DIY solar panels using PVC pipes.

AllenA

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Anyone attempt to build solar panels using PVCs connected with Ts? Say using 1/2 inch or 3/4? Something that would end up looking like the panels that are sold. Instead of using irrigation hoses in loops? It is more expensive but surely sturdier and probably easier to assemble by gluing. Also should not require a frame to keep its shape so it could be lighter. I hope! Several can be connected to form 4x10 panels and painted black. They would be spaced a bit due to the Ts so less coverage, true. One can put a reflective material under it to reflect sun back on it from below. Maybe sheet metal to last? Another idea is to make each panel out of 2 rows shifted on top of each other. A bit less coverage on the bottom rack but probably good enough. I also noticed that schedule 40 is also available in as small as 1/8" if smaller is better?

Should end up being very sturdy and raise temperature quite a bit. Easy to build and looks like the commercial stuff but much cheaper. Any thoughts?
 

Bama Rambler

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I was intrigued so I did some down and dirty calculations using online prices and came up with about $250 for a 4' x 10' panel DIY ½" Sch 40 PVC. That didn't include glue nor the fittings to connect the panels together or to the system. I used 1½" x 1½" x ½" Tees for the header, and I figured for two layers, one offset above the other.
 

iamnos

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Jul 23, 2018
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Kelowna, British Columbia
I did a quick and dirty DIY panel with poly pipe. We've had a terrible start to the swim season with lots of cloud and rain, so I haven't had a great chance to really see how it works, I've mostly had it bypassed as to not lose heat. I ran the 1.5" going to the returns which then goes to 6 reducing Tees (1/2") for the headers. There's 50' of 1/2" poly on each Tee. On the few warm sunny days we've had where I had it running through the panel, you can definitely feel that the water is warmer coming in, and that's on a day when the ambient temperature is probably mid 70sF and the pool temp is a bit warmer. I still need to add some temp sensors to get a better idea of how its performing. I've used an infrared thermometer to check the outside temp of the poly pipe before and after the panel, and I'm seeing around a 6-8F gain depending on the day.

As I said, this was quick and dirty try. After working with the poly, I'd probably go PVC next time. Poly just likes to kink if you look at it funny. The one issue with PVC though is that it will degrade in the sun. I'd suggest at the very least painting it black to help prevent the UV from damaging it over time.

EDIT:
A few tips after having read a LOT on this topic. If I do rebuild mine (and put it ontop of the pergola like I originally planned), I'd build it like a ladder on the roof of my pergola, which is almost flat, but has a slight angle to face the south. The idea is, the water fills the main tube (1.5") along the lowest edge of the pergola, and then reduces to the 1/2" risers running "up" to the higher point of the pergola, where it would then return from the opposite side of the pergola This way the water will naturally fill all the lines.
See a similar layout here, but he's using all 1/2" copper: Experimental Solar Collector Using Hybrid Copper/Aluminum Construction
That's pretty similar to what I want to build. It also has the advantage of being self draining for those of us that have to worry about that sort of thing in the winter.

To get even better, like mentioned in that link, you can put aluminum fins over those lines. This protects the PVC from the sun as well as collecting heat from the space between the risers and because aluminum transfers heat relatively well, most of that would get absorbed by the PVC.
 
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mas985

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I was intrigued so I did some down and dirty calculations using online prices and came up with about $250 for a 4' x 10' panel DIY ½" Sch 40 PVC. That didn't include glue nor the fittings to connect the panels together or to the system. I used 1½" x 1½" x ½" Tees for the header, and I figured for two layers, one offset above the other.
I would assume that the solar capture area is much smaller than the physical area. So is the 4'x10' physical or capture area? How much 1/2" pipe is being used?
 

Bama Rambler

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The 4' x 10' was occupied area, not solar area. I was just curious if it was feasible cost wise, but at $250 for parts I'd rather buy manufactured panels.
 

mas985

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Building the panel that way has a lot of empty space that is not collecting the solar radiation so the panels will end up being very inefficient.
 

iamnos

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Jul 23, 2018
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Kelowna, British Columbia
Only efficiency in terms of the space the panel takes up. The design has some added benefits, like draining via gravity, minimizing air trapped inside, and helping to ensure even flow between all the risers (which helps with efficiency)
 

mas985

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Only efficiency in terms of the space the panel takes up.
That determines how many panels can be installed. So the more wasted space there is, the less energy that can be collected from the sun.

The design has some added benefits, like draining via gravity, minimizing air trapped inside, and helping to ensure even flow between all the risers (which helps with efficiency)
All those benefits are available with standard panels as well. Plus the thinner the tubes, the more efficient the panels will be due to a decrease in heat loss. Heat gain is proportional to the tube diameter while heat loss is proportional to the surface area of the tubes. So larger tubes with large air gaps between them are going to be less efficient than thinner tubes side by side which is why nearly all commercial panels use very thin tubing.
 
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iamnos

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Jul 23, 2018
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Kelowna, British Columbia
That determines how many panels can be installed. So the more wasted space there is, the less energy that can be collected from the sun.

All those benefits are available with standard panels as well. Plus the thinner the tubes, the more efficient the panels will be due to a decrease in heat loss. Heat gain is proportional to the tube diameter while heat loss is proportional to the surface area of the tubes. So larger tubes with large air gaps between them are going to be less efficient than thinner tubes side by side which is why nearly all commercial panels use very thin tubing.
I was only comparing to homemade panels, not commercial ones. There are pros and cons on the size of the pipe and spacing. smaller pipes side by side, will only ever expose 50% of the pipe surface to the sun when it is overhead, whereas allowing space between them can allow more sun as it moves through the sky. Then, as I mentioned, putting "fins" fitted over the pvc can help absorb the heat hitting the back of the panel and helping to transfer it to the pipe.
 

mas985

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PVC is very poor thermal conductor. About 3x slower than copper. It will help some but not as much as you think. Commercial panels of that type of design are generally about 40% less efficient than full tube panels and they are all metal design. It is far more efficient to have direct radiance rather than relying on conduction.

We have seen many DIY designs on the forum and after a detailed analysis, I don't think we have never seen a DIY panel that approaches the efficiency and $/BTU of commercial panels. There are very good reasons they are designed the way they are.
 

AllenA

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Hi all, thanks for contributing to the discussion. I could only add some more now...

Bama, how did you get to such an estimate?Please note further below my rough estimates.
I wanted to keep the tees as small as possible to ensure that I can fit as many pipes as possible within a panel. Using 1.5 " reducing Ts would lead to quite a bit of spacing since each T is (2x57mm) 4 inches wide:

I'm not sure if it is important to have such a large main in each panel such as this or other commercial products. They may be able to manufacture their main channel very large with tiny reducers but I cannot:

I would have the main feed line feed all the panels in "parallel" instead as I show below to keep using 1/2 inch tees within each panel. Something like this:
1591309254223.png

My Cost Estimate
- 10 ft 1/2 inch schedule 40 pipe at HD in bulk is $ 1.62 each
- 1/2 inch Ts are 44 c. each

A 1/2 inch T would be 50 mm (~2 inch) wide, so:
In a single 4 ft (48 inch) wide layer, we can place 24 pipes/Ts.
Double layered requires 48 pipes / Ts. There would be slight horizontal spacing between the overlapping pipes.

So the cost of a double layer as I can see would be 48 x (1.62 + 44) = $ 98.88. That's ~500 ft. Which gives us 0.7 cu. ft. or 5.2 Gal.
As you mention, need to add glue, connection to main and also black (high quality) paint.
Single layered panel weight is at least 24 * 1.643 lb = 40 lbs. Best keep them separate until the install on the roof.
Compared to Heliocol's 4x10 panel (from Amazon), is 24 lbs.

Sizing of collectors
Seems that 1/8 or 1/4 inch are more expensive and not easy to find so let's forget about those... unless if someone can help find Ts and other fittings.

A thought about "smaller is better". I'm not sure... if you slow down the flow rate enough, I believe the temperature will rise just the same. So it might also be possible to do this with 3/4. Or? What are your thoughts? Of course you'll need the same total throughput.

So, for example, using 3/4 inch pipes (~2.3 inches wide end to end) we can only fit 20 pipes (single) or 40 pipes in double in 4 ft wide panels. But, the area of a 3/4 inch pipe is 0.44 sq in compared to 0.2 sq in for a 1/2 inch pipe, so we'd have more than double the amount of water in the pipe getting heated. If the flow rate at the pump remains the same, it would mean that water remains in the pipes longer before returning to the pool. Basically, more water in the collectors during the same period of time.

I am in AZ, so pool is warm enough now, and have too much on my plate now anyway but plan to try something out before end of season. At least a prototype.
Allen
 

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RonsPlc

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Just a thought from someone that has dealt with PVC, and CPVC in the past.
For anything that is going to be used in a heated manner, (hopefully) use CPVC, as PVC breaks starts to deform as the heat inside builds.
You might be better off using PEX. The connectors are smaller, allowing more tubing inside your collector, and it is heat tolerant. PEX is used for most "In Floor" home heating applications these days.
 

mas985

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If you stick with 1/2" and 1/2" header, the flow rate through each pipe is going vary quite a bit and the panel efficiency will suffer. Again, this is why commercial panels use large headers and small tubing. There is very little head loss through the header flow so that each tube has close to the same pressure and thus the same flow rate. When the header is the same size as the tubes, the flow will favor the tubes closest to the feed points.
 

AllenA

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Hey Ron,
Yes, I did think about PEX. Does it come in rigid form? Rolled tubes would be annoying to work with.
Hey mas,
I thought about this quite a bit. I'm not sure there would be a difference. Of course I am just making layman assumptions and we'd need a fluild engineer to evaluate. I see it, in my design, the feed line would distribute to the panel branches and presume would reach equilibrium. In fact as I understood, there will always be pressure equilibrium in a system. Flow rate should also be the same.

When it is getting primed, water will flow left to right in the feed line until the last panel. Once there is no more space, water will start to rise in the rightmost panel but soon enough pressure will also rise there. So water will start to rise in the before last panel and so on. Like a diagonal going right back to the left. Now on top, there will be more pressure on the right since all flow must go right. Which means that pressure on the top left will be less allowing water to flow out from the top left.
 

AllenA

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Hey Ron,
I just noticed this which states that uninstalled pex exposed to sunlight may fail. I imagine this means when it has no water. The collector will need to be drained frequently. Also chlorine seems to be a problem. So I am not sure if PEX is a good idea.

Maybe PVC is not better either... will keep researching. But I noticed that if you paint PVC with UV resistant paint, it should be fine. My exposed pool plumbing was painted by the plumber in gray for probably the same reason.
 

iamnos

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Jul 23, 2018
56
Kelowna, British Columbia
Generally speaking, high flow rate is actually better. Since heat transfers faster the greater the difference in temperature, the colder the water is, the more heat it will pull from the panel.
 

AllenA

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iamnos, fair enough. but still, I imagine that while a higher flow rate will render an overall higher volume of heated water to be returned to the pool, it should have a lower temperature since it sits less time in the pipe.

Since I only want to extend my season, I would likely not run the system much in summer heat and the pipes would remain dry. And I assume that that's when the pipes will be the hottest since nothing is drawing heat from them? Or can they get even hotter when wet? Perhaps when wet but no flow? I put out a PVC pipe on my deck in direct sunlight today. Using a temp sensor, it's external temp was about 15F above ambient temp (85 F). It's internal temp about 3-4 F above the external temp of the pipe. My sensor could reach about 2 feet deep. I'll keep checking this pipe, especially when it will get really hot here. Seems next week will be 102 F. In AZ, we can get up to 120F so it would be good to ensure that the pipe (PVC) would never reach 140F when dry, assuming that that's when it will get the hottest. If it does, CPVC may be the better choice. But then again, I wonder if ~20 F internal temp above ambient temp is good enough as you mention @mas985 due to PVC's (and assuming also CPVC's) heat transfer is low. Of course the pipe is not painted black, not yet at least.
 

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iamnos

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Jul 23, 2018
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Kelowna, British Columbia
AllenA
To overall increase the temperature of the water in your pool, a higher flow rate is better.
Now, that doesn't mean go and buy a more powerful pump, but it does mean that building a panel to keep flow rates as high as possible, everything else being equal, will result in the pool being warmer than it would with lower flow rates.
 

AllenA

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I have a VS. No problem there... but I prefer low flow rates since I run it 24/7 already. My ultimate setup would be to let it heat up slow but constantly skipping daily periods that would otherwise cool the water. Electricity consumption is ways away between high and low flow rates.