R&D: Prototype Solar Timber Kiln

EMI's Fabrication Workshop in Uganda uses thousands of pieces of timber a year to build cabinets, trusses, and furniture for partner ministries. For the species and quantities that EMI needs, the timber is often only available as freshly cut. Upon arrival at EMI’s workshop, the timber moisture content can exceed 100% (more than half of the wood’s weight is water). To minimize shrinking and cracking, EMI’s fabrication workshop targets below 12% moisture content before using the timber. 

Traditionally, wet timber is air-dried in open stacks outdoors. Because timbers near the outside of the stack receive direct sunlight and were in contact with dry air, the timber stack dries unevenly. Every few weeks, a crew of men are hired for the labor-intensive task of rotating the timber stack. Depending on the initial moisture content and weather conditions, three to six months are typically required to adequately air-dry the timber. 

The prototype solar timber kiln can hold roughly 80 pieces of 2”x6” rough-cut timbers that are 14-ft long. Transparent roof sheets allow solar energy to enter the kiln, and 12V radiator fans circulate the warm air. In the solar kiln, timber dries more evenly, the stack does not need to be rotated, and drying time is reduced from three to six months down to three to six weeks.