Author Topic: Polycarbonate roof sheeting for solar hot water  (Read 5445 times)

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Roadie

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Polycarbonate roof sheeting for solar hot water
« on: February 20, 2015, 04:17:33 PM »
Hi all,my first post , thanks for allowing me on your fantastic and very helpful forum for R/E,
Has anyone here tried the polycarbonate double or triple wall roofing sheet as a form of solar water heating,it occurred to me one day that perhaps this would be ideal as a heat exchanger,with the underside painted black,and some form of manifold ie such as split plastic drain pipe on each end,sealed with sikaflex or something similar,it is relatively cheap in my opinion to enable them to be as long as feasibly possible,or shorter and used in tandem,
Solar energy will not happen overnight

Mary B

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Re: Polycarbonate roof sheeting for solar hot water
« Reply #1 on: February 20, 2015, 05:08:34 PM »
I use it as a cover for my collector... I don't think it would stand up to hot water...

DanG

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Re: Polycarbonate roof sheeting for solar hot water
« Reply #2 on: February 20, 2015, 05:11:33 PM »
Having liquid touching the polycarb is probably a sure way to degrade the sheeting, but...  having it being the cover sheet might make sense if the ALL the details are covered. There are 25mm thick tri-wall panels that might be fun to experiment on for very small scale installations...

Solar water heaters can & do stagnate - the heat 'stagnates' and accumulates when no mechanism to transport or shed it exists.

A collector can reach stagnation temperatures up to 200C when empty of fluids. Residual fluids flashing to steam is bad news. Traditional tempered glass panels handle all that. The polycarb panels would be melted puddles.

Some quick spec's off generic products:
  Thermal Expansion Delta T @ 104 F: 0.03 in./ft.  <---  must be allowed for, 3/16" heave per six foot run
  Optimal Service Temperature Range:  -40 F to +248 F (- 40 C to 120 C)
  Maximum Service Temperature:  270 F (132 C)
  Minimum Service Temperature:  - 103 F (-75 C)
  Heat Deflection Temperature:  275 F
  Softening Temperature (Load: 2.2 lb.) 300 F

Anyhow - In my opinion if there are safeguards against overheating it is still not worth it since tempered glass panels, even used panels, are available.

(I nabbed two 4'x8' black chrome water heater panels w/ shipping damage both for $99, their pebble-surface tempered glass stashed away for somewhen!)

Roadie

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Re: Polycarbonate roof sheeting for solar hot water
« Reply #3 on: February 21, 2015, 05:20:03 AM »
I have a friend that was asking about keeping his 35ft poly tunnel warm using R/E sources,obviously keeping it as cheap as possible for materials,that's why I mentioned these roofing panels,the plan being to heat a large insulated water tank,which could then be pumped around a pipe system inside the poly tunnel at night to keep the chill off to extend the growing season a little, also poss be useful in the production of a small scale methane generator being to keep the slurry temp at around 35degress or so,this would be the batch system of methane production which I have tried successfully before but had problems initially getting the process going due to temperature variations,

I guess really that the idea of using the polycarbonate triwall roofing sheets came about because they are readily available and cheapish , not really expecting them to last forever but like you said DanG would be ok for fun and experimently purposes,
Solar energy will not happen overnight

Mary B

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Re: Polycarbonate roof sheeting for solar hot water
« Reply #4 on: February 21, 2015, 03:01:43 PM »
An often used technique is to place black painted barrels of water along the south side. Once up to temp they hold it well through the night as they radiate heat back into the greenhouse.

Bruce S

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Re: Polycarbonate roof sheeting for solar hot water
« Reply #5 on: February 23, 2015, 12:16:45 PM »
Roadie;
Welcome to the forum!
If you and your friend are using PVC for the connecting pipe, remember to paint them black as well.
2 reasons, PVC is cheap-ish but prone to UV and will become brittle :-(, painting them black will also help in keeping the fluids warm and radiate the warmth.

I have had private emails about people lining an entire back wall with these, along with a small 12Vdc pump to move the fluid around for better radiant heat transfer, but have NOT had the chance to try it myself on our small (2M*3M) setup.

You also seem to have found what others have,,, Methane is hard to get going when the ground is the insulation  :o.
I used the 6mil black pond liners on top of the ground to do mine.
Keep us up on how you're doing.

Cheers
Bruce S
 
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Roadie

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Re: Polycarbonate roof sheeting for solar hot water
« Reply #6 on: February 24, 2015, 03:16:57 AM »
Thanks for the advice all,yep will post more when I get it up and running again,something I was pondering the other day was how do they run Diesel engines on methane,is that possible or are they large gasoline engines converted,poss not the right section to post this but just a thought
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kc7noa

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Re: Polycarbonate roof sheeting for solar hot water
« Reply #7 on: March 26, 2015, 12:32:56 PM »
Running on wood gas might be a better solution .... unless you can produce and store methane ...

Roadie

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Re: Polycarbonate roof sheeting for solar hot water
« Reply #8 on: March 27, 2015, 12:59:57 PM »
Is it relatively easy to compress methane into a standard gas bottle
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Bruce S

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Re: Polycarbonate roof sheeting for solar hot water
« Reply #9 on: March 30, 2015, 06:45:05 AM »
Is it relatively easy to compress methane into a standard gas bottle
Yes & No;
There is the right way, which when done right doesn't use more power than it takes to make Methane.
Then there's the wrong way ,,, that blows up and destroys everything close by.

Perhaps you have a method you would like to share?

A kind word often goes unsaid BUT never goes unheard