Solar drying of sawn lumber in Spain

A solar heated experimental drying kiln was installed in Madrid (INIA-Forest Industries Department) to study the efficiency of solar drying of sawn lumber in Spain, as compared with normal air drying. The kiln has been designed as a low cost semi-greenhouse type, but was equipped with a semi-automated control of the drying schedules. The performance of the solar kiln has been studied during ten test runs over a period of two years particularly with respect to drying rate, initial and final wood MC, reliability and efficiency. The results have proven that the solar kiln is capable of drying (economically) from an initial moisture content of 70 to 80%, to a final MC of 8 to 10% up to 3.5 times faster than air drying. With respect to checks, splits and internal stresses, the final wood quality is mostly better, not only compared to normal air drying but also to conventional kiln drying.