Build your own flat panel solar thermal collector

I've seen a few different designs for solar water heaters (on this site and others) and I wanted to share my own. It is quite an efficient design since every square inch of collector surface is in direct thermal contact with the water being heated. You can easily modify the design to any size you like. I made mine 8ft long by 22" wide so that it can fit between the rafters in my attic. Tests showed that system output averaged about 530 Watts, heating 20 litres of water from 24 degrees C (75 degrees F) to 47 degrees C (117 degrees F) in one hour.

Aside: I'm in the middle of re-roofing my house and plan to build in a transparent section of roof in one area. Then I can experiment with different solar collector designs like this one and install and remove them easily from inside my attic instead of having to go out on my roof. It will make the plumbing easier too. The drawback is that if a collector springs a leak, it will leak into my home instead of into my gutter.

For information on this and other projects of mine see my website IWillTry.org.

Step 1: Concept

The collector is made from corrugated plastic sheet, commonly used for making signs. It has multiple square channels running lengthwise from end to end. When I first saw this type of sheet I immediately thought, "Wow, this would make an excellent flat panel solar collector if only there was a way to pipe water through all those little channels." Several weeks later, a method of doing so occurred to me. If a slot of the right width is cut lengthwise in some ABS pipe (so the cross section looks like a "C") then this pipe can be fit over the end of the corrugated plastic. The seams can be sealed to make everything water tight. The sheet can be painted black and viola... you have a flat panel solar collector.

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. In practice the maximum temperature is difficult to guarantee. Water may stop circulating, or may drain out completely for a number of reasons and the panel will overheat. Therefore this may not be a practical design for residential installation but it is an inexpensive, easily built experimental system that produces as much or more hot water than commercially available systems. Mine cost about $60 in materials (about $4.00 per square foot) and about 6 hours of construction time.

Comments

[lucindanl]

Does the length of the hose make a difference? I want to build something to keep a worm composting bin from freezing this winter. My bin is a disused cement water cistern w/o access to AC power. It’s about 6’ x 6’ x 3’ and lined with plastic. I plan to surround it with hay and cover it with insulated panels, but I’ll need a heat source, beyond the composting itself, as I live in the northeast where we have substantial freezing. I’m wondering if the thermal siphoning would work if I used substantially more hose – like 75’ to 100’ – coiled on the bottom of the bin and buried under the compost. The tank and panel could be placed as high as needed as long as the hose could be lower. Do you think this would work? Also, would freezing during the night destroy the panel?

[glorybe]

I doubt that a worm composting bin would do well wuth this kind of heating. One freeze and it is all over and conversely one day of over heating and your worms are dead. Perhaps some sort of hor rock like they sell for turtles that has an internal thermostat would be reliable.
If you get enough bio activity and pretty good insulation you may never need additional heat.
Have you ever seen a truck load of chips from a tree chipper smoldering away? Hopefully the bio activity in a worm compost may not get that drastic but if the worms get busy and you add heat at the same time i think you would have a real mess on your nahds.

[Marcos]

What if you dug your bin into the ground, to insulate, and maybe even absorb any warmth from the earth? Then you'd need a smaller solar collector, if any.

I live in the SF Bay Area, where temps are moderate compared to the Frozen East. I keep my worm bin in an outdoor shed, raised slightly from the cement paver floor and it's fine.

[avid0g]

This sound really great.  If the collector is above the cistern, you will need a pump, so I hope you have a downslope to place the solar collector.  The length of hose will slow down the siphon but the biggest drag is elbows and collector heat loss; avoid them.  You need a low-pressure check valve to prevent back-flow and a water storage tank/bladder above the compost.

The cistern sounds like a great way of having Thermal Mass.  If you can keep the soil Under it away from moving ground water, sink the insulation deeper into the soil around it and use the additional mass of the soil underneath to ride through cloudy days.  The insulation and surrounding soil may need to be covered with tarp to drain away moisture.  It may take a while to heat the soil underneath, but the solar collector would eventually get there.  

Rigid hose under the compost sounds great.  Of course the plumbing and collector would need substantial insulation, since it will be out in the cold.  The water is in a closed loop and not used for drinking or for moisture, so you can load it with a non-toxic antifreeze and black dye for improved heat absorption.  (We are on a web page with a transparent absorber!)  

It is also a good idea to provide some heating from above.  This could be rubber hose and/or bladder on top of soil and/or transparent insulation (bubble-wrap or white closed-foam) above the rest to let in light.  

Good Luck!

[MauricePelchat]

I did a similar panel usign a black corolast sheet, but no back panel to hold the assembly. I just suspend it to the wall. I use it to heat my pool. I make water go fast through the panel, so is doesn't overheat and get more efficient, because if a black panel get too hot it emits it heat back as infrared.

I tried the first setup by using ABS pipe, but there was always leaks along the pipe. I tried with many type of glues and regular silicone doesn't seems very good at this.

Finally I bought a plastic plank, cut it in two narrower planks, made a deep groove to make the coroplast enter it. I use using workbench saw and multiple pass to avoid plastic overheating. Finally I glued the plank to the board using epoxy. It worked but it is expensive. The groove was deep enough, so there was a free space below the insert to have water to get in.

I didn't had any problem about overheating, since the sheet is not in a enclosed area. If water doesn't circulate it just get hot quickly but not enough to damage it. The panel releases it heat into the air. Actually I make water circulate at a speed of 4 gallon per minute. The panel is 4x4 feet, and water raise from 2°F when passing through it. Sure when you consider a pool of 10000gal, divided by 240 gal per hour it would take 42hr to get a complete 2°F increase. But this is relatively small panel. I intend to install four 4x8 panel on the roof, so I could get a 2°F increase 8 time faster so the pool would gain 2°F increase in 5-6hr.

The key to the efficiency again is to make water circulate quickly trought the panel, so the every F° gets into the water and not back into the air. Surprisingly I get the same 2°F increase on colder days (60°F outside) than on hot days (90°F).

Last I had to make 2 perpendicular 1/2 hole at the top to collect the water (through 2 short copper pipe to which I plug my hose). With only one, some part of the panel where gettting hotter. The panel is installed verticaly so the hot water return is a the top. This way panel temperature is even.

[jhearty]

OK, so my wife and I finally got one of these built and tested.  We built it as a drainback system and used plain water dyed black using pond dye.  We did not paint the panel.  We got frosted tempered glass panes from Craigslist to build this and the next ones.  We used an old hot water circulator pump also from Craigslist.

We did a 4 hour test on a clear day, readjusting the panel angle a few times during the test.  The full spreadsheet is available but I was not sure if it could be posted here, so I just posted a screen shot of it.  It is a 1.814 square meter panel with 37.85 liters (10 gal) of water in the system.  We used a 55 gallon plastic drum for the tank.  The tank and hoses were not insulated.

At the 1 hour mark average power was 951 watts, 52% efficient.  At 2 hours, 768 watts, 42%.  At 3 hours, 593 watts, 33%.  At 4 hours, 464 watts, 26%.  We also did a stagnation test with no water in it, and it got up to 152 degrees F on a 45 degree day.  We are looking forward to mounting it permanently and testing reliability/longevity.  One thing we still need to do is get UV clear paint to help protect the panels from UV breakdown, and see if that affects the efficiency much.

[Dilynda]

I have a roof solar panel installed and a huge holding tank for hot water usage in my home can I use this system to heat my pool and if so what adjustments would be needed to incorporate the pool?

[avid0g]

 I recommend that you add more collectors if you want to heat your pool.  It is usually not necessary to reach a high temperature for pools so the new collectors can be dedicated to the pool, and be less expensive since they need less insulation and can use cheaper plastics.  It is always a good idea to insulate the pool surface when not in use.

The pool heating may overload your current hot water system so that it cannot ride through cloudy and/or cold days; then you are using fossil fuel.  :-(

If your home is well insulated, you may be able to use some of that domestic hot water energy for air heating or radiant floor heating.  ;-)  This is also a good use for excessive hot water from the solar pool heaters. They can provide preheated water before a final boost from the domestic hot water system.  This loop would Not use potable water.  It would run on a separate loop requiring a pump, heat exchanger(s) and second thermostat.  

[ivanjacob]

i made a thing with the same concept
water heater for swimming pool

[jfoerster]

Are you still using this set-up? Have there been any water leaks in the joints to date? This same material was used as a heat exchange condenser plate for a desalination prototype and it did very well as compared to traditional fin-and-tube condensers. I'm about to start building a prototype using the Coraplast material (anyone besides me always read that as "chloroplast"?) as a condenser and was wondering if you have any comments and observations on the longevity of the joints you used. The actual study analyzing the performance of the material is titled "Performance of a greenhouse desalination condenser: an experimental study" by Al-Khalidi, A.A.T. Zurigat, Y.H. Dawoud, et al.

For what it's worth, the better commercial solar pool heaters run at about 80% efficiency and here's a DIY unit that hit 78%.

http://rimstar.org/renewnrg/solar_pool_heater_diy_fp.htm

[wolfkeeper]

For permanent installs, wouldn't a steel central heating radiator used as a heat exchanger, with double glazing on top, work nearly as well or better and avoid the problem of potentially melting?

[phredder]

You did a nice job on your thermal collector. I built a similar design several years ago to heat my kids pool that was 12 feet in diameter and 3.5 feet high. Mid summer the pool temperature would get up to around the 90 degree mark, without the collector the temp would be below 70. I used the full 8 x 4 black sheet if coraplast and used 1.5 inch a.b.s. for the ends. The a.b.s. ends were 4.5 feet in length. I didn't make a continues cut along the length of the a.b.s., rather I started my cut about two inches from the end, then I'd cut an 11 inch cut, leave another uncut portion of about 3/4 inch, make another 11 inch cut, leave another portion of material uncut, and so-on down the length of pipe until I got to 48 inches, I then left the last 6 inches uncut. Before I slid my coraplast in the a.b.s. I had to notch the coraplast to fit the uncut portions of the pipe. My reason for this type of slotting was to add strength to the pipe to resist the internal pressure of the water that was being pushed by a 1.5 h.p. pool pump. The hose I was using was 1.5 inch black sump pump hose. Not the most attractable pool hose but functional. My biggest concern was what adhesive to use to join the pipe and coraplast. At that time the only info I could find on coraplast was from the manufactures data sheets and modelers/hobbyists who use coraplast to build their projects. I did used silicone but next time plan to use urethane, the stuff the automotive industry uses to adhere windshields to vehicles. the was fastened to a 8x4 sheet of plywood and then the whole assemble screwed to my shed roof that face south. The collector remained on the roof for 3 years and withstood everything except the cats claws.

[napjax3000]

The process seems workable. I am seriously considering giving this a try. Hope it turns out ok.

[gearskin]

Since this plastic solar thermal collector can only reach a maximum temperature of about 80 Fahrenheit before it might melt (like you mention), do you think you could use this collector as a sort-of preheater for a metal solar thermal collector? I don't have any experience building or using them, myself, so I don't know if that would help the process at all, but with my rudimentary understanding, it makes sense :P

[macrumpton]

The plastic sheet material appears to be Coroplast, a fluted polypropylene panel available in thicknesses from 2mm to 12 mm in a wide variety of colors (including black). According to the Coroplast.com site the temperature properties of it are:

Normal temperature performance range	-17 degrees F to 160 degrees F
Melting point	162 degrees C, 324 degrees F

The one fly in the ointment is that it is virtually impossible to reliably glue anything to it, especially if there is stress on the joint or low temperatures which can make the joints very brittle. I have spent several years wrestling with this material (in a quest to make a folding boat out of it) and the best ways to attach anything structural to it are staples, pop rivets, nuts and bolts. and heat sealing other things made of polypropylene to it. Hot glue can be used if the result is not going to be stressed while cold or wet and there is no peeling force.

Your best bet for local sources are sign shops which often have 4'x8' sheets in the 4-5mm thickeness. they also have 2-3mm thick smaller panels which are used for real estate and election signs.

[iwilltry]

Hi bell017, That's 80 degrees C (176 degrees Fahrenheit) and that is plenty hot enough for most applications. This issue isn't that a hotter temperature is desirable. Panels are more efficient at lower temperatures so generally you don't want the panel to get much hotter than the desired final temperature of the water (ex not over 50 degrees C for residential water heating). The issue is that there's no safeguard to prevent hotter temperatures from being reached occasionally. During it's lifetime there are any number of reasons the water could stop circulating. If that happens the panel will overheat very quickly and you have meltdown ;-). The same is true even if it is just used as a preheater. So... while it's a great experimental unit, it's not a good choice for permanent installation. That is, unless you install it in open air without glazing in which case it probably will not overheat (that's the way many commercially available pool heating panels are constructed).

[gearskin]

Ah, I guess I should have read that again before I replied. 80 Celsius is plenty hot enough for me :) I've been interested in solar thermal energy for a year or so now, but I've either not had the time or the money to get something started. What are some of the big reasons that water might stop circulating?

[iwilltry]

Some reasons water could stop circulating: 1. System develops a leak and the water leaks out. 2. Air gets into a thermosyphoning system causing vapour lock. 3. Pump failure in a non-thermosyphoning system (could happen due to power outage, faulty temperature sensor, bad connection, etc). It's unlikely any solar hot water installation (even commercially available ones) will operate without one of these happening occasionally.

[carlos1w]

This is very nice.  Exactly what I need for improving my last project:  http://www.instructables.com/id/Hybrid-solar-panel-photovoltaic-and-thermal/.  Do you think that this corrugated plastic exists that is somewhat rigid?

[devonfletch]

Polycarbonate 'structured' roofing 'Polygal' and other brand names is pretty stiff, and comes in various thicknesses 6, 8, 10, 16mm (1/4" to 5/8"). But it's dear as poison, and for experiments, best to source offcuts or second-hand. Note that this product should be sealed with non-acetic roofing/plumbing silicon only, (it is allergic to polyurethane and other sealants). Also, it is UV-protected on one side only: if you install it upside-down, it will die in 6 months. But it would be a good base for solar cells, and it' easy to cut by score-and snap, or jigsaw, and can be heat-bent with care.

[carlos1w]

I know that pc leeches BPA, but I would not call it deadly.  Could you point me to some reference on why it is "dear as poison" (I would certainly want to know!).  THANK YOU.

[devonfletch]

I installed this roofing product for 10 years, and it was the most expensive roof (except titanium!) available, $50-60/sq m here in Oz. Perhaps 'dear as poison' is a local expression. It means inordinately expensive, maybe it is less so in other parts of the world.  In any case, it is very versatile, due to its impact-resistance, insulation properties and easy handling.
Another handy material is the stainless steel sheet, salvaged from dead clothes dryers (the drum is often SS), and commercial (and increasingly, domestic) refrigerators and other appliances.

[carlos1w]

Excellent, thank you!  I was not aware of the "australianism" :)

[lensam69]

Yes, They make a rigid version that is sandwiched between two aluminum plates. Call sign supply companies (i.e. Grimco)

[carlos1w]

The site at grimco has lots of interesting plates that would work nicely.  I also found out that it is not good to mix polycarbonate with water, unless you keep a strict separation of the medium and the water you will actually use in your home (BPA leeches out of the polycarbonate).

[fbujold]

Build the same concept several years ago out of black coroplast and the only weak link was the PL adhesive sealant. Tried at least 7 or 8 different product and the final champion was marine goop. (http://www.eclecticproducts.com/ag_adhesives.htm) Available at home depot and other fine hardware strores. Make sure to sand the coroplast and pipe surface for improved adhesion.

[weldor]

I believe that what is being referred to as "thermal siphoning" is actually a natural type of circulation called convection. It is also called "ebullient cooling" when the process is used to transfer heat out and a way from (as a method of cooling a piece of machinery (typically an engine).

To avoid air bubbles it is a good idea to install your fill point at the lowest point of the system. This is because air always rises to the top. The expansion tank should also have a safety relief valve from a water heater installed. Better yet, use a water heater as the expansion tank.

[paladin42]

neat concept. would like to know how to apply this to home use. can you use your existing hot water heater as a storage tank and can you hook it up directly to your water line. if yes to the former how do you keep the stored water hot until use?

[iwilltry]

You could use your existing hot water heater as a storage tank. You could not put this system directly in line though. City water pressure would burst the joints. You would required a heat exchanger in the tank (do a web search on Solar Wand) and a pump to circulate the water when it is sunny. The tank keeps the water hot till use (it's insulated). During non-sunny periods you can run the tank normally. A well built system would switch automatically between normal and solar operation as needed.

[votecoffee]

You could use this with an existing system, but you are right in that you would need a check valve on the output and a pressure regulator on the input side that would greatly reduce the pressure.  If you can not find a pressure regulator that will bring the pressure down sufficiently, you could use a storage tank and float valve to fill the tank to a set height.  Either way, you will need a pump to get the water pressure up higher than house pressure for the check valve to open and let water in.

[paborralho]

I forgot the important comment, I think it is better if the "in" and "out" of the panel are opposed, to avoid water circulating by the shortest path. Paulo Borralho "There are lots of Yesterdays and Tomorrows"

[iwilltry]

Agreed. My bad. Someone else pointed it out too. It's especially important for a pump operated system. For a thermosyphoning system it is not as important since there is a negative feedback in that faster flowing channels heat up less, causing the flow rate to decrease, while slower moving channels heat up more causing the flow rate to increase.

[lucastro]

  I am a plastics fabricator and had a similar idea a while back.. Great to see it works! I would, however, strongly recommend using a polycarbonate twin wall (coreflute) sheet instead of what is used for signage. It can be bought in varying thicknesses and has a UV protective coating. also being polycarb, it will resist higher temperatures and be alot stronger... What I had in mind was to use twinwall as not only the water 'membrane' but as the insulation as well, laminated together 'cross ply' front and back to make it super strong... you can also buy capping for these sheets that will perform the same function as your 'c' tubes. Nice work!

[Sandisk1duo]

wouldn't it be better if you painted the collector black?

[iwilltry]

It is painted black. See Page 3, item 17. You can also see it painted in one of the images on Page 4.

[Sandisk1duo]

sorry i didn't notice that

[adrian.ccs]

Hi iwilltry, thanks for the guide but one question, is the corrugated panel double so that water pass right through it??? or how does this work?

[iwilltry]

The corrugated panel has square channels that run through it so water can pass right through.

[vinyard]

Where do you get the corrugated plastic sheet?

[iwilltry]

I got mine from Home Depot. $17 for an 8' x 4' sheet.

[madrasi]

If you are worried about it springing a leak there is an easy fix for that. Since it fits inside the rafters you could build a box around it using some old car tire tubes, cut them up to where you can line the inside of the box with them since you can glue them together to fit your need. Then put in a big enough hose to drain the water to an outlet of your choosing,maybe to the gutter system. From there you can put in a on/off valve just before it turns to go out through the roof. All you need is a few more 2x4's and plywood which you might already have and the inner tubes should be free from the junk yard and your still doing it all on the cheap. Good luck

[davey703]

I've been planing on doing this ideas myself with a car radiator, I'm just a bit confused about the thermo siphoning, or how it is judged, in your design once inplaced at its angle, is the cold water feed entering from the top or the bottom??

[iwilltry]

The cold water should exit from the bottom of the storage container and feed into the bottom of your collector (radiator in your case). The hot water should exit the top of your collector and feed into the top of the storage container. The collector should be lower than the storage container for effective thermo-syphoning.

[davey703]

I'm using a car radiator, a small copper cylinder and extension tank(if the water overheats) all connected by copper pipes, what would be the main causes if the system doesn't work, or the thermo-siphoning doesn't work....in diagram 1 to 10

[iwilltry]

Without seeing how you've set up your system, it's difficult to say, but the usual cause of thermo-siphoning issues are:

• air locks
• collector not low enough relative to storage tank
• connecting tubes not large enough in diameter
• connecting tubes not providing a continuously rising (for hot tube) or continuously falling (for cold tube) path for the water to follow
  

I don't know what diagrams you are referring to.

[bi018792]

great idea."i will try" one myself

[UK_Westy]

If the storage container was below the height of the solar collector, I assume a pump could be used to pump it back up to the top and let gravity take it's cause ? Do you think a drill pump fitted to a rechargable hand drill running off a solar panel work ?

[iwilltry]

Yes. It is usually much more convenient for the solar collector to be mounted higher than the storage container. Therefore a pump must be used to circulate the water. A drill pump may work, but I don't know if they are designed for continuous duty, and I don't think they are very efficient (ie you may require a bigger solar panel than you think). If you have access to AC power, I would recommend using that instead of adding photovoltaics. You might try an AC aquarium pump or a sump pump. But then you either have to turn it on and off manually, or design a thermostat to turn it on when the collector is hotter than the storage container.

[UK_Westy]

Hi, This is great I have been looking at using solar power to heat water for a child's paddling pool. Basically, heat water one day and use the following. I was thinking of using a solar powered pump, but thermo-siphoning costs nothing ! If I used a double glazed unit (I have a couple lying around) instead of the plastic sheeting would this create too much heat and indeed melt the corrugated plastic sheeting ? Also, if the system was plumbed into a supply and as water was drained out, and fresh water replaced by the use of a ball valve, if the whole system was at an angle as you suggested when filling, wouldn't it enable the air to be removed constantly ?

[iwilltry]

If you use double glazing you probably will get too hot for the plastic parts inside. It is possible to design a system that will expel air automatically. You simply need to ensure that at any point in the system there is a path that rises continuously from there to the highest point (highest water level) in the system, and that the highest point is the surface of the water in the storage container which is exposed to the atmosphere. For me that would have meant drilling holes in the side of my cooler (one at the bottom for the exit and one at the top for the inlet). Then air bubbles would simply rise through the system and be released to the atmosphere. I did not want to drill holes in my cooler so I opted to bring the exit and inlet tubes in from the top which introduces the problem of trapping air and makes it necessary to take steps to remove the air in order to get thermo-syphoning to work.

[onebitpixel]

I wonder if this could this be utilized within a pool system that would help keep it heated as well as filtering... while it is moving through the hose and through the filter assembly...

[AbelK89]

I'm been planning on trying this idea... and will post any ideas upon trying.

[Jalloy]

(removed by author or community request)

[iwilltry]

Hi Jalloy,
You are welcome to add it. If you like, please also check my website www.iwilltry.org where I have some other solar projects. Cheers.

[dasdew2]

WHAT DO I NEED

[leebryuk]

I had looked into installing a skylight collector into my home in Florida. The insurance company stated that if I did so I would loose my homeowners insurance. That whole hurricane (wind and water) business. I would love to put an above the roof collector. It takes no time at all to heat to a blistering temp. I've also seen systems that use a glycol (antifreeze) exchange system for greater efficiency. Fun project though. As an aside, Saab's old 95 and 96 models used thermo-syphoning for many years to cool the car's engine. Cheap and easy.

[poe622524]

Dear Sir I don't understand What are the reason for the Insurance company to do this, why ?

[CyberBill]

Skylights (made of thin plastic) are considerably weaker than a 1/8 - 1/4" piece of plywood. In a hurricane they'll rip right open, and you'll end up with a very messy inside!

[Bullmoose]

Awesome Article! Thanks! What kind of plastic is the panel? I wonder if it's one of those types that leeches poisonous chemicals into the water. Not a problem though if one were to use a heat exchanger rather than attempting to directly heat the potable water. Also, how long do you think it will take for the plastic to breakdown, turn brittle, start leaking, etc...? Keep it up.. This is great stuff!

[iwilltry]

Much of that information can be found on my own website IWillTry.org. Scroll down to the comments where there is some discussion of materials and lifetime. Thanks. -Rob

[Tom the Tinker]

This is just what I am looking for to heat a greenhouse, to supply us with winter salad greens.

[kas83]

any ideas how to convert this cheaply to an electricity?

[WTHAI]

You could build a few Stirling engines. there's an instructable on here somewhere about how to build one.

[WonderWheeler]

Fafco or Fabco made solar pool collectors before about 1977 with the square water channels. It used some kind of Polyethylene (PE) I believe. It was based on plastic corrugated boxes the inventor saw in Japan. They then changed to a similar design with round channels. They apparently held up better to thermal stresses and pressure and were easier to repair when there was a puncture. Standard panel size was 4'x10'. I acted as contractor installing a dozen systems about 1979.

[zdbrad]

I spoke with Rob back in the winter and since then, I've been messing with this. I purchased a sheet of 1/8" black coroplast and the consistent problem I've been having is keeping it from leaking. I finally bought a tube of Lexel (it's supposed to adhere to polyethelene and abs) and so far, it's doing ok... except right where the edge/end of the coroplast slides into the abs caps. Still a few drips there but I'm doing some patching today. To put this to use as a hot tub heater, I'll need to put this panel higher than the tub, which I think means I'll need a pump. I'm a little concerned whether the Lexel may be too elastic and will not be able to hold against the pressure of a pump though. Does anyone have any opinion on that? Someone had suggested I just use Gorilla Glue for it all... maybe on my next try. Also, based on what Rob wrote on May 3, it may be best if I don't put the panels in an enclosure and just lay them (it) out, as is, on the roof. Which brings me to another question. If the coldwater in is lower than the water surface of the tub and the hotwater out is higher than the water surface, will it still themosyphon? What about if the panel is mounted sideways instead of lengthwise... still with the hot out at the top... will it thermosyphon? Lastly, since I don't know how to tie this into the pump/water system of the hot tub, I'll need to just stick the hoses in the top under the cover... and hope I don't lose the heat I'm trying to bring in! btw, I did put the in and out on opposite sides of the panel.

[iwilltry]

It was quite a chore getting a leak free system on my first panel too. I had best results with a product called Goop. If you mount the panel higher than the tub, and have a closed system (no leaks, no air in the system and both inlet and outlet hoses submerged in the tub), then the pressure in the panel will actually be negative. Imagine for example, that you now poke a hole in the panel in this configuration. The hole will leak air into the panel rather than leaking water out of the panel. If you add a small aquarium pump to circulate the water, it's unlikely you will increase the pressure much. You won't likely get thermosyphoning unless you can get the entire panel below the surface of the water in the tub. And unless you can mount the panel several feet lower than the tub, a small aquarium pump will probably give a higher flow rate. Good luck. Would love to see some pictures of your panel.

[paborralho]

Congratulations! I Hope it lasts more than mine. Sure it will "boil", once you put it behind a glass. 2 Years ago I tried a similar one with policarbonate (supports up to 180°C), and PVC (not suitable for hot water). With glass glazing I had nearly 1000W/m2. It is really great, because the plastic is very thin and heats the water fast. Although, I had problems with the PVC and the silicone adhesive. Finally I got back to Air to Water Heating, Not so efficient but more reliable. Keep Going Paulo Borralho "There are lots of Yesterdays and Tomorrows"

[bladetiff]

This seemed like a really understandable project but how do I get use of the water and would it be possible to use this to get hot water into inground pool to extend the pool season a little on each end

[iwilltry]

This type of panel should work well for pool heating. In the case of an in ground pool, the panels must be located higher than the pool, so you must use a pump to circulate water through them. You won't be able to rely on thermo-syphoning. Depending on the size of the pool you may need a lot of panels to see a significant result. Because water won't flow with the pump turned off, it will be easier for the panels to overheat and possibly melt. Therefore, I would recommend not to install the panels in an insulated frame with transparent cover. Just lay them directly on a roof or some surface exposed to the sun.

[GregorN]

Nice one! I liked!

[fegundez1]

I would suggest adding a couple of ball valves to the ends,they are cheap and would be effective for working on the unit.Also the collector looks a lot like the solar pool heater panels i have seen here in sunny Fla. I was thinking of trying something like this using some old ones but wouldn't adding a small pump/switch setup make it so you could recirculate the water so you would have a good supply?Plumbing it to a 30 gal tank in the house would be great,but how would you know when to turn on/off water to keep it operating right without some kind of small recirculation?

[iwilltry]

There's a reason the title of this instructable is "Build your own solar thermal collector" and not "Build your own solar thermal system". My intent was building and testing the collector itself, so I included only a minimum of additional components to do just that. If this was to be installed as a thermo-syphoning system, the only additional component needed would be some kind of check valve to prevent water circulation in the opposite direction when the collector is cooler than the tank. You would also need to ensure the tank was located higher than the panel which is not usually feasible for rooftop installation. Piping also needs to be quite large in order to ensure adequate flow in thermo-syphoning systems. Using a pump to circulate the water is more effective and this is my intent in the final installation. The pump can be powered off a small solar PV panel (thus it would operate only when there was useful heat to transfer). This is becoming the most common method in commercial systems. The alternative is to have a temperature sensor in the tank and in the panel and operate the pump whenever the panel is warmer than the tank.

[brbellard]

Has anyone thought of building a closed system that is charged with C02. The carbon dioxide gas will retain more heat in a closed system than a air filled system.

[brbellard]

I have built a system using the tank out of an old water heater (painted black) and used a wood box lined with sheet metal. I topped it off with a heavy glass and installed a bicycle value to suck air out one end and fill the other with C02. It seems to work well.

[iwilltry]

Another benefit of using a pump is you can use a "drain-back" tank and keep your panel and piping empty except when the pump is on. When you turn the pump off, all the water drains out of your panels into the drain-back tank. This is a good precaution against leaks since the panel is much more likely to spring a leak than your piping or the drain-back tank. If you can find a self-priming pump with enough suction, you can put it in the exit pipe from the panel instead of in the inlet pipe. That ensures that the water in your panel will always be at a lower pressure than the surrounding air, so if you develop a leak, you will draw air into the panel instead of spraying water out of it.

[ivanbg]

How can I make such a device to provide for the entire house.

[iwilltry]

That's a topic on which several books have been written. I would highly recommend reading up on the subject. A few key points: 1. Solar thermal panels like this work well in combination with radiant floor heating. The panels are used to heat up an insulated storage tank. Fluid is pumped from the tank through pipes under the floor to heat the home. 2. I would not recommend this particular design for permanent installation. It is not robust enough. 3. It's not usually cost effective to build an array and storage tank large enough to provide ALL of a home's heating needs (depending on location). Solar heating is almost always used as a supplemental system.

[stone1716]

I am new to the site. I make signs, like you talked about. So this is very interesting to me. You can also purchase 10mm corplast in black (I pay $24 US, for 4'x8') instead of 3mm white. Some of the corplast signs we have used, have withstood 24/7 weather conditions, for 4 + years now. They are the 3mm type, the 10mm should last much longer. They are not only thicker in width but the pvc walls are thicker also. The corrugations are larger too (do not know how that would effect the heat ratio? and if it would out-way the life of replacement?). I will be testing the project in the near future, I have to admit complete ignorance, as to how to determine any effenciency?

[iwilltry]

A 10mm panel should work just as well as a 3mm panel. The main consideration is heat loss which is roughly proportional to panel surface area. Changing the thickness from 3mm to 10mm doesn't significantly increase the surface area so it should have little effect. It may even perform better because the wider channels may result in a higher thermo-syphon flow rate. However, it would be over 3 times heavier when filled with water so it would need to be well supported.

[vksalian]

Can anyone tell me how to circulate water in open solar water heater, in which the 2 pipes from solar collector are directly immersed in open tank containing water, which has to be heated. I dont want to use any water pumps. Please suggest....

[fieldman]

Total avoidance of pumps requires that your collection system is thermosyphon. That is, the storage tank for heating is at a higher level than your collector. In practical terms this means that a pipe from your collector goes from the top of your collector to the top of your heat exchanger (say a tank of some sort) The return pipe goes from the bottom of the storage tank to the bottom of the collector. Inside the storage tank is a coil of copper pipe or other appropriate heat exchanger. This is in series with your hot water system.

[fieldman]

If the collector is on a first floor porch and transfers heat to a second floor collector and you recover this heat through a heat exchanger in the second floor receiver. Your scenario must be reversed. To be on the safe side the usable water should be at a higher pressure than the heat exchanger water. IOW the collector should be a separate system and have a means of collecting the heat from it for your use.

[iwilltry]

Whether water flows in and out of the storage tank itself, or just flows through a tube inside the storage tank makes little difference. If you don't want to use a pump, just make sure the point at which you remove heat (the tank) is higher than the point at which you add heat (the collector). Then thermosyphoning should happen automatically as long as you have no air in the pipes. The higher the tank is above the collector, the higher your flow rate will be. Flow rate will depend on a number of other factors as well (ex pipe length and diameter and temperature difference between tank and collector).

[fieldman]

And that says it all.

[vksalian]

Ok thanks. Now i will try to get ideas about how to remove air from pipes. Actually i am trying to build a solar water heater with very low cost. If the above idea succeeds, then i can eliminate the usage of storage tank (which adds to cost of the heater). I want to heat the water directly in the bucket itself, by putting inlet and outlet pipes of collector into the bucket which contains water.

[Kiteman]

That's an excellent design solution. I think you can get similar, thinner sheets of the plastic that is already darkened (you can certainly get thinner sheets that are coloured, but they are usually smaller, for craft work). I especially like the idea of installing it under an existing transparent roof - that would be a trick many people could use to get round planning regulations. My in-laws' conservatory has a roof made of sheets like this, but around 3/4 inch thick - depending on the strength of the sheets and walls, your idea could be incorporated into such roofs with relative ease, I suspect. Even leaving the sheet transparent, there would be quite a warming from the air trapped within the conservatory.

[iwilltry]

I know that there are black plastic corrugated sheets manufactured somewhere since I've seen them used for signs. Clear and white were the only ones available at Home Depot, though, so that's what I used. It would be nice to find a panel made of ABS. Then ABS cement could be used for all the joints which would be much stronger than the silicone adhesive. I think that installing something like this under an existing solid roof would still capture quite a bit of heat. I haven't done the math but I'd guess you would achieve on the order of 20% efficiency. As the roof heats up it would radiate almost equally from either side, but convective transfer would be much higher from the top side.

[vksalian]

Can you please tell me whether it is possible to circulate water within an open system solar water heater. eg: The 2 pipes from collector are immersed in an open tank containing water. please help...

[das300]

This can be improved but its a great idea. I have seen one in youtube that uses a felt material and black building plastic to cover the felt and then plastic corrugated sheet over it making it very applicable for a roof. you can adapt that design into this one to make improvements as well as some safety adds in case it over heats or leaks ( gutter system under plastic using building plastic and a lower gutter ) . Well done though ..

[Leroy]

I've been reading instructables for several years now. Yours is the best so far. Thanks for posting it. Everybody who lives in California should make one of these right now.

[pangavamanos]

Wow! I sure enjoyed your project. Has me thinking of ideas for my on test. BTW Wasn't glazing over. Didn't understand it all but that is ok. Learned a ton. Thanks JL

[Mur]

Whilst replacing my car's air filter I thought: How would old car radiator's, perhaps linked together, differ from the older copper pipe and fin design or the corrugated plastic?

[iwilltry]

Car radiators would probably work, and might be a good option if you can get them for free, but remember, you're trying to absorb energy from radiation, not convection, so having fins oriented in a single plane perpendicular to incident sunlight is more ideal. The fins of a radiator would tend to shade each other, so it is not an efficient use of material. However, as long as no sunlight passes directly through the radiator, it should still absorb well, and since the path from fin to water is short, it should transfer heat well. All of this is just my best guess.

[hassi]

Maybe run the heated water from the Cloroplast (tm) collector through the radiator. The pass air through the radiator; might provide some daytime heating... Just a thought...

[icarson]

As a sign builder, the black coroplast would be better choice, as one of the properties of coroplast resistant. so unless you use specific paint using a solvent it will not bond all that well. I just got a sample of 16mil coroplast (5/8") and will build a test bed .It should have much longer life span as walls are much thicker. The major drawback is life span. In direct sunlight, and that is what you want for heat, they typically last 2-3 year before they start to decay. I would not wish to replace them that often, so copper although more expensive is more reliable. Good article, as it sparked some ideas

[hassi]

This collector is a great application. Maybe "industry" will come up with a UV-resistant "coroplast?" Super Instructable...Keep us informed...

[icarson]

should have been :as one of the properties of coroplast is chemical resistance

[walusimbi]

I am thinking of moving to uganda and I am in the process of building a house there. It was when I was on holiday there last month when I noticed the water in the watering pipe got very hot through the day. I will be very interested to know how it's working after you install it in your home

[antar]

I live in Mexico. Have a 15,000-gallon pool and built and inexpensive solar water heater by placing in a circular serpentine shape 600 meters of 3/4 inch black poliduct (not sure how you call this in the States). It is a very thick-walled black hose used to run water either underground or above ground. I connected it to the pool´s 0.75 Horse power pump. The water comes out of the poliduct at about 37 degrees Celsius, but I loose a lot of flow rate by the time the water get´s back to the pool. I suspect because of this the system is not very efficient at this time of the year. Even when I operate the pump from 10 am to 5 pm the pool water doens´t go beyond 25 degrees celsius. It was at 20 Celsius before installing this system. I have a blue thermal cover on the pool. I don´t know what to do to make it work better. After reading some of the comments on your project I thought about converting it into a parallel collector using 1 inch PVC pipe on the top and the bottom and 4 or perhaps 6 100-meter-segments of this serpentine 3/4 inch hose(poliducto)as the network of parallel pipes connected to the i inch PVC. Do you believe it would help? Do you have any ideas? Thanks in advance for your help...Antar

[iwilltry]

Breaking your tubes into parallel segments should give a huge improvement. In theory you should get 2x the flow rate if you use two 300 meter sections in parallel. You should get 4x the flow rate if you use four 150m tubes in parallel. You should get 6x the flow rate if you use six 100m sections in parallel. 6x the flow rate doesn't necessarily mean 6x the heat transfer though since the water has less time to heat up and will come out at a lower temperature, but it will likely be a huge improvement. Good luck and please post back and let me know how it works out.

[antar]

Great news. Thank you for your quick reply! I´ll start tomorrow and certainly will post the results next week. What do you believe is better to use for the header PVC pipe: 1.5 or 1 inch? Remember the hose is 3/4 inch. Or if you believe the polidcut hose should be any other diameter, please let me know. I can still exchange it at Home Depot (yes Home Depot recently opened stores in Mexico). Also, as a way of improving temperature and hopefully efficiency, I thought about alternating in parallel the serpentine poliduct and lines (just straight tube, no serpentine)of either 3/4 or 1/2 inch copper tubing. So the panel would consist of three 200m sections of poliduct loops alternating with three straight copper tubes of whatever length it takes between headers. I know this could add up to the cost, but if you believe it would help substantially I would do it. I hope this is not too confusing. Any other ideas for improvement are welcomed.

[iwilltry]

Hi antar, I'll send you a private message to discuss the design, then we can post the results back here after you try it out.

[LordGarion]

In Arizona they take a lot of black garden hose and connect them all together stick them in the pool in a way that all the air is removed from the hose, cap each end then run it up on the roof of the house in a zig-zag pattern then run it back to the pool. Then put both ends under water and uncap them and siphon from one end. After you get it flowing it should continue on it's on as long as you keep the "intake" end well under water. Not sure if it will get as hot as this way but it doesn't need any power to run and it eliminates the need to nail through shingles(never a good idea if it can be helped)

[iwilltry]

I've heard of people using black garden hose in this manner for very cheap (though somewhat inefficient) solar heating. However, based on everything I've read and my own experiments, I'm quite certain that the system you described would not thermo-syphon. In order for thermo-syphoning to work, the heat input (the hose) must be located lower than the cold supply (the pool). Thermo-syphoning happens because of an imbalance in water density on one side of a closed loop system compared to the other side causing water to flow in a direction such that the density imbalance is sustained. This won't happen with the heat source higher than the cold supply because whatever direction you start the flow, the density imbalance created will tend to force the flow back in the opposite direction. To illustrate the point: Imagine a circle of tubing full of water with a heat source at the bottom and a cold source at the top. Suppose you start the water flowing clockwise. The left side will get hot and the right side will get cold. Thus the left side, being less dense, will rise and the right side, being more dense, will sink. The density imbalance acts to keep the water flowing clockwise, so it will continue to circulate by itself. Now repeat with the heat source at the top and the cold source at the bottom. You start the water flowing clockwise. The right side gets hot and the left side gets cold. The density imbalance drives the flow counter-clockwise (opposite to the initial direction) so the flow will not self-sustain. OK, so start the flow counterclockwise instead. The left side gets hot and the right side gets cold. Now the density imbalance drives the flow clockwise (again opposite to the initial direction) so the flow will not self-sustain. Thus the heat input MUST be lower than the cold supply in order for thermo-syphoning to take place. Otherwise a pump is required to circulate the water. All solar pool heaters I've ever seen use a pump. I agree that nailing into shingles is best avoided, but how do you fasten a hose to a roof in a zigzag pattern without nailing into the shingles? And if there is a method of doing so, couldn't you do the same with a flat panel? I'm not planning on mounting panels to the outside surface of my roof at all. I'm installing clear polycarbonate panels in a south facing section of my un-insulated attic. I'll be installing the solar collectors on the underside of the roof (between rafters), so no nailing into shingles will be required.

[icarson]

It late so might not be processing this correctly

. In your "thermal conductance of a typical flat panel collector." your calculation of 25 watts for the fins. I got, but you did not do the tube itself. 4 .25" tubs that are 4 mm thick would greatly increase the efficiency.

0.4 W/mm/degreeC * 7741.92 mm2 (6.35 mm wide x 304.8 mm long *4 qty) /4 mm = 774.19W/degreeC.

Which would make the copper 799 w/ degreeC

Really tire so might be out of my head, but seems correct.

[iwilltry]

Interesting point I had not considered that. You are right about the tube walls having a high conductance, but the heat still has to get to the tube wall before it can be conducted to the water inside. The amount of sunlight that would hit the tubes directly is less than 1/20 of the sunlight that hits the fins (assuming 1/4" tubes and 3" fins). So 1/20 of the total energy received could be conducted directly into the water directly while the remainder would have to be conducted through the fins. If you could fill the panel with all tubes and no fins then you'd be rockin'. There is another heat transfer mechanism at work in tube and fin designs which is the fins heating up the air in the panel and the air heating up the tubes. I suspect this convective heat transfer is actually the dominant mode of heat transfer in tube and fin type panels, even though they may be designed for heat transfer by conduction, not convection.

[LinuxH4x0r]

Iwilltyr this! My idea was to run hoses through your driveway (think reverse radiant floor heating). Your driveway also has the advantage of retaining heat (heat mass) at night. The thicker the driveway, the more heat it will hold. I'm currently in arental house, but after I start building my house I will try this. Nice instructable, and good luck with the solar.

[conductor_AJ]

I figured I would just put male garden hose connectors on all four corners then make "unions" out of short pieces of hose with female ends and cap off the ones not used. That way I would be able to run them in a series.

[linmar]

You can in theory connect these sort of panels in series or parallel. The trouble with series is that you have the outlet of one panel feeding in to the next. This means that the second panel is operating at higher temperature and will have greater heat losses to the surroundings and therefore won't be as efficient. With parallel flow, the flow is split (equally if you set it up properly) to each panel and the water is essentially going through a single pass. Again, like in the series system there is a limit to the temperature level that can be achieved. If more panels are added, the flow is split over more panels which means that the speed of flow through each panel is slower and therefore the water is in the panel for longer and able to absorb more energy, however it will reach a limit. With enough sun and the panels insulated sufficiently the water may reach boiling at which point it just won't get hotter. (Yes if you were to pressurise the system it could work like a car radiator system but realistically other limitations are going to kick in before then for these systems we are talking about). The most likely limit will be below boiling where the panel temperature is reached where the heat losses from the panel to the surroundings matches the heat gained from the sun input. If you were to graph the outlet temperature from a panel you would find that it would eventually reach a limit where the water coming out would not become any hotter now matter slow the flow through the panel. This temperature/flow limit is a function of the insulation of the panel shell and glazing as well as how efficient it is at picking up the solar energy input. This is probably more to do with a pumped system but the same limitations will exist in a thermosyphon system as well.

[linmar]

Kudos to you for having built it. One thing to note is that you will get better efficiency from the panel if the inlet and outlet pipes are at opposite corners. This will give a balanced flow for all the tubes in the panel. With the inlet and outlet on the same side (ie near the icebox/table in the picture) the the tubes in the panel nearest the inlet and outlets will be receiving more flow than those further away. This will be reducing you efficiency of the panel. I've considered use of this same panel but it was the issues of sealing the header tubes to the panel so I've instead headed in the direction of using 20mm or 40mm PVC pipe. I'm after a long term installation for my pool heating so I'm prepared to pay the extra for the PVC and not have the issues with leaks etc in the future.

[iwilltry]

Good point about putting the inlet and outlet nipples on opposite corners. I should have done that. It's not as important in a thermo-syphoning system since the flow rates have a tendency to balance naturally (i.e. a slow channel will heat up more, making the water in that channel less dense, which will tend to increase the flow rate in that channel) but it will still have an effect. If an external pump is used, then placing inlet and exit tubes on opposite corners becomes even more important. I suppose I could get an idea of how even the flow rates are across all channels by measure the variation in surface temperature over the whole panel during operation. The hotter the panel, the slower the channel.

[linmar]

It will still help even for a thermosyphon system but as you say the flows will be so slow anyway. Even so if the inlet and outlet are on the same side the length of the flow paths will not be the same and this will affect the flows. That is, the flows nearest the inlet/outlet side will have a shorter path, resulting in a lower friction loss and therefore greater flow. The fact that the header you are using is significantly larger than the 'tubes' in the panel probably negates this as the flow losses along the header won't be significant. I'm not so sure that the small change in density will that you are talking about will offset this but then this is getting a bit of an academic exercise for a trial system like this. For my final install, it is a pumped system and I'm after each little bit I can squeeze out it. My first trial system used some old solar water heating panels (picked up second hand) that I gutted for the aluminium shell and glass cover. I new it wasn't a long term installation but I tried some coils of black irrigation spreadout in each panel (five installed). It all worked fined until the water flow was stopped and the heat inside the panels melted the tubing. These were way too efficient for what I wanted to heat a pool and using copper or metal tube with the pool (salt) water would be be a longterm solution.

[linmar]

Just to add to my last comment. For my system of a pool heating system I DO NOT want higher temperatures (because of the risk of scalding swimmers) so my arrangement has no glass (or other transpartent) cover. This sort of cover to provide additional insulation is only warranted where the panel temperatures are quite high and the heat losses to the surrounding air would be too high. For pool type water heaters the temps aren't that high and the efficiency isn't usually that critical. I live in the tropics and have had a length of water filled PVC pipe (painted flat black) on the roof for months just to make sure it would stand up to the temperatures my system would need. For those who are interested there is a better option than ABS. ABS is actually only marginally better than PVC at increased temperatures and from what I've looked at costs a whole lot more. (As my system is looking at about 300m of 40mm PVC then cost is an issue for me). There is a type of PVC called "Chlorinated PVC" sometimes referred to PVC-C or C-PVC that has much higher temperature ratings. C-PVC is actually good for domestic hot water service straight from a standard hotwater system so I expect the panel material would become an issue before then. C-PVC was about the same cost as ABS last time I used it. C-PVC has it's own glues but since this and the ABS glues are designed to bond with the C-PVC or ABS then I'm not sure how they would bond with the panel material since this is a different material.

[Truik]

Wow! I have been looking at the instructables for solar thermal panels and this one really makes a lot of sense. That is one cool design! I was wondering...I always see these ingenious solar thermal designs but they always rely on creating a suction hose into a cooler and I wonder about the practical application of the completed product. I want to add a small pump to slowly draw the water through the solar thermal panel and power it using a solar photovoltaic panel I just happen to have waiting for just such a project. I would ultimately like to have the thermal collector hooked directly into my existing water supply and have it feed to a tankless water heater in my house. The idea being the tankless water heater would only have to heat the water from whatever its "input temperature" is at the moment to its desired output temperature. If the water came from the thermal collector instead of the city water supply, it would expend less electricity since it would have to raise the temperature far less since it was already coming in warm from the solar collector. Any thoughts on how to connect everything and make it work?

[iwilltry]

A cooler is just a practical insulated tank for testing collector performance. It's clearly NOT a reasonable choice for final installation. For final installation, a good choice would be to install a Solar Wand heat exchanger into a non-powered hot water tank prior to your tankless heater. The solar wand inserts into the tank's existing fittings and gives you an input and output tube you can connect in series with a pump and collector. A cheaper option if you only want hot water at a particular time of day is to nix the tankless heater all-together, and run an electric tank (with solar wand) on a timer. Most of the time the tank is heated by solar, but the timer is programmed to power the tank (boosting it to operating temperature) an hour or so before you need it each day. Note that whichever system you choose, it will be even more efficient if you shower in the evening (after heating all day from solar) instead of the morning (after cooling down all night).

[conductor_AJ]

Excellent!!! I have a stack of that sign material THREE FEET HIGH. I'll be making swimming pool heaters!!!

[dolanbaker]

Hi, I have been thinking about doing something similar for a few months now - since the elections here and seeing thousands of these corrugated plastic posters.

Well, today I finally got around to buying a sheet of black corrugated plastic and was thinking about how to connect the ends to some PEX pipe I have.

Then I saw this site, you beat me to it ;-)

Its great to see that it works as well as hoped it would, I can now build with confidence.
Coroplasthttp://coroplast.cat-x.net/CategoryListView.aspx?id=1 is the material you are looking for and is available in black.

[iwilltry]

Great. Thanks for the link. I'll have to get some in black and try it out.

[pollag]

transparent cover? Would very thick or very thin glass be better for performance? What do u guys think?

[iwilltry]

Glass itself is a poor insulator. It is the boundary layer of air next to the glass (or between the glass panes in the case of a double-paned setup) that does the insulating. Therefore, performance should not be affected much by the thickness of the glass. Use what is most economical while still strong enough not to break easily. Transparent polycarbonate roofing sheets such as SunTuf often used for greenhouses may be a better choice than glass. This is what I will be using for the roofing above my panels in the final installation. Don't use transparent PVC roofing panels though. They won't take the heat.

[p07gbar]

That is sooo clever

[oilman]

I plan to build a rig somewhat of the type you have done. Thanks for validating some of my ideas and giving me some new ones. One idea I had was not to paint anything black. The paint acts as an insulator as does the plastic. My design is to use a clear acrylic sheet on top of a wooden waterproofed frame. The liquid (water & denatured alchohol) will be dyed black so that the first absorbtion of sunlight will be to the liquid itself. The dyed water will then run through a baseboard to heat the interior of my house or to a heat exchanger to pre-heat & heat hot water. I might have to se a small pump to keep the fluid moving but hopefully I can do all of that using good old gravity.

[iwilltry]

Sounds interesting. I would love to see your results. Will you post it as an instructable?

[horape]

Thanks for your answer. How critical are the dimensions? Ie, would any shape with the same area work similarly or there is some important relations on the size? (I'll need something like this on a remote area were I'm moving to, I'll have no electrical power so I'd like to make it here, and a square collector would be lots easier to fit on the car) Other question, it seems that ABS tubing is not available in this country. I'm offered Termofusion (Polypropylene Random Type 3), PVC (you said no good), Polyethylene, and Polypropylene. What would you suggest? Thanks!

[iwilltry]

The dimensions are not critical. Only the area. If you are going to rely on thermo-syphoning alone, a wider and shorter panel (ex 4ftx4ft) would be better. This will decrease resistance to water flow and thus increase the flow rate.

As for all those plastics, your guess is as good as mine. I found this site that lists the "Vicat softening temperature" of some of those plastics. PVC may work OK if you make proper allowances for thermal expansion and ensure that there is as little force as possible acting on the tube while it is in a softened state.

[horape]

Would this work "for real"? Ie, would this collector connected to an insulated 200lts or so tank be comparable to a commercial system? Are commercial systems good enough to rely on them for domestic hot water? (BTW, I'll be living soon on a almost-ever sunny place, so I think that if they're good somewhere, they should be good there) Thanks!

[iwilltry]

Yes, this would work for real. In my experiment it took about 1 hour to heat 20 litres of water by 23°C. Therefore it would take about 10 hours to heat 200 litres by the same amount. This would be comparable in power output to a commercial unit, but likely not comparable in durability. A commercial system would be less likely to leak, and would be more tolerant of severe weather conditions, UV damage, etc. If installed under existing transparent roofing as I intend to do, UV is the only real concern. I'm not certain how it will hold up over time, but it is simple enough to build that I'm willing to give it a shot.

[iwilltry]

As for the reliability of commercial systems, as far as I know, they can be as reliable as the sun. If you're lucky enough to have direct sunlight year round then you're set. Before natural gas and electricity became widespread, solar water heaters were much more common than they are now. This is long proven technology that simply faded away because fossil fuels were cheap and more reliable.

[WyldStyl3]

Slightly off topic, but how about an instructable on how to make a table saw similar to the one you have made? That is a great idea!

[iwilltry]

It's on the list. Sooner or later it will be up. Thanks for the comment.

[iwilltry]

A further note on material choice. I tried using PVC (polyvinyl chloride) tubing in an early prototype. It is available in 1" diameter which seemed more convenient, but it softened and buckled (I also hadn't allowed enough room for thermal expansion), ripping the glued seam wide open. Later I looked up the specs for ABS and PVC and found that the usable temperature range for ABS extends about 20 degrees C higher than PVC. Therefore I don't recommend using PVC tubing.

[cheordinario]

great, the design, the maths. i'll do one. what's ABS material you wrote above?

[iwilltry]

I was just saying it would be nice if you could find a corrugated plastic sheet made of ABS (Acrylonitrile butadiene styrene) which is the same material the tubing is made of. Then you could use ABS cement to bond them which forms a very strong bond, as if it were a single piece. I wasn't able to find any corrugated sheets made of ABS (though I didn't look very hard) so I used what was available. Incidently, the silicone adhesive that I used in this instructable didn't form a very strong bond. It is more of a sealant than an adhesive. I have also tried GOOP before and that worked better than the silicone sealant I tried this time. I recommend experimenting with some different adhesives on sample pieces to see what works best.