Novel Indoor Educational I-V Tracer for Photovoltaic Modules

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. Please improve explanation of digital potentiometer task in the system. Converter’s operating voltage Vset adjustment is unclear!

2. Referring to the end of section 3.1, the power balance must be sustained. It is hard to understand that Pout > Pin and jet the battery must be discharged?

3. What is the purpouse of the battery application if the paper obejctive is a photovoltaic I-V tracer? It seems easier to use variable resistor?

Author Response

We sincerely appreciate the time and effort you have dedicated to reviewing our work. The authors wish to express their gratitude for your insights, which are pivotal in enhancing the quality of our manuscript.

In general response to your review, we would like to say that modifications have been included in order to clarify the fact that the CN3722 by Consonance Electronics, although designed to be a battery solar charger, can be successfully used as a photovoltaic I-V tracer.  CN3722 and similar Narrow Voltage DC-DC Converters allow the control of its duty cycle (and consequently the working point of the PV model connected to them) by an external resistor network. Including a digital potentiometer in this resistor network allows a program to automatically sweep all the points of the I-V curve, which is the target.

In this sense, we have clarified that circuits like CN3722 can be successfully used for a new application different from the one that they were designed for. Section 3.1 (lines 136 onwards) has been enhanced to explain this point, which was blurred before.

Your suggestions about the paper have been bolded in the following lines. Right after that, our comments and corrections have been included. We hope that the modifications included in the text, thanks to your comments, make it easier to understand and improve its quality.

 

1. Please improve explanation of digital potentiometer task in the system. Converter’s operating voltage Vset adjustment is unclear!

Thank you for your comment regarding these two points, which were not adequately explained. In response to your feedback, we have made modifications in the revised manuscript from line 136 onwards, highlighting them in orange. My co-authors and I expect these new explanations will help clarify this point related to Vset and the task that the digital potentiometer carries out in the design.

2. Referring to the end of section 3.1, the power balance must be sustained. It is hard to understand that Pout > Pin and jet the battery must be discharged?

My co-authors and I agree with you that further explanation is needed about how the CN3722 works. This is a very specific characteristic of this integrated circuit, which was not fully commented on in the first version of the paper so as not to overextend the document. Following your suggestions, new explanations have been included from lines 177 onwards in the revised manuscript. The new text has been highlighted in orange.

3. What is the purpouse of the battery application if the paper obejctive is a photovoltaic I-V tracer?

This concern was addressed at the beginning of this review, and section  3.1 (lines 136 onwards) was enlarged to clarify this point in the revised manuscript.

It seems easier to use variable resistor?

Indeed, a variable resistor or rheostat can be used to modify the load connected to the PV module. This method has been widely covered in the literature [1][2].  However, this solution implies some issues that the proposed design tries to overcome:

• If there are programmable rheostats, their price will probably be higher than the solution presented in the paper.
• The rheostat will get hot, causing a variation in its resistance. Consequently, measurements will not be stable, compromising the instrument's repeatability.  
• The rheostat can not have a linear response; otherwise, points in the knee of the I-V curve (where the maximum power point is) will be difficult to measure due to the sharp response of the PV module in this important region.
• The volume and weight of the rheostat are significant to dissipate the generated heat.

Many authors have tried using a MOSFET transistor operating in the linear region as a resistor [3][4]. However, the method proposed in our manuscript, among other advantages, allows more precise control of the PV module's operating point.

 

[1] A.Q. Malik, S.J. Bin Haji Damit, "Outdoor testing of single crystal silicon solar cells ", Renewable Energy, 28,2003, pp.1433-1445

[2] E.E. Van Dyk, A.R. Gxasheka, E.L. Meyer, "Monitoring current-voltage characteristics of photovoltaic modules", IEEE PVSC, 2002, pp. 1516-1519.

[3] Y. Kuai, S. Yuvarajan, "An electronic load for testing photovoltaic panels", Journal of Power Sources, 154, 2006, pp. 308-313.

[4] N. Forero, J. Hernandez, G. Gordillo, "Development of a monitoring system for a PV solar plant", Energy Conversion & Management, 47, 2006, pp. 2329-2336.

Reviewer 2 Report

Comments and Suggestions for Authors

I think, the article is interesting and well written. The topic is current, the education of a new generation of experts is important. Photovoltaic energy sources will have an important place in the energy mix. But I have some comments, see below. I recommend accepting the article after major revision.

Comments:

- Lines 37, 47 - Instead of the reference format [4][5][6] or [7][8][9][10], it is better to write [4-6] or [7-10]. Similarly throughout the rest of the text.

- Fig. 1 - Why is the figure caption above the figure, all other figures have the figure caption properly below the figure.

- Line 50 - LED light sources are not suitable for photovoltaic cells testing . Their emission spectrum is discrete and not continuous. Incandescent light sources better resemble the spectrum of the Sun, because they glow on the principle of "Black Body Radiation".

- Table 1 - The unit should be in the table heading in bracket, in the columns should be values only.

- The I-V characteristics depend on the temperature. I think, for example, the article doi: 10.1109/JPHOTOV.2021.3108484 could be inspiration for authors and it could be mentioned in references.

- Line 205 – The units (mV, mA) should not be written in italics font. They should be written in standard font. Similarly the units (V) on lines 245, 247, (W/m²) on lines 261, (mA) on lines 170, 271.

- Fig. 7 - Why the proposed I-V tracer don't measure till the short circle current.

- Ref. 18 - I think, the name of the journal is bad.

Author Response

My co-authors and I appreciate your wise revision of the manuscript. Some editing issues that we had overlooked were accurately pointed out, which undoubtedly will improve the document's quality after this revision. Moreover, other technical and conceptual matters that were not well explained in the text, such as the impossibility of reaching the shortcircuit current, have been addressed in this new version of the paper. 

Your concerns about the paper have been bolded below. Right after that, our comments and corrections will be explained. We hope that the modifications included in the text, thanks to your comments, make it easier to understand and improve its quality.

• Lines 37, 47 - Instead of the reference format [4][5][6] or [7][8][9][10], it is better to write [4-6] or [7-10]. Similarly throughout the rest of the text.

We appreciate your comment. The revised version of the paper addresses this issue according to your recommendation.

• - Fig. 1 - Why is the figure caption above the figure, all other figures have the figure caption properly below the figure.

Indeed, the image caption was wrongly placed. The revised version solves this problem. The caption has been highlighted in yellow.  

• Line 50 - LED light sources are not suitable for photovoltaic cells testing . Their emission spectrum is discrete and not continuous. Incandescent light sources better resemble the spectrum of the Sun, because they glow on the principle of "Black Body Radiation".

We fully agree with your observation. The spectral deviations exhibited by LEDs can indeed differ significantly from the solar spectrum. In response to your comment, we have corrected the paper by removing the mention of LEDs.

• Table 1 - The unit should be in the table heading in bracket, in the columns should be values only.

The indicated corrections have been made. Units in the referred table are in brackets in the revised version. We also realised that Figures 4 and 7 units were in brackets and have been corrected, too.

• The I-V characteristics depend on the temperature. I think, for example, the article doi: 10.1109/JPHOTOV.2021.3108484 could be inspiration for authors and it could be mentioned in references.

We appreciate this observation, highlighting the need to maintain sufficiently short tracing times to ensure no significant temperature variations occur under the proposed tracer's operating conditions. In the revised version, the following sentence has been included and highlighted:

(line 235)

According to [26] thermal stability is crucial, as temperature fluctuations would otherwise lead to deviations between measurements due to temperature-induced effects on the module's performance.

• Line 205 – The units (mV, mA) should not be written in italics font. They should be written in standard font. Similarly the units (V) on lines 245, 247, (W/m²) on lines 261, (mA) on lines 170, 271.

Considering your comments, the entire manuscript has been thoroughly reviewed and revised following your guidance.

•  Fig. 7 - Why the proposed I-V tracer don't measure till the short circle current.

This limitation of the proposed system was indicated in the third paragraph of section "3.5 LabVIEW application." However, following your comment, the corresponding text has been revised to clarify this explanation further. The following text has been added and highlighted in yellow in the revised version of the document:

(line 272)

The current version of the proposed hardware does not allow for direct measurement of Isc, except through estimation based on other points of the I-V curve. This limitation is compounded by the fact that the CN3722 development board is adjusted to charge a Lithium battery (4.2 V). Thus, given the Buck internal topology of the CN3722, the input voltage will never be lower than 4.2 V. Even more, if the losses of the internal switching elements of the CN3722 development board are considered, the minimum operating voltage should be around 5 V, specifically 5.2 V, according to the manufacturer. Consequently, this imposes a lower limit on the voltage that can be applied to the photovoltaic module.

• Ref. 18 - I think, the name of the journal is bad.

We appreciate your valuable feedback on the reference section of our manuscript. We've corrected the reference, and the revised version highlights the journal's right title in yellow. 

Reviewer 3 Report

Comments and Suggestions for Authors

Report on Electronics-3340061

In this manuscript the authors proposed the use of novel low-cost I-V curve tracer that can be used in indoor laboratories for teaching purposes in the place of ordinary calibrated commercial I-V tracer (Keysight B2902B). They proved that for a low-power photovoltaic modules illuminated by a halogen lamp, the proposed new I-V tracer deviates just 1.3% from the commercial one in the measure of the maximum power of PV modules. The proposed I-V tracer shows an advantages as a low cost for its production, the use of electronic components with high availability in the market, and the inclusion of a LabVIEW application that allows control, visualization, and storage of the curve data for subsequent analyses.

The manuscript was written consistently and the work performed is of interest to the Electronics journal readership. I would recommend the manuscript to be accepted for publication without need of additional analyses and use of more references.

Author Response

My co-authors and I appreciate your comments regarding the manuscript. We are glad that you found the topic and the way in which we have covered the issue interesting.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for addressing my comments, I have no more remarks.

Reviewer 2 Report

Comments and Suggestions for Authors

I think, my comments were accepted. I can recommend the article to publication.