European Association for the Development of Renewable Energies, Environment and Power Quality (EA4EPQ) International Conference on Renewable Energies and Power Quality (ICREPQ’12) Santiago de Compostela (Spain), 28th to 30th March, 2012 Solar kiln drying of tropical hardwoods using a system with a slagbed acting as roughened absorber and heating storage medium R. Clarke and R. Saunders Department of Physics University of the West Indies St. Augustine, Trinidad and Tobago Phone/Fax number: 1 868 662 2002 (ext 82051)/ 1 868 662 9904, e-mail: ricardo.clarke@sta.uwi.edu, ramsey.saunders@sta.uwi.edu Abstract. This work addresses the analysis of a low temperature, forced-air, solar kiln timber dryer operated in Trinidad and Tobago (10˚N, 61˚W). The design is a 6 m 3 capacity kiln with a 36 m 2 collector external to the kiln which has a single glass cover with a slagbed roughened absorber and heat storage. Slag is the by-product in the manufacture of steel which is easily and cheaply available locally. The effectiveness of the system was proven in drying tropical hardwoods to a final equilibrium moisture content of dry basis, 16%. High quality products were obtained, in 2-5 weeks depending on climatic conditions, wet or dry season, species and thickness of the lumber. Tests carried out clearly indicated that solar kiln drying is about twice as fast as natural drying, and that the drying times are comparable with conventional kiln drying using electrical heating. These results demonstrated the great potential that such a renewable energy system using locally available materials possesses. Key words Solar, timber, kiln, drying, moisture content. 1.0 Introduction Solar drying offers an alternative method of drying timber using a renewable energy source. Solar timber drying in the Caribbean is still not well developed where the commercial aspect is concerned. Most of the solar kilns operated are basically research type systems. Solar timber drying research done prior to this work, at the University of the West Indies (U.W.I.), St. Augustine has resulted in a scaled–down greenhouse timber dryer that dries hardwood in about 2-3 weeks [1]. There are several designs of solar kilns around the world, most being research kilns and not in commercial operation [1]. A few of these designs are however becoming available as production models [2]. Drying is the most energy demanding process in solid lumber production. This drying process has become increasingly costly with rising fuel prices. Developing countries with a timber resource that can be used to manufacture finished products either for local use or export often lack the capital to build high-cost drying kilns. Caribbean states with timber resources such as Guyana, Belize, Dominica, and Trinidad and Tobago are located in the tropics where ambient temperatures and insolation are high. In addition solar energy is advantageous in that it is clean, inexpensive and inexhaustible. In the Caribbean the daily insolation of the region varies between about 7 KWh/m 2 during the dry season to about 4 KWh/m 2 during the rainy season. Solar drying provides an alternative method using renewable energy to remove the moisture from wood. Although solar drying may take longer, 5 to 14 days, than conventional kiln drying, depending on locality and climate, the small capital investment, low running cost, and ease of operation make this kind of lumber drying attractive for emerging industrial nations. Following the trend of environmentally friendly systems, renewable energy technologies such as solar drying ensures adequate health, safety and environmental standards. Therefore, the primary aim of this work is to evaluate a prototype solar timber kiln [3] to effectively dry timber, which can be made available, on a commercial scale, in the tropics for medium to small saw millers and wood workers. 2.0. Description of the solar dryer The design unit under consideration is a low temperature, solar-heated, forced-air, 6 m 3 timber dryer which consists of the kiln and an external solar collector. In a comprehensive review of solar-energy drying systems it was noted that some conventional dryers and most