Do Solar Blankets Heat The Pool

Kidkoffee

Member
Jun 26, 2019
15
Toledo, OH
Okay, I know this has been discussed in more than a few threads here, but I’d like to add a thought that I think (?) most people are missing... 1. Pool cover makers advertise as much as a 10-20 degree heat rise from using their solar cover. 2. Naysayers constantly write that solar covers don’t heat the pool any more than the sun does without the cover, but only stop evaporation overnight. 3. I’ve also read a lot about different colored covers working better or worse than others. Here’s my take (and I’m definitely open to being corrected here if I am missing something):
Logic tells me that yes, a pool cover should not “amplify the sun’s rays” or act as a traditional heater, but the fact that they stop evaporation (in the daytime as well as at night!) tells me that they do/can, in fact, raise the temperature quite a bit. Doesn’t water boil quicker on your stove when you keep the cover on your pots and pans?? I agree that MORE evaporation occurs at night when the temp goes down, and that this is the main benefit, but the cover does still lock in the heat during the day. I also believe that a clear cover works best at this because it lets the sun’s rays shine through to the water better, so it doesn’t stop or hinder the natural heating process from the sun like a dark or reflective cover can. Most importantly, I’ve been using solar covers all my life (my parents pool and now mine), and they have ALWAYS raised the water temperature in the pool. I remember the first year we got one for my parents’ pool when I was a kid and my dad was amazed at how well it worked, and we almost never used the gas heater anymore. Anyway, it just irks me somewhat when I read about how “solar covers don’t heat the pool.” They just do. If you put a solar cover on in the morning on a sunny 90 degree day, the water temperature will rise quicker than if you do not in every single case in my experience. Now, the 10-20 degree rise will definitely not happen in a single day, it’s cumulative because you will start with a higher temp the next day due to less overnight evaporation. I guess what I’m saying is that the semantics of why or how don’t really matter to me. At the end of the day, in my experience, they heat the pool. If using a solar blanket equals warmer water, then it is heating the pool, right? Like others though, I’m very skeptical about cover thickness, micro bubbles, diamond bubbles, etc, helping the process in any way...Thoughts?
 

cowboycasey

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if I have my cover on with the pump off it will heat the top 8 inch layer of water to almost 90 degrees.. hot enough you can put your arm in the water and feel where it gets cold... so the pool water can be 70 degrees with a 90 degree hot layer :)

so yes, it does heat the water
 
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Donldson

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There is a significant distinction between "X heats Y" and "X allows Y to get hotter". The former indicates energy has been added, the latter indicates energy has been lost slower than it has been gained. As a passive cover is incapable of adding energy it is false to say that it is heating the water. To say that solar covers heat water is as wrong as saying that a gas heater insulates the water.
 

cowboycasey

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how is a solar cover passive if it is adding heat... mine has the diamond bubbles on it and amplifies the heat the sun is applying to the cover..

I love testing and I can test this :)

2 bowls, 1 temp sensor in each, 1.5 cups of water in each..

1 no cover and 1 with a solar cover, what will happen :)
 

magiteck

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May 20, 2020
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The sun heats the water. The solar blanket allows the pool to retain that heat, allowing the pool to grow warmer over time.

It’s an argument of semantics and wanting to use correct verbiage.

The “human blanket” comparison above. The body produces the heat. The blanket allows the surrounding area to retain it.

The distinction is the heat source. The optimal solar blanket needs to allow the maximum amount of solar energy through to the water, and then prevent the maximum amount of loss.
 
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cowboycasey

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here is the test setup..
1618083315686.png

this is right when I put them out there.. 1 is no solar and 2 is solar.. the solar jumped 1 degree before I got a snapshot of the temp, they were both at 72...
1618083384488.png
this is number 1 no solar after 1 hour
1618083579888.png

This is solar after 1 hour
1618083662681.png
1618083785728.png
 

cowboycasey

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so if solar does not heat the water how did the water get 15 degrees hotter than the other water in bowl #1?
 

magiteck

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so if solar does not heat the water how did the water get 15 degrees hotter than the other water in bowl #1?
In your example, the Saran Wrap is not producing heat. It is preventing heat loss. The heat is coming from the sun, passing through the wrap, and then heating the water. The wrap is then retaining that heat allowing for cumulative heat gain.

Put the two containers in a dark closet. Over time, both will stabilize at room temperature, because there is no heat source.
 

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Kidkoffee

Member
Jun 26, 2019
15
Toledo, OH
Do you also believe that a blanket provides heat to someone wrapped in it?
Ha. I do believe that if you were to lay in direct sun wrapped in a dark blue or reflective tarp, you would be far more comfortable than if you were wrapped in a clear plastic blanket with micro bubbles! Like I said, I’m not sure if they amplify the suns rays. I believe that it’s possible though...like a magnifying glass. My main point was that if you had 2 pools side by side, one with and one without a solar cover, the covered pool will be hotter even before the night time evaporation. I’ll say again that I agree that the MAIN benefit is heat retention, but I believe there is at least a little bit of “solar amplification” going on as well. Like others have said about the first few inches of the water being hot...that doesn’t happen without a cover.
 

Kidkoffee

Member
Jun 26, 2019
15
Toledo, OH
In your example, the Saran Wrap is not producing heat. It is preventing heat loss. The heat is coming from the sun, passing through the wrap, and then heating the water. The wrap is then retaining that heat allowing for cumulative heat gain.

Put the two containers in a dark closet. Over time, both will stabilize at room temperature, because there is no heat source.
Put a solar panel in a dark closet and you have no energy either...
 

Donldson

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I believe that it’s possible though...like a magnifying glass.
Magnifying glasses do not amplify anything. They concentrate the light from a large surface to a small point. Since a solar cover is the exact same size as a pool there is no opportunity to concentrate light.

but I believe there is at least a little bit of “solar amplification” going on as well.
Your belief is irrelevant. The laws of physics do not provide for "amplification" of something without the added energy coming from somewhere. Neither you nor Casey have offered a good answer for where that extra energy comes from.

Put a solar panel in a dark closet and you have no energy either...
And?
 

magiteck

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May 20, 2020
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Ha. I do believe that if you were to lay in direct sun wrapped in a dark blue or reflective tarp, you would be far more comfortable than if you were wrapped in a clear plastic blanket with micro bubbles! Like I said, I’m not sure if they amplify the suns rays. I believe that it’s possible though...like a magnifying glass. My main point was that if you had 2 pools side by side, one with and one without a solar cover, the covered pool will be hotter even before the night time evaporation. I’ll say again that I agree that the MAIN benefit is heat retention, but I believe there is at least a little bit of “solar amplification” going on as well. Like others have said about the first few inches of the water being hot...that doesn’t happen without a cover.
I think the hard part of the “first few inches” test is that cold water will sink in warmer water. So without circulation the warmer water would rise to the top, no? Plus the surface water I think would naturally absorb more solar energy.

In any case - I’m 100% an advocate of solar blankets and see the real world difference exceptionally well here in Wisconsin where we have a lot of cool nights. I just think all of the amplification stuff is hard to prove and so to be the most accurate Id just say that they help to retain solar heat. My personal feeling is that a clear cover would work the best — because it would allow the most solar pass-through and color should have no bearing on evaporative loss.
 

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