Black polythene sheeting ( 200μm) is used as the thermal absorber, while the transparent one is used for covering both the thermal collector area and tthe drying area. Cardboard paper is used as the back insulator on the absorber sheeting. The dryer frame and trays are both made from wood (and plywood), but, if durability is desired, from metal, painted to prevent corrosion. The dryer is placed along, or in parallel with an East – West axis to maximise its exposure to solar radiation and slightly tilted at 30 to induce natural air flow when the fan is not triggered by the higher dryer temperature. The solar photovoltaic (PV) driven fan is used for forced air circulation to enhance drying. The thermostat control is set at a temperatutre of 60 C. Moisture control in the product is achieved by regulation of the drying process based onintensity of solar radiation.
The dryer can process 50 kg of fresh tomatoes in about 15 hours (i.e. about 2 working days)