Solar Panel Technology Comparisons

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I started my solar system for this swim season and it has peaked at around 75ºF as the weather has been a little inconsistent. The following is the minimum/maximum/average air temperature and end-of-day water temperature.

........... <----- Air ------>
Date .... Min. ... Max. ... Avg. .. Water
3/22 ... 41.9 ... 54.5 ... 47.2 ... 57 ... Start before solar turned on
3/23 ... 40.3 ... 59.2 ... 48.4 ... 59 ... solar started in afternoon
3/24 ... 33.6 ... 66.6 ... 49.3 ... 62
3/25 ... 35.5 ... 69.2 ... 51.8 ... 65
3/26 ... 43.0 ... 70.7 ... 57.5 ... 69
3/27 ... 43.4 ... 77.9 ... 58.2 ... 72
3/28 ... 41.4 ... 70.3 ... 56.2 ... 74
3/29 ... 47.4 ... 64.0 ... 55.2 ... 75

I have an opaque electric safety cover so don't get the benefit of a clear bubble-type solar cover which would not only heat more during the day but also lose less heat at night. Even so, the water temp gets to around 20ºF higher than the average air temp. In the peak of the summer when the sun's heating is more intense, I get around 25ºF higher than the average air temp.

Richard
 
Hi, I am new to TFP and would appreciate learning from your collective experience. I am looking at installing a solar heating system for my pool and would be curious to know what systems people think are best. In particular I am trying to decide between the Powerstrip vs. panel . The pool is ~50,000 g with ~1100 sq ft surface area. I am limited by roof area to ~ 14 4X12 panels ~(60% coverage), whereas I could likely get 90% coverage with the powerstrip. However, my pool contractor advised against the powerstrip reporting leakage problems. Any advice, and reports of experience with the powerstrip would be greatly appreciated.

Thanks,

Chris
 
Welcome to the forum, may your pool always be trouble free...

One thing that might be helpful is if you could fill in where you are at, as some choices might be climate related... Try filling out the stuff in the "User Control Panel" which you can find on the top banner right under where it says "TFP" on the left.

I'm not familiar with the powerstrip you mention, but it sounds like one of the "rubber mat" type collectors. IMHO, if all you are trying to heat is the pool, then the rubber mat collectors are probably a good choice. However, if you want to make more use of the collectors than that (i.e. home heating and or Domestic Hot Water,) then I think the glazed panels are a better choice, albeit a more expensive and more complicated one.

Gooserider
 
Water_man said:
Great thread about solar panels, Richard.
Where did you post all the other design details of your system?
I mean hardware, panel mounting, plumbing, flow control, etc.
Click to expand...
I didn't, except some in my signature. There are 12 Fafco panels that are mounted on a single-story roof of the house. These are very long runs both to/from the house and especially down the length of the house for the panels. Pipes are 2". Flow control is via a Jandy valve triggered by IntelliTouch (I have an IntelliFlow pump) that has a sensor on the top middle panel and another sensor on the plumbing near the filter. The flow rate is 48 GPM so 4 GPM per panel. Remember that I have an opaque tan-colored automatic safety cover so I don't get much benefit of direct heating of the pool during the day except when it's open for 1-2 hours most days.
 
amjohn said:
Here is our ongoing saga of solar panel installation. I am adding to it as we go. I still need to put the plumbing pics up next, as I am a little behind where we are on work. It is a on-ground installation, but many aspects are similar. Anyways, it is another thing to look at as you think through your process.
adding-solar-bear-panels-to-our-agp-the-process-with-pics-t11410.html
Click to expand...

I read, amjohn, your post and it is an impressive project. I'm considering installing a 160 Sq ft ground mounted system but I don't have the time to go through all the phases of design and intsllation that you and chemgeek went through. I'm looking for an all-included kit with the hardware , plumbing parts and flow control and I posted an inquiry here Solar Heating kit from soup to nuts but so far nobody has come up with a reference to a kit.
 
Hey, sorry to dredge up an old thread, but this really has piqued my interest. I've spent the last several hours researching solar heating alternatives and stumbled across this thread. Wow... what a lot of information!

I'm in sunny Southern Alberta, where we get some pretty good hot, long days in June - August. I've got a 15x33 AG and have had pretty good success in the past with only a couple of 2x20 mats in the summer. One year, after several really hot days in June, by leaving the solar cover on during the day, we had the pool up to 94F -- way too warm, but it was an experiment to see just how warm we could get the pool. That said, the same year July pool temperatures were down in the low to mid 80s, and August was a write off -- too many unusually cloudy days and rain meant that we were only able to achieve low 70s. By Sept. the best we could get was mid to high 60's so it was time to shut it down.

I know that with only 80 ft^2 of Sunheater panels, we are sub-optimal and clearly, the best answer is to add more mats. Currently, the panels are on a deck next to the pool, and there really isn't any easy way to add more sq. ft. without some new construction. That is certainly in the plan, but we likely won't get to it this year. With all that in mind, I've had some of the same thoughts as launboy -- why not try some DIY glazing.

As I understand it, the purpose of glazing is to reduce the cooling effect of wind and lower ambient air temps. If I understood some of the earlier comments, it sounds like the benefits of glazing were diminished when ambient air temps were high -- like in the hot summer months.

That said, it seems to make sense, at least where I live, to add some glazing - or at least some environmental protection - during the shoulder months. Here's a thought... tell me if it makes sense, or if I'm out to lunch.

Commercial green houses use real glass walls and roofs, but many smaller, or domestic greenhouses, are covered in polyethylene. Would it make sense to cover the panels with a polyethylene cover, for at least the earlier and later months? It could be as simple as attaching a cover over the panels and stapling the polyethylene to the panel support. AND, if it does make sense, since I will run water through the panels whenever there is sun and the temperature of the panels would never get more than a few degrees above the pool temperature, would I have to remove it during the hotter months?




Gooserider said:
launboy said:
Anyone ever thought of making their own glazed panels out of flat black pool heater panels? I've been considering trying it out this fall. During the summer the normal panels do fin for our pool, and hopefully will work for the hottub too.

I'm more worried about the fall and winter. I don't think the panels will do much during our cold snowy Wis. winters, but during the spring and fall I think a home-made box around a mat would help quite a bit. What do you all think?

Thanks,
Adam
Click to expand...

It might work, but I'd be worried about what the peak temperatures might get to - the mats are designed for a fairly low operating temperature, and even if you stagnate them, are going to radiate any excess heat picked up if they are used as designed. If you enclose them, then you prevent them from radiating excess heat, and greatly raise their operating temperature - this may exceed their safe operating temperature, especially if you stagnate them for any reason.

IIRC the mats are generally intended to work around 100*F, with a maximum stagnation temp around 130*F or so. Glazed plates can run in the 120-140*F range, and can easily get over boiling if stagnated, which is higher than most mat material can take as I understand it. For instance EPDM is usually only good to about 180*F or so...

There is a reason why most glazed panels are made with metalic guts, and are normally installed with copper plumbing rather than PEX or other plastics.

Gooserider
Click to expand...
 
I'm not sure if polyethylene transmits infrared well. You can hold a sheet of it up between you and a fire to see if you can still feel the heat. About half of the sun's energy is in the infrared and half in visible (there's a small amount in UV) so it's important to not block too much of the infrared. If you were to use glass, it would need to be "untreated" so as not to reflect infrared.

At any rate, you can certainly make your own glazed panels and you are correct that the purpose is to prevent cooler air temperatures, especially with wind, from carrying away heat from the panels. So you want the material to be reasonably well insulating of heat. Don't forget to leave an air gap between the panel and the glazing (plastic). Double glazed glass is often used, though anything you do will probably be a lot better than the raw panels that you are using now.
 

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chem geek said:
I'm not sure if polyethylene transmits infrared well. You can hold a sheet of it up between you and a fire to see if you can still feel the heat. About half of the sun's energy is in the infrared and half in visible (there's a small amount in UV) so it's important to not block too much of the infrared. If you were to use glass, it would need to be "untreated" so as not to reflect infrared.

At any rate, you can certainly make your own glazed panels and you are correct that the purpose is to prevent cooler air temperatures, especially with wind, from carrying away heat from the panels. So you want the material to be reasonably well insulating of heat. Don't forget to leave an air gap between the panel and the glazing (plastic). Double glazed glass is often used, though anything you do will probably be a lot better than the raw panels that you are using now.
Click to expand...


Quick update:

Yesterday I finally got my solar panel connected and a solar blanket fitted. In the morning (0730) the water temp was a chilly 61 deg. F (16C). It was a sunny day, and the air temp got to about 87F (31C). By just after suppertime ~1900 the water temp was up to 70F.

This morning, the water temp had dropped to only 68F (17C).

I've decided to try a temporary experiment with covering the panels.
I didn't build a fire, but this morning around 0800 I went out and held a piece of polyethylne up between my face and the sun. It blocked some of the IR -- likely because is translucent rather than transparent, but it certainly didn't block it all. I hope is that the gains I get from protecting the panels from breezes will more than make up for the minimal IR loss.

I just got finished covering the panels with polyethylene and turned on the water. After letting the panels run for about 20 minutes to stabilize their temperature, at 0910 I read the following:

Pool Temp 68F (20C)
Air Temp 67F (19.5C)
Panel Exit Temp 70F (21.1)

I know it's only one data point, but it looks like the polyethylene isn't blocking too much IR, since the panel output is warmer than the ambient air temp.

Unrelated to the covering the panel, I think I can draw the conclusion that with only a 2 degree rise from input to output, the panel must have fairly decent flow.

If anyone is interested, I'll let you know how the rest of it goes.
 
Holding the polyethylene between you and the sun is a fine test. When you are covering the panels, are you doing this with some sort of box or structure so that the polyethylene is above the panels with an air gap in between? If not, then you won't get a lot of benefit -- the polyethylene would just be like an extension of the panel thickness if it were touching the panel. You need an insulator between the panels and your polyethylene and an air gap with still air works for that (similar to what is done with double-paned windows).
 
Another thing to keep in mind, though it isn't critical in a temporary cover, is the question of how UV stable the plastic is... Direct sun can be brutally hard on materials, including many plastics like poly... If it isn't rated for UV exposure, it may quickly discolor and / or break down and disintegrate. How big a concern this is depends on how much you care...

Another thing to consider is what happens if you have a power failure, or the pump goes bad during a peak sun period - if you lose the cooling from circulating water will your mats overheat?

Not saying don't do it, just stuff to think about...

Gooserider
 
chem geek said:
Holding the polyethylene between you and the sun is a fine test. When you are covering the panels, are you doing this with some sort of box or structure so that the polyethylene is above the panels with an air gap in between? If not, then you won't get a lot of benefit -- the polyethylene would just be like an extension of the panel thickness if it were touching the panel. You need an insulator between the panels and your polyethylene and an air gap with still air works for that (similar to what is done with double-paned windows).
Click to expand...

OK.. it's been a few days.... here are the results.

I didn't build a box structure (yet?), but the panels wrapped in poly are kind of baggy with plenty of air gaps. I would estimate <10% area touching. We've had some breezy days with air temperatures cooler than the water temperatures, and yet with the panels wrapped in poly, we've made some gains. Without doing a clear A-B comparison, it's difficult to tell whether I'm actually better off than with bare panels, but I think I am. On those breezy days, if I slip my hand under the poly, the 'inside' air temp. seems a little higher, although it could just be an illusion since I don't get the wind cooling effect on the back of my hand. Regardless, at least for now, I'm gonna leave the poly on.

Here are the gains since installation.

...................Water....Air
16 July 0740.....68......62
16 July 1900.....77.....73
17 July 0830.....73.....59
17 July 1700.....80.....75
18 July 0715.....75.....57
18 July 1700.....78.....72
19 July 0745.....75.....59
19 July 2150.....76.....57
20 July 0700.....75.....73
20 July 2120.....78.....60
21 July 0740.....72.....54
21 July 2150.....78.....61
22 July 0730.....76.....61
22 July 1915.....79.....69
23 July 0715.....75.....57
Missed the evening reading
24 July 0900.....76.....68
24 July 1800.....82.....82.....Partial cloud and breezy
25 July 0730.....79.....61.....Sunny and breezy
25 July 1735.....84.....84.....First real sunny and calm day after about a week of cloud wind and rain.


Our pool has been down for a few years, but the last time we had it running several years ago, on 100 degree days, we've seen as much as a 10 deg increase, losing only 2 or 3 degrees at night with the solar blanket on. We haven't seen those kind of increases yet this summer, but we gained 6 yesterday, and another 5 today. Not too bad. If we can hold 80-85 I'll be pretty happy.
 
Gooserider said:
Another thing to keep in mind, though it isn't critical in a temporary cover, is the question of how UV stable the plastic is... Direct sun can be brutally hard on materials, including many plastics like poly... If it isn't rated for UV exposure, it may quickly discolor and / or break down and disintegrate. How big a concern this is depends on how much you care...

Another thing to consider is what happens if you have a power failure, or the pump goes bad during a peak sun period - if you lose the cooling from circulating water will your mats overheat?

Not saying don't do it, just stuff to think about...

Gooserider
Click to expand...

Good thoughts. I think I'll run with the poly cover for the rest of the year and see how much damage / discolouration I see in a couple of months. Fortunately, we don't suffer from many power failures, but the possibility is very real. I'm not sure if the panel will be any worse than without the cover. Since it doesn't self drain now, in the case of a power failure, it would stay filled with water and could likely become over heated. I think on a calm hot day, regardless of the poly cover, a power failure could be catastrophic.

If all goes as planned, this will only be a temporary installation. We expect to build a large shed / pool house next to the deck next year and move the panels to the roof. When we do that, I'll will get a few more panels and will plumb them right so that the self drain when the pump shuts off. With 2 or 3 times the area, I'll have the capacity and recovery time that I'm looking for without having to resort to all this jiggery-pokery.
 
dfenrick said:
OK.. it's been a few days.... here are the results.
Click to expand...
It looks like you are getting a roughly 15ºF gain, but are your "air" numbers the average of day and night or just the daytime temps? Also, are you using any sort of solar cover on your pool?

Ideally, you would want the poly cover not to flap around. The whole idea of creating an air gap is to create still air since that is more insulating since heat transfer is then limited by diffusion. If the poly flaps around, then there will be heat transfer by convection which isn't good. This is one reason why glazed panels used sturdy fixed glass to create a still air gap.
 
Doing the hypothetical on the power failure scenario - w/o the cover, I wouldn't expect the mats to reach failure temps, as they would presumably start radiating more heat as they warmed up, presumably losing enough to keep them below meltdown temps... If they have the poly cover on them, then you have effectively given them some insulation, which might be enough to keep them from radiating / convecting off as much excess heat, leading to reaching a higher temp, with possibly bad consequences, depending on just what the failure temps are... I have no idea if this would be the case or not, since I don't know the specs on your mats, let alone just what the cover does to change the thermal picture and so forth...

Gooserider

dfenrick said:
Gooserider said:
Another thing to keep in mind, though it isn't critical in a temporary cover, is the question of how UV stable the plastic is... Direct sun can be brutally hard on materials, including many plastics like poly... If it isn't rated for UV exposure, it may quickly discolor and / or break down and disintegrate. How big a concern this is depends on how much you care...

Another thing to consider is what happens if you have a power failure, or the pump goes bad during a peak sun period - if you lose the cooling from circulating water will your mats overheat?

Not saying don't do it, just stuff to think about...

Gooserider
Click to expand...

Good thoughts. I think I'll run with the poly cover for the rest of the year and see how much damage / discolouration I see in a couple of months. Fortunately, we don't suffer from many power failures, but the possibility is very real. I'm not sure if the panel will be any worse than without the cover. Since it doesn't self drain now, in the case of a power failure, it would stay filled with water and could likely become over heated. I think on a calm hot day, regardless of the poly cover, a power failure could be catastrophic.

If all goes as planned, this will only be a temporary installation. We expect to build a large shed / pool house next to the deck next year and move the panels to the roof. When we do that, I'll will get a few more panels and will plumb them right so that the self drain when the pump shuts off. With 2 or 3 times the area, I'll have the capacity and recovery time that I'm looking for without having to resort to all this jiggery-pokery.
Click to expand...
 
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