Do-It-Yourself Water Heating Solar Collectors Comparison

Now fully assembled, our group of water heating solar collectors finally have their day(s) in the sun to prove how well they work.

| September/October 1981

071 water heating solar collectors - main view

The candidates for our water heating solar collectors 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 EARTH NEWS' single-plate in-line and our double-plate in-line (both copper-equipped).


In "Do-It-Yourself Solar Collectors Comparison," we began the process of testing three water heating solar collectors and a homemade unit designed and built by MOTHER EARTH NEWS' research staff. That initial article described the basic procedures involved (and the minor difficulties we ran into) in assembling the four solar 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; 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-degree-Fahrenheit 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.

Our results reflect the average number of British Thermal Units (one BTU is the quantity of heat required to raise one pound of water 1 degree) produced per square foot of collector, per hour, over the course of the period extending from the beginning of the morning heating cycle until the collectors reached maximum heat level (usually about 140 degrees, by 1:00 p.m.).

Finally, as is the case with any test, our numbers are only as accurate as were the monitoring equipment and methods used. By calibrating our Heliotrope General SAS-3 thermistors before and after the evaluation (and disqualifying any of the "thermometers" that had more than 3 percent inherent variation from the mean), taking flow measurements every half-hour with a graduated cylinder and stopwatch, and using a quality digital ohmmeter to measure thermistor resistance, we feel that we have achieved an overall accuracy of plus or minus 10%. That means that the numbers we provide could be off by 10 percent, in either direction, from the correct figure.

web master
9/25/2012 4:31:48 AM

Solar Products Manufacturer The comparison of solar water heating products is very helpful to Consumers. Now a day’s many solar products manufacturing companies provide technical details of the products.

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