In my quest for lowering my carbon footprint and heating bill, I decided to embark on a homemade project that would fulfill both needs. Being cheap, I scoured Freecycle for materials to build a soda can solar collector. Essentially it is a device with a bunch of glued together columns of soda cans. They are all painted black with holes drilled in the bottoms of them to allow the passage of heated air. I used about 200 cans all collected from soda that was consumed. (See the attached picture). This site has several versions that got me started on my plans: BuildItSolar
I started out by using a door to a shed I had just laying in the basement that was no longer used. I framed it out using some 2×4’s from Freecycle and with some liquid nails then glued in some insulation (my only purchase from Lowe’s $8) to the back and sides to make the air chambers. Using some more 2x4s I sectioned off a portion of the bottom and top for distributing the air to the can columns then collecting it at the top. At the bottom where the air comes into the device there are a few cans that act as pre-heaters. I glued the cans in place with sealant glue. The black painted cans were glued into place as columns for the main energy collectors with holes drilled into the top and bottom of the 2x4s that led into and out of the columns. This made the pathways for the air to travel through the solar heat collector.
To get air into and out of the device I drilled holes for the inlets and outlets and used some metal from an old exhaust I had at the outlet to hook a dryer vent hose to a window mount that I created (see 2nd picture). On the inside of the window mount I added an old computer fan. This pulled air from the device into the house thus drawing in the warm air. Lastly I covered the device face with glass from acquired from Freecycle and sealed it. The sun shines through the glass and heats up the cans. The air is pulled through the can columns and heated up.
Now onto the testing, using a house thermometer and an oven thermometer I tested the inlet air and the outlet air into the house. First day with decent sun (about 10% cloud) from 9:30am to 2:30pm. At about 10am the sun was full bore onto the device the outside temperature was around 25 degrees F. Incoming air to the house was 105 degrees F. At 1pm it was about 30 degrees outside and the incoming temp was around 109 degrees. That was pretty good for a start. A few weeks later it was -15 degrees outside, but the heater was still cranking out around 95 degrees to the inside. I bet the numbers would have been higher if I had implemented a duct line that drew air from inside the house to feed the heater instead of using the outside air. Those numbers “seem” like a huge success.
Here are the drawbacks. The fan I used just had a switch on it. A nice thermostat would have worked well but it would need 2 sensors one for temp of device and one for inside the house and added cost which would increase the time to the return on investment. Running the fan off of a cheap electrical solar panel would have been the perfect mod to that setup but would add some cost as well. The glue I used for the cans still smells bad when it heats up, this is not so green to me, and has kept me from using the heater until I get time to rebuild it completely with some high heat gasket sealant or something similar. The black paint had vapors when painting the cans black, again not so green, but I already had the paint and wanted to use it up. The heat is only high enough to pump into the house for about 5 hours a day where I live in the northern mid-west. I am usually not at home to turn the device on or off at this time.
All told it worked better than I thought it would but it would need to be integrated more into the house to make it worthwhile. Maybe mounting it on the side of the house with the inlet and outlets cut into the wall like I have seen on a few other designs at BuildItSolar. Guessing what my energy savings could have been using the device every day I would say it might save $5-$15 dollars a month, depending on the amount of sun received. In my area I just don’t get enough sun. A good use for it would be to heat a garage on a Sunday for a couple of hours while you are working on a project. For a few dollars spent the heat is amazing that comes out the first time you turn the switch. With a little better planning on my part the soda can solar collector could have be much better. I still call it a successful test though.