Optimization of Shingled-Type Lightweight Glass-Free Solar Modules for Building Integrated Photovoltaics

Round 1

Reviewer 1 Report

This is a good manuscript designing and analyzing the shingled-type lightweight glass-free solar modules for building integrated photovoltaics. In the manuscript, the author detailed described the methods to build a lightweight shingled-type PV module using ETFE to reduce the weight and using Al honeycomb structure to provide the mechanical rigidity. And then the module is tested and show the pretty good stability. However, there are some questions/issues in the manuscripts, I suggest publishing it after the minor change/modification. 
1.    Some spelling and wording issues, for example, “High-power and lightweight photovoltaic (PV) modules are suitable for building-integrated photovoltaics systems because of their limited installation areas and heavy weight”, is the heavy weight a benefit here? 
2.    The author clear show the conversion power reduction after stability test, but haven’t detailed discuss the reasons behind the reduction. It would be great to discuss or add characterizing pictures/data in the conversion power reducing.

Author Response

Response and Rebuttal to the Reviewers’ Comments

Manuscript ID: applsci-1711164

Title: Efficient thin crystalline silicon photoanode with lithium fluoride based electron contacts

Authors: Min-Joon Park, Sungmin Youn, Kiseok Jeon, Soo Ho Lee, Chaehwan Jeong

Dear editor,

According to the reviewers’ comments, we have specifically revised our manuscript via proofreading by native English reviewer. All the changes described here are highlighted with yellow background in our revised text.

Response and Rebuttal to the reviewer's reports

REVIEWERS REPORT(S):

Reviewer: 1

This is a good manuscript designing and analyzing the shingled-type lightweight glass-free solar modules for building integrated photovoltaics. In the manuscript, the author detailed described the methods to build a lightweight shingled-type PV module using ETFE to reduce the weight and using Al honeycomb structure to provide the mechanical rigidity. And then the module is tested and show the pretty good stability. However, there are some questions/issues in the manuscripts, I suggest publishing it after the minor change/modification.

1. Some spelling and wording issues, for example, “High-power and lightweight photovoltaic (PV) modules are suitable for building-integrated photovoltaics systems because of their limited installation areas and heavy weight”, is the heavy weight a benefit here?

Our Reply:

Thanks for your comments. As reviewer’s comments, we revised the sentence as below.

(In abstract, Page 1) High-power and lightweight photovoltaic (PV) modules are suitable for building-integrated photovoltaic (BIPV) systems. Due to the characteristics of the installation sites, the BIPV solar modules are limited by weight and installation area.

2. The author clear show the conversion power reduction after stability test, but haven’t detailed discuss the reasons behind the reduction. It would be great to discuss or add characterizing pictures/data in the conversion power reducing

Our Reply:

Thanks for your comments. We greatly agree with the reviewer’s comments. A study on conversion power reduction after a reliability test is significant for the commercialization of BIPV modules. Accordingly, we are studying a reliability test of harsh conditions (e.g., DH 3000) on our PV modules. However, the experimental data of the DH 3000 test were not included in this study due to the too long test period. As reviewer’s comments, we added some discussions and references about the reliability tests as below.

(In result & discussions, Page 5)

After ML 2400, we confirmed that the decrease in the FF value was the cause of the reduction of the conversion power of the PV module. This result shows a phenomenon caused by cracks or damage occurring during the ML test [21].

On the other hand, the I_SC value decreases after the DH 1000 and TC 200 tests. The mechanisms for degradation of conversion power during damp heat exposure are at-tributed as follows: (1) delamination among the encapsulation polymer and the solar cells or front/back covers due to adhesion loss, (2) grid corrosion due to the by-product such as acetic acid. Moisture is well known to cause problems with polymers and adhesions. Un-fortunately, EVA has a high moisture absorption rate and poor stability in a humid envi-ronment [22]. Moreover, absorbed moisture by EVA adhesive can generate a by-product of acetic acid and increase the series resistance due to grid corrosion [23]. The decrease in the ISC value after the TC 200 test was caused by discoloration of PV module. Wohlgemuth et al. analyzed the I-V measurement after conducting the thermal cycling test, and found that P_M decreased due to the decrease of I_SC [24]. They concluded that transmittance decreases due to the change in color of EVA after thermal cycling, resulting in a decrease in current.

(In references, Page 7)

21. Wohlgemuth, J.H.; Kurtz, S.; Reliability testing beyond qualification as a key component in photovoltaic’s progress toward grid parity, 2011 International Reliability Physics Symposium, 2011 IEEE International Reliability Physics Sympo-sium 2011, 5E.3.1-5E.3.6
22. Mclntosch, K. R.; Powell, N. E.; Norris, A. W.; Cotsell, J. N.; Ketola, B. M., The effect of damp-heat and UV aging tests on the optical properties of silicone and EVA encapsulants, Prog. Photovolt: Res. Appl. 2011, 19(3), 294-300.
23. Shi, X.-M.; Zhang, J.; Li, D.-R.; Chen, S. J., Effect of damp-heat aging on the structures and properties of ethylene-vinyl acetate copolymers with different vinyl acetate contents, J. Appl. Polym. Sci. 2009, 112(4), 2358-2365.
24. Wohlgemuth, J. H.; Petersen, R. C., Reliability of EVA modules, 23th IEEE Photovoltaic Specialists Conference 1993, 1090-1094.

Reviewer 2 Report

In this study, the authors fabricated glass-free and shingled-type PV modules with an area of 1040 mm × 965 mm, which provide more conversion power compared to conventional PV modules at the same installed area. Further, they employed an ethylene tetrafluoroethylene sheet instead of a front cover glass and added an Al honeycomb sandwich structure to enhance the mechanical stability of lightweight PV modules. It is very interesting and suitable published in Applied Science. However, it needs to be revised before accepted for publication. The comments are as follows:

1. What is novelty of this study? The authors should compare with similar studies by other researchers and discuss in manuscript.
2. The explanations of Fig. 3~Fig. 5 are too less. The authors should describe the differences of I-V curve for these three PV modules.
3. The conclusions of this study are very weak. The authors should point the highlight of this study in conclusions.

Author Response

Response and Rebuttal to the Reviewers’ Comments

Manuscript ID: applsci-1711164

Title: Efficient thin crystalline silicon photoanode with lithium fluoride based electron contacts

Authors: Min-Joon Park, Sungmin Youn, Kiseok Jeon, Soo Ho Lee, Chaehwan Jeong

Dear editor,

According to the reviewers’ comments, we have specifically revised our manuscript via proofreading by native English reviewer. All the changes described here are highlighted with yellow background in our revised text.

Response and Rebuttal to the reviewer's reports

REVIEWERS REPORT(S):

Reviewer: 2

In this study, the authors fabricated glass-free and shingled-type PV modules with an area of 1040 mm × 965 mm, which provide more conversion power compared to conventional PV modules at the same installed area. Further, they employed an ethylene tetrafluoroethylene sheet instead of a front cover glass and added an Al honeycomb sandwich structure to enhance the mechanical stability of lightweight PV modules. It is very interesting and suitable published in Applied Science. However, it needs to be revised before accepted for publication. The comments are as follows:

1. What is novelty of this study? The authors should compare with similar studies by other researchers and discuss in manuscript.

Our Reply:

Thanks for your comments. Martins et al. conducted various studies on the production of lightweight modules. However, research on improving the conversion power of lightweight modules is very important for BIPV systems because of the limited installation area. For this reason, we studied the combination of a shingled-type PV design and a glass-free lightweight design with an Al honeycomb sandwich structure. As reviewer’s comments, revised the introduction as blow.

(In introduction, Page 2)

However, conversion power enhancement of lightweight PV modules for BIPV systems has not yet been studied. In this study, we combined a shingled-type PV design and glass-free lightweight module with an Al honeycomb sandwich structure on the rear side.

2. The explanations of Fig. 3~Fig. 5 are too less. The authors should describe the differences of I-V curve for these three PV modules.

Our Reply:

Thanks for your comments. As reviewer’s comments, we added more explanations and references as below.

 (In result & discussions, Page 3)

The value of the PM decreased about 2.7% compared to the value of the PM without electri-cal losses. This phenomenon is expected to reduce the PM due to laser scribing damage [15]. To minimize PM loss, we will optimize the laser scribing process.

(In result & discussions, Page 4)

Compare with the I-V curve of separated cell in Fig. 3 (b), the value of short circuit current (ISC) and fill factor (FF) decreased by approximately 0.11 A and 0.009. The value of the PM decreased about 4.5% compared to the value of the PM without electrical and optical losses. In case of conventional PV modules with metallic wire interconnections, the PM reduction rate is about 4.8% [20].

(In references, Page 7)

20. Haedrich, I.; Eitner, U.; Wiese M.; Wirth H., Unified methodology for determining CTM ratios: Systematic prediction of module power, Sol. Energy Mater. Sol. Cells 2014, 131, 14-23

3. The conclusions of this study are very weak. The authors should point the highlight of this study in conclusions.

Our Reply:

Thanks for your comments. As reviewer’s comments, we added more highlight of this study as below.

(In conclusion, Page 6)

In our lightweight shingled-type PV module, 4.8 M2-size Si solar cells were more integrated compared to the optimized conventional PV module at the same area.

Author Response File: Author Response.docx