Experimental Validation of a Thermo-Electric Model of the Photovoltaic Module under Outdoor Conditions

Round 1

Reviewer 1 Report

The topic of this paper is interesting to the readers, within the scope of the journal, however prior its publication changes must be done.

The use of English must be improved. The paper includes several grammatical and syntax errors.

The Introduction must be revised. The authors must present the general research area to unfamiliar readers and at most to present the current state-of-the-art in order to show the contribution/novelty of their work. Authors must describe/analyse more the current mentioned references and must include many more related references, such as the following:

Seritan G.-C., Enache B.-A., Adochiei F.-C., Argatu F.C., Christodoulou C., Vita V., Toma A.R., Gandescu C.H., Hathazi F.-I., Performance evaluation of photovoltaic panels containing cells with different bus bars configurations in partial shading conditions, Revue Roumaine des Sciences Techniques - Électrotechnique et Énergétique, Vol. 65, No. 1-2, 2020, pp. 67-70.

Damianaki K., Christodoulou C., Kokalis C.-C.A., Kyritsis A., Ellinas E.D., Vita V., Gonos I.F., Lightning protection of photovoltaic systems: Computation of the developed potentials, Applied Sciences, Vol. 11, No. 1, (DOI) 10.3390/app11010337, 2021.

A separate discussion section that will comment on the produced results must be included.

Conclusions must summarize the work presented within the paper.

Author Response

Summary of corrections made in the paper

Experimental validation of a thermo-electric model of the photovoltaic module under outdoor conditions

(Manuscript ID: applsci-1218204)

We thank the reviewers for their valuable comments on our paper, which have substantially improved the quality of our paper. We have made a concerted effort to address all the reviewers concerns. Below we quote and respond to each reviewer’s comments.

Reviewer 1:

The topic of this paper is interesting to the readers, within the scope of the journal, however prior its publication changes must be done.

1. The use of English must be improved. The paper includes several grammatical and syntax errors.

2. The Introduction must be revised. The authors must present the general research area to unfamiliar readers and at most to present the current state-of-the-art in order to show the contribution/novelty of their work. Authors must describe/analyse more the current mentioned references and must include many more related references, such as the following:

Seritan G.-C., Enache B.-A., Adochiei F.-C., Argatu F.C., Christodoulou C., Vita V., Toma A.R., Gandescu C.H., Hathazi F.-I., Performance evaluation of photovoltaic panels containing cells with different bus bars configurations in partial shading conditions, Revue Roumaine des Sciences Techniques - Électrotechnique et Énergétique, Vol. 65, No. 1-2, 2020, pp. 67-70.

Damianaki K., Christodoulou C., Kokalis C.-C.A., Kyritsis A., Ellinas E.D., Vita V., Gonos I.F., Lightning protection of photovoltaic systems: Computation of the developed potentials, Applied Sciences, Vol. 11, No. 1, (DOI) 10.3390/app11010337, 2021.

3. A separate discussion section that will comment on the produced results must be included.

4. Conclusions must summarize the work presented within the paper.

Author Response File: Author Response.docx

Reviewer 2 Report

The model equations are known. Most of the model parameters are not provided which is very important as they impact the results. The experimental data are not very significant to show the temperature influence on power due to the chosen period and to sensor deviation. I don't see any relevant added value for the readers.

Author Response

Summary of corrections made in the paper

Experimental validation of a thermo-electric model of the photovoltaic module under outdoor conditions

(Manuscript ID: applsci-1218204)

We thank the reviewers for their valuable comments on our paper, which have substantially improved the quality of our paper. We have made a concerted effort to address all the reviewers concerns. Below we quote and respond to each reviewer’s comments.

Reviewer 2:

1. The model equations are known. Most of the model parameters are not provided which is very important as they impact the results. The experimental data are not very significant to show the temperature influence on power due to the chosen period and to sensor deviation. I don't see any relevant added value for the readers.

Author Response File: Author Response.docx

Reviewer 3 Report

Minor Revision

In this manuscript, the author presented an interested paper which presents a dynamic thermo-electric model of the PV module which consists of coupled thermal and electric parts. Whereas the thermal part is described by heat balance equation for five layers, while the electric part is described by a double-diode model. The author validate this model by implement using the PV tracking system under outdoor conditions, and compare the results with the static model made in Ansys Transient Thermal and empirical equation for the output power calculation under 3 typical weather conditions.

In general, this is a good manuscript. However, there are some issues need to be addressed/clarified.

1. Line 120, the author needs to clarify the use of a Power Meter and Hall effect sensor. Is it for DC and AC measurement separately?
2. Line 121, might be “a several-local-and-one-global PLC”.
3. Line 123, should be “are sampled every 5 minutes”.
4. Line 155, the author need to add reference for “One of those”.
5. Line 166, should be “by [3], ”
6. Line 193, the author need to describe it clearly how Figure 2 indicate “clear days are quite rare in Slovenia for aforementioned month, so cloudy days are the most prevalent”.
7. Figure 3, the font size needs to be larger. Currently it is hard to see.
8. Line 211, what does the author mean “appropriate result”?
9. Line 234, need to clarify why “is also evident from Table 1 (calibration time)”.
10. Line 236, grammar mistake. It can be “Another important reason xxx is dirt.”
11. Line 240, not clear what the author wants to say. Can be something like “will be seen as an inner factor of the electric model?”
12. Line 241, grammar mistake. Can be “as an essential part xxx, the optical loss that significantly contributes to xxx, strongly depends on xxx”.
13. The author mentioned “The advantage of the proposed model is that the optical losses change as a function of the incident angle of the Sun’s rays and not as a constant value, which is generally very important for a fixed PV system. However, the manuscript does not show the importance of this advantage. How does the proposed model makes a difference including this consideration. It would be helpful to show the strength of the proposed by comparing the results predicted of the proposed model and other predicted models.

Comments for author File: Comments.pdf

Author Response

Summary of corrections made in the paper

Experimental validation of a thermo-electric model of the photovoltaic module under outdoor conditions

(Manuscript ID: applsci-1218204)

We thank the reviewers for their valuable comments on our paper, which have substantially improved the quality of our paper. We have made a concerted effort to address all the reviewers concerns. Below we quote and respond to each reviewer’s comments.

Reviewer 3:

In this manuscript, the author presented an interested paper which presents a dynamic thermo-electric model of the PV module which consists of coupled thermal and electric parts. Whereas the thermal part is described by heat balance equation for five layers, while the electric part is described by a double-diode model. The author validate this model by implement using the PV tracking system under outdoor conditions, and compare the results with the static model made in Ansys Transient Thermal and empirical equation for the output power calculation under 3 typical weather conditions.

In general, this is a good manuscript. However, there are some issues need to be addressed/clarified.

1. Line 120, the author needs to clarify the use of a Power Meter and Hall effect sensor. Is it for DC and AC measurement separately?

2. Line 121, might be “a several-local-and-one-global PLC”.

3. Line 123, should be “are sampled every 5 minutes”.

4. Line 155, the author need to add reference for “One of those”.

1. Line 166, should be “by [3], ”

1. Line 193, the author need to describe it clearly how Figure 2 indicate “clear days are quite rare in Slovenia for aforementioned month, so cloudy days are the most prevalent”.

1. Figure 3, the font size needs to be larger. Currently it is hard to see.

1. Line 211, what does the author mean “appropriate result”?

1. Line 234, need to clarify why “is also evident from Table 1 (calibration time)”.

1. Line 236, grammar mistake. It can be “Another important reason xxx is dirt.”

1. Line 240, not clear what the author wants to say. Can be something like “will be seen as an inner factor of the electric model?”

1. Line 241, grammar mistake. Can be “as an essential part xxx, the optical loss that significantly contributes to xxx, strongly depends on xxx”.

1. The author mentioned “The advantage of the proposed model is that the optical losses change as a function of the incident angle of the Sun’s rays and not as a constant value, which is generally very important for a fixed PV system. However, the manuscript does not show the importance of this advantage. How does the proposed model makes a difference including this consideration. It would be helpful to show the strength of the proposed by comparing the results predicted of the proposed model and other predicted models.

Author Response File: Author Response.docx

Reviewer 4 Report

• Regarding the format of the document, some suggestions are as follows.

Keywords must be separated by semicolons.

English must be revised due to the fact that there are some typos concerning plural and singular. For example, in line 154, “… a different mathematical models exists for …” is not properly written.

In line 201 “ANSYS” is found, whereas “Ansys” is used in the rest of the manuscript.

In figure 3 a) the term “emperical” appears, which seems to be a mistake.

The format of references must be revised following the template. For example, the abbreviated names of journals must be used.

• About the content of the manuscript, these issues are commented.

In the keywords, terms like “PV module” or “photovoltaic” could be included.

The introductory section consists on a single and excessively long paragraph. It should be divided into some paragraph to facilitate reading.

As the authors comment, the real temperature of PV cells is higher than that measured with temperature probes or sensors. In fact, there is some research in this regard. For instance, the work of King et al. is commonly cited to reflect such a difference:

• King, D., Boyson, W., Kratochvil, J.: Photovoltaic array performance model. Tech. rep., SAND2004-3535, /http://www.sandia.gov/pv/docs/PDF/King%20SANDS.pdf

Regarding the estimation of PV cells from weather conditions like ambient temperature and incident irradiance, some well-known works have been left unnoticed. Namely, the following models constitute essential references in the topic:

• Ross AG. Flat-plate photovoltaic module and array engineering. In: Proc. 1982, Annu. Meet. Am. Sect. Int. Sol. Energy Soc., Houston, Texas; 1982. p. 4321–4.
• Faiman D. Assessing the outdoor operating temperature of photovoltaic modules. Prog Photovoltaics Res Appl 2008;16:307–15. https://doi.org/10.1002/pip.813.

Moreover, aiming at enhancing the contextualization, the increasing application and investigation of PV generation in smart grids and microgrids could be slightly mentioned, if the authors agree. Some papers recently published in the MDPI dealing with these topics are suggested:

• Garcia-Torres, F.; Vazquez, S.; Moreno-Garcia, I.M.; Gil-de-Castro, A.; Roncero-Sanchez, P.; Moreno-Munoz, A. Microgrids Power Quality Enhancement Using Model Predictive Control. Electronics 2021, 10, 328. https://doi.org/10.3390/electronics10030328.
• González, I.; Calderón, A.J.; Portalo, J.M. Innovative Multi-Layered Architecture for Heterogeneous Automation and Monitoring Systems: Application Case of a Photovoltaic Smart Microgrid. Sustainability 2021, 13, 2234. https://doi.org/10.3390/su13042234.
• Dairi, A.; Harrou, F.; Sun, Y.; Khadraoui, S. Short-Term Forecasting of Photovoltaic Solar Power Production Using Variational Auto-Encoder Driven Deep Learning Approach. Appl. Sci. 2020, 10, 8400. https://doi.org/10.3390/app10238400.
• Wang, J.; Li, K.-J.; Liang, Y.; Javid, Z. Optimization of Multi-Energy Microgrid Operation in the Presence of PV, Heterogeneous Energy Storage and Integrated Demand Response. Appl. Sci. 2021, 11, 1005. https://doi.org/10.3390/app11031005.

In subsection 2.1 the experimental setup is described, where automation-related equipment is scarcely commented. Namely, a PLC and a supervisory system are mentioned, but they are underestimated given their relevant role in the operation and surveillance of the PV tracker. Therefore, it would be desirable to mention, at least, the models of hardware and software involved in such equipment for a proper description.

Concerning the Matlab/Simulink environment, the specific version and toolboxes that have been used should be given for the interested reader.

As the authors know, the ideality factor, n, is one of the parameters of the equivalent circuit model, both using one or two diodes. In this sense, it is quite surprising that there is no comment about the value that this parameter adopts. Even, there are two ideality factors due to the fact that the two-diode model is managed. To solve this issue, the authors should explain that this value is between 1 (ideal diode) and 2 (more realistic diode), as well as indicating the values that they have considered to implement their model.

Equation 12 assumes that the photo-generated current is equivalent to the short circuit current. This is a common approximation, but the authors should explicitly indicate such assumption for a clearer presentation of the model. This equation belongs to the Appendix I.

Table 2 reports the electrical features and parameters of the studied PV module. It is advised to mention that these values are provided by the manufacturer for STC.

The electrical model is scarcely presented in subsection 2.2 but there is no explanation about how the parameters of such a model are adjusted. The reported model is implicit, so it requires solving techniques like numerical methods. If empirical IV curves have been used to adjust some of the parameters, for example the parasitic resistances, it should be clearly expounded.

In lines 281-282 the effect of degradation in power generation is slightly commented. In this regard, that statement could be enriched by mentioning some effects of degradation like cell cracking, yellowing, browning, etc.

The achieved results are validated on the view of error metrics (RMSE and MAE); however, there is no comparison with previous literature. Moreover, the common practice when modeling PV cells/modules under the electric equivalent circuit is obtaining the estimation of generated current, so the RMSE is obtained for such magnitude.

 In addition, it is unclear the novelty or contribution of the reported research. The authors should emphasize the novelties and benefits in order to state the relevance and opportunity of their research. This must be mainly highlighted in the discussion or conclusions.

Author Response

Summary of corrections made in the paper

Experimental validation of a thermo-electric model of the photovoltaic module under outdoor conditions

(Manuscript ID: applsci-1218204)

We thank the reviewers for their valuable comments on our paper, which have substantially improved the quality of our paper. We have made a concerted effort to address all the reviewers concerns. Below we quote and respond to each reviewer’s comments.

Reviewer 4:

Regarding the format of the document, some suggestions are as follows.

1. Keywords must be separated by semicolons.

2. English must be revised due to the fact that there are some typos concerning plural and singular. For example, in line 154, “… a different mathematical models exists for …” is not properly written.

3. In line 201 “ANSYS” is found, whereas “Ansys” is used in the rest of the manuscript.

4. In figure 3 a) the term “emperical” appears, which seems to be a mistake.

1. The format of references must be revised following the template. For example, the abbreviated names of journals must be used.

1. About the content of the manuscript, these issues are commented.

In the keywords, terms like “PV module” or “photovoltaic” could be included.

1. The introductory section consists on a single and excessively long paragraph. It should be divided into some paragraph to facilitate reading.

1. As the authors comment, the real temperature of PV cells is higher than that measured with temperature probes or sensors. In fact, there is some research in this regard. For instance, the work of King et al. is commonly cited to reflect such a difference:

King, D., Boyson, W., Kratochvil, J.: Photovoltaic array performance model. Tech. rep., SAND2004-3535, /http://www.sandia.gov/pv/docs/PDF/King%20SANDS.pdf

1. Regarding the estimation of PV cells from weather conditions like ambient temperature and incident irradiance, some well-known works have been left unnoticed. Namely, the following models constitute essential references in the topic:

Ross AG. Flat-plate photovoltaic module and array engineering. In: Proc. 1982, Annu. Meet. Am. Sect. Int. Sol. Energy Soc., Houston, Texas; 1982. p. 4321–4.

Faiman D. Assessing the outdoor operating temperature of photovoltaic modules. Prog Photovoltaics Res Appl 2008;16:307–15. https://doi.org/10.1002/pip.813.

10. Moreover, aiming at enhancing the contextualization, the increasing application and investigation of PV generation in smart grids and microgrids could be slightly mentioned, if the authors agree. Some papers recently published in the MDPI dealing with these topics are suggested:

Garcia-Torres, F.; Vazquez, S.; Moreno-Garcia, I.M.; Gil-de-Castro, A.; Roncero-Sanchez, P.; Moreno-Munoz, A. Microgrids Power Quality Enhancement Using Model Predictive Control. Electronics 2021, 10, 328. https://doi.org/10.3390/electronics10030328.

González, I.; Calderón, A.J.; Portalo, J.M. Innovative Multi-Layered Architecture for Heterogeneous Automation and Monitoring Systems: Application Case of a Photovoltaic Smart Microgrid. Sustainability 2021, 13, 2234. https://doi.org/10.3390/su13042234.

Dairi, A.; Harrou, F.; Sun, Y.; Khadraoui, S. Short-Term Forecasting of Photovoltaic Solar Power Production Using Variational Auto-Encoder Driven Deep Learning Approach. Appl. Sci. 2020, 10, 8400. https://doi.org/10.3390/app10238400.

Wang, J.; Li, K.-J.; Liang, Y.; Javid, Z. Optimization of Multi-Energy Microgrid Operation in the Presence of PV, Heterogeneous Energy Storage and Integrated Demand Response. Appl. Sci. 2021, 11, 1005. https://doi.org/10.3390/app11031005.

1. In subsection 2.1 the experimental setup is described, where automation-related equipment is scarcely commented. Namely, a PLC and a supervisory system are mentioned, but they are underestimated given their relevant role in the operation and surveillance of the PV tracker. Therefore, it would be desirable to mention, at least, the models of hardware and software involved in such equipment for a proper description.

1. Concerning the Matlab/Simulink environment, the specific version and toolboxes that have been used should be given for the interested reader.

1. As the authors know, the ideality factor, n, is one of the parameters of the equivalent circuit model, both using one or two diodes. In this sense, it is quite surprising that there is no comment about the value that this parameter adopts. Even, there are two ideality factors due to the fact that the two-diode model is managed. To solve this issue, the authors should explain that this value is between 1 (ideal diode) and 2 (more realistic diode), as well as indicating the values that they have considered to implement their model.

14. Equation 12 assumes that the photo-generated current is equivalent to the short circuit current. This is a common approximation, but the authors should explicitly indicate such assumption for a clearer presentation of the model. This equation belongs to the Appendix I.

15. Table 2 reports the electrical features and parameters of the studied PV module. It is advised to mention that these values are provided by the manufacturer for STC.

16. The electrical model is scarcely presented in subsection 2.2 but there is no explanation about how the parameters of such a model are adjusted. The reported model is implicit, so it requires solving techniques like numerical methods. If empirical IV curves have been used to adjust some of the parameters, for example the parasitic resistances, it should be clearly expounded.

17. In lines 281-282 the effect of degradation in power generation is slightly commented. In this regard, that statement could be enriched by mentioning some effects of degradation like cell cracking, yellowing, browning, etc.

18. The achieved results are validated on the view of error metrics (RMSE and MAE); however, there is no comparison with previous literature. Moreover, the common practice when modeling PV cells/modules under the electric equivalent circuit is obtaining the estimation of generated current, so the RMSE is obtained for such magnitude.

19. In addition, it is unclear the novelty or contribution of the reported research. The authors should emphasize the novelties and benefits in order to state the relevance and opportunity of their research. This must be mainly highlighted in the discussion or conclusions.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have conducted the requested changes.

The paper has been significantly improved.

It can be accepted for publication.

Reviewer 4 Report

The revised version of the manuscript addresses the provided suggestions in a proper manner. The quality and presentation of the paper has been enhanced. Congratulations to the authors for their efforts.