Mother’s Flat Plate Solar Collector

By The Mother Earth News Editors
Published on January 1, 1981
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Three different flat plate solar collectors were compared with a commercial collector (the rectangular unit at right) for performance.
Three different flat plate solar collectors were compared with a commercial collector (the rectangular unit at right) for performance.
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Press the aluminum fins to form a groove which fits around the collector's fluid-carrying lines
Press the aluminum fins to form a groove which fits around the collector's fluid-carrying lines
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Staple the aluminum plates printed sides in before slipping them over the tubes
Staple the aluminum plates printed sides in before slipping them over the tubes
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TOP: Seal the seams with silicone caulk. BOTTOM: Drilling pilot holes allow you to pound in or remove the nails more easily.
TOP: Seal the seams with silicone caulk. BOTTOM: Drilling pilot holes allow you to pound in or remove the nails more easily.
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Tack the collector together, using 1
Tack the collector together, using 1" aluminum roofing nails. Trim away the excess glazing
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Diagram shows the parts and assembly method for the collector.
Diagram shows the parts and assembly method for the collector.

One of the most important considerations in designing a multi-tube solar collector is the establishment of even flow through all the lines in the device. Because of pipe friction and related hydraulic concerns, it’s all too easy to end up effectively bypassing one portion of a heater’s tubes, while letting the fluid move too quickly through the other parts of the collector, to be thoroughly warmed. Considerable research has been dedicated to overcoming this difficulty. The success or failure of such efforts is one of the factors that separate a top-notch collector from a mediocre one.

So when MOTHER EARTH NEW’ research staff set out to build a solar water heater that could be easily duplicated by the average handyman, they elected to avoid the problem entirely! Rather than attempting to mass a large number of copper tubes inside an insulated box–which is the most frequently used approach–our workers decided to assemble a single-pass, in-line flat plate solar collector that can be duplicated as many times as is necessary to get a particular water-heating job done.

Hot Stuff

During the course of building and testing several different models–which were compared both with each other and with a standard commercial collector–our team not only developed an impressively effective water heater, they also discovered some interesting time- and money-saving shortcuts. For instance, a unit that was constructed from copper pipe with copper fins soldered to the tubes actually achieved only a 1°F higher temperature than did a similar collector built with recycled .007″ aluminum printing plates sandwiched and stapled over the pipe … and the rate of temperature rise was nearly the same!

Most important, the collector performed almost as well as a costly commercial unit that had been purchased for comparison purposes. When we linked three of our homemade jobs together to achieve a square footage similar to that of the “benchmark” collector, the water temperature rose only 1°F per hour more slowly in our setup. And our “did ’em ourselves” devices produced water temperatures that peaked only 7°F lower than did those of the liquid heated by the store-bought model … at an amazing 140°F!

Build It

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