Experimental Measurement and Numerical Simulation on the Snow-Cover Process of Solar Photovoltaic Modules and Its Impact on Photoelectric Conversion Efficiency

Round 1

Reviewer 1 Report

The presented paper is about the effect of snow thickness on photovoltaic module power generation efficiency is discussed by numerical simulation as well as a experimental setup.  Work is useful in understanding the working of Solar panel under the extreme weather conditions. I have some Queries regarding this work: 

1. What is photovoltaic snow?  (authors mention this in Abstract) 

2. I request to author to use full form of abriviation used in the article when first time reported. e.g. CFD used in abstract but fullform is missing in the text. 

3.  Figure 8 and figure 10 shows the Photovoltaic power generation efficiency(%) for different test parameters. In these figures author claim 100% efficiency for the potovoltaic plate, and as the thickness of snow changes this reduce to 7%. What is the meaning of 100 % photoconversion efficiency? it should be written properly and explain.

Author Response

Thank you so much for your letter and precious time on this manuscript! We also deeply appreciate the valuable and helpful comments by the reviewers. Those comments are very important for improving the paper and guiding our future research work. According to the comments, we have made corrections and responses point by point which we hope to meet with approval. The corrections are all marked in red in the resubmitted manuscript. The responses to the comments of the editor and reviewers are as follows:

 

Note: Italics are the reviewers' original comments.

Reviewer #1:

1. What is photovoltaic snow?  (authors mention this in Abstract) 

Thank you for your careful guidance. The use of “photovoltaic snow” is our negligence. What we meant is snow accumulation on photovoltaic module. The original sentence is revised as “At the same time, a measurement platform of snow accumulation on photovoltaic module and photoelectric conversion efficiency is constructed.”(marked in red in page 1, lines 18-19)

2. I request to author to use full form of abriviation used in the article when first time reported. e.g. CFD used in abstract but fullform is missing in the text. 

Thank you for your careful guidance. The full form of CFD used in abstract is Computational Fluid Dynamics. We have added the above content into the following and marked it in red in the revised manuscript. (marked in red in page 1, line 16)

3. Figure 8 and figure 10 shows the Photovoltaic power generation efficiency(%) for different test parameters. In these figures author claim 100% efficiency for the potovoltaic plate, and as the thickness of snow changes this reduce to 7%. What is the meaning of 100 % photoconversion efficiency? it should be written properly and explain.

Thank you for your careful guidance. The meaning of 100 % photoconversion efficiency is that the photoconversion efficiency of photovoltaic modules when there is no snow accumulation. The decrease to so-called 7% is relative to the 100% in the absence of snow cover. To explain clearly, we have added the following content in the manuscript.(marked in red in page 8, line 215-216)

“When there is no snow, the photoconversion efficiency of photovoltaic modules is 100%.”

 

Reviewer 2 Report

This paper presents experimental and theoretical modeling of snow covering of solar battery. All materials and research results were clearly presented. Here some comments to authors for improving paper.

1.In title there is "Modulea", and it seems that the word "and" is missing. Please check title.

2.Please check the paper for typos. For example on page 2, sentence, which starts "Besides, monthly...", "When" is written with capital letter.

3.In experimental part, please specify the temperature of module and ambient temperature. Also please specify the model of solar battery and its characteristics. Showing the I-V characteristics of the battery in normal conditions and under covered conditions is recomended. 

4.Also energy generation of solar battery and solar radiation during snowy day is recomended to be shown to evaluate the efficiency of the battery in this conditions.

5.It should be specified how much time it took for snow to slide from solar battery or it was made manually. What was the tilt angle of solar battery during sliding of snow? It would be better to show different angles and its effect on velocity of sliding and power generation. 

6.Authors should specify what is the difference between their work and other works on this topic and show their contribution. 

Author Response

Thank you so much for your letter and precious time on this manuscript! We also deeply appreciate the valuable and helpful comments by the reviewers. Those comments are very important for improving the paper and guiding our future research work. According to the comments, we have made corrections and responses point by point which we hope to meet with approval. The corrections are all marked in red in the resubmitted manuscript. The responses to the comments of the editor and reviewers are as follows:

 

Note: Italics are the reviewers' original comments.

Reviewer #2:

1.In title there is "Modulea", and it seems that the word "and" is missing. Please check title.

Thank you for your careful guidance. We have changed the title to the following in the revised manuscript and marked it in red:

“Experimental measurement and numerical simulation on the snow cover process of solar photovoltaic modules and its impact on photoelectric conversion efficiency”

2.Please check the paper for typos. For example on page 2, sentence, which starts "Besides, monthly...", "When" is written with capital letter.

Thank you for your careful guidance. We have checked the errors in the article and corrected them in the revised manuscript (marked in red in the article).

3.In experimental part, please specify the temperature of module and ambient temperature. Also please specify the model of solar battery and its characteristics. Showing the I-V characteristics of the battery in normal conditions and under covered conditions is recomended. 

We agree with the reviewer's suggestion and explain that the module temperature is -10℃ and the ambient temperature is -12℃. The model and characteristics of solar PV module: single crystal silicon, size: 650mm×350mm, maximum power (P_max): 100w, open circuit voltage (V_oc): 22.1V, working voltage (V_dc): 18.5V, short circuit current (I_sc): 6A, working current (I_mp): 5.4A. Due to the limited experimental conditions, we will explain the I-V curve of the battery under normal conditions and coverage conditions in the subsequent study. We have added the following to the revised manuscript (marked in red in page 8, lines 194-200):

“We conduct the experiment on the roof of the Electrical Engineering College of Xinjiang University. The surface temperature is -12℃ and the average snowfall rate is 69.3%. The temperature of the PV module is - 10℃ and the ambient temperature is -12℃. The solar cells used in the experiment are monocrystalline silicon solar cells, with dimensions of 650mm×350mm, maximum power P_max: 100w, open circuit voltage V_oc: 22.1V, working voltage V_dc: 18.5V, short circuit current I_sc: 6A, and working current I_mp: 5.4A.”

Regarding the unfinished work and outlook, we added the following in the revised manuscript (marked in red in page 14, lines 390-398):

“In this paper, the characteristics of photovoltaic cells were not fully considered when studying the snow accumulation process of solar photovoltaic cells, and the variable of sliding angle was not considered when studying the snow-skiing on the surface of solar cells. Therefore, in the next study, we will test the energy generation and solar radiation of solar cells to further evaluate the efficiency of solar cells. We will compare and study the I-V curve of solar cells under normal conditions and coverage conditions. In addition, for the snow-skiing phenomenon on the surface of solar cells, we will add the solar cell tilt angle as a variable to illustrate the impact of different angles on the sliding speed and power generation.”

4.Also energy generation of solar battery and solar radiation during snowy day is recomended to be shown to evaluate the efficiency of the battery in this conditions.

Thank you for your careful guidance. At present, our experiment uses the same photovoltaic panel and the same radiation intensity of light. Later, we will consider testing the energy generation and solar radiation of solar cells in the following experiments to further evaluate the efficiency of solar cells. Regarding the unfinished work and outlook, we added the following in the revised manuscript (marked in red in page 14, lines 390-398):

“In this paper, the characteristics of photovoltaic cells were not fully considered when studying the snow accumulation process of solar photovoltaic cells, and the variable of sliding angle was not considered when studying the snow-skiing on the surface of solar cells. Therefore, in the next study, we will test the energy generation and solar radiation of solar cells to further evaluate the efficiency of solar cells. We will compare and study the I-V curve of solar cells under normal conditions and coverage conditions. In addition, for the snow-skiing phenomenon on the surface of solar cells, we will add the solar cell tilt angle as a variable to illustrate the impact of different angles on the sliding speed and power generation.”

5.It should be specified how much time it took for snow to slide from solar battery or it was made manually. What was the tilt angle of solar battery during sliding of snow? It would be better to show different angles and its effect on velocity of sliding and power generation. 

Thank you for your careful guidance. The process of solar cell snow-skiing is manual. The tilt angle of the solar cell is 45 degrees when the snow slides. Due to the lack of experimental conditions, different angles and their effects on sliding speed and generating speed will be explained in the subsequent study. We added the following to the revised manuscript(marked in red in page 10, lines 262-268):

“This experiment is mainly to simulate the sliding process of snow on the surface of photovoltaic modules. The snow is made manually, and the tilt angle of solar cells is 45 °. This experiment is very important to explore the relationship between the sliding distance of the snow on the surface of the PV module and the power generation efficiency of the PV module, and to analyze the change characteristics of the power generation efficiency of the PV module during the sliding process.”

Regarding the unfinished work and outlook, we added the following in the revised manuscript (marked in red in page 14, lines 390-398):

“In this paper, the characteristics of photovoltaic cells were not fully considered when studying the snow accumulation process of solar photovoltaic cells, and the variable of sliding angle was not considered when studying the snow-skiing on the surface of solar cells. Therefore, in the next study, we will test the energy generation and solar radiation of solar cells to further evaluate the efficiency of solar cells. We will compare and study the I-V curve of solar cells under normal conditions and coverage conditions. In addition, for the snow-skiing phenomenon on the surface of solar cells, we will add the solar cell tilt angle as a variable to illustrate the impact of different angles on the sliding speed and power generation.”

6.Authors should specify what is the difference between their work and other works on this topic and show their contribution. 

Thank you for your careful guidance. After consulting the relevant literature, we found that most of the research on the impact of snow on the power generation efficiency of photovoltaic modules was carried out through experiments. In this paper, CFD is used to simulate the process of snow accumulation on the surface of solar PV modules with different tilt angles, and the influence of snow accumulation on the power generation efficiency of solar PV modules is analyzed. In addition, the photovoltaic snow and photovoltaic conversion efficiency test platform shall be built. Through the experiment of the influence of snow thickness and snow distance on the power generation efficiency of PV modules, the influence of snow thickness and snow area on the power generation efficiency of PV modules is discussed. We made the following modifications in the revised manuscript (marked in red in page 2, lines 83-89):

“However, most studies have used experiments to study the impact of snow cover on photovoltaic power generation, and there are few studies on the simulation of the snow cover process through CFD. Based on numerical simulation, this paper studies the influence of snow cover on the surface of a series of solar photovoltaic modules with different tilt angles analyzes the snow cover process on the surface of solar photovoltaic modules and discusses the relationship between the snow cover and the tilt angle of photovoltaic modules. On this basis, the impact of snow cover on photovoltaic modules on the efficiency of photoelectric conversion is studied through experimentation. At the same time, the test platform of photovoltaic snow and photovoltaic conversion efficiency is constructed. Through the experiment of the relationship between snow thickness and snow sliding distance and the power generation efficiency of PV modules, the influence of snow thickness and snow area on the power generation efficiency of PV modules is discussed.”

 

 

Reviewer 3 Report

Major issue:

Please consider that snow can exists in different types: https://en.wikipedia.org/wiki/Classifications_of_snow

Therefore, please specify what type of snow was considered and tested.

Works 7-13 points real issue of photovoltaic energy generation but it is as simple as possible – snow deposition parameters have to be discussed. In classic situations snow deposition parameters depends on surface type and condition, surface temperature and  snowfall rate. Snowfall is only discussed as process of snow disappearing from the panel. Next, the snow presence on panel is related to temperature, solar radiation and snow layer height and density as well as its clarity. It is common knowledge but here is not used?

Thus a diagram of analyzed meteorological processes have to be presented as first figure.

The beginning of 2 section is unclear to me: “In order to study the change of the flow field, it is necessary to consider the impact of various variables such as pressure and the density of flow, establish a theoretical model of the flow field, and solve the partial differential equations in the model through the numerical iteration assisted by computer [22]. To describe the flow field, there are three basic laws involved: the law of conservation of momentum, the law of conservation of mass, and the law of conservation of energy.”

Beside snow modeling with the use of rules for liquid require more references and discussion. “Moreover, runge-kutta method is used to solve the equation of motion of dust particles.” – looks more reasonably. Thus there is a potential big gap in proposed model of liquid- dust particle type that require additional thermal balance modelling.

Minor corrections

“Through the experiments conducted on the effects of snow thickness and snowskiing distance on the power generation efficiency of photovoltaic modules, a discussion is conducted about the effects of snow thickness and snow area on the power generation efficiency of photovoltaic modules.” For me, this sentence is difficult to read

Figure 3 à I think a more precise term is the density of snow

Author Response

Thank you so much for your letter and precious time on this manuscript! We also deeply appreciate the valuable and helpful comments by the reviewers. Those comments are very important for improving the paper and guiding our future research work. According to the comments, we have made corrections and responses point by point which we hope to meet with approval. The corrections are all marked in red in the resubmitted manuscript. The responses to the comments of the editor and reviewers are as follows:

 

Note: Italics are the reviewers' original comments.

Reviewer #3:

1. Please consider that snow can exists in different types: https://en.wikipedia.org/wiki/Classifications_of_snow.Therefore, please specify what type of snow was considered and tested.

Response:

Thank you for your careful guidance. According to the reviewer's suggestion, we explained in the revised manuscript that the snow used in the experiment was a natural storm. We added the following contents to the revised manuscript (marked in red in page 8, lines 205-206):

“The snow used in this experiment is a natural storm[24].”

2. Works 7-13 points real issue of photovoltaic energy generation but it is as simple as possible – snow deposition parameters have to be discussed. In classic situations snow deposition parameters depends on surface type and condition, surface temperature and  snowfall rate. Snowfall is only discussed as process of snow disappearing from the panel. Next, the snow presence on panel is related to temperature, solar radiation and snow layer height and density as well as its clarity. It is common knowledge but here is not used? Thus a diagram of analyzed meteorological processes have to be presented as first figure.

Response:

Thank you for your careful guidance. We conduct the experiment on the roof of the Electrical Engineering College of Xinjiang University. The surface temperature is -12℃ and the average snowfall rate is 69.3%. We added the following content in the revised manuscript (marked in red in page 8, lines 194-196).

“We conduct the experiment on the roof of the Electrical Engineering College of Xinjiang University. The surface temperature is -12℃ and the average snowfall rate is 69.3%.”

In this study, we only consider the impact of snow cover on output power of the photovoltaic panels. The temperature, solar radiation, snow layer height and density and its clarity are not taken account, but we will study the influence of these factors on output power of the photovoltaic panels in future research.

3. The beginning of 2 section is unclear to me: “In order to study the change of the flow field, it is necessary to consider the impact of various variables such as pressure and the density of flow, establish a theoretical model of the flow field, and solve the partial differential equations in the model through the numerical iteration assisted by computer [22]. To describe the flow field, there are three basic laws involved: the law of conservation of momentum, the law of conservation of mass, and the law of conservation of energy.” Beside snow modeling with the use of rules for liquid require more references and discussion. “Moreover, runge-kutta method is used to solve the equation of motion of dust particles.” – looks more reasonably. Thus there is a potential big gap in proposed model of liquid- dust particle type that require additional thermal balance modelling.

It is necessary to study the change of the flow field around the PV module when studying the snow process on the surface of the PV module. In this process, we consider the influence of various variables such as pressure and flow density, establish a theoretical model of the flow field, and solve the partial differential equations in the model through the computer-aided numerical iteration method. Our research on convection field is based on three basic laws: the law of conservation of momentum, the law of conservation of mass and the law of conservation of energy. According to the suggestion of the reviewer, we added the liquid-dust heat balance model to the article. We added the following to the revised manuscript(marked in red in page 3, lines 116-120):

“According to the heat balance equation, the liquid-dust particles in the snow accumulation process of PV modules meet the following equation:

d/dt (k + U) = N^e + Q

where d/dt is the total time derivative, K is the kinetic energy of the substance in the control volume, Ne is the power of external forces, Q is the energy supply from external sources per unit time.”

4.Through the experiments conducted on the effects of snow thickness and snowskiing distance on the power generation efficiency of photovoltaic modules, a discussion is conducted about the effects of snow thickness and snow area on the power generation efficiency of photovoltaic modules.” For me, this sentence is difficult to read

Response:

Thank you for your careful guidance. We have revised the related content into the following and marked it in red in the revised manuscript (marked in red in pages 1-2, lines 18-22, 92-95):

“Through the experiment of the relationship between snow thickness and snow sliding distance and the power generation efficiency of PV modules, the influence of snow thickness and snow area on the power generation efficiency of PV modules is discussed.”

5.Figure 3  I think a more precise term is the density of snow

Response:

Thank you for your careful guidance. We have made changes in the revised manuscript (marked in red in page 6, lines 148-149 ).

 

Round 2

Reviewer 1 Report

Author answer all the queries raised by the reviewer. I want to congratulate the authors and recommend this manuscript for publication. 

Reviewer 2 Report

Dear authors, thank you for your work.

I recommend to consider effect of different angles on velocity of sliding. Also please consider energy generation during several snowy days in future work.

Reviewer 3 Report

The revised version of the publication is precise and pleasant to read. Congratulations to the authors.