Passive solar is great BUT you will need an large space to build one on. Having only room for 10'x12' GH's, the huge, black barrels would take up practically all of my growing space. Also, since all I grow are tropical plants, I don't think it is even possible to put enough barrels inside to keep the temperature above 55F. On cold, cloudy days, even here in the deep south, there would be little if any heating of that water, so how do you maintain heat when the outside temperature is in the 20's? Just asking.
