A Trombe wall is a very good example of a passive heat source, in the sense that there are no mechanical parts used for the simple version of the technology. A trombe wall is a very thick wall, consisting of a glass pane secured to an inner wall, with a space between the two. The inner wall is usually a material with good thermal storage properties. When the sun hits the glass on the outer side of the wall, the heat radiates through to the inner wall which absorbs it. The war