This is a fascinating subject. In my experience I would estimate that a floating panel would be just above water temp depending on the thermal path from the water to the surface being heated by the sun. I would guess water temp plus 10 F. The above land panel will heat just like a dark car and reach, likely, 120 F or more.

If water is at 70F then the difference is 120-80 or 60 F. does that seem useful??

@ F. Kurt Shafer Is there any practical experience proving this?

Thank you for your response.

No just based on my common sense. Would you disagree? No, you cannot disagree because I have only suggested possibilities. I recommend you take a panel and run some tests.

As you know, PV/T is the technology which is used to produce electricity and heat. However, some applications focus on extracting the heat (cool the PV) with no useful utilization of the thermal energy. It is currently a hot research topic. However, it shows good progress financially for grid-connected PV systems. Back to your question to cool the PV using float PV system. If we classify the river/lake/sea/ocean in a region with low, medium and high temperature than your idea expected to be suitable for medium. This because in a low-temperature environment, the PV still cold, and we do not need to cool it. However, in high environmental temperature, the water itself will be hot and not good enough to cool the PV.

Enclosed are some of our recent research paper conducted in PV/T to cool the PV.

1. Alwaeli, Ali HA, Kamaruzzaman Sopian, Hussein A. Kazem, and Miqdam T. Chaichan. "Novel criteria for assessing PV/T solar energy production." Elsevier-Case Studies in Thermal Engineering (2019): 100547.

2. Ali H. A. Alwaeli, Hussein A. Kazem, Miqdam T. Chaichan and K. Sopian, “Experimental investigation of using nano-PCM/nanofluid on a photovoltaic thermal system (PVT): Technical and economic study”, Thermal Science and Engineering Progress (2019), 11, pp.213-230.

3. K. Sopian, Ali H. A. Alwaeli, Hussein A. Kazem, “Advanced photovoltaic thermal collectors”, Proc IMechE Part E: J Process Mechanical Engineering, 13 August 2019, pp. 1-8.

4. Ali H. A. Alwaeli, Hussein A. Kazem, Jabar Yousif, Miqdam T. Chaichan and K. Sopian, “Mathematical and Neural Network Models for Predicting the Electrical Performance of a PV/T system”, Wiley-International Journal of Energy Research, 28 August 2019, Vol. 43, Issue 10, pp. 1-18.

5. Ali H. A. Alwaeli, Hussein A. Kazem, Jabar Yousif, Miqdam T. Chaichan and K. Sopian, “Mathematical and neural network modeling for predicting and analyzing of nanofluid-nano PCM photovoltaic thermal systems performance”, Elsevier-Renewable Energy RE, February 2020, Vol. 145, pp. 963-980.

6. Ali H.A. Al-Waeli, K. Sopian, Jabar Yousif, Hussein A. Kazem, John Boland, Miqdam T. Chaichan, “Artificial neural network modeling and analysis of photovoltaic/thermal system based on the experimental study”, Elsevier-Energy Conversion and Management (ECM, ISSN: 0196-8904), UK, Vol. 186, 15 April 2019, pp. 368–379.

7. Ali H.A. Al-Waeli, Miqdam T. Chaichan, Hussein A. Kazem, K. Sopian, “Evaluation and analysis of nanofluid and surfactant impact on photovoltaic-thermal systems ”, Elsevier-Case Study of Thermal Engineering, Vol. 13, March 2019, pp. 100392.

8. Ali H. A. Alwaeli, K. Sopian, and Hussein A. Kazem, Hameed B. Mahood, Anees A. Khadom Miqdam T. Chaichan, “Modeling and experimental validation of a PV/T system using nanofluid coolant and nano-PCM”, Elsevier-Solar Energy SE, (ISSN: 0038092X), UK, Vol. 177, January 2019, pp. 178-191.

9. Ali H.A. Al-Waeli, Miqdam T. Chaichan, Hussein A. Kazem, K. Sopian, Adnan Ibrahim, Sohif Mat and Mohd Hafidz Ruslan, “Comparison study of indoor/outdoor experiments of a photovoltaic thermal PV/T system containing SiC nanofluid as a coolant”, Elsevier-Energy, (ISSN: 0038092X), UK, Vol. 151, May 2018, pp. 33-44.

10. Ali H.A. Al-Waeli, Miqdam T. Chaichan, Hussein A. Kazem, K. Sopian, Javad Safaei, “Numerical study on the effect of operating nanofluids of photovoltaic thermal system (PVT) on the convective heat transfer”, Elsevier-Case Study of Thermal Engineering, Vol. 12, June 2018, pp. 405-413.

11. Ali H.A. Al-Waeli, K. Sopian, Hussein A. Kazem, Jabar Yousif, Miqdam T. Chaichan, Adnan Ibrahim, Sohif Mat and Mohd Hafidz Ruslan, “Comparison of prediction methods of PV/T nanofluid and nano-PCM system using a measured dataset and Artificial Neural Network”, Elsevier-Solar Energy SE, (ISSN: 0038092X), UK, Vol. 162, March 2018, pp. 378-396.

12. Ali H.A. Al-Waeli, K. Sopian, Miqdam T. Chaichan, Hussein A. Kazem, Adnan Ibrahim, Sohif Mat and Mohd Hafidz Ruslan, “Evaluation of the nanofluid and nano-PCM based photovoltaic thermal (PVT) system: An experimental study”, Elsevier-Energy Conversion and Management (ECM, ISSN: 0196-8904), UK, Vol. 151, November 2017, pp. 693–708.

13. Ali H.A. Al-Waeli, Miqdam T. Chaichan, Hussein A. Kazem, K. Sopian, “The use of different types of nanofluids (Al2O3, CuO, and SiC) to enhance Photovoltaic Thermal PV/T collectors”, Elsevier-Energy Conversion and Management (ECM, ISSN: 0196-8904), UK, Vol. 148, September 2017, pp. 963–973.

14. Ali H.A. Al-Waeli, K. Sopian, Hussein A. Kazem, Miqdam T. Chaichan, “Photovoltaic/Thermal (PV/T) Systems: Status and Future Prospects”, Elsevier-Renewable and Sustainable Energy Review (RSER, ISSN: 1364-0321), USA, September 2017, Vol. 77, pp. 109-130.

15. Ali H.A. Al-Waeli, K. Sopian, Miqdam T. Chaichan, Hussein A. Kazem, Husam Abdulrasool Hasan, and Ali Najah Al-Shamani, “An experimental investigation of SiC nanofluid as a base-fluid for a photovoltaic thermal PV/T system”, Elsevier-Energy Conversion and Management (ECM, ISSN: 0196-8904), UK, Vol. 142, 15 June 2017, pp. 547–558.

16. A Fudholi, K Sopian, MH Yazdi, MH Ruslan, A Ibrahim, Hussein A Kazem, “Performance analysis of photovoltaic thermal (PVT) water collectors”, Energy Conversion and M-anagement (ISSN: 01968904), UK, Vol. 78, 2014, pp. 641-651.

Thank you for your response dear @Hussein A Kazem

The system integrates existing land based photovoltaic technology with a newly developed floating photovoltaic technology. Because module temperature of floating PV system is lower than that of overland PV system, the floating PV system has better generation efficiency than overland PV system.

https://pdfs.semanticscholar.org/3384/0dba6bb3f82ac68cde86fbbbae588a5bc180.pdf

I fully agree with F. Kurt Shafer S Kalaiselvan

If you use standard PV simulation software and procedures, you need to change the PV panel operating temperatures. See this article how to adapt these for the floating solar microclimate

Sustainability Assessment Framework and Methodology with Numerical Simulation Model for Floatovoltaic Energy System Planning and Assessments

https://authors.elsevier.com/a/1dZ0b7tDQ9Gx-L

Interesting paper! Thank you dear @FC Prinsloo.

Aboubakr El Hammoumi

We must note that the main cooling mechanism for PV modules on Earth is convection, in which wind speed plays a crucial role. On water surface, the wind has higher speed and more regular pattern (that's why off-shore wind farms have higher capacity factors than on-shore ones). On-shore wind has lower speed and irregular pattern due to morphologies of the land and cities. Therefore, if we compare a floating PV with a far located rooftop PV (installed at the same height) under one climate condition, the floating PV will work at a lower temperature.

This gain due to lower temperature is less during winter months because during winter, the temperature of water, which has high thermal capacity, does not go down very much.

Researchers already made experiments to compare the temperature of floating and conventional PV. Here I put a few important researches which experimentally studied floating PV and temperature effect:

1.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/pip.3039

>>> shows if we compare floating PV with roof-top PV, floating PV will experience lower module temperature, mainly because of different wind profiles.

2.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/pip.3367

>>> shows that when floating and conventional PV installed close to each other, one on land the other on water, then the temperature difference is very low, because both will experience similar wind profile.

3.

https://www.sciencedirect.com/science/article/pii/S0038092X21002395

>>> shows the importance of climate. In a cold climate putting modules on water does not give a big cooling advantage, but in hot climate it does.

Thanks a lot Hesan Ziar for all of these details.

Dear Aboubakr El Hammoumi , Your question is very generic.

We may not come up with certain differences. It is very important to study the environment of the systems you would like to investigate.

The water cooling effect may vary depending on the climate where the system is going to be installed.

The operating temperature might not be always lower for the floating systems, this is very important to keep in mind.

What I recommend is to model the floating system you have considering the heat transfer mechanism of your system. you need to check which kind of heat transfer mechanism you may have for your system, how is the structure of your floater, what is the material of that, how you can define the heat transfer coefficient for that. and for sure you need to model your land base system with a similar attitude. Then the temperature difference is meaningful.

I suggest you to read our work in this field. Article Simulation of performance differences between offshore and l...

Good luck with your research :)

Thanks a lot for your answer Sara Golroodbari , I fully agree with you.

This scientific contribution will be very useful in your research.

Dear Aboubakr El Hammoumi,

In order to complement the answer of S Z. Sara M. Golroodbari, I can give an example for considering the structural side of the floater in floating photovoltaic (FPV) plants. Zero-angle FPV structure has utilized not only the air cooling effect of water but also the water-cooling effect when PV modules are in close contact with the body of water. Ocean Sun structure for instance.

Thank you for Dear Hesam-Edin Hayati Soloot for your comment.

Although floating PV panels set at zero angle can benefit more from the water cooling effect due to their close contact with the water body, the absorption of solar radiation can be less. From this point, it is better in FPV systems to place the PV panels at a well-chosen tilt angle so that they can benefit from both the water cooling effect and solar radiation. In the tropics and especially for locations far from the equator, the tilt angle of the FPV panels is not a significant issue. In these regions, the flat position of panels is preferred to ensure maximum heat transfer. But in other locations, it is recommended to set the FPV panels at an optimal tilt angle.

Thanks in advance for your reply and for sharing your idea (Aboubakr El Hammoumi). I want to reflect my idea based on real and experimented data of an article which was written by Torunn Kjeldstad and published in the Solar Energy journal. In contrast to your statement, Ocean Sun has examined its innovative structure (zero-tilt) with the help of the Institute for Energy Technology in Norway (a place far from the equator as you said). They mounted a well-instrumented 6.48 kW installation at Skaftå, Norway. They found that "by comparing a module string in thermal contact with water with a module string with an air gap between the water and the modules, we find that the water-cooled string had on average 5–6% higher yield compared to the air-cooled string". Therefore, generally without considering the location of a FPV plant, a zero-angle structure yields more power output even if it is placed far from the shore.

You can find more info by clicking on the link below

Article Cooling of floating photovoltaics and the importance of wate...

In Addition, you can find issues related to other aspects of this structure in my article titled "Conference Paper FLOATING PHOTOVOLTAICS: A SWOT ANALYSIS

I will be looking forward to hearing your thoughts.

BR - Hesam

Thank you Dear Hesam-Edin Hayati Soloot for the clarification.

You are welcome

Dear S Z. Sara M. Golroodbari,

As regards your question, I want to attract your attention to not only one of the less pronounced points in the literature but also a more important effect and difference of ground-mounted PV module installation and floating PV, that is "Heat Island Effect". According to the paper titled "FLOATING PHOTOVOLTAICS: A SWOT ANALYSIS": Recent studies indicate that large PV power plants cause heating island effect with an ambient temperature by 3 - 4 °C higher than the wildlands at night. However, in the Floating PV plants, the cooling water effect lowers or could even nullifies the heat island effect.

I apologize for my ignorance but what do you mean by overloaded PV modules?

I also see some comments here stating that the water can be too hot?! Without running any test or survey, my assumption (correct me if I am wrong) is that water is never hotter than the HOT DARK surface under direct sunlight ...

You are welcome dear Shahab Moghadam , I think you mean overland and not overloaded. Anyway, overland (or terrestrial) PV modules refer to PV modules installed on land.