The potential of commercial preservation of tomatoes using a mixed-mode solar drying technology in rural Botswana

Globally, the agricultural value chain is adversely affected by high postharvest losses estimated to be 30-50%. Efficient and affordable preservation technologies to mitigate the enormous postharvest losses are scarce in sub-Saharan Africa. Botswana is endowed with abundant sunshine but has little evidence of utilization of solar drying technology to preserve products as a method of reducing postharvest losses. This paper presents the findings of a study on the potential for commercial preservation of tomatoes using a mixed-mode solar drying technology in a Botswana rural setting. The study (i) assessed the needs and practices around preservation of agro-produce with particular reference to the type of agricultural products that are in need of preservation; (ii) assessed the enabling factors for solar drying that included environmental and solar thermal conditions in Botswana; (iii) assessed the available technologies to determine the different types of solar dryers, and (iv) evaluated the potential of using an enhanced mixed-mode forced air convection technology, taking into consideration possible thermal energy storage options in view of the intermittency of the solar energy source. From the survey, tomato emerged as the produce with the highest potential for preservation by use of solar drying technology. The assessment of the solar energy levels indicated sufficiency for solar drying irradiation higher than 200kW/m2 in all the locations analyzed in Botswana. The wind velocity was found to be of average 4 m/s, relative humidity for both winter and summer averaged 51 % and sky clearness index was above 80%. All these are favorable conditions for solar drying. For commercial preservation, the use of mixed-mode solar dryer with additional enhancement of energy and photo-voltaic (P-V) ventilation was recommended.