On one of my previous posts, Build a simple solar water heater, I recently received the comment below from a reader named John Hearty who built his own solar water heater following a similar design. I emailed John requesting some photos, and he was kind enough to oblige. Here are the pictures he sent me. Click on the images for higher resolution versions.
I have read your blog and another one you commented on about using Coroplast for thermal collector panels with great interest. I think Coroplast is an excellent material for a collector mainly because of itâ€™s higher temperature tolerance. My wife tested baking a sample at 250 degrees F and it came out feeling just about as rigid as normal. We also filled it with water and put it in the freezer and it did not deform from the ice.
I am however concerned about freezing problems, more due to glued joints at the ABS pipe at the top and bottom of an assembled panel bursting. I plan to have a large holding tank of water used directly with the panels without a heat exchanger to the holding tank so Iâ€™m not too interested in using a bunch of anti-freeze. I am planning to build a drainback system using these panels, and just painting them black.
I also saw that polypropylene does not tolerate UV light well and will become brittle and break after long exposure. Coroplast can however be made special order with a UV absorber mixed in with the polypropylene. I am getting some regular Coroplast from a local sign shop that does not have the UV protection, so Iâ€™m looking into paints that absorb the UV. If the prototype works well Iâ€™ll look into getting UV protected Coroplast for additional panels.
And a couple weeks later:
My wife and I finally got one of these built and tested.Â We built it as a drainback system and used plain water dyed black using pond dye.Â We did not paint the panel.Â We got frosted tempered glass panes from Craigslist to build this and the next ones.Â 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.Â The full spreadsheet is available but I was not sure if it could be posted here.Â It is a 1.814 square meter panel with 37.85 liters (10 gal) of water in the system.Â We used a 55 gallon plastic drum for the tank.Â The tank and hoses were not insulated.
Starting temp was 53.8 F. At the 1 hour mark the temp was 92.7 F, average power was 952 watts, 52% efficient. At 2 hours, 117 F, 768 watts, 42%. At 3 hours, 127 F, 593 watts, 33%. At 4 hours, 130 F, 464 watts, 26%.Â We also did a stagnation test with no water in it, and it got up to 152 degrees F on a 45 degree day.Â We are looking forward to mounting it permanently and testing reliability/longevity.Â 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.
Thanks John for sharing your results.