To Dry Food: Solar food-dryers are used for drying fruits and herbs.
To heat homes and industries: Air can be heated in glass-covered vent boxes, and introduced into a home. See Clear Dome Solar’s latest space heater.
By passing air over solar-heated metal, air can be pre-heated for a home or a factory or a grain-storage bin (crop-drying), saving on fossil-fuel useage. Canada’s own patented Solarwall (by Conserval) is the world’s leading example of this.
Solarwall not only absorbs solar energy on its dark outward-facing side (transferring solar heating to air at an efficiency of 75%) but, with its shiny backside, also reflects radiated heat losses from the building back toward the building. R-value? 55.
Using tin snips or a large sheath knife, cut into the top of a can, making four or five “pie” sections. Bend these down into the can at an angle. Cut completely around the side of the can near the bottom, and remove the bottom. After several (or many) cans are prepared this way, stove-pipe them together…the bottoms will jam onto the tops. Lay several “pipes” out into an open box, spray-paint them black, and cover the face of the box with plastic or glass, leaving openings at the bottom of the box (to let cool air in) and the top (to let warmed air out). [Design by Dennis Fath of H.D. Mechanical in Edmonton, Alberta, Canada.]
A good page for Solar Air Heating for do-it-yourselfers is here at: Build It Solar – The Renewable Energy site for Do-It_Yourselfers.