Round 1

Reviewer 1 Report

1. In abstract please clearly present the aim of your research and the main findings. Give some quantitative results to make more interesting for readers.

2.  the title is cleaning the PV panels using drone: How the drone will clean the PV panels. It uses water or without water? more explanation are required. 

3. How the drone will measure the quantity of dust or verify if there is dust on PV panels

4. Is there any camera and how it works, how it will communicate with operators or it is fully automatic system

5.  In fig 10, the voltmeter is connected in series, the resistor in series What is the output what is the measured value. the voltmeter and the load must be connected in parallel. Please avoid this kind of mistakes

6. how many panels are used to perform experiment. You said 60 Watt but you have more than 4 panels. Please clarify

7. how the panels are connected and what is the output power

8. What is the used load to measure the current?

9. how you calculate the dust volume? which measuring tool is used? 

10. Fig.15. is not clear how the power will increase without cleaning?

11. same technical problem in table 7. the power increases without cleaning

12. the cleaning will take place at which time to avoid affecting the output power, this needs to be discussed. 

13. the paper needs to be reformulated to show the method of dust and power measurement in addition to the cleaning method

 

Author Response

Authors Reply:

The authors are very grateful to the Editor for considering our submitted manuscript. We have revised the manuscript that incorporates the reviewers' recommendations we received and highlighted the changes made in red colour. This letter provides point-by-point answers to the comments made by the respected reviewers.

Reviewer #1

 

Comments 1:

In abstract please clearly present the aim of your research and the main findings. Give some quantitative results to make more interesting for readers.

Authors Reply:

Thanks for your valuable comments. The abstract has been almost rewritten as given below:

This study demonstrates that a drone flying above photovoltaic (PV) panels can clean the dust and enhance the panels efficiency. If operated regularly, the drone's downward thrust generated during its cruise at a certain height above the panels can remove most of the accumulated dust. Sandstorms are frequent in Saudi Arabia, creating dust deposition on PV panels, which acts as a shield against solar radiation. As a result, the energy absorption from solar radiation is reduced and subsequently, the panels' energy output is reduced. The experimental investigation is conducted at KFUPM university's beach, Dhahran, Saudi Arabia, to prove the effectiveness of the drone-based cleaning of the PV panels. Volumes of 20, 50, and 100 CC of dust were spread on the panel during different experiments. The experimental results showed that the back thrust of the drone could remove most of the dust and improve solar panels' energy output performance. For example, for 50 CC dust spread on the panel, the current increased from 1.34 A to 2.16 A (61.2% increase) relative to the pre and post drone flight for horizontal movement of the drone. Similarly, for vertical and diagonal movements, the current increased by 69.83% and 68.03% for a dust spread of 20 CC. Furthermore, a dust reduction of 74.64%, 57.0%, and 78.4% are realized during horizontal, vertical, and diagonal paths of the drone flight for 50 CC dust spread.

 

Comments 2:

the title is cleaning the PV panels using drone: How the drone will clean the PV panels. It uses water or without water? more explanation are required.

Authors Reply:

The title has been changed as follows:

Cleaning of Photovoltaic Panels Utilizing the Downward Thrust of a Drone

The cleaning method utilizes only the downward thrust of the DRONE generated during its cruise over PV panels, and water is not used.

 

Comments 3:

How the drone will measure the quantity of dust or verify if there is dust on PV panels.

Authors Reply:

In the present study, the authors tried to prove the effectiveness of the DRONE's downward thrust towards cleaning the regular dust accumulated on the panels. So, the DRONE can be programmed to fly over the panel/s as per the pre-defined schedule fed to the DRONE. However, for future work, DRONES can be programmed to monitor the PV panels and detect dust deposition and defects through several types of installed cameras.

 

Comments 4:

Is there any camera and how it works, how it will communicate with operators or it is fully automatic system.

Authors Reply:

The present scope of work did not include the camera. However, dust deposition and panel defects can be detected for future work using imaging and AI analysis.

 

Comments 5:

In fig 10, the voltmeter is connected in series, the resistor in series What is the output what is the measured value. the voltmeter and the load must be connected in parallel. Please avoid this kind of mistakes

Authors Reply:

Figure 10 has been corrected.

 

Comments 6:

how many panels are used to perform experiment. You said 60 Watt but you have more than 4 panels. Please clarify

Authors Reply:

For this proof of concept study, only one PV panel is used.

 

Comments 7:

how the panels are connected and what is the output power

Authors Reply:

Only one panel is used for the proof of concept, so there are no interconnections.

 

Comments 8:

What is the used load to measure the current?

Authors Reply:

It is a variable load, basically a laboratory resistor.

 

 

Comments 9:

how you calculate the dust volume? which measuring tool is used?

Authors Reply:

Dust is collected manually and measured using a labelled transparent tube.

 

Comments 10:

Fig.15. is not clear how the power will increase without cleaning?

Authors Reply:

The panel was not cleaned for the first two weeks, during which the current decreased and then cleaned due to heavy rain in the third week and the current increased to the original value of ~3.0 A. This is mentioned in the notes attached to Table 7 and also in the text on page 11 before Figure 15.

Comments 11:

same technical problem in table 7. the power increases without cleaning

Authors Reply:

The panel was cleaned in the third week due to rain; hence, the current increased to the original value of ~3.0 A. This is mentioned in the notes attached to Table 7 and also in the text on page 11 before Figure 15.

 

Comments 12:

the cleaning will take place at which time to avoid affecting the output power, this needs to be discussed.

Authors Reply:

Moreover, the cleaning would be done according to a preset schedule or after sand storms to minimize shading interruption and power losses.

 

Comments 13:

the paper needs to be reformulated to show the method of dust and power measurement in addition to the cleaning method

Authors Reply:

Dust is measured using a graduated tube manually before and after cleaning. Accordingly, the following text has been added in Section 3.1, page # 8:

The quantity of dust is measured using the graduated cylinder/tube by manually collecting the left-over dust on the panel surface after the DRONE flight. This exercise was done for each experiment.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper studies drone application for air cleaning of solar panels which is an interesting topic. However, the experiments carried out for this study involves the cleaning process of PV module lying parallel to the ground surface (which is not in the real/installed case) and the contribution of this study is not enough to publish in energies. It is just a practical application of drone (paper title saying too) with few results. The intelligent cleaning system and/or comprehensive study of related factors is expected for publication in such a journal. Few of the other major comments are:

1.       The effect of dust deposition on solar panel is already studied widely.

2.       Is this cleaning method effective when various panels are present side by side on a large site? Moreover, air flow duration, air speed, particle sizes, PV module inclination angle, spacing between modules, wind direction on site, wind speed on site, etc. are few of the factors that can affect such cleaning system. These factors should also be studied.

3.       In abstract “In addition, the drone may also detect defects (like hot spots and sticky material not cleaned) on solar panels.”. Thermal camera is used for this purpose in drones. The present paper does not study any such method as mentioned in abstract and conclusion.

4.       The figure 12 shows the cleaning process of PV module lying parallel to the ground surface. The inclination angle is one of the factor affecting particle removal.

5.       Irradiance and other conditions are not shown along with measurements.

Author Response

Reviewer #2

 This paper studies drone application for air cleaning of solar panels which is an interesting topic. However, the experiments carried out for this study involves the cleaning process of PV module lying parallel to the ground surface (which is not in the real/installed case) and the contribution of this study is not enough to publish in energies. It is just a practical application of drone (paper title saying too) with few results. The intelligent cleaning system and/or comprehensive study of related factors is expected for publication in such a journal. Few of the other major comments are:

 

Comments 1:

The experiments carried out for this study involves the cleaning process of PV module lying parallel to the ground surface (which is not in the real/installed case)

Authors Reply:

Thanks for your valuable comments. The chosen orientation represents the worst-case scenario. If the panels are tilted as in practice, then blowing the dust would be much easier and more effective using the drone

 

Comments 2:

The effect of dust deposition on solar panel is already studied widely.

Authors Reply:

We based our study on the necessity of dust removal based on the already performed studies. The technique we propose is efficient for cleaning large PV fields where other automatic techniques require a lot of water, instrumentation and equipment like robots. In this part of the globe, Saudi Arabia, we have water scarcity in addition to a lot of dust and sand storms, so the present method, which does not require water, will be an excellent way out.

 

Comments 3:

Is this cleaning method effective when various panels are present side by side on a large site? Moreover, air flow duration, air speed, particle sizes, PV module inclination angle, spacing between modules, wind direction on site, wind speed on site, etc. are few of the factors that can affect such cleaning system. These factors should also be studied.

Authors Reply:

As the reviewer kindly indicated, the panels in a solar plant are put side by side on separated rows and all are tilted towards the south direction (in the northern hemisphere) for better efficiency. Usually, these rows are separated in practice for maintenance and other operations. Naturally, the dust will be blown towards the tilt due to gravity for all panels. Therefore, having many panels side by side would not create any issues for the proposed system. We expect that more wind speed will help the cleaning process. The wind direction should have a minimal effect as the dust and particles will only go towards the tilt. However, these factors could be included in future work.

 

Comments 4:

In abstract "In addition, the drone may also detect defects (like hot spots and sticky material not cleaned) on solar panels.". Thermal camera is used for this purpose in drones. The present paper does not study any such method as mentioned in abstract and conclusion.

Authors Reply:

We indicated that the same drone used for cleaning could also be used for PV panels defect detection. However, it is for future work and out of the scope of the current paper.

 

Comments 5:

The figure 12 shows the cleaning process of PV module lying parallel to the ground surface. The inclination angle is one of the factor affecting particle removal.

Authors Reply:

Yes, the inclination factor is an advantage for cleaning operations, but in the present case, the authors are trying to prove that DRONE-generated downward thrust can be utilized for dust cleaning accumulated on the panel/s. Since it can remove dust from the horizontal surface, it should be more effective when the panel/s is/are tilted.

 

Comments 6:

Irradiance and other conditions are not shown along with measurements.

Authors Reply:

The objective of the present study is to see the performance of the PV panel output before and after DRONE cleaning. This is irrelevant to the amount of irradiance and other conditions.

 

The authors are very grateful to the reviewers for their constructive comments that enhance the paper's readability. We hope that our reply meets the reviewers' satisfaction.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

1. The updated version shows that the paper is well written. However, the introduction can be improved by discussing the future and interest of PV energy in Saudi Arabia, this paper can be discussed and cited (Renewable energy resources and workforce case study Saudi Arabia: review and recommendations, Journal of Thermal Analysis and Calorimetry 141 (1), 221-230

 

2. Fig 15 needs some clarifications indeed why in week 2 the power is less than power in weeks 3 4 ....

 

3. More references form Energies journal or other journals can be discussed an cited. Economic analysis and Comparison of stand alone and grid connected roof top photovoltaic systems 2021 6th International Conference on Renewable Energy: Generation and …

Author Response

Using Drones for Cleaning Photovoltaic Solar Panels

Point-By-Point Reply to Reviewers' Comments

We would like to express our deepest gratitude to the respected anonymous reviewers and Editor-in-Chief of the 'Energies Journal' for their valuable comments on our submitted manuscript. We believe that their constructive suggestions significantly enrich the quality and readability of the paper. We have tried our best to modify the paper substantially according to the received recommendations. Additionally, we have gone through the manuscript and taken care of the grammatical mistakes and typos. The revised version of the manuscript is submitted for further consideration.

Editor's Comment

(I) Please check that all references are relevant to the contents of the manuscript.

(II) Any revisions to the manuscript should be marked up using the "Track  Changes" function if you are using MS Word/LaTeX, such that any changes can be easily viewed by the editors and reviewers.

(III) Please provide a cover letter to explain, point by point, the details of the revisions to the manuscript and your responses to the referees' comments.

(IV) If you found it impossible to address certain comments in the review reports, please include an explanation in your appeal.

(V) The revised version will be sent to the editors and reviewers.

Authors Reply:

The authors are very grateful to the Editor for considering our submitted manuscript. We have revised the manuscript that incorporates the reviewers' recommendations we received and highlighted the changes made in red color. This letter provides point-by-point answers to the comments made by the respected reviewers.

Reviewer #1

 

Comment 1:

The updated version shows that the paper is well written. However, the introduction can be improved by discussing the future and interest of PV energy in Saudi Arabia, this paper can be discussed and cited (Renewable energy resources and workforce case study Saudi Arabia: review and recommendations, Journal of Thermal Analysis and Calorimetry 141 (1), 221-230.

Authors Reply:

We would like to thank you for both constrictive comments and suggestion. The paper that was suggested draws attention to the significance of our ongoing research. A reference (E. M. Barhoumi et al., “Renewable energy resources and workforce case study Saudi Arabia: review and recommendations,” J Therm Anal Calorim, vol. 141, no. 1, pp. 221–230, Jul. 2020, doi: 10.1007/S10973-019-09189-2.) has been added in the revised manuscript, and the following section has been included in the introduction:

It is anticipated that Saudi Arabia will invest over $50 billion in order to achieve its goal of producing more than 40 GW of solar energy by 2032 [4].

Comment 2:

Fig 15 needs some clarifications indeed why in week 2 the power is less than power in weeks 3 4 ....

Authors Reply:

Heavy rain cleaned the panel at the end of the third week, and consequently, the output power was increased, as shown in Fig 15. The paragraph before Fig 15 in the paper is modified as follows:

At the start of week 1, when the panel was cleaned, the power was more than 62 W and reduced to 53.3 W by the end of the first week and further reduced to 45.72 W by the second week. The power regained the original output of around 62 W at the end of the third week because the panel surface was cleaned due to heavy rain during that week.

Comment 3:

More references form Energies journal or other journals can be discussed an cited. Economic analysis and Comparison of standalone and grid connected roof top photovoltaic systems 2021 6th International Conference on Renewable Energy: Generation and …

Authors Reply:

A reference (E. M. Barhoumi, S. Farhani, P. C. Okonkwo, M. Zghaibeh, F. K. al Housni, and F. Bacha, “Economic Analysis and Comparison of Standalone and Grid Connected Roof Top Photovoltaic Systems,” in 2021 6th International Conference on Renewable Energy: Generation and Applications (ICREGA), 2021, pp. 223–228. doi: 10.1109/ICREGA50506.2021.9388224) with an estimated figure for the PV panel cost has been added. The sentence below has been added:

It is anticipated that 57 percent of the total cost of the PV system will be accounted for by the cost of the PV panels [5].

Following, three references have been included from Energies:

[7]          D. Olivares et al., “Determination of the Soiling Impact on Photovoltaic Modules at the Coastal Area of the Atacama Desert,” Energies 2020, Vol. 13, Page 3819, vol. 13, no. 15, p. 3819, Jul. 2020, doi: 10.3390/EN13153819.

[9]          M. King et al., “Mathematical Modelling of a System for Solar PV Efficiency Improvement Using Compressed Air for Panel Cleaning and Cooling,” Energies 2021, Vol. 14, Page 4072, vol. 14, no. 14, p. 4072, Jul. 2021, doi: 10.3390/EN14144072.

[10]        E. Aljdaeh et al., “Performance Enhancement of Self-Cleaning Hydrophobic Nanocoated Photovoltaic Panels in a Dusty Environment,” Energies 2021, Vol. 14, Page 6800, vol. 14, no. 20, p. 6800, Oct. 2021, doi: 10.3390/EN14206800.

 

The authors are very grateful to the reviewers for their constructive comments that enhance the paper's readability. We hope that our reply meets the reviewers' satisfaction.

Author Response File: Author Response.docx

Reviewer 2 Report

1-It is just a practical application of drone with few results. The chosen orientation for such a study should be with different inclinations to get better/comprehensive results. There are many factors that should be considered for such a study. Those are mentioned in earlier review stage comments.

2-“Therefore, having many panels side by side would not create any issues for the proposed system”. It should be studied for a research paper rather than such a statement.

3-“The wind direction should have a minimal effect as the dust and particles will only go towards the tilt”. In high wind velocity scenarios, it will obviously have significant impact. Its only one factor. There are many others factors mentioned in earlier review stage comments.

4-“The objective of the present study is to see the performance of the PV panel output before and after DRONE cleaning. This is irrelevant to the amount of irradiance and other conditions”. The irradiance and other conditions have direct effect on PV power. What are the conditions before and after cleaning? It should be indicated for a research paper.

Author Response

Using Drones for Cleaning Photovoltaic Solar Panels

Point-By-Point Reply to Reviewers' Comments

We would like to express our deepest gratitude to the respected anonymous reviewers and Editor-in-Chief of the 'Energies Journal' for their valuable comments on our submitted manuscript. We believe that their constructive suggestions significantly enrich the quality and readability of the paper. We have tried our best to modify the paper substantially according to the received recommendations. Additionally, we have gone through the manuscript and taken care of the grammatical mistakes and typos. The revised version of the manuscript is submitted for further consideration.

Editor's Comment

(I) Please check that all references are relevant to the contents of the manuscript.

(II) Any revisions to the manuscript should be marked up using the "Track  Changes" function if you are using MS Word/LaTeX, such that any changes can be easily viewed by the editors and reviewers.

(III) Please provide a cover letter to explain, point by point, the details of the revisions to the manuscript and your responses to the referees' comments.

(IV) If you found it impossible to address certain comments in the review reports, please include an explanation in your appeal.

(V) The revised version will be sent to the editors and reviewers.

Authors Reply:

The authors are very grateful to the Editor for considering our submitted manuscript. We have revised the manuscript that incorporates the reviewers' recommendations we received and highlighted the changes made in red color. This letter provides point-by-point answers to the comments made by the respected reviewers.

 

Reviewer #2

 Comment 1:

It is just a practical application of drone with few results. The chosen orientation for such a study should be with different inclinations to get better/comprehensive results. There are many factors that should be considered for such a study. Those are mentioned in earlier review stage comments.

 

Authors Reply:

Thanks for your valuable comments. We agree that this work is a practical application of a drone. However, it is an important application with a huge impact on the efficiency of solar panels and, consequently, solar energy.

For the purpose of this paper, the authors have considered the worst scenario of keeping the panel horizontal before and after cleaning the panel using the drone to avoid the effect of gravity pull-down. At our geographical location, the panels are usually tilted 20 to 22 degrees from the horizontal and facing south to maximize sun exposure most of the year. The study of different inclinations is out of the scope of the current study and could be performed in future work.

Comment 2:

"Therefore, having many panels side by side would not create any issues for the proposed system". It should be studied for a research paper rather than such a statement.

Authors Reply:

We have conducted an experiment with 8 side-by-side panels, and observed that a couple of rounds of drone flight cleaned all panels as expected from this study. A video clip of this experiment is available in case the reviewer wants to see it.

Comment 3:

"The wind direction should have a minimal effect as the dust and particles will only go towards the tilt". In high wind velocity scenarios, it will obviously have significant impact. Its only one factor. There are many others factors mentioned in earlier review stage comments.

Authors Reply:

We agree with the reviewer that wind speed and direction will impact the solar panels' efficiency. However, in this study, we focused only on the effect of cleaning the panels by the drone under the same effect of wind direction and all other meteorological parameters.

Comment 4:

"The objective of the present study is to see the performance of the PV panel output before and after DRONE cleaning. This is irrelevant to the amount of irradiance and other conditions". The irradiance and other conditions have direct effect on PV power. What are the conditions before and after cleaning? It should be indicated for a research paper.

Authors Reply:

We agree with the reviewer that irradiance and several other factors directly affect PV power. However, the objective of this study is to analyze the effect of cleaning the panels using only the downward thrust of the drone with no water and at the same time without touching the panel's surface. Here in Saudi Arabia, water is scarce, and we are looking for cleaning technologies that do not use water.

 

The authors are very grateful to the reviewers for their constructive comments that enhance the paper's readability. We hope that our reply meets the reviewers' satisfaction.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Nil