Mother's Do It Yourself Solar Water Heating Project
We compared the performance of Mother's DIY solar water heater to commercial products. Here are the results!
September/October 1981
By Mother Earth News Editors
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LEFT : The candidates for our solar water heater comparison are mounted in place and ready for their days in the sun. Shown from left to right are the Suntree Solar, the SolaRoll, the BTU Bucket, the unknown /and subsequently eliminated/ commercial panel, MOTHER's singleplate in-line and MOTHER's double-plate in-line (both copper-equipped/. RIGHT: The water to ""feed"" the entire collector lineup was drawn from a 55gallon drum by five pumps, and then returned to the top of the reservoir through valves.
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Now fully assembled, our group of competing collectors finally have their day(s) in the sun to prove how well they work for solar water heating.
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SOLAR WATER HEATING COMPARISON: PART II
In our last issue we introduced-for the purposes of comparison — three solar collector kits and a homemade unit designed and built by MOTHER's research staff. That initial article described the basic procedures involved (and the minor difficulties we ran into) in assembling the four water heaters. We also promised to finish the story with a side-by-side performance comparison of the units. By contrasting the relative efficiencies found during testing with the cost of the panels (and taking the ease and quality of construction into consideration, as well), we hoped to be able to pick a "best bet" for the handy —person interested in putting together his or her own solar water-heating setup.
Well, after over a week spent in the sun running the collectors on a test stand (and many more days compiling the data for the various units), we're finally ready to complete our report. But before we reveal the results, we'd like to tell you a bit more about just how we tested the collectors, so that you'll be better able to understand just what our figures do, and don't, mean.
DOES SCIENCE PROVIDE QUESTIONS OR ANSWERS?
First of all, you should know that an evaluation like ours can easily be misinterpreted. For one thing, we tested the panels on hot summer days ...and because there was less temperature difference between the collectors and the air around them than there would have been on a cold day-factors such as the emissivity of the absorber (the rate at which it expels the heat it has taken in), the insulation value of the box, and the air tightness didn't play roles as large as they would have in a cold climate in the dead of winter. The results from a test staged in a 0° outside temperature could have been quite different.
Another thing to keep in mind, when reviewing our results, is that they shouldn't be directly compared to those produced by a testing lab. We made no attempt to monitor the incoming solar radiation, so we can't provide conversion efficiencies for the devices we tested. Nor did we insulate the delivery or return lines or the storage tank. Thus the rate of temperature rise of our setup would not give a good indication of exactly how much hot water might be supplied by the collectors in an actual installation. We sought only to provide equal running conditions for all the panels being tested.
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