate the feasibility of this technology for the State of Qatar

Thank you for your comments and recommendation. The bifacial technology has already being demonstrated in the state of Qatar. Currently, Qatar has 800 MW site operational in Al Kharsaa and there additional two PV sites will be operational next year with a capacity of 400 MW each (Ras Laffan & Misaeed). Work is in progress to develop a techno-economic study to include the cost of cleaning to the PV site Operation & Maintenance (O&M).

 

Author Response File: Author Response.pdf

Reviewer 2 Report

 

Excellent research work and great contribution of practical knowledge.

following corrections are required;

Line #60-#61: "silicon SHJ modules" to be replaced with "SHJ PV modules."

Line #77: "foudn" to be replaced with "found".

Line#78:  "Horisontal Irradiane" to be replaced with " Horizontal Irradiance".

Line#180: " mnpact" to be replaced with " Impact".

 

Author Response

May 2^nd , 2023

Manuscript ID: sustainability-2345613

Dear Reviewers,

Thank you for having the time to review our paper “Performance of monofacial and bifacial silicon heterojunction modules under desert conditions and the impact of PV soiling”. Here is our respond to your feedback including the details on the revised manuscript. Revisions to the manuscript are marked up using the “Track Changes” function.

Responses to Reviewers’ Comments – Reviewer #2

Excellent research work and great contribution of practical knowledge.

Following corrections are required;

Line #60-#61: "silicon SHJ modules" to be replaced with "SHJ PV modules."

Corrected: SHJ PV modules (Line 62-63).

Line #77: "foudn" to be replaced with "found".

Corrected, as recommended by the journal to reduce the number of self-cited papers, the reference and the sentence have been removed (Line 79-80)

Line#78:  "Horisontal Irradiane" to be replaced with " Horizontal Irradiance".

Corrected: Horizontal Irradiance (Line 81)

Line#180: " mnpact" to be replaced with " Impact".

Corrected: Impact (Line 184)

Author Response File: Author Response.pdf

Reviewer 3 Report

The presented article describes the results of field studies of photovoltaic modules of one-sided and two-sided design, depending on various parameters. The topic of the article is relevant and may be of interest to specialists and researchers in the fields of solar energy and photovoltaic modules. The authors did a certain search for sources, they obtained interesting results, however, as comments and recommendations, several points should be noted:

1. The authors should describe in more detail the proposed technology of photovoltaic modules. To the proposed technology of photovoltaic modules, it is advisable to display several diagrams and figures explaining it.

2. What is the service life of the considered modules during their operation in the proposed region?

3. The authors should indicate in more detail the scientific novelty of the presented work, since the results they obtained are very obvious.

4. Perhaps the authors should indicate in the work the theoretical calculation formulas that predict the generated power of the modules and compare them with the obtained full-scale results - such calculations and comparisons will enhance the scientific component of the work.

5. Figures 2, 3, 4, 5, 6 and 8 should be enlarged. The reference in the text to Figure 5 should be indicated before the figure itself. Figure 8 should be moved up in the text, immediately after its first mention. What conclusions can be drawn from Figure 8? Table 2 is recommended to be abbreviated or draw conclusions from Figure 8 instead it.

6. What is the optimal period and technology of module cleaning suggested by the authors based on the research?

7. Of interest is the economic efficiency of using the proposed module and its payback period compared to a single-sided photovoltaic module.

8. Where and how do the authors plan to use their results? Authors should add a section "Directions for further research", where they should describe the planned work of the authors on the topic under consideration. Also, the authors should add a paragraph with the contributions of each of the authors to the content of the work.

9. The authors should consider modern works on the topic under consideration, as there are many studies on the topics proposed by the authors, and then highlight the fundamental scientific differences from them.

10. For the region under consideration, it is advisable to use the technology of encapsulation with a two-component polysiloxane compound in the composition with double-sided high-voltage matrix PV converters, which increases their service life, optical and electrical efficiency (for example, 10.4018/IJEOE.2020040106, etc), as well as solar radiation concentrators for double-sided illumination of double-sided PV converters with the removal of thermal energy , which will increase both the electrical power and efficiency of the module, and its overall efficiency (for example, 10.4018/978-1-5225-3867-7.ch004, etc). In the simple planar version, the temperature of the PV modules reached 50 degrees, which negatively affects the generation of electrical energy. These technologies are appropriate for use in the region under consideration and, perhaps, the authors should consider them in a literature review or in directions for further research.

In general, the presented article leaves a positive impression, however, it is not without flaws. After eliminating these remarks and taking into account the recommendations made, the presented article may be of interest to the readers of the journal "Sustainability".

Minor editing of English language required

Author Response

May 2^nd , 2023

Manuscript ID: sustainability-2345613

Dear Reviewers,

Thank you for having the time to review our paper “Performance of monofacial and bifacial silicon heterojunction modules under desert conditions and the impact of PV soiling”. Here is our respond to your feedback including the details on the revised manuscript. Revisions to the manuscript are marked up using the “Track Changes” function.

Responses to Reviewers’ Comments – Reviewer #3

1. The authors should describe in more detail the proposed technology of photovoltaic modules. To the proposed technology of photovoltaic modules, it is advisable to display several diagrams and figures explaining it.

The paper attempted to focus more on the performance of the two technologies. However, a brief on the silicon heterojunction and module technologies (monofacial and bifacial) was provided.

2. What is the service life of the considered modules during their operation in the proposed region?

Generally, 20 to 25 year service life of PV module is provided by the manufacturer. No specific climatic region is considered for the lifetime. To the best of our knowledge limited study has shown the performance throughout 20 to 25 years, yet.

3. The authors should indicate in more detail the scientific novelty of the presented work, since the results they obtained are very obvious.

The paper consider the PV performance in a specific climatic conditions, particularly, desert climate. In such a climate, PV module manufacturer and end users are interested in the silicon technology with a lower temperature coefficient to reduce the impact of high operating temperature in the field. Additionally, the paper findings presented the impact of PV soiling and the associated cleaning frequency. The latter is important for the PV site O&M.

4. Perhaps the authors should indicate in the work the theoretical calculation formulas that predict the generated power of the modules and compare them with the obtained full-scale results - such calculations and comparisons will enhance the scientific component of the work.

The calculated energy yield was described (Line 96-98).

5. Figures 2, 3, 4, 5, 6 and 8 should be enlarged. The reference in the text to Figure 5 should be indicated before the figure itself. Figure 8 should be moved up in the text, immediately after its first mention. What conclusions can be drawn from Figure 8? Table 2 is recommended to be abbreviated or draw conclusions from Figure 8 instead it.

Figures 2, 3, 4, 5, 6 and 8 have been enlarged.

The reference in the text to Figure 5 has been indicated before Figure 5.

Figure 8 has been moved up in the text, immediately after its first mention.

The conclusion of Fig. 8 has been presented in the summary section (Line 306-323).

Table 2 is presented to provide additional data that help understanding the environmental impact and module cleaning on the energy yield. The data can be used, for instance, by other authors to reproduce the results or design of experiments.

6. What is the optimal period and technology of module cleaning suggested by the authors based on the research?

Depending on the raining seasons and the occurrence of rainfalls, it was suggested that bifacial technologies require less cleaning frequency during summer months compared with monofacial technology. For out test site specifically, monofacial technology has been cleaned every two months. However, this is a site specific cleaning frequency since it depends on varying environmental parameters.

Silicon heterojunction technology has been recommended for high operating temperature climatic conditions (Line 333-335).

7. Of interest is the economic efficiency of using the proposed module and its payback period compared to a single-sided photovoltaic module.

Indeed, very important point and good idea for further techno-economic study to look the impact of, for example, the O&M cost on the return of investment.

8. Where and how do the authors plan to use their results? Authors should add a section "Directions for further research", where they should describe the planned work of the authors on the topic under consideration. Also, the authors should add a paragraph with the contributions of each of the authors to the content of the work.

Direction for further research has been added to the conclusion section (Line 346-348).

The contributions of each authors have been provided using the online tool.

9. The authors should consider modern works on the topic under consideration, as there are many studies on the topics proposed by the authors, and then highlight the fundamental scientific differences from them.

From the authors view pints, the introduction has been structured according to the following paragraphs as follows:

- Latest status of the PV market and the role of bifacial technology.

- Identifying the gap in literature, particularly, desert climate regions.

- narrow the focus of the paper to the impact of temperature and soiling.

- Finally, give a brief on what will be discuss in this paper (paper outline).

Additional paragraph has been added (Line 58-60) to discuss the difference in the bifacial gain obtained in this study.

10. For the region under consideration, it is advisable to use the technology of encapsulation with a two-component polysiloxane compound in the composition with double-sided high-voltage matrix PV converters, which increases their service life, optical and electrical efficiency (for example, 10.4018/IJEOE.2020040106, etc), as well as solar radiation concentrators for double-sided illumination of double-sided PV converters with the removal of thermal energy , which will increase both the electrical power and efficiency of the module, and its overall efficiency (for example, 10.4018/978-1-5225-3867-7.ch004, etc). In the simple planar version, the temperature of the PV modules reached 50 degrees, which negatively affects the generation of electrical energy. These technologies are appropriate for use in the region under consideration and, perhaps, the authors should consider them in a literature review or in directions for further research.

Indeed the impact of module materials (encapsulant and back sheet) has an important role in increasing the module performance and reliability in desert climate. The impact of PV module materials on the PV performance and reliability is a topic of our coming study.

In general, the presented article leaves a positive impression, however, it is not without flaws. After eliminating these remarks and taking into account the recommendations made, the presented article may be of interest to the readers of the journal "Sustainability".

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Congratulations