DIY solar heating

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Yoav

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LifeTime Supporter
Jul 9, 2010
64
Pardes Hanna, Israel
Hi all,

Since I live in a very hot and sunny area, a part of my recently completed project involved placing a shading net over the pool.
Funnily enough the kids complain the water's too cold now.
Never thought that could happen in our parts... :shock:

So, I was thinking of starting a new project - use the abundant solar heat to warm up the pool water a bit.
My working assumptions:
1. will build 1 or more solar panels
2. modeled after a regular domestic hot water solar panel
3. the panels will be have a black background material, and many smaller-diameter black pipes running from one end to the other
4. will use a small 12V bilge pump to circulate the water slowly through the panels during the daytime
5. low cost, simple parts
6. no metals (?)

A few questions:
1. Has anyone here done something like that before?
2. Any ideas on how to build the panels?
3. What should I build the panels from?
4. What would the ideal ratio be between the number and diameter of the pipes within the panel?

This seems like a fun project!
Appreciate any input you have,
Yoav.
 
Yes, there are several posts around the forum from people who have done very similar things.

I suggest a few modifications. Commercial panels are more efficient and more reliable than anything you can build yourself for anything near their price. Making the myriad connections to the individual tubes is leak prone. Better to get that part done commercially. Second, using either your existing pool pump or a larger solar only pump will make the system far more efficient. You get the maximum efficiency when the flow rate is maximized.
 
I know commercial panels would be far superior to anything I would build, but as I do in other areas and hobbies of mine - I love taking on projects not just for the sake of the end result, but for the fun and experience I get when doing things from scratch myself :-D

So, off I went and built the first prototype. Just a simple PoC.
The result was... it worked, but is still far from being efficient enough to make much of a difference.
The water coming out was only 0.5 C warmer than the water in the pool, with a flow rate of 360 litres per hours (I have a small pool...).
Although things would improve if the panel was a closed metallic structure AND was positioned properly, this is clearly a matter of increasing efficiency (as you've pointed out Jason).

Its a 2 x 1.5 meter "panel" which I have placed on the ground for this test, made from a black sheet of plastic over which I've placed the pipe structure and covered with a transparent sheet of plastic. The main issue here is clearly the heat transfer pipes going through the panel.
I used 14 4mm PVC pipes which are obviously the opposite of what's needed - they are insulators instead of conducting the heat into the water.

So, I can either scale things up, use a denser matrix of pipes over larger areas, or I can use metal piping instead.
As I've said in my first post, my assumption is that I don't use metal anywhere, and this is where I need help.
(BTW, the commercial panels I've checked out all use either iron or copper pipes for conducting heat within the panels).
I am afraid that using metal pipes anywhere in a closed water system would introduce increasing amounts of metals and rust into the water which I have no idea how to handle.
Is this concern valid or relevant?
 
Yoav said:
I know commercial panels would be far superior to anything I would build, but as I do in other areas and hobbies of mine - I love taking on projects not just for the sake of the end result, but for the fun and experience I get when doing things from scratch myself :-D
Click to expand...
I understand, I think there are many on this board that thrive on being diy-ers(look at how many have built their own hands most/all of their IG pools).

Yoav said:
So, off I went and built the first prototype. Just a simple PoC.
The result was... it worked, but is still far from being efficient enough to make much of a difference.
Click to expand...
Yeah for prototypes!!!
Yoav said:
The water coming out was only 0.5 C warmer than the water in the pool, with a flow rate of 360 litres per hours (I have a small pool...).
Click to expand...
The temp delta is great, you do not want a large temp delta (inefficient), however you do want a high flow rate.
Yoav said:
I used 14 4mm PVC pipes which are obviously the opposite of what's needed - they are insulators instead of conducting the heat into the water.
Click to expand...
The sungrabbers I have are made of a polyolefin, my guess would be they are PE with some stabilizers in it. This material is also an insulator, so I guess I would not give up on plastic since it is cheap and form-able. What color is your tubing? Black seems best.
Yoav said:
So, I can either scale things up, use a denser matrix of pipes over larger areas, or I can use metal piping instead.
As I've said in my first post, my assumption is that I don't use metal anywhere, and this is where I need help.
(BTW, the commercial panels I've checked out all use either iron or copper pipes for conducting heat within the panels).
I am afraid that using metal pipes anywhere in a closed water system would introduce increasing amounts of metals and rust into the water which I have no idea how to handle.
Is this concern valid or relevant?
Click to expand...
Like I said, If it was me, I would continue to use plastic. Cheap, easily formed into dense parallel pipes. If you haven't already looked at them, look at fafco, sungrabber, etc. to see what the plastic panel type collectors look like.
 
Leebo, I don't know why, but that was hilarious :lol:

Thanks a lot for your help, linen, Leebo.
With your feedback and my successful PoC, I am now on a quest for finding the best kinds of plastic for the job. I even found a company that makes polymers that are as conductive as aluminum (for heat sinks, which is amazing!), so its all down to efficiency vs. price and availability.

I do know now of two things that need improving.
1. my bilge pump - I need 3x the flow if I want to turn over half the volume of the pool in 10 hours.
Jason already pointed it out in the beginning. My intuition was that the faster I run the water through the pipes, the lower the output temperature would be - which was the opposite of what I wanted. What I did not grasp until I stopped to think about it is that even though the input-output temperature delta would decrease as the flow increased, the total energy transferred to the water should actually be higher (my reasoning is that the the efficiency of the panel-to-pipes heat transfer should grow as the panel-to-pipes temperature difference rises, and as linen pointed out, the smaller the input-output delta, the lower the loss of the entire system).
Hope I did not bend reality here to suit my needs... :hammer:

2. a bad plastic smell that comes from the water when I first turn things on. When the water is not running, the plastic gets really hot which seems to be the cause. One solution would be to place it all on a timer which starts at sunup. Any other ideas or comments? maybe I am using the wrong kind of plastic...

Cheers!

p.s I'm still curious though about the metals...
 
Oh trust me....we found the tree on the heater it wasn't a laugh for us. It also took out about 3 sections of fence, an old camper that we were going to build into a changing "house" and cracked the window on an old car we had stored behind the pool. It stunk until we got the insurance check. Let's just say for all the "junk" that got ruined and the home-built heater.....my in-laws made out OK.

As for the heater itself. We're thinking of building another one next year, but are still going rounds on the design. We used pipe that was the same size as our skimmer pipes. We found that while yes it does improve the temp of the pool some, it left some to be desired. My brother-in-law wants to try and go to a larger pipe next go-round, however I vote for a smaller pipe with much more surface area such as this design.
http://rimstar.org/renewnrg/solar_pool_ ... diy_ds.htm

Either way will improve the temp some.....it's just playing around to get the perfect plan.

As for the "smell". We had this issue some to. In fact we didn't use the heater very often, and each time we fired it up we had to "bleed" some of the water from the pipes as it was a prime growing spot for algae. We're still working on a drain or something to get around this issue.
 
I'm sorry Leebo - did not mean to laugh at your misfortune.
Its this media; one never can gauge the entire content from text alone.
For some reason I found it funny - probably because I perceived it as a humorous cynical remark as to how the heater stopped working, and my affinity to slapstick...

Glad no one got hurt.
Yoav.
 
don't feel sorry for us at all.....we made out VERY nice on it. Almost enough to buy a new solar heater with the insurance money.

Too bad we spent it all on Baquacil. :rant: :rant: :rant: :rant: :rant:
 

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