The use of a combined solar heat pump rice drying system was being developed as an alternative to conventional mechanical dryers and evaluated by Best et al. The experimental equipment developed was a modified 7 kW R-22 air conditioning unit and was combined with a solar collector for a more precise control of temperature and humidity. Thin-layer solar drying experiments were conducted at Matsuyama, Japan, with medium grain rough rice by Basunia and Abe, using a mixed-mode natural-convection solar grain dryer. The data of sample weight and dry-bulb and wet-bulb temperatures of the drying air were recorded continuously continuously from morning to evening for each test and were then fitted to the Page model, based on the ratios of the differences between the initial and final moisture contents and the equilibrium moisture content (EMC).