On the south side of my (proposed) log cabin, I have the following 2 options. Which is a better plan? The cabin is wider than it is deep, with the wide side being on the south. One story. I can put lots of glass and sliding glass doors on the south side. Direct gain solar? or I can put a sliding glass door on the south, and then build panels that fasten to the south side. The panels are just 6" frames with glass fronts, and black plastic tubing filled with water on the inside. The back of the panel would be foil-faced to reflect the light back to the tubing. Theoretically, the glass heats the plastic tubing and holds the heat. There are top and bottom vents cut into the south side of the cabin. The cold air goes from the cabin into the glass collector mounted on the cabin, its warms and rises, and then goes back into the cabin from the top vents. The top vents will have a way to close them when the collector isn't warmer than the inside air (manual at this point). Also, maybe put a non-electric fan in there, too, to help blow the air into the cabin. This is all conjecture at this point....don't know if it will actually work. The question is, though...... which is better - direct gain from lots of windows (and good insulated curtains), or a quasi-solar collector on the entire south side of the house (plus one sliding glass door)?