Floating Photovoltaic Plants as an Effective Option to Reduce Water Evaporation in Water-Stressed Regions and Produce Electricity: A Case Study of Lake Nasser, Egypt

Round 1

Reviewer 1 Report

This is an interesting manuscript on the effects of floating photovoltaic plants on reducing evaporation. It would be useful for water resources and energy. Nevertheless, there are several questions on evaporation estimation.

1. The Penman-Monteith equation (1) was used to calculate the evaporation from Lake Nasser. However, PM equation is proposed for reference crop evaporation, not open water evaporation.  It would be problematic. Penman equation with tunned wind function would be more suitable.

2. Was the the climatological and solar energy data of the Aswan city used to calculate the surface water evaporation? It should be noted that the climate over the land is substantially different from that in the water surface. 

3. Considering the lake-atmosphere interaction, the climatology would be substantially altered by the large lake.  Accordingly, the climate would be altered different among the four cases, especially for Case 1. Were the alterations on the climate considered when calculating the evaporation of different cases?

4. Is there seasonal variation on the area of the lake?

Author Response

On behalf of the authors, I would like to express my gratitude for the precise and valuable reviewing comments for our manuscript. Thank you very much for your devotion and precious comments. We hope that the valuable ‎ editor and reviewer comments have been right answered. All modifications according to the editor and reviewers' comments have been highlighted in red color in the revised manuscript. ‎

Reviewer #1:

This is an interesting manuscript on the effects of floating photovoltaic plants on reducing evaporation. It would be useful for water resources and energy. Nevertheless, there are several questions on evaporation estimation.

The authors would like to thank the reviewer for devoting his valuable time to evaluating the manuscript and for offering insightful comments to improve the overall quality of our manuscript.

Comment 1: The Penman-Monteith equation (1) was used to calculate the evaporation from Lake Nasser. However, PM equation is proposed for reference crop evaporation, not open water evaporation.  It would be problematic. Penman equation with tunned wind function would be more suitable.

Response: From reviewing the previous studies that utilized the floating photovoltaic panels for covering the water bodies, the Penman-Monteith equation was used to calculate the reservoirs’ evaporation before considering the floating photovoltaic panels [29, 30]. So, in the current study, we used the Penman-Monteith equation to calculate the evaporation from Lake Nasser before considering the floating photovoltaic panels.

Comment 2: Was the the climatological and solar energy data of the Aswan city used to calculate the surface water evaporation? It should be noted that the climate over the land is substantially different from that in the water surface.

Response: In the present study, we used the Egyptian meteorology and Solar Energy Database of Lake Nasser location, south of Aswan, Egypt (22°25′N 31°45′E).

I agree with you, but according to previous studies that dealt with the study of the effect of floating photovoltaic panels on the rates of evaporation of water bodies, all of them were based on the climatological and solar database for the location of water bodies.

Therefore in this study we used an Egyptian meteorology and Solar Energy Database of Lake Nasser location, south of Aswan, Egypt (22°25′N 31°45′E).

Comment 3: Considering the lake-atmosphere interaction, the climatology would be substantially altered by the large lake.  Accordingly, the climate would be altered different among the four cases, especially for Case 1. Were the alterations on the climate considered when calculating the evaporation of different cases?

Response: I agree with you, but according to previous studies that dealt with the study of the effect of floating photovoltaic panels on the rates of evaporation from water bodies, all of them were based on the climatological and solar database for the location of water bodies.

The present study is a comparative study between the four proposals cases to cover Lake Nasser with floating photovoltaic (FPV) panels with different coverage rates, and this comparative study were done under the same conditions of Egyptian meteorology and Solar Energy Database of Lake Nasser location, south of Aswan, Egypt (22°25′N 31°45′E).

 Comment 4: Is there seasonal variation on the area of the lake?

Response: Certainly, there is very little change in the surface area of the water body of the lake during the seasons of the year.

But the space that was mentioned in the research was taken from the latest Egyptian reports (International Lake Environment Committee; Ministry of Water Resources and Irrigation (High Dam); and the official website of Aswan Governorate).

Reviewer 2 Report

Paper deals with modern topic - using floating PV panels. It can be observed that such methods are analyzed becouse of increasing costs of energy.

Authors prepared and presented their analyses quite clear and paper can be interested to readers.

I found few minor things that should be improved:

1. There are too long numbers in tables (even 10 digits) - it is difficult to read, authors should consider change units to make them shorter.

2. I recommend language editing by native speaker.

3. Conclusions are poor, it looks more like summary, results must be commented wider.

Author Response

On behalf of the authors, I would like to express my gratitude for the precise and valuable reviewing comments for our manuscript. Thank you very much for your devotion and precious comments. We hope that the valuable ‎ editor and reviewer comments have been right answered. All modifications according to the editor and reviewers' comments have been highlighted in red color in the revised manuscript.

Paper deals with modern topic - using floating PV panels. It can be observed that such methods are analyzed becouse of increasing costs of energy.

Authors prepared and presented their analyses quite clear and paper can be interested to readers.

I found few minor things that should be improved.

The authors would like to thank the reviewer for devoting his valuable time to evaluating the manuscript and for offering insightful comments to improve the overall quality of our manuscript.

Comment 1:  There are too long numbers in tables (even 10 digits) - it is difficult to read, authors should consider change units to make them shorter.

Response: According to the comment, the authors revised all Tables to avoid very long numbers in tables and make them short in the revised manuscript. See Tables 1-3, Pages 9 and 10.

Comment 2:  I recommend language editing by native speaker.

Response: Language is revised.

Comment 3:  Conclusions are poor, it looks more like summary, results must be commented wider.

Response: According to the comment, the authors revised the conclusions to make it more clear in the revised manuscript. See Section 4 conclusion, Page 12.

Round 2

Reviewer 1 Report

The authors responded my comments well. I think it is ready for publishing.