The evaporator and condenser
were integrated in the drying chamber and the water storage tank was set up in the system to
recover the heat effectively and improve the utilization of solar energy. Based on a total required heat
of 23.157 MJ for drying 10 kg of radish process, the theoretical analysis results illustrated that when
the daily average radiation intensity was 0.480 kW/m2 the system run at solar drying (SD) mode; when
the daily average radiation intensity ranged from 0.430 kW/m2 to 0.480 kW/m2 the system run at the
solar-assisted heat pump drying (SAHPD) mode; when the daily average radiation intensity was less than
0.430 kW/m2, the system run at the heat pump drying (HPD) mode. The experimental results showed
that the coefficient of performance of the drying system was ranged from 3.21 to 3.49 at the SAHPD
mode. Furthermore, the SAHPD can save energy consumption by 40.53% in terms of heat recovery and
thermal storage. The payback period for drying radish, pepper, and mushroom in the life span of the system
was 6 years, 4 years, and 2 years, respectively. Therefore, it can be concluded that mushroom is the
most suitable material to be dried in this system.