Cheap DIY solar collector

[amdx]

I ran across this site, the guy has a neat idea for an inexpensive solar
collector.

http://www.iwilltry.org/w/index.php?title=How_to_build_a_simple_solar_water_heater

Mike

 

[amdx]

Let's see - 96x22 gives us 2112 sq inches or 1.36257792 sq meters

Assuming a solar input of 1 kW/sq m in clear sun, his solar input is 13623
Watts.

If he's getting 530 Watts out, then his panel's efficiency is 530/1363 or
38%.

The flip side is that he's seeing losses of 62%.

I don't think that's quite so terrific, but I spotted (and I'm sure you
can too) a couple of major improvement begging to be made. On the other
hand, it's a definite improvement over ground-temperature showers.

Any idea what the efficiency of a well designed copper collector is?
I've done a search and haven't found any numbers.
Mike

 

[[email protected]]

| amdx wrote:
|
|> I ran across this site, the guy has a neat idea for an inexpensive solar
|> collector.
|>
|> http://www.iwilltry.org/w/index.php?title=How_to_build_a_simple_solar_water_heater
|
| Let's see - 96x22 gives us 2112 sq inches or 1.36257792 sq meters
|
| Assuming a solar input of 1 kW/sq m in clear sun, his solar input is
| 13623 Watts.

Huh? Where'd you get that number?


| If he's getting 530 Watts out, then his panel's efficiency is 530/1363
| or 38%.
|
| The flip side is that he's seeing losses of 62%.
|
| I don't think that's quite so terrific, but I spotted (and I'm sure you
| can too) a couple of major improvement begging to be made. On the other
| hand, it's a definite improvement over ground-temperature showers.

Maybe he could use the black color and absorb more sunlight. It would have
to be black in the IR range, as well.

I think it would be more efficient at a higher temperature, with focused
sunlight from a wider capture. The plastic would have trouble with that.
How about corrugated metal (aluminum?) with a black powder coat that can
absorb a lot of light and IR, in a mirror enhanced capture array?

Still, the plastic approach is a nice cheap way to supplement hot water.

 

[AJH]

Also note that Solar Mike in NZ had discussed a similar collector
using twin and perhaps triple wall polycarbonate. I'm pretty sure he was
using copper for the manifolds.

I've tried this twin wall at lat 51 UK, just aiming for a hot air
solar roof at no significant cost above a "normal" roof.

Biggest problem so far has been the expansion differential between the
hot back and the cold front, significant bending over a 1.2m trial
sheet, so I'm guessing it will be a problem with 4m roof width.

I think the idea suggested of a plenum underneath with black fabric
absorber between inlet and outlet will prove better but I have no idea
of what pressure differential either side of the cloth and flow rate
to use. If the pressure above and below the cloth is too low then
there is scope for a short circuit for the air.

Measuring the heat output at the differential temperature is the
challenge, I've made straight through estimates with a walker's
anemometer and the temperature difference, not allowing for mistakes
in measuring it, looks like 40% in direct sunlight, we don't get much
of that in my target months of Oct Nov and Feb, Mar,Apr &May.

On a 36m2 roof that's potentially 40kW to dump in the summer's direct
sunlight but catch 5% of that in the winter and it's a big
contribution.

AJH

 

[Cosmopolite]

Works like crap. This isn't the greenhouse glazing. Coroplast is that cheap
signboard used to make political and other short-lived signs. If you listen
closely you can hear it decompose when sunlight shines on it. Painting it
black will help a little with the solar degradation but it won't stop it. If
that thing lasts a summer, I'd be quite surprised.

I have to disagree with this. We have used black coroplast for flange
protectors, sitting outside for years, wihout noticable degradation.

We tried this idea, a while back, but had too many problems sealing the
coroplast to the headers

Polypropylene is very hard to glue and should be welded, but coroplast
is too thin for that.

Polypropylene is an excellent heat exchanger material.

 

[[email protected]]

Polypropylene is very hard to glue and should be welded, but coroplast
is too thin for that.

3M makes a good adhesive for coroplast.

Nick

 

[Cosmopolite]

3M makes a good adhesive for coroplast.

Nick

Thank's for the tip. Went to 3M site and found Scotch-Weld 4693 H,
which is sold as a consumer item. I will try to find some and test it on
Coroplast.

 

[amdx]

Thank's for the tip. Went to 3M site and found Scotch-Weld 4693 H, which
is sold as a consumer item. I will try to find some and test it on
Coroplast.

I think 3M # DP-8005 is the recommended adhesive, I don't know about
Scotch-Weld 4693 H, it may be fine.
Mike

 

[[email protected]]

I think 3M # DP-8005 is the recommended adhesive, I don't know about
Scotch-Weld 4693 H, it may be fine.

....3M recommends it for polypropylene. It comes in a $15 red and white tube.
I made a heat exchanger by gluing up multiple coroplast sheets separated by
small coroplast spacers into a brick.

Nick

 

[Paul Carmichael]

El Tue, 26 Aug 2008 10:35:27 -0400, Neon John escribió:

The cheapest one I ever made was on my restaurant's flat roof. I
started out simply tossing out a couple hundred feet of black
industrial-grade 1" water hose onto the roof. The combination of the
black tar roof and the black hose would have the contents near boiling
in under an hour.

This is what I'm about to try to extend the pool season. I was thinking
of about 5o mts of black irrigation piping and a little pump to circulate
the water. The roof's 5 mts by 2.5, at about 30 degrees and faces south
east. I'm guessing I'll perhaps get the pool up by a degree or 2 in
October/November. 30,000 lts of water is going to take some warming up.