Stack panels?

[2002sheds]

Hi All,
I can't find the answer via search, so I thought I'd ask... aside from the obvious (panels shade each other, so the it will take longer for all of them to be hot), is there a reason to not stack at least some of our passive solar pool heating panels? We have 5 panels, each around 8 feet tall and 4 feet wide. I'd like to make two stacks at one end of the pool -- one would have 3 panels, the other 2. I would construct a "table" for them to rest upon, and that table would run the length of the narrow side of our above ground pool, which is a 16 feet wide by 32 feet long Intex Ultra Frame.

The end that I have in mind is full sun. It also happens to be where the filter and pump are located, so installation would be straightforward.


Bad idea? Genius? Any feedback will be welcomed.


Thanks,
David

 

[Brett S]

Only the panels with direct sun exposure would provide any meaningful amount of heating. The other panels wouldn’t even get warm. If you just stack the panels with no water running through them then eventually the bottom panels would get warm through radiant heating, but as soon as you start circulating water through them the top panel would stay reasonably cool as it’s heat is transferred to the water and then to the pool, but the bottom panels would no longer have any source of heat.

 

[Donldson]

I don't understand this idea. Panels absorb sunlight and convert it to heat.

Put another way: would you stack two photovoltaic solar panels and expect to get any electricity out of the one at the bottom?

In fact, the pool ones would be worse. If the air temperature were lower than the water temperature the shaded panel would actually radiate some of the heat from the water in to the air, cooling the water.

 

[2002sheds]

Hi Don, Brett,
Thanks for the replies. Brett, that is my main question -- how much heat would be lost as the water is traveling through the panels -- especially if one is above another...? I would route the water through successive panels (instead of across the top of all of them, for example), so the answer to that question is everything...

Don, of course I wouldn't expect a electric solar panel below another to generate much of anything, but that is a completely different scenario and technology. I am guessing that the entire pool panel (not just the front) gets hot when placed in the sun, and my original question is about that -- how hot would additional panels get?

If the outermost panel stays cool on the back while in the sun and water running through it, then the answer is super clear about how to proceed. But if the back of that top panel also gets incredibly hot, then will the panel below it also get hot, warm, or not at all ?


Thanks,
David

 

[mas985]

To maintain panel efficiency, the panels themselves should not increase in temperature more than about 3-5 degF. More than that and efficiency drops (i.e. heat loss increases). By stacking the panels, you double the surface area for heat loss but heat gain remains the same. So if the single layer panels are running at 80% efficiency, stacked panels would run at 60% efficiency. There is no upside to stacking panels only a downside.

 

[Donldson]

my original question is about that -- how hot would additional panels get?

None hot. It would get none hot. The only hot it would get is from the water, which means losing heat. So you're right, it isn't quite the same as a photovoltaic. Photovoltaics have diodes to prevent them from discharging energy in the shade, your system would have no such protection.

This is not a "bad idea", this is a "literally making it worse" idea.

 

[2002sheds]

Hi Big D,
Copy that.

Thanks,
David

 

[2002sheds]

Hi Mas,
Thanks. I am getting the picture. Now I know why I couldn’t find it described anywhere. Back to the original spacing...

Thanks,
David

To maintain panel efficiency, the panels themselves should not increase in temperature more than about 3-5 degF. More than that and efficiency drops (i.e. heat loss increases). By stacking the panels, you double the surface area for heat loss but heat gain remains the same. So if the single layer panels are running at 80% efficiency, stacked panels would run at 60% efficiency. There is no upside to stacking panels only a downside.

None hot. It would get none hot. The only hot it would get is from the water, which means losing heat. So you're right, it isn't quite the same as a photovoltaic. Photovoltaics have diodes to prevent them from discharging energy in the shade, your system would have no such protection.

This is not a "bad idea", this is a "literally making it worse" idea.