Overall statement:

The impact of dust accumulation on PV performance in two locations in Egypt was investigated in this study. The locations are Cairo and Benisuef. For comparison sake, the authors used the same PV modules in two different locations and tested them in outdoor conditions. Moreover, indoor testing was carried out, as well. The study presents the materials and methods used to carry out the experiments and results of those experiments to both demonstrate the impact of dust on PV electrical performance and the extent of such impact in two different locations.

The strengths

1) The introduction presents the research background into the topic and the problem statement of the study well, while the literature review is very brief. Moreover, the authors mentioned the concept of Photovoltaic Soiling Index (PVSI) multiple times in the introduction. 2) The materials and methods are provided. 3) The references provide sources related to the topic and generally up to date.

Weaknesses:

1. The authors did not present the solar irradiance and ambient temperature profiles for the two tested locations.
2. The uncertainty analysis was not provided. It is preferable to show the uncertainty of the equipment used, or at least provide the error percentage of each device.
3. Figure 5, the x-axis shows the irradiance in Wm2, I believe this is a typographical error because the unit of irradiance is w/m2.
4. The incident irradiance is kept constant and is under 11 W/m2, why wasn’t the system either tested under standard testing conditions, or have the solar simulator emulate the amount of irradiance in the tested locations?
5. Where was the T-type thermocouple placed, when placed on the surface of PV? Some researchers place multiple thermocouples (2, or 3 to cover top and bottom, or top, centre and bottom, respectively) and average the readings.
6. Was the used irradiance probe, a lux meter? It appears to be a lux meter. If so, what is the justification for using it? Given that it measures illuminance & is there an accurate method of converting the measured values into power per meter squared?

Conclusions and recommendations:

Overall, the paper presents a brief case study. The paper could have been better structured and made more thorough to include aspects such as providing the electrical efficiency of either module, in addition to the ‘weather profile’ of both tested locations. Moreover, to view the performance in indoor conditions under STC. Moreover, to consider the variation in power output by the tested systems, in real-time, as dust is being accumulated and present the findings. Furthermore, to use a pyranometer instead of a lux meter (if the lux is used). Note: Pyranometers measure the solar irradiance. sometime a reference cell is used instead of pyranometer. The type of dust accumulated is a very important factor to declare and the various characteristics of such material, using FESEM, XRD, EDS, Spectral mapping, etc., should be presented in future research.

• This is a post-publication review. The adherence to journal guidelines is not considered as the paper has already been processed by the editorial team of the journal