Performance of a greenhouse solar dryer for drying macadamia nuts

A multi-purpose greenhouse solar dryer was used to dry in-shell macadamia nuts in order to investigate its performance. The dryer comprises a parabolic roof structure covered with polycarbonate sheets on a concrete floor. The dryer is 9 m in width, 12.4 m in length and 3.45 m in height. Six 15-W DC fans powered by two 50-W PV modules were used to ventilate the dryer. The dryer was installed at a macadamia nuts producer in Loei Province, Thailand. In investigating the performance of the dryer, three drying tests were conducted. For each test, 730 kilograms of in-shell macadamia nuts were dried in the dryer. It was found that the moisture content of the macadamia nuts was reduced from 16% (wb) to 3% (wb) within 5 days, which is shorter than the natural sun drying for 3 days. Results obtained from these tests also showed that drying air temperatures in the dryer varied from 35°C to 60°C. The macadamia nuts dried in this dryer were completely protected from animals and rain. In addition, good quality of macadamia nuts was obtained. The estimated payback period of this greenhouse solar dryer for drying macadamia nuts is about 1 year.