Performance of an Integrated Solar-Greenhouse Photovoltaic Ventilated Dryer with Clay-CaCl2 Energy Storage Desiccants for Tomato Drying

The use of solar energy in drying of perishable crops such as tomatoes is a good alternative to the problem of post-harvest processing in tropical eastern African countries. A review of the literature revealed that most of the solar crop drying systems developed during the last five decades have small loading capacity and cannot operate during the night. Therefore, an integrated solar greenhouse dryer system [SGDS] with Clay-CaCl2 desiccant energy storage system was designed and tested. Such SGDS have the advantage over other solar systems of high loading capacity and structural simplicity. In addition, they have relatively good thermal crop drying performance compared to most solar dryers. However, their main limitation, like most solar dryers, is their inability to dry at night. Therefore, to enhance night-time drying capacity, a prototype SGDS integrated with a low-cost Clay-CaCl2 desiccant energy storage system was designed, fabricated, and tested. The drying performance of this prototype was evaluated using loads of fresh tomatoes during October – December 2019 at Nairobi, Kenya. The dryer was able to dry fresh tomatoes from 93.9% (mcwb) to 8.3% (mcwb) within 27hours with solar greenhouse drying efficiency of 23% during daytime and desiccant drying efficiency of 19.9% during nighttime. The drying rate for the two-day light drying was 0.985kg/h and 0.875kg/h respectively and that in night drying using desiccants was 0.34kg/h. Based on these results, it was concluded that prototype solar greenhouse dryer with Clay-CaCl₂ energy storage has great potential for drying perishable produce such as tomatoes in tropical countries.