This was a fun project. Tim whipped this out in a days work, using old scrap sheet metal, painted it black with flat black spray paint. We were gifted an old piece of glass from an old sliding glass door, and built the heater around the size of the glass. He built a wooden box with scrap 1×6’s, and a reused piece of plywood. Lined the box with used Styrofoam installation, then put in the metal pieces. Put the glass on, sealed with tar sealant. He predrilled 3 inch holes, one at the top of the Unit and one at the bottom. Then we used drainage PVC pipes to draw the cool air out of the Composting Toilet space into the bottom hole, as the sun shines the air is pulled into the unit, warming up and rising creating a natural suction, the heated air is then piped out the top of the unit back down (assisted by a computer fan installed into the bottom pipe) to the bottom of the composting toilet unit, heating it up from the bottom, and hopefully preventing it from freezing. Will keep this post updated to see how it goes. Occasionally we run our generator (on cloudy days) and plug in the composting toilet’s built in heater too. Hopefully this Solar Heater will help us offset some of that.