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Question

Points to clarify on - Floating PV on reservoirs

Hello everyone,

I am working on my project dissertation where I am suppose to calculate the cooling effects of the solar module of floating PV with ANSYS CFD. I have chosen a reservoir site from India for my work.

In this regard I have few points to clarify:

1. The wind effects on the water bodies such as reservoirs. I assume lakes and ponds have constant breeze across the water surface however in case of reservoirs how these effect going to be?

2. Along with wind, how does the waves does effect.

3. Safety aspects for mooring for FPV and

4. floating PV structures materials - How ecofriendly are they?

I hereby request you all to share the points on these please.

Regards

Answers

Best Answer

Some utilities used cooling ponds to reduce the temperature of the cooling water used in the condenser before it was returned to a body of water.  However, the EPA has pretty much required cooling towers or some other means to restrict the rise in temperature of once through cooling systems.  If I was to do this project, I would start there.  I am assuming that he is talking about putting PV panels on some kind of platform that would sit out in a lake or reservoir.  The heat transfer from some kind of a panel would strongly depend upon the materials of construction and the means of securing the platform.  I know that MIT did some work on "offshore" wind platforms.  That work was mostly aimed at how to secure the platform with a large wind turbine mounted on it.  Wind will have more of an impact on the panel and the platform, rather than the water temperature.  Also, for an inland reservoir, I don't think it would be safe to assume that there is a constant wind speed that is continuous.  Some days, there will be no wind.  Some days there will be a storm.  I would suggest to break this problem down into manageable pieces.  I would start with the structure itself and estimate the conduction heat transfer between the panels/platform and the water.  The panel temperature would have to be estimated.  Rooftop solar panel suppliers should be able to provide some kind of idea of what that temperature might be.  The panels are then attached to a floating platform, part of which will be submerged.  Heat would then be transferred to the platform and subsequently to the water.  For the initial analysis, I would assume the water temperature to be constant.  It is probably not, but the mass of the reservoir is likely to be much, much greater than the mass of the platform.  This large body of water provides a significant opportunity to absorb heat.  Further, the water body will cool off at night and on days when the sun is not shining.  Evaporation from the surface further cools the water as does any wind.  Thus, constant water temperature could be a reasonable assumption.  From there, the conductivity of the platform and the panels would have to be known, as well as the surface contact area.  Then a fairly straight forward heat transfer calculation can be made.  Waves in a reservoir should be small and have very little impact.  Wind will cool the panels directly.  For mooring, I would suggest looking at the MIT work or contacting someone that is working on offshore wind.  Regarding safety, anything that goes on a platform in the water has to be hermetically sealed.  Water and electricity don't mix.  I have been told that the cost of any equipment for a platform is roughly 4 times the cost of that same equipment on land.

Chandrakiran S's picture
Chandrakiran S on Jul 17, 2020 10:07 pm GMT

Dear Carl,

Thank you sir, for the detailed explanation on my question. I would consider the points suggested. However I have few more points to discuss on, I am actually in calculation of evaporation rate of reservoir in 2 cases ie. with FPV and without. The issue I am still need to obtain is wind profile over water surface. As you identified, wind cannot be considered as contant hence I assume to be variant in 4 seasons (though in India considered 3 seasons - 90, 120,60 and 90 days) with variant wind speeds and average temperature of the days. I have read a article stating that the wind profile across the surface of the water is strong however slow in speed compared to 3 to 4 meters above surface where wind flows at high speeds. 

The evaporations rates have been proportional to difference of max and min temp of the day. Hence majority of value are in summers only (5.87 mm/day) considering 2 m/s wind speed, though the wind speeds are high in the rest seasons the rates have been in linear with temperature only in rest 3 cases (4.43, 3.55, 2.51 mm/day) considering 3, 6, 5 m/s of wind speed. I am wondering why wind doesn't effect?

This calculation done with help of Penman Monteith equations. Also due to contant shading of the water with Floating PV, the water doesn't get heatedup as faster as the uncovered surfaces. I shall consider rest of the points regarding waves, mooring. 

Regards,

Kiran

Carl Bozzuto's picture
Carl Bozzuto on Jul 21, 2020 2:19 pm GMT

I suspect that the calculations assume that the slip velocity at the surface of the water is zero.  If so, the wind speed only changes the thickness of the boundary layer at the surface of the water.  I would think that someone using cooling ponds has run into this.  I don't have any direct experience.
 

Chandrakiran S's picture
Chandrakiran S on Jul 25, 2020 12:18 pm GMT

Thanks for your message sir.

I don't have any direct experience with these projects, but I suggest you contact people involved with the Orlando projects. I think they are building a second, larger project.

 

Chandrakiran S's picture
Chandrakiran S on Jul 16, 2020 5:14 pm GMT

Hello John,

Thank you for the reply. I shall contact them as well.

 

I posted a paper about a year ago that included a brief section (2.1.2) on floating PV arrays (post linked below)

https://www.energycentral.com/c/cp/photovoltaic-plus-storage-%E2%80%93-part-1-technology

I verified that the reference in that section was still valid, so I have also repeated that below.

The bottom line for much of the U.S. is that property for PV projects are still inexpensive enough to where the challenges for floating arrays  are not justified.

-John

Chandrakiran S's picture
Chandrakiran S on Jul 16, 2020 5:27 pm GMT

Hello John,

Thank you for the reply and sharing the info. As you suggested in the report, FPV in Asian and European countries is increasing the projects capacity and numbers. Though there is huge gap between China and rest of Asia, countries like Japan, India and even Singapore are catching up. 

But I assume the current situtaion in US is also similar. They didn't have the big share in the FPV until now, but are there any future prospects for these projects? Since central and south-central regions of US have almost constant weather through out the year compared to coastal parts which have high risks of Hurricanes etc, why can't the projects planned in these regions?

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