Friday, February 24, 2012

Low tech solar collector

During the winter I have been working on a cold frame type structure that I could use to hold plants through the winter and harden off seedlings. I also want to use it to hurry up growth of my entrance planters at my gardening job. So after searching the Internet for a while I found a passive solar unit that uses recycled two liter bottles. I have a stack of shower doors that I was able to bring home from a remodel. I have also gotten two hot water heaters that were being replaced. A plan began to take shape.

Currently I am working on building the solar collector tray. Essentially it is a shallow wooden box. I have ½ inch black tubing threaded through a long sleeve of plastic two liter bottles that have the bottoms cut out. The neck of a bottle slips into the cut out base of the next bottle to form a chambered sleeve . That long row of bottles and tubing is laid into the tray. Then the shower doors are laid on top and attached and the whole box is tilted toward the sun at the correct angle (more or less) for our latitude. Here's what it looks like-

The first thermometer shows the temperature on a piece of black plastic outside the box and the center picture is inside the box.  There is a difference of about thirty degrees F after just about five minutes.
The last picture shows the poor thermometer after I closed the box up and took a thirty minute lunch break! The thing blew up! I guess the solar collection part works anyway.
Big thanks to Barbara, Terry, Shannon, and everyone else who provided two liter bottles!


  1. explosion?!! who knew being green could be so dangerous?!

  2. How do the plants enter the equation? Does the cold frame then set on top of the box or do the plants then go inside the box? There doesn't seem to be much room for plants in there.

  3. Ron, this part I am showing is just the collector portion. It will heat water which will travel through the tubing in the bottom of a cold frame. I am connecting everything else up first to see what kind of temperatures I will need to adapt to in the cold frame. The cold frame will just be bales of straw sitting on the slab with shower doors on top. Two separate structures. There will be a hot water heater in the loop too to help store the heated water, but it is just for storage of heated water.