Long-Term Performance Analysis Using TRNSYS Software of Hybrid Systems with PV-T
Round 1
Reviewer 1 Report
The review comments for the manuscript, 'Long-term performance analysis using TRNSYS software of hy-2 brid systems with PV-T', is given below,
- In general, English language throughout the article does not meet the standards of scientific community. It is advised to re-write the article with the help of an expert of English language.
- Few typos are there in the manuscript. Authors should fix the typos---Grammatical errors throughout the manuscript. Units need to be checked.
- The organization is not good in this paper (headings/sections/numbers) and the authors must add the organization of the whole paper at the end of the Introduction section. Check the numbering of sub-heading.
- Author may add graphical abstract for quick understanding of the work done.
- References needed to be updated. I suggest the following: 10.1016/j.desal.2017.11.007 and 10.1016/j.enconman.2018.05.011
- Nomenclature table to be added at the end for the various types shown in Figure 2, which helps the readers for quick and easy understanding.
Author Response
I would like to wholeheartedly thank the Reviewer for his time, patience, and efforts to review the paper. It will help me improve it to a better scientific level.
Comment 1:
In general, English language throughout the article does not meet the standards of scientific community. It is advised to re-write the article with the help of an expert of English language. Few typos are there in the manuscript. Authors should fix the typos---Grammatical errors throughout the manuscript.
Response:
The author deeply regrets that the quality of written English in the manuscript was not good enough. The whole text was checked to find and modify the grammatical and vocabulary-related mistakes by a native speaker. The final version of the manuscript passed the proofreading process to improve both language and organization quality.
Comment 2:
Units need to be checked.
Response:
Done.
Comment 3:
The organization is not good in this paper (headings/sections/numbers) and the authors must add the organization of the whole paper at the end of the Introduction section.
Response:
Done. The organization of the whole paper has been added at the end of the Introduction section.
Comment 4:
Check the numbering of sub-heading.
Response:
The numbering of the headings and sub-headings has been corrected.
Comment 5:
Author may add graphical abstract for quick understanding of the work done.
Response:
In this case, it was decided not to add graphical abstract.
Comment 6:
References needed to be updated. I suggest the following: 10.1016/j.desal.2017.11.007 and 10.1016/j.enconman.2018.05.011
Response:
In the manuscript, a second proposed article was cited that referred to the peer-reviewed article more thematically.
Comment 7:
Nomenclature table to be added at the end for the various types shown in Figure 2, which helps the readers for quick and easy understanding.
Response:
Done. Attachment A is provided at the end of the manuscript, with a short description of the components used in transient models.
Please review any changes made to the manuscript in the attachment with the track-changes mode word file.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Thank you for submitting your paper Long-term performance analysis using TRNSYS software of hybrid systems with PV-T” to the Journal of Energies.
The paper draws attention to a significant subject. I have found the paper very interesting.
The article is well written and well structured as a scientific text; the literature review is comprehensive and up to date. However, several issues need to be addressed properly before the paper is being considered for publication.
My comments including major and minor concerns are given below:
- The title is too general; numerous studies have been done on this topic. The title should enhance the innovativeness of this study.
- Please add a brief description between two consecutive paragraphs.
- In the introduction, in my opinion, it is possible to create a separate section relative to the state of the arts. Most importantly, the authors should emphasize the real contribution of this work compared to recently published work. Other studies can be included, such as:
- Energy reliability-constrained method for the multi-objective optimization of a photovoltaic-wind hybrid system with battery storage, Energy, Volume 156, 2018, Pages 688-708, ISSN 0360-5442, https://doi.org/10.1016/j.energy.2018.04.062.
- The validation of a novel lumped parameter model for photovoltaic thermal hybrid solar collectors: a new TRNSYS type, Energy Conversion and Management, Volume 188, 2019, Pages 414-428, ISSN 0196-8904, https://doi.org/10.1016/j.enconman.2019.03.030.
- Do not cite too many grouped articles, otherwise, the single contribution is not clear.
- The methodology section should be improved considerably, which is my major concern. Furthermore, it is important to put in evidence the following points:
- The proposed methodology has numerous advantages, such as:
- The main novelties and objectives of the present work can be summarized as:
- All figures should be explained much more.
- The aspect related to the climate is very important, it can be useful to identify the area analyzed using a global classification such as Köppen-Geiger climates Classification.
- Worldwide geographical mapping and optimization of stand-alone and grid-connected hybrid renewable system techno-economic performance across Köppen-Geiger climates, Applied Energy, Volume 276, 2020, 115507, ISSN 0306-2619, https://doi.org/10.1016/j.apenergy.2020.115507.
- Using the Köppen classification to quantify climate variation and change: An example for 1901–2010. Environmental Development, 6, 69-79, 2013, 10.1016/j.envdev.2013.03.007.
- Conclusions that are too summarized should be implemented.
- Please make sure that the Nomenclature includes all the parameters used in the equation.
Author Response
I would like to wholeheartedly thank the Reviewer for his time, patience, and efforts to review the paper. It will help me improve it to a better scientific level.
Comment 1:
The title is too general; numerous studies have been done on this topic. The title should enhance the innovativeness of this study.
Response:
Choosing a title is one of the key considerations when writing an article. In my opinion, the title reflects the contents of the manuscript. Modifying the title would require lengthening it, which I think is not a good idea.
Comment 2:
Please add a brief description between two consecutive paragraphs.
In the introduction, in my opinion, it is possible to create a separate section relative to the state of the arts. Most importantly, the authors should emphasize the real contribution of this work compared to recently published work. Other studies can be included, such as:
Energy reliability-constrained method for the multi-objective optimization of a photovoltaic-wind hybrid system with battery storage, Energy, Volume 156, 2018, Pages 688-708, ISSN 0360-5442, https://doi.org/10.1016/j.energy.2018.04.062.
The validation of a novel lumped parameter model for photovoltaic thermal hybrid solar collectors: a new TRNSYS type, Energy Conversion and Management, Volume 188, 2019, Pages 414-428, ISSN 0196-8904, https://doi.org/10.1016/j.enconman.2019.03.030.
Response:
As recommended by the reviewer, many changes were made to the manuscript. Additionally, in the manuscript, proposed articles were cited.
Comment 3:
Do not cite too many grouped articles, otherwise, the single contribution is not clear.
Response:
Where possible, the suggested changes to the manuscript were applied.
Comment 4:
The methodology section should be improved considerably, which is my major concern. Furthermore, it is important to put in evidence the following points:
The proposed methodology has numerous advantages, such as:
The main novelties and objectives of the present work can be summarized as:
Response:
Done. Thanks again for your due consideration.
Comment 6:
All figures should be explained much more.
Response:
Please see in the attachment the changes made in that matter.
Comment 7:
The aspect related to the climate is very important, it can be useful to identify the area analyzed using a global classification such as Köppen-Geiger climates Classification.
Worldwide geographical mapping and optimization of stand-alone and grid-connected hybrid renewable system techno-economic performance across Köppen-Geiger climates, Applied Energy, Volume 276, 2020, 115507, ISSN 0306-2619, https://doi.org/10.1016/j.apenergy.2020.115507.
Using the Köppen classification to quantify climate variation and change: An example for 1901–2010. Environmental Development, 6, 69-79, 2013, 10.1016/j.envdev.2013.03.007.
Response:
Thanks again for your due consideration. I admit that I have encountered this classification for the first time. However, due to its transparency, I will definitely use it in the future. In the present article, it has also been added to chapter 2.1. Additionally, in the manuscript, the first article was quoted.
Comment 8:
Conclusions that are too summarized should be implemented.
Response:
Done.
Comment 9:
Please make sure that the Nomenclature includes all the parameters used in the equation.
Response:
Done.
Please review any changes made to the manuscript in the attachment with the track-changes mode word file.
Author Response File: Author Response.docx
Reviewer 3 Report
The novelty, methodology, and result presentation in the study were very well written.
- The authors should, however, cite some other studies in the result section, that either corroborates or disapproves of the findings of their simulation
- More recent articles should be cited in the introduction regarding PV analysis as relating to the decrement in performance with increasing solar irradiation, thus need for hybrid systems
Author Response
I would like to wholeheartedly thank the Reviewer for his time, patience, and efforts to review the paper. It will help me improve it to a better scientific level.
Comment 1:
The authors should, however, cite some other studies in the result section, that either corroborates or disapproves of the findings of their simulation
Response:
As mentioned in the introduction to the article, the author did not find in the available literature information about the influence of the temperature coefficient of photovoltaic cells for long-term PV-T operation in hybrid systems. This article filling this knowledge gap.
Comment 2:
More recent articles should be cited in the introduction regarding PV analysis as relating to the decrement in performance with increasing solar irradiation, thus need for hybrid systems
Response:
Done. In the manuscript, one of the proposed article was cited that referred to the peer-reviewed article best thematically.
Please review any changes made to the manuscript in the attachment with the track-changes mode word file.
Author Response File: Author Response.docx
Reviewer 4 Report
The paper describes the (simulated) impact of changing PV temperature coefficient and configuration on the performance (electrical and thermal energy production) of a PV-T system. It provides some interesting and quantified results that indicate the (in)significance of the various options.
Some comments I have:
* p3 line 104: kWh/m2 i.o. kWh I assume?
* p4 Fig 2: for clarity, for the reader not familiar with the technical blocks in TRNSYS (like me), it would be beneficial to indicate the functionalities of each block also visually, rather than its Type number (even though it is partly also present in the text).
* p5 line 147: In order to be able to get the beneficial cooling impact for the PV part, should you also not program the heat pump to retrieve heat from the DHW if the temperature becomes too high?
* p5 section 3.3: while model A, using the PV-T system without taking out the heat is an understandable reference for comparative reasons, one more fundamental case would be to compare against a PV system. This would imply using the same collector area, but a much higher packing factor, and determine how much electrical energy can be extracted (compared to the ~99 kWh for the PVT-T system), that can later be partly be converted for heat production via a heat pump. Roughly PV could yield >200 Wp/m2 and thus ~200 kWh/m2 annually. Would such an approach not be more straightforward (depending on heat pump efficiency)? Can you please comment on this?
* p6 Fig. 3: it would be clearer to plot here actual daily production, rather than cumulative energy produced. This might allow a better visual distinction between when the difference between models and coefficients is more pronounced (as is done for the heat component in Fig. 7). If you want to indicate the overall annual electricity production for all options, that is already clear from Fig. 4?
* p8 line 245: I guess you mean the cell temperature in Model C is "only" slightly lower, while you could expect it to be even lower, more in the range of Models B and D?
* p8 Fig. 6: why is the averaged temperature for Tank C not included in the graph (as B and D)? And why is the temperature of Tank B higher than that of Tank D? If more thermal energy is generated with Model D (graph in Fig 4), I would intuitively expect a higher temperature for Tank D? Or maybe I misunderstood because of the 2 tanks used for Model D?
* p9 line 275: at first glance, such a COP seems rather low for a water-to-water heatpump. Can you hypothesize on this?
Author Response
I would like to wholeheartedly thank the Reviewer for his time, patience, and efforts to review the paper. It will help me improve it to a better scientific level.
Comment 1:
p3 line 104: kWh/m2 i.o. kWh I assume?
Response:
The unit has been corrected. It should be 1.041 kWh/m2.
Comment 2:
p4 Fig 2: for clarity, for the reader not familiar with the technical blocks in TRNSYS (like me), it would be beneficial to indicate the functionalities of each block also visually, rather than its Type number (even though it is partly also present in the text).
Response:
Done. Attachment A is provided at the end of the manuscript, with a short description of the components used in transient models.
Comment 3:
p5 line 147: In order to be able to get the beneficial cooling impact for the PV part, should you also not program the heat pump to retrieve heat from the DHW if the temperature becomes too high?
Response:
In the C and D Models, it is not possible to get the temperature in the DHW tank above the set value of the degree of overheating (set to 2°C), because switching on/off the heat pump is controlled by the differential controller (Type 2b).
Comment 4:
p5 section 3.3: while model A, using the PV-T system without taking out the heat is an understandable reference for comparative reasons, one more fundamental case would be to compare against a PV system. This would imply using the same collector area, but a much higher packing factor, and determine how much electrical energy can be extracted (compared to the ~99 kWh for the PVT-T system), that can later be partly be converted for heat production via a heat pump. Roughly PV could yield >200 Wp/m2 and thus ~200 kWh/m2 annually. Would such an approach not be more straightforward (depending on heat pump efficiency)? Can you please comment on this?
Response:
Thank you for your very apt comment. In this article, I did not want to consider the packing factor issue, as it has already been described in many publications, although poorly in the long-term perspective. I would like to elaborate on this topic in further research and in the forthcoming publication. At the same time, there is a lot to do in terms of optimizing the system's operation in cooperation with the heat pump.
The simulation results that I conducted in TRNSYS show that under the same conditions as assumed in the article, with an increased value of the packing factor to 0.9 and β = 0.003 K– 1 PV yield is ~ 150 kWh/m2.
Comment 5:
p6 Fig. 3: it would be clearer to plot here actual daily production, rather than cumulative energy produced. This might allow a better visual distinction between when the difference between models and coefficients is more pronounced (as is done for the heat component in Fig. 7). If you want to indicate the overall annual electricity production for all options, that is already clear from Fig. 4?
Response:
Thank you for your attention. In fact, maybe it would be better for the person analyzing the graph to use 4 graphs for each value of B. But these 16 charts would appear in the work, which I find inappropriate. Moreover, changes in daily production are quite small for individual models, which would be difficult to capture on separate charts. The option presented in the paper seems to me to be the best for interpreting the results among the many tested by me. My data availability statement is that data are available on request. So for the person interested in the details, I can always submit the data.
Comment 6:
p8 line 245: I guess you mean the cell temperature in Model C is "only" slightly lower, while you could expect it to be even lower, more in the range of Models B and D?
Response:
Thanks again for your due consideration.
During the preparation of the simulation, I expected that Model C would achieve the lowest cell temperature among the models under consideration during the summer period. But this did not happen because the heat pump power was too small. It seems that the only correct solution is to use a heat pump with power modulation to adapt its cooling power to changing environmental conditions.
Comment 7:
p8 Fig. 6: why is the averaged temperature for Tank C not included in the graph (as B and D)? And why is the temperature of Tank B higher than that of Tank D? If more thermal energy is generated with Model D (graph in Fig 4), I would intuitively expect a higher temperature for Tank D? Or maybe I misunderstood because of the 2 tanks used for Model D?
Response:
Averaged temperature for Tank C is not included in Figure 6 because the tank is loaded with the energy produced by the heat pump. Including averaged temperature in Tank C in the graph could lead the reader to erroneous conclusions.
The average temperature of the water in Tank D is controlled by a differential controller at a level not exceeding 50°C. In Model B, there is no such limitation, therefore the temperature of the fluid is higher because each portion of the heat generated in PV-T should be stored in the tank. Of course, it is not without significance that the Model D has two tanks, not one.
Comment 8:
p9 line 275: at first glance, such a COP seems rather low for a water-to-water heatpump. Can you hypothesize on this?
Response:
The two models of PVT and heat pump hybrid installations shown are not ideal. The low COP value of the heat pump is due to a mismatch between the heat pump's heating power and PV-T power and using of a heat pump with constant cooling power. The introduction of these modifications in the next planned versions of the simulations should bring an increase in COP.
Please review any changes made to the manuscript in the attachment with the track-changes mode word file.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The article has been extensively revised. I suggest accepting it in the present form.
