I have been trying to figure out how to make a cheap solar thermal panel. Like this instructable, I settled on plastic. There is one BIG problem with making a solar thermal panel out of plastic.
Overheating.
The problem, put simply, is that plastic solar thermal panels, if built like traditional solar thermal panels, cannot turn themselves off if they start to overheat. You cant just paint a plastic panel black and slap some glazing on it. If you stop removing the heat from the panel, and the panel is built from plastic, it will soften or melt eventually. This was recognized by Rob in his instructable:
"because the whole collector is made of plastic, it is important that the temperature doesn’t get too high or it will soften and possibly spring a leak. 80 degrees C (176 degrees F) is about the limit. Don’t think it can get that hot? Think again. ...Therefore this may not be a practical design for residential installation"
The problem is figuring out how to make a solar panel turn off. If you can figure this out, then solar thermal panels could be built of plastic and the cost reduced to a point where it is affordable to everybody. (i.e. $1000 per panel to $200) Why is this important? Because heating our homes (air and water) accounts for the majority of energy we consume in our homes. If solar thermal panels were cheap, we could heat our house with them and save billions every year.
So this is where I am coming from. I want to find a way to build a solar thermal panel from commonly available materials and have it compete with commercial systems. The design I have come up with may be the answer, or it may not, but if the instructable community would work on this problem with me, the benfits to our society could be huge.
check out the blog I created for this idea for more info and for updates as I have them.
Blue Skies,
Alex
Overheating.
The problem, put simply, is that plastic solar thermal panels, if built like traditional solar thermal panels, cannot turn themselves off if they start to overheat. You cant just paint a plastic panel black and slap some glazing on it. If you stop removing the heat from the panel, and the panel is built from plastic, it will soften or melt eventually. This was recognized by Rob in his instructable:
"because the whole collector is made of plastic, it is important that the temperature doesn’t get too high or it will soften and possibly spring a leak. 80 degrees C (176 degrees F) is about the limit. Don’t think it can get that hot? Think again. ...Therefore this may not be a practical design for residential installation"
The problem is figuring out how to make a solar panel turn off. If you can figure this out, then solar thermal panels could be built of plastic and the cost reduced to a point where it is affordable to everybody. (i.e. $1000 per panel to $200) Why is this important? Because heating our homes (air and water) accounts for the majority of energy we consume in our homes. If solar thermal panels were cheap, we could heat our house with them and save billions every year.
So this is where I am coming from. I want to find a way to build a solar thermal panel from commonly available materials and have it compete with commercial systems. The design I have come up with may be the answer, or it may not, but if the instructable community would work on this problem with me, the benfits to our society could be huge.
check out the blog I created for this idea for more info and for updates as I have them.
Blue Skies,
Alex
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Signing UpStep 1: Use Polypropylene, not Polycarbonate
Until I have a chance to redo the figures (maybe in a week or so), to any users out there who wants to build this panel:
Don't use polycarbonate!
Turns out that this plastic degrades in long exposure to hot water. Following up on some user comments, I checked out Coroplast, which is actually polypropylene plastic. long story short, coroplast is MUCH cheaper, MUCH more water-resistant (its used for plumbing) and easily recyclable. Not even any question about what is the better option.
However, you will have to heat-weld the manifold because polypropylene does not glue easily. Read about it at Wikipedia. Until I have the time to test this, and unless you want to give it a try, I recommend just thinking about this idea and coming up with more ways to make it better. There is obviously a lot we can do!
Don't use polycarbonate!
Turns out that this plastic degrades in long exposure to hot water. Following up on some user comments, I checked out Coroplast, which is actually polypropylene plastic. long story short, coroplast is MUCH cheaper, MUCH more water-resistant (its used for plumbing) and easily recyclable. Not even any question about what is the better option.
However, you will have to heat-weld the manifold because polypropylene does not glue easily. Read about it at Wikipedia. Until I have the time to test this, and unless you want to give it a try, I recommend just thinking about this idea and coming up with more ways to make it better. There is obviously a lot we can do!
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I saw this site and I need your inputs. I want to have at least one guide for now. Thanks in advance!
Just as a side, I was considering clear pipes and adding particles to the flow (there's a company that does exactly that - adding particles to (and removing them from) liquid flow for various industrial needs.
I don't need you to show me the problem. Please understand that I ACTUALLY MANUFACTURED a system like this, after talking to the ENGINEERS at two companies, one of the Polygal (a two hour drive out to Kibbutz Ramat Hashofet).
So let me explain once again: The Polygal is only the structure and insulation. The black piping is what takes the heat, and YES it has worked without failure for over 10 years! I'm not sure what happens when there is no water in the pipe. Seems to me the air heats up, builds up pressure and moves out the pipe, thus cooling it down.
Your right its not a matter of brand, but that company treats its PC so that it is ready for roofing and roof conditions, and, as I stated, it worked already, and works for at least one company for many years. BTW take a look at this - no insulation at all... http://www.youtube.com/watch?v=sBAi_TVNaiM
I have two questions:
1) Why you use silicon carbonate, not just coal particles, which is much cheaper?
2) Do you think is enough to stop the flow of water to stop heating?
Finally, EXCELLENT INSTRUCTABLE!!!
En respuesta a sus preguntas:
1- Silicon carbonate fue la unica particula negra que pude encontrar de 60um y en pequena cantidad. Cualquier particula que no se disuelva en el liquido y que a la vez sea negra y suficientemente pequena puede servir, por ejemplo el 'coal slag'.
2- Si-- toma un minuto para que bajen las particulas, y despues de eso el liquido deja de absober luz (calor).
For the Instructables Anglophone community: Thanks for your kind reply. As often happens, an answer causes another question: Why 60um? Could not be 1mm or 2, or whatever else measure?
as the particles get smaller, the force of the water relative to the force of gravity gets bigger. This means that if you use bigger particles you will have to increase the flow rate to keep the particles up. If you have a small circulation pump, then you will need smaller particles. If you have a very large pump or lots of water pressure, then you can use bigger particles.
let me know if you need a translation and I can ask my mother. I was born in Mexico but move to the U.S when I was a baby. My whole family speaks Spanish but not me. ;(
I can read English almost perfectly, aided with Google translator, if the text is wrote in English as yours. I say this because there are others that are wrote in slang.
So far it's been much easier using dorm room fridge radiators, and window glass.
That being said, I do have an idea for your 'ible readers.
I've recently built a CNC Guinea Pig cage.
I used a white coroplast. however the sign shop I bout it from also carries the same material in clear.
Advantages are, CHEAP... I think I picked up a 4x8 sheet for $25(though online can be much cheaper if you can talk your way out of shipping). Temp resistant. Well, it'll withstand 60PSI at 200F! So as long as you're using water to move the heat, all should be well.(melting is somewhere over 350F)
This Place has some 'good stuff' rated for hurricane country. they even sell end caps, premade!
The reason i am attempting this is because I want to find a way to make a cheap solar panel that can be manufactured. Smart tinkerers like yourself will always be ahead of the curve. Its all the other people out there who cant do that, don't have the time, don't think they can, or just don't want to... but would go solar if it was cheap and easy.
Long term, it MAY develop brittleness... not an issue if it's overglazed, like in your design.
If it's a big concern, one of the optional coatings is UV resistance. don't remember which site, or which product, but the number was 98% light transmission, with "High" uva/uvb resistance.
Just on a side note... Sonic welding is expensive, but best.
Thermal welding works well too though.
I mention this, cause you can cut a few inches on the bottom of the panel in half, Remove the top portion, sand the bottom smooth, form, and weld.
If you're willing to sacrifice the outer most 2 channels... you can make your entire panel from just the one sheet! and if you do the thermal/sonic welding well, it'll never come apart!
If that doesn't make enough sense... I could draw up a cut /weld diagram... but you probably got what I meant :-)
thanks!
as a side note a potentially better route could be to eliminate the wire mesh altogether. It would be best if a separate box housed a filter, say right at the input and output ports. The problem here is insuring that the particles mix. The reason it works with the channels is because the flow pushes the particle to the top of the channel, causing an increase in resistance and decreased flow. The flow is then diverted to another channel, increasing the flow and raising the particles. meanwhile the previous channel has low flow, so the particle start to fall... The whole thing make the particles spread out.
The best solution I think is a design that lets the particles spread out while eliminating the problems with the manifold (via your technique, for example) and eliminating the wire mesh.
That is an issue I hadn't thought of...
My solar heaters don't use an in-water heat absorber like yours does.
I think it may be possible to change the U shape a little and still imbed it.
Actually, this is making me think that the thickness of the plastic I used in the manifold was super over-kill. 1/32 would probably do. And that is already flexible. I could bend it around and thermal/sonic weld it, then use polyester resin to fill the sides (while also puting an input and output port in).
You seem to have some experience with sonic/thermal welding. Any advice/pointers/urls I could check out? I have set aside some money to develop this idea (not a lot, but certainly enough to invest in some reasonably-priced tools)
My experience to date is NOT with waterproof welding. Just structural.
That being said, my work hasn't let the dust from pet bedding through, and I didn's SEE any leaks last time I washed the pan... So it MIGHT be waterproof. Just don't know.
my "plastic welding torch". Was the cheapest piece of junk I could find that would still do the job, with my skills. If you have the cash, go for one of these.
If you're budget is REALLY low, this was the cheapest one I've ever seen. If you're willing to practice and looks aren't too important, an old junky solder iron should do a passable job, as long as it has temperature control. The cheapest of the cheap iron-style plastic welders are set up like that. So much so, in fact, that most of them look like the seam irons that Hobby Lobby sells, for seamstresses.
Fuzzy
This was in novemeber and the water was coming from my well. It was not terribly cold outside, so the ambient was warmer then the water temp. Also, its possible that the water temperature from the well fluctuated during the measurement.
So, bottom line is I need to run some closed-loop tests with a circulation pump.
Until I do that (or somebody else out there builds one and does it) I would venture to say that its going to turn out well. The "absorber" plate is more like an "absorber engine", since the particles form a convention current with turbulent flow bringing them into the sun and back into the liquid in a cycle. Its a total-new type of absorber with totally new physics. All aspects of the design can be controlled. For example, by using larger particles you can increase the flow rate because the particles sink faster which would probably increase the efficiency.
Great idea.
Cheers
Mark
What I am thinking is that in a production panel, the whole thing would be insulated. The back would have foam and the front a panel of polycarbonate. I would put some reflective foil back there to reflect the light out of the panel.
this paper is interesting, and apparently looked into using vents to cool a plastic plate absorber, to no avail. The combination of a vent with an absorber plate that can turn off should put a nail in the coffin of the overheating problem.
thanks fuzvulf! (and great username)
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In my searching, it looks like coal slag (byproduct of coal fired metal plants) would work better (certainly cheaper and in abundant supply), but it needs to be sifted.
www.usmix.com/black_beauty_coal_slag_idf.phtml
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L
Perhaps a simple thermistor circuit or even a slightly more complex sensor and IC circuit could be used?
Not entirely sure if that is what you mean by "turn off" but it is just an idea.
So now that you have hot water running to your house, how do you convert that to space heating on the cheap?