Thermodynamic Analysis and Comparison of Two Small-Scale Solar Electrical Power Generation Systems

Round 1

Reviewer 1 Report

In this manuscript, the authors prepared “Thermodynamic Analysis and Comparison of Two

Small-Scale Solar Electrical Power Generation Systems”. The environmental temperature effect on V-I performance of PV cell and electric efficiency comparison of two systems at different irradiation values. The obtained cells shows exhibited excellent performances for PEC cell. It could be considered for publication after some revisions,

• The abstract should be revised: add some experimental results like the efficiency of the cell, etc.
• Keywords should be revised.
• Why the author used different energy storage technology in the table, the author explains the percentage-wise of the above technology.
• What is the difference between The J-V and I-V study?
• What is the rule of the Irradiation effect on cells?
• Why changing different Environmental temperature on PV cell at constant 800 mV/m2.
• Figure 12 explained more details.
• A comparison study of two different systems explained more details.
• Correct all equation in the same format (eq. 29)

Author Response

Thanks for your review. We have carefully revised the manuscript and response to your conmments, point by point. Please see the attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

This is a very interesting paper and I enjoyed reading it.  I have some suggestions:

1. Reference numbers were left out as question marks in a couple of places:page 3, line 74, 78 and 91.  Page 9 second sentence
2. Punctuation marks are not needed and should be removed at the end of the equations.  Currently there are either periods or commas after every equation.
3. Page 4 - Figure 2 is very helpful and informative.  However it seems like Table 2 should be listed closer to the sentence in lines 116-117.
4. Table 3 has some unusual symbols  Normally temperature and changes in temperature are depicted by a capital T.  In this table changes in temperature are shown by both a lower case and upper case letter t. This trend is continued through the paper as shown by delta lower case t in equation 1 and lines 137 and 139 on page 6. Also entropy is typically shown as a capital S not lower case, as is enthalpy with H.
5. Table 2 - it might be helpful to have the standard temperature for the PV cell at the top of the list so that more direct comparisons of temperature between the systems can be made.
6. The square root of partial oxygen pressure is listed differently in equations 18 and 30 - may want to keep consistent
7. The past tense should be used and in many places in the paper is not.  There are many places were is should be replaced by was or were. Page 3 (line  95 (are to were), 100, 103, 105, 108); Page 4 (line 122, 129 cold tank was set at); Page 7 (line 159), Page 11 (line 190, 191,194, 200, 209 (are to were); Page 12 (line 213, 214, 222, 223, 224), Page 13 (line 230, 233, 237, 255, 245, 247, 248), Page14 (line 252, 253, 254, 255, 256, 272, 276, , 278 (are to were), 279, 282 (are to were).
8. Some awkward or split comma sentences:  Will try to point them or out of make suggestions in the following comments.
9. Pg 2 line 44-45  Suggested change: Several research groups over the past several decades have explored low- and medium temperature solar thermal power generation systems.l
10. Pg 2 line 47-48 should be reworked; Several experimental and theoretical studies have examined ORC driven solar thermal power generation systems. 
11. Sentence 48-50 needs to be reworked.
12. Sentence 58-59 ending system, and also examined the control for heat storage systems and operational strategies.
13. Page 3 line 63-65 not a complete sentence
14. line 66 - suggestion: Although a PV cell has a ...... , a sole PV system is ..   Or change to plural Although PV cells have a ...., sole PV systems are.. Keep those changes for the next sentence as well
15. line 80 suggestion: change trends of the output power of a year round PV system and the...
16. 81-84 is a run on sentence, please change to two sentences.
17. same with line 89-94
18. line 103 - change while to when
19. Page 4 line 110 to keep the system operating continuously or to keep a continuous system operation
20. line 116 replace exit with exist and lower case letter for nomenclature
21. line 119-120 is unclear
22. line 121-126 is a very long sentence and should be broken up
23. 127-129 suggestion: The required collector tube length and heat loss can be obtained by modeling the PTC collector tube when the inlet temperature of the heat transfer liquid is known.
24. Page 7 line 147-148 - list processes as a list after colon leaving out using word process repeatedly  Example - ORC system: compression, heat absorption, expansion and heat rejection processes. 
25. It might be helpful to list 3 assumptions directly after the sentence 149 (before Fig 3)
26. Line between 154-155,  Get rid of For and it in sentence The outlet enthalpy value of the working pump fluid can be computed as follows:
27. last sentence on page 7 = real irradiation values and environmental temperatures are obtained
28. Page 8 - keep consistent - replace all is calculated or is determined to can be (line after lines 160, 161 & 164)
29. Change casual wording in line  158 (first step), 166 (we can)
30. fragment in front of sentence after equation 12 where FPV is the filling factor should be at end of sentence before equation 10.
31. Page 11 Sentence 180-183 is a split comma.  Might be better as 
32. The paragraph on same page lines 185-203 contains many run-on or split comma sentences.  It would be beneficial if the word firstly was removed as well. The sentence on lines 206-207 should also be reworked.
33. Page 12, Figure 6 & 7  I am not sure if the capital letter for Required PV cell area is needed
34.  Suggestions: line 213-214:  The effect of irradiation and environmental temperature on the outlet temperature was investigated when the molten salt mass flow rate was 2.0 Kg/s and the collector tube's inlet temperature was 200 C.
35. Suggestion line 216 Thus the following results were obtained on a 23 m...
36. Lines 217-220 are okay but it would read better if broken into two statements about effects of increasing irradiation
37. Line 227 - split comma  Suggestion: The heat losses of dual molten tanks also changes when the environmental temperature changes.
38. Page 13
39. line 230  Suggestion: ... temperature, the results are presented in Figure 10.
40. lines 234 -235 Suggestion: The heat loss trend of the molten salt tank when the environmental temperature increases from 15C to 45C is shown in Figure 11.
41. line 240-21 Suggestion: These two systems adopt two energy storage types: thermal and hydrogen energy storage. Thus it is necessary to investigate the storage type's effects on the system's performance. 
42. line 242 were (are) both 5 kE... performances were compared.
43. 245-246 irradiation value refers to the direct normal irradiation value for the STORC-MSHS system, in contrast the irradiation value refers to the total irradiation value for the SPV-PEMWE system in the model establishing system.
44. line 247-250 run on sentence 
45. Page 14 lines 252-257 run on sentences
46. unclear sentence on lines 258-260
47. line 266 temperature increases also leads
48.  Conclusion   The mathematical... were established in this study, while the electric efficiencies with .. were calculated ... Cut out the word meanwhile.  Start next sentence The effects of two .....on the system performances were also investigated.  The main conclusions from this work are presented as follows:
49. Page 15  line 285  per cell increases
50. line 306 draft
51. References 17 and 18 only list the first page of the publication.

Author Response

Thanks for your review. The manuscript has been carefully checked and revised, point by point, please the detailed information in the attached file.

Author Response File: Author Response.pdf

Reviewer 3 Report

The author compares two small-scale solar electrical power generation systems. The literature review requires further elaborations, the methodology is sufficient, the results are well presented but could have been discussed further. My concerns are as follows:

1. Issues with referencing can be seen, probably during the compiling process of latex files.
2. The manuscript requires proofreading. Some sections have grammatical errors.
3. The paper lacks intensive literature using past studies to identify gaps. This should be properly undertaken to motivate readers.
4. Most of Section 3 can be moved to the appendix. Nomenclature and symbols can be moved to the start of the manuscript.
5. The uncertainties in modelling the two systems have not been described or discussed properly.
6. Was the model tested with observations from a site which include ramps in incoming irradiance or extreme temperatures?
7. The limitations of the study have not been properly discussed.

Author Response

Thanks for your review. The manuscript has been carefully checked and revised, point by point, please the detailed information in the attached file.

Author Response File: Author Response.pdf

Reviewer 4 Report

The authors presented a study on modeling two solar electrical power generation systems. However, it was not clear why these two systems should be compared.  Since they are very distinct, what are the hypothesis to be tested through comparison?  There is little information regarding the input parameters, nor the model validation.  The results were not compared with experiments or other literature.  Without such information, it is not possible to evaluate the contribution of the paper.

Author Response

Thanks for your review. The manuscript has been carefully checked and revised, point by point, please the detailed information in the attached file.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors have made the suggested changes.