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.
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. :-)
[ I make solar panels, but not water heaters. ]
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/
> 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 ...
> 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. :-)
> [ I make solar panels, but not water heaters. ]
> --
> Morris Dovey
> DeSoto Solar
> DeSoto, Iowa USAhttp://www.iedu.com/DeSoto/
I was wondering how well that stuff would work in a solar collector.
TekSupply sells it for greenhouse covering but it isn't cheap.
My nearly free solar water heater, which isn't worth photos because
it's all salvaged material and home-made parts and would be difficult
to duplicate in detail, is a batch heater made from a 40 gallon
electric water heater tank in a close-fitting greenhouse with
aluminized bubblewrap insulation over styrofoam behind and whatever
glazing I'm testing over the top and front. The insulated top and
front covers fold out to reflect the sun onto the tank, sort of. Trees
limit its sun exposure to 10AM to 2PM so it doesn't need to track over
much of an azimuth anyway.
It will heat a laundry load of water to 100 - 130F depending on the
weather. Empty it can reach 190F and damage itself.
The screw-in heater element openings look like pipe thread but they
aren't. It is a straight thread sealed by the rubber gasket. If you
don't have machine tools to make fittings you might be able to salvage
burned-out elements to plug them. On mine one holds the thermometer
and the other the cold water inlet which extends down to the lower
side of the tank.
Jim Wilkins
wrote:
>> amdx wrote:
>> > I ran across this site, the guy has a neat idea for an inexpensive solar
>> > collector.
>I was wondering how well that stuff would work in a solar collector.
>TekSupply sells it for greenhouse covering but it isn't cheap.
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.
The stuff you're talking about would probably make an excellent collector
since it's UV-resistant and strong. Too bad it costs so much.
>My nearly free solar water heater, which isn't worth photos because
>it's all salvaged material and home-made parts and would be difficult
>to duplicate in detail, is a batch heater made from a 40 gallon
>electric water heater tank in a close-fitting greenhouse with
>aluminized bubblewrap insulation over styrofoam behind and whatever
>glazing I'm testing over the top and front. The insulated top and
>front covers fold out to reflect the sun onto the tank, sort of. Trees
>limit its sun exposure to 10AM to 2PM so it doesn't need to track over
>much of an azimuth anyway.
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.
The hose wasn't very UV-resistant so when the first leak appeared, I replaced
it with that semi-rigid direct-burial PVC pipe that is used for underground
water and well service. I can't recall whether it was 1.5" or 2" but it held
enough to fill a 50 gallon compartment of my dishwashing sink. That one was
in place for several years until I closed the place.
For more conventional circumstances, the cheapest and longest lived collector
I ever made was based on some plans TVA published in the wake of the first
A-rab oil embargo. It consisted of a sheet of (preferably) galvanized metal
or fiberglass corrugated roofing material, framed in wood (I used redwood
1X6s) and painted flat black. A PVC pipe with holes in it at the top dribbled
water down the grooves in the roofing. It was caught in a slit PVC pipe
gutter at the bottom. The glazing initially was window glass but after the
first hail storm :-(, I had tempered glass made for it. No fancy e-coatings
or anything like that existed back then but the unit still performed well. The
back of the panel was insulated with foil-backed fiberglass batting held in
place with screen wire.
Initially I had trouble with condensation on the inside of the glass causing a
significant loss in output, probably due to reflections. I solved that
problem in, IMHO, a fairly clever way. On every other trough, I made mounds
of semi-solid epoxy shaped to cause the water to splash up in the air, far
enough to strike the glass. After experimenting, I found that 6 such mounds
along every other trough would cover the glass adequately with splashed water.
I then put a tiny bit of surfactant in the water. This caused the water to
sheet off the glass rather than bead up. Back then I used just a little
automatic dishwashing rinse additive (which doesn't foam). Now I'd try one of
the spray shower treatments. They don't foam either.
A small boiler circulating pump circulated water up to the collector and back
through a copper coil inserted between the element holes in an old electric
water heater tank.
I used two parallel runs of 1/2" dead-soft copper tubing. I pushed it in
through the top hole at a tangent. With a little help from a pusher stick, I
could get it to follow the inside curve of the tank and form several turns of
a spiral. I brought the tubing out through holes drilled in the flange-type
elements. The tubing was silver-soldered in place.
I built a simple little controller that ran the pump whenever the collector
temperature was a few degrees hotter than the tank water. It consisted of two
thermocouples, one fastened to the corrugated roofing and one immersed in the
tank water. They were connected voltage-bucking so that the output voltage
was the difference between the two junctions. (actually, you could view this
as a single thermo-COUPLE with one junction at the collector and the other in
the water heater).
A simple comparator operated a relay when about 0.1 millivolt of positive
output was detected. This was a Type T (copper-Constantine) TC so 0.1 mv is
about 7 degrees differential. That is, the roof collector was about 7 deg
hotter than the tank. The comparator has enough hysteresis so that the
difference would have to be near zero before turning the pump off.
My mounting was also clever. I made a V-shaped device out of two pieces of
2X6 about 2 ft long. I placed this on the crown of the roof to protect it.
Over the top of that I ran a couple of stainless steel cables. On one end
they attached to the collector. On the other they attached to a cast iron
sewer vent pipe. On the bottom of the collector were attached two more
cables. They played out at about 45 deg angles and attached to gutter
mounting nails. I didn't want to mar my roof in case this didn't work out -
thus the non-invasive mounting technique.
I was concerned a little about this mounting relative to wind but after a
near-tornado passed through that blew off shingles without bothering the
panel, I rested easy. Of course, the plumbing also helped anchor it down.
This system supplied all my hot water needs whenever the sun shown and help
even under light overcast. It was a total loss during the long heavy overcast
periods we experience here in winter. The unit was naturally freeze-proof, as
the water drained back to an insulated surge tank (old well-pump tank) when
the pump turned off. I lived in the house about 3 years after building the
thing and it worked fine. The subsequent owners kept it operational for quite
some time. I went on the road and lost touch after a few years. I do know
that it is gone now, not surprising since it's been 30+ years.
Modern black-anodized aluminum corrugated roofing should work about as well,
if not a little better, though it'll probably need cross-bracing to remain
rigid. Today I'd look at some tempered E-glass or maybe that greenhouse
glazing mentioned above. I'd look at it but not necessarily use it, depending
on the cost. Plain old glass worked well enough. The cost of this is so low
that if one panel is marginal then simply build another.
John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
Save a tree, kill a beaver
Neon John wrote:
> wrote:
>
>
>>
>>>amdx wrote:
>>>
>>>> I ran across this site, the guy has a neat idea for an inexpensive solar
>>>>collector.
>
>
>>I was wondering how well that stuff would work in a solar collector.
>>TekSupply sells it for greenhouse covering but it isn't cheap.
>
>
> 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.
> The stuff you're talking about would probably make an excellent collector
> since it's UV-resistant and strong. Too bad it costs so much.
>
>>My nearly free solar water heater, which isn't worth photos because
>>it's all salvaged material and home-made parts and would be difficult
>>to duplicate in detail, is a batch heater made from a 40 gallon
>>electric water heater tank in a close-fitting greenhouse with
>>aluminized bubblewrap insulation over styrofoam behind and whatever
>>glazing I'm testing over the top and front. The insulated top and
>>front covers fold out to reflect the sun onto the tank, sort of. Trees
>>limit its sun exposure to 10AM to 2PM so it doesn't need to track over
>>much of an azimuth anyway.
>
>
> 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.
>
> The hose wasn't very UV-resistant so when the first leak appeared, I replaced
> it with that semi-rigid direct-burial PVC pipe that is used for underground
> water and well service. I can't recall whether it was 1.5" or 2" but it held
> enough to fill a 50 gallon compartment of my dishwashing sink. That one was
> in place for several years until I closed the place.
>
> For more conventional circumstances, the cheapest and longest lived collector
> I ever made was based on some plans TVA published in the wake of the first
> A-rab oil embargo. It consisted of a sheet of (preferably) galvanized metal
> or fiberglass corrugated roofing material, framed in wood (I used redwood
> 1X6s) and painted flat black. A PVC pipe with holes in it at the top dribbled
> water down the grooves in the roofing. It was caught in a slit PVC pipe
> gutter at the bottom. The glazing initially was window glass but after the
> first hail storm :-(, I had tempered glass made for it. No fancy e-coatings
> or anything like that existed back then but the unit still performed well. The
> back of the panel was insulated with foil-backed fiberglass batting held in
> place with screen wire.
>
> Initially I had trouble with condensation on the inside of the glass causing a
> significant loss in output, probably due to reflections. I solved that
> problem in, IMHO, a fairly clever way. On every other trough, I made mounds
> of semi-solid epoxy shaped to cause the water to splash up in the air, far
> enough to strike the glass. After experimenting, I found that 6 such mounds
> along every other trough would cover the glass adequately with splashed water.
>
> I then put a tiny bit of surfactant in the water. This caused the water to
> sheet off the glass rather than bead up. Back then I used just a little
> automatic dishwashing rinse additive (which doesn't foam). Now I'd try one of
> the spray shower treatments. They don't foam either.
>
> A small boiler circulating pump circulated water up to the collector and back
> through a copper coil inserted between the element holes in an old electric
> water heater tank.
>
> I used two parallel runs of 1/2" dead-soft copper tubing. I pushed it in
> through the top hole at a tangent. With a little help from a pusher stick, I
> could get it to follow the inside curve of the tank and form several turns of
> a spiral. I brought the tubing out through holes drilled in the flange-type
> elements. The tubing was silver-soldered in place.
>
> I built a simple little controller that ran the pump whenever the collector
> temperature was a few degrees hotter than the tank water. It consisted of two
> thermocouples, one fastened to the corrugated roofing and one immersed in the
> tank water. They were connected voltage-bucking so that the output voltage
> was the difference between the two junctions. (actually, you could view this
> as a single thermo-COUPLE with one junction at the collector and the other in
> the water heater).
>
> A simple comparator operated a relay when about 0.1 millivolt of positive
> output was detected. This was a Type T (copper-Constantine) TC so 0.1 mv is
> about 7 degrees differential. That is, the roof collector was about 7 deg
> hotter than the tank. The comparator has enough hysteresis so that the
> difference would have to be near zero before turning the pump off.
>
> My mounting was also clever. I made a V-shaped device out of two pieces of
> 2X6 about 2 ft long. I placed this on the crown of the roof to protect it.
> Over the top of that I ran a couple of stainless steel cables. On one end
> they attached to the collector. On the other they attached to a cast iron
> sewer vent pipe. On the bottom of the collector were attached two more
> cables. They played out at about 45 deg angles and attached to gutter
> mounting nails. I didn't want to mar my roof in case this didn't work out -
> thus the non-invasive mounting technique.
>
> I was concerned a little about this mounting relative to wind but after a
> near-tornado passed through that blew off shingles without bothering the
> panel, I rested easy. Of course, the plumbing also helped anchor it down.
>
> This system supplied all my hot water needs whenever the sun shown and help
> even under light overcast. It was a total loss during the long heavy overcast
> periods we experience here in winter. The unit was naturally freeze-proof, as
> the water drained back to an insulated surge tank (old well-pump tank) when
> the pump turned off. I lived in the house about 3 years after building the
> thing and it worked fine. The subsequent owners kept it operational for quite
> some time. I went on the road and lost touch after a few years. I do know
> that it is gone now, not surprising since it's been 30+ years.
>
> Modern black-anodized aluminum corrugated roofing should work about as well,
> if not a little better, though it'll probably need cross-bracing to remain
> rigid. Today I'd look at some tempered E-glass or maybe that greenhouse
> glazing mentioned above. I'd look at it but not necessarily use it, depending
> on the cost. Plain old glass worked well enough. The cost of this is so low
> that if one panel is marginal then simply build another.
>
> John
> --
> John De Armond
> See my website for my current email address
> http://www.neon-john.com
> http://www.johndearmond.com <-- best little blog on the net!
> Tellico Plains, Occupied TN
> Save a tree, kill a beaver
>
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> collector.
>
>