As it is getting into winter here, I am playing with an idea for solar heating that I thought of a few months ago. It may not help people in the Northern Hemisphere much now, but I'll report on the progress I'm making. I am going to start experimenting with a small unit to heat an aquarium system I'm working on. The 300 liter aquarium is in an outside building with no insulation, and a 300 Watt heater basically never stops working to keep the temperature up above 20 degrees Celcius. The idea I had was using left-over pieces of 6 mm multi-wall polycarbonate sheeting used in my research system as a simple flow-through solar water heating panel. I have designed the basic plumbing, but before I spend too much time making the actual unit, I thought I'd give the idea a go.
First test was filling a 25 liter blue drum up with water and leaving it in the sun. It heated slowly, but topped out at around 26 degrees. I then siliconed up one end of a 0.5m square polycarb sheet. I left the white backing paper on it, but step two of the experiment will be to paint the back black.
Although the experiment is very crude (the thermometer is cheap and the probe touches the polycarb sides) the results are promising. The water heats up rapidly, and reaches 36 degrees Celcius in about 30 minutes (a rise of over 16 degrees Celcius). I'm not sure what the max of this configuration can be, but it is not far above 38 degrees Celcius.
I am hoping that with the back painted black, I will be able to hit 40 degrees Celcius in 30 minutes flat. The water volume of the entire panel (without plumbing) will be around 1.5 liters, thus it is not a massive panel. I have a fair amount of it at my disposal though, and if the black panel is going to give me 40 degrees fast, I'm willing to see how it goes on the 300 liter aquarium. With 45 minute rotations and around 9 hours of direct sun, I'll have 12 rotations on the panel. The 0.5 square meter unit will thus only heat about 18 liters of water a day, which makes me think that I will have to go for 30 minute rotations and bigger panels. On two of these panels, I will then heat 54 liters of water a day. Still, it beats having a 300 watt heater on 24 hours a day!
Thanks for all the interesting responses and linkes. I'll definately go through them as soon as I have a bit of reading time.
Perhaps I should just add some more info on this little tinker project. I'm in a temperate region, thus not too cold in winter. If I chose to go with goldfish, I would not need to heat the water at all, but I am trying to keep plants and bacteria happy by attempting to keep system temperature at 25 degrees Celcius in winter. The system I'm trying to work a heating solution out for is a small aquarium, thus also not a large volume of water. I'm somewhere in between aquarium heater and very basic solar heating country. I have painted the panel black at the back, and then the clouds arrived. I reached 42 degrees Celcius in a burst of direct sun, but I'm sure I can do better. Thus for this project, the really basic will work. On my larger system, I will definately look at all the suggestions here.
Thanks for all the replies.
Tricky part on the small aquarium set up will be how to operate it and avoid the risk of cooking the fish on a sunny day. Do you have any way to control with a thermostat?
I think you will get some heat gain on sunny days at least and yea, you may be able to balance it with the timer. Hope it works well for you.
Well, after getting around half our average annual rainfall in just two days, the sun is out agian and I can continue tinkering with the little panel. It has been painted black at the back, and depending on the angle at which it is turned towards the sun, I can get the water to between 45 and 50 degrees Celcius. Now to set up the jig with which to cut 5 mm slots into 32 mm PVC pipes to accomodate the panel, and to test it in its completed configuration. I have enough pmultiwall for around 4 of these, and I'm sure that will be enough for a basic (read primative) set-up to heat the 300 liter aquarium.
Anyone with suggestions for the perfect mounting angle between the panel and the incoming sunlight?
I can't really see from the picture, but with the back side painted black, is the front side (pointed to the sun) white as in the picture? You should avoid this being white as it would reflect most of the sun. All sides being black should be best I think.
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I am at 34 degrees South, and am targeting winter sun angles only. I will research it to see what is the most effective angle for my position. Thanks for the feedback Mitchell.
Mudvet - no, the back is now black and the front clear (no new picture). I did the first test to see what can be done before I went down to the hardware store to get the black spray paint. The picture is of the multiwal with its original white backing. I thought that the light should get in to the panel, thus I left the front clear. I'll paint both sides black and give it another run.