Performance Prediction and Optimization of Multi-Mirror Combined Solar Dish Collector

Round 1

Reviewer 1 Report

Authors present an analytical model to calculate and optimise the performance of multi-mirror combined solar dish collector. They compared the results with the ones from a commercial tool. An optimization model has been developed for maximizing the annual average net thermal efficiency.

 

In my point of view, authors wrote a great introduction, which reveals to the reader important achievements on the theme.

About section 2, I would like to suggest the improvement of the information regarding expressions 12 to 15. Expressions seems right to me, but it can lead to misunderstandings or confusions, since no examples or important scenarios are presented. My suggestion for the authors is to present values on a graph or table for those different quantities using 2 or 3 scenarios. On that section, figure 1 has an underline label “fp”. On line 132 “f0” is not presented on figure 1 and on lines 121 and 133 “point p” should be “point P”, to better perception.

The main observation I can made is about the manuscript and data organisation. In my opinion, figures on section 3 should be merged, there goal should be better detailed, and their comparison should be organised in a table, for example. The text presented in this section by the authors, in my opinion, is so repetitive in terms of conclusions and descriptions. This figure merge will allow them to compare and discuss just once.

About the method, as a reader, I would like to understand what is the algorithm or at least methodology used on the commercial programs as SolTrace, in order to compare with the proposed one? Can authors compare both?

Also, can authors systematise the limitations of the proposed method? Is it possible to obtain any conclusion about it with the obtained results? Why?

 

Regarding the presented text, I suggest authors to improve the formality of that, for example avoiding terms as “we” or “us” or short terms as “eqs”. Moreover, figures and tables should be referenced on the text before their appearance on the manuscript. Also, every distance between generical points A and B, should be marked as  instead of AB.

At the discussion and conclusions, I suggest to clearly present the innovation about the method and the applications of combined solar dish collector. Also, in my opinion authors should compare their results of combined solar dish collector with other technologies, even if they did not test their model on it. It will allow the readers to compare combined solar dish collectors with other ones, motivating them to use the proposed methodology by the authors of this manuscript.

Author Response

Dear sir/madam,

Thank you very much for your kind and suggestive comments for our manuscript to Applied Sciences entitled “Performance prediction and optimization of multi-mirror combined solar dish collector” (applsci-1481935). We appreciate you valuable comments and suggestions to improve it. With regard to your comments and suggestions, we wish to reply as follows:

Comments of reviewer 1:

Authors present an analytical model to calculate and optimise the performance of multi-mirror combined solar dish collector. They compared the results with the ones from a commercial tool. An optimization model has been developed for maximizing the annual average net thermal efficiency. In my point of view, authors wrote a great introduction, which reveals to the reader important achievements on the theme.

Major comments:

1. About section 2, I would like to suggest the improvement of the information regarding expressions 12 to 15. Expressions seems right to me, but it can lead to misunderstandings or confusions, since no examples or important scenarios are presented. My suggestion for the authors is to present values on a graph or table for those different quantities using 2 or 3 scenarios. On that section, figure 1 has an underline label “fp”. On line 132 “f0” is not presented on figure 1 and on lines 121 and 133 “point p” should be “point P”, to better perception.

Respond： We add a table to show it as following:

Table 1, value of the heat loss coefficient ξ = q/DNI used for two kinds of receiver

	Heat loss rate q	the heat loss coefficient ξ
receivers with glass window	1.67*103W/m2	18.177
receivers without glass window	1.63*104W/m2	168.25

“point p” has been revised as “point P”.

 

2. The main observation I can made is about the manuscript and data organisation. In my opinion, figures on section 3 should be merged, there goal should be better detailed, and their comparison should be organised in a table, for example. The text presented in this section by the authors, in my opinion, is so repetitive in terms of conclusions and descriptions. This figure merge will allow them to compare and discuss just once.

Respond:

The two tables give the results for two different cases. Considering that if the focal length of each mirror is uniform, the spot on the receiver is altered by the change of the mirror position, resulting in a greater loss. So, the system is firstly optimized based on the case that the focal length of each mirror is al-ways equal to the distance from the mirror center to the receiver. Then we have the results of Table 1.

Table 1. The optimal annual net thermal efficiency and optimized parameters of the multi-dish system for the optical error ranging from 1-5mrad, each focus length of mirror equals the distance from the receiver.

Optical error (mrad)	Radius of receiver (m)	Focal length of system (m)	Optimal net thermal efficiency	Intercept factor
1	0.09	7.5	0.8630	0.9892
2	0.10	7	0.8605	0.9881
3	0.11	6.5	0.8583	0.9898
4	0.12	6	0.8526	0.9857
5	0.14	6	0.8482	0.9861

Usually, in order to save cost, all mirrors of the combined dish system are considered to a uniform mirror focal length. And the table 2 is the result after re-optimization.

Table 2. The annual thermal efficiency under optimal design with the same focus length of the mirror.

Optical error (mrad)	Radius of receiver (m)	Focal length of mirror (m)	Net thermal efficiency	Intercept factor
1	0.09	8.5	0.8620	0.9880
2	0.10	8	0.8587	0.9860
3	0.11	8	0.8570	0.9883
4	0.12	7.5	0.8512	0.9841
5	0.14	7.5	0.8479	0.9857

 

3. About the method, as a reader, I would like to understand what is the algorithm or at least methodology used on the commercial programs as SolTrace, in order to compare with the proposed one? Can authors compare both?

Respond:

The algorithm for Soltrace is given in detail in ref 34 of the manuscript, the main idea is to trace rays from different position of the sun through stochastic methods to choose the solar ray, it need huge computation to obtain high accuracy results. In section 3.1, in order to ensure the reliability of the comparison results, we compared the results of the proposed model with that calculated by Soltrace code under the same physical condition. Figure 4 shows the validation results for a 3m×3m combined dish system respectively with a circular receiver. On the whole, the presented method is in good agreement with the results of the SolTrace method.

(a)

(b)

Figure 4. Validation of the intercept factor of 3 m × 3 m combined dish system with different receiver radius (a), and system focal length (b).

 

4. Also, can authors systematise the limitations of the proposed method? Is it possible to obtain any conclusion about it with the obtained results? Why?

Respond: the model applied the Gauss model for optical error distribution, it may introduce some error, however, for the present solar dish system, the incident angle is 0, and the optimized rim angle is about 45゜, the error should be rather little. However, if the rim angle is designed to near 90゜ although it is not good design, the incident angle to the mirror with larger rim angle will become larger, then calculation error may become large, and the model may not fit for it. It needs further study to give conclusion.

 

 

 

5. Regarding the presented text, I suggest authors to improve the formality of that, for example avoiding terms as “we” or “us” or short terms as “eqs”. Moreover, figures and tables should be referenced on the text before their appearance on the manuscript. Also, every distance between generical points A and B, should be marked as instead of AB.

 

Respond: Thank you for your support and kind suggestion.

Us has been deleted.

eqs has been revised as equation.

       We add explanation as, OE and OP are the distance between the point O and E, and P respectively; OT is the distance between the point O and T, to expain them as distance of two points in line 159 and 174.

 The figure and table has been adjusted before the text.

 

6. At the discussion and conclusions, I suggest to clearly present the innovation about the method and the applications of combined solar dish collector. Also, in my opinion authors should compare their results of combined solar dish collector with other technologies, even if they did not test their model on it. It will allow the readers to compare combined solar dish collectors with other ones, motivating them to use the proposed methodology by the authors of this manuscript.

Respond: thank you for your kind and good suggestion.

We have revised the first sentence of the discussion part to clearly show the innovation of the method as “In this work, the calculation model for direct calculation of optical efficiency for the optical performance of a combined dish concentrated solar system with a cavity receiver is firstly proposed and is validated with SolTrace”. In the end of the first paragraph of conclusion, we add a sentence to show the innovation again as:

It is the first model to directly calculate the optical efficiency and the first optimizing method of the combined solar dish system.

       Because of lack of the experimental data, it is hard to compare the accuracy of the present method with the other methods, we mainly compare its advantage in computation velocity which is given in second paragraph of the conclusions part.

 

We hope that the changes having been made to the manuscript meet to your
satisfaction.

 

With best regards

Dr. Weidong Huang, Associate Professor
Department of Environmental Science and Engineering
University of Science and Technology of China
Hefei, China, 230026

Author Response File: Author Response.docx

Reviewer 2 Report

This paper «Performance prediction and optimization of multi-mirror combined solar dish collector» presents an optical model, which can be used to analyze and optimize the optical performance of a combined solar antenna system. Based on a direct calculation method, the reflection coefficients, which were proposed in their earlier work, are first the optical efficiency of one mirror in a combined dish system, and the optical characteristics of the entire system are obtained by integrating the entire mirror system. Compared to the results calculated using SolTrace, the proposed method is in good agreement with it. The proposed method allows to perform calculations much faster than in SolTrace, while maintaining the reliability of the results. Thus, the optical model proposed in this article is effective for studying the optical characteristics of a combined tray system. On the example of a combined solar antenna system with an area of ​​62.25 m2, based on this analysis method, the optical characteristics of a multi-mirror combined solar antenna system are used with a change in the focal length of the system, the radius of the receiver and the optical error.

In my opinion, the article meets all the requirements of the journal, has novelty, scientific and practical significance, is written in clear language and can be recommended for publication.

Author Response

Dear sir/madam,

Thank you very much for your kind support for our manuscript to Applied Sciences entitled “Performance prediction and optimization of multi-mirror combined solar dish collector” (applsci-1481935). Your support to our study is the most motive force for us.

 

With best regards

Dr. Weidong Huang, Associate Professor
Department of Environmental Science and Engineering
University of Science and Technology of China
Hefei, China, 230026

 

Reviewer 3 Report

Dear Author(s)

• The title of the Manuscript is general, it should be specially adjusted and include the terms intercept factor and optical efficiency.
• The radius of curvature of the mirrors (249) should be presented in the abstract. Is it the same focal length of the optical system?
• Writers (author), if the receiver was at a focal length, the optical efficiency would not be optimal? Did you already know about this?
• In line 17, a sentence is presented that seems to have an editorial problem.
• In line 17, the abstract section and in other sections the method are mentioned quickly, while according to the title, it is not a model evaluation parameter?
• Line 23, the sentence has problems in terms of editing.
• The numbers in line 25 of the abstract are announced in Table 2 for the focal length of 8 meters. Now the question is, if this distance was more, the thermal efficiency would not be higher?
• In line 25, the phrase mirror panels is not used in the title or even in the abstract, so it should be deleted
• Why is the collector octagonal (line 121). Why in your study, the dish is not completely covered with a mirror. Was mathematical analysis difficult or impossible? Under these circumstances, can this object be called a dish collector?
• In line 134, from the interconnection of two equations, a relation is presented that is wrong. The correct relation is: tan∅_rim = (x₀ / (2f₀-f_n)), if you have used it in calculations, do not you think your study will make many mistakes?
• Line 184 states that the distance between the mirrors is large, but its schematic in Figure 1 does not confirm this.
• Dear author (s), the mirrors used in this study were spherical in shape, but you presented the relation related to the parabolic dish in line 203?! Can you explain?
• Equation 4 was not found in reference 30.
• In Equation 5, the multiplication sign should either be used or not used at all.
• In line 185, are the mirrors not glued together in the system under study? In big enough or small enough?
• In Equation 13, r is introduced.
• In line 203, you presented the equation for the parabolic dish, but the dish of your study was spherical. How do you justify this?
• In line 262, the receiver radius is assumed to be 0.1 m. Why? Because heat loss is important.
• In Figure 6, the range of the receiving radius is 0 to 0.15 meters. What is the reason for choosing this range? Of course, the INTERCEPT FACTOR has almost reached a maximum in exchange for a receiver radius of 0.1 meters.
• In line 287, what was the basis for choosing the focal length of 8-10? Is the focal length of the mirrors considered in their selection?
• The content presented in lines 348 to 355 is quite obvious. Therefore, it is not necessary to write it.
• In line 372, with increasing focal length from 7 meters to 8 meters, thermal efficiency has decreased from % 86.0 To %85.87 Finally, this value (85.87%) are introduced as the best case according to the cost. Is it economically analytical?
• Dear Author, In line 432, there is an editorial error. Use Rate instead of Velocity.

 

 

Author Response

see attached file.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Authors have respond to my previous comments.