Saturday, August 8, 2009

Matt's "$1K" Solar Water Heating System

This is Matt's version of the $1K type solar water
heating system.  Matt tried a few new things that might be just what you
are looking for.  One of Matt's innovations is what might be the worlds
first bicycle powered groove forming machine!

Matt is a very good craftsman, and
provides a wealth of interesting alternative ways of making the components.


Some of the unique features of Matt's

- A unique forming machine to
form the groove in the aluminum fins.

- A new method of attaching the fins to the copper tubes.


- A copper heat exchanger that
uses 6 parallel coils of 3/8 inch copper pipe.


- a galvanized metal collector


- A steel tank instead of the
EPDM lined plywood tank.

- Glass for glazing instead of polycarbonate.

Thanks very much to Matt for taking
the time to document this project!

All the details on Matt's system here...

For those who have not seen it, the $1K Solar Water Heating system aims at providing a quality solar water heating system with a high solar fraction that is simple and easy to build and will work in cold climates.
All the details on the $1K system here...

More examples of $1K systems here...


  1. The groove forming machine is very innovative! But how could you do that to a vintage banana seat bike? ;-)
    Using steel in stead of wood is a good idea. I've started building a hot air collector (Wayne Langille's design) using steel studs. I never thought to use just the track, but it makes perfect sense. Steel is cheaper than wood and around here most of the wood we can buy had leaves on it last week!
    I thought about a similar method of attaching the fins to the copper risers. I figure to rivet a full 4" wide length of aluminium to the back formed fin. It might cost a bit more, but no staples or wood next to the hot metal and it provides a tiny bit more thermal mass.
    Great job!

  2. Hi Rowland,
    I like a lot of what Matt has done. On the connection of the tube to the fin, I think that what you really want is lots of heat transfer area (ie have the fin wrap as much of the tube as possible), and a very thin to no gap at all between the aluminum and the copper. I guess that I still like the groove that wraps the tube all the way down to the backing board plane, and then the 2nd strip of aluminum under the tube. This basically wraps the tube 360 degrees, and the staples really pull the the aluminum tightly down to the copper and make the gap very thin.
    By the time the staples are in place, you just can't see any space at all between the fin and tube, and the silicone acts as an adhesive to make sure that the gap stays that way forever. The small panel tests shows only a 4% drop in heat output for this vs a copper fin soldered to the copper tube, so, to me, its demonstrated that it performs well.
    It seems like the 4 inch wide strip riveted to the back of the fin could work well, but I think that some kind of tool to force close contact of the two pieces of aluminum to the tube and hold it there while riveting would be needed to avoid gaps that would be heat transfer road blocks.
    It would be nice to do a small panel test to compare the several methods (Matt's, Kevin's, Woodsy's, and mine) to see which actually performs better -- any volunteers?
    Adding thermal mass to collectors is not a good thing -- they do better with less thermal mass. To me, this is the biggest disadvantage of the plywood backing board -- it adds mass to the collector.

  3. I like what Matt has done here! The roll forming is something I was told to do from the start by my dad. He of course has all the tooling to make a nice metal roll in a couple of hours, but since we live some 1500 miles apart, I told him to hold off making a roll forming set-up.
    Now I am interested in the roll forming again. What if you had a roll form jig set up to form slightly less than 1/2 the fin, and then doubled the fins by riveting them together? You could make two separate pieces, one for top, and a smaller one for bottom.

  4. I see the logic in Thermal Mass = BAD for collectors, but aren't the fins, in effect, a form of thermal mass?
    I like Tom's ViseGrip method for holding the fins tight to the riser for riveting. It would also ensure a thin as possible film of silicon between the two.

  5. Hi Rowland,
    Yes -- agree that Tom's vice-grip clamps look very effective -- I had forgotten about those. His fins are near perfect when you look at the end view.
    It seems like a well shaped groove that is riveted to a flat backing sheet of aluminum while being clamped in place by the vice-grip clamp and with just a bit of silicone between would be a near perfect absorber fin. The flat backing sheet would only need to be about half the width of the fin. This would be a good way to get rid of the plywood backing sheet. I guess the only down side is that it looks like more work.
    On the fin, its only job is to absorb the solar energy that falls on it and conduct it to the tube. If you could find something with high conductivity, and no or little thermal mass that would be fine -- its only the conductivity that counts.

  6. I'll make a deal with you gary. Since you have the test equipment. If I make and send you a test version of my panel you can do the testing. Just let me know the dimensions so we can do apple to apple. Matt

  7. Hi Matt,
    That would be great.
    You can see how they look here:
    The absorber part consists of two fin sections -- each fin section is 6.5 inches wide, and 24 inches long. The fin sections fit onto a U shaped section of copper tubing. The two ends of the U project out of the collector, and the supply and return are hooked up to the two ends of the U.
    The fin sections are 6.5 inches wide by 24 inches long.
    The backing board is 19 inches wide by 30.5 inches high.
    The fin material that I use is 0.018 inches thick.
    If you can supply the fins mounted to the tubes, I have plenty of the backer boards and glazing around. If you want to make the package more compact by not soldering the two fins into the U shape, that will keep the package size down.
    I'll email you my shipping address.
    Should be interesting.


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