Development and Performance Evaluation of a Novel Solar Dryer Integrated with Thermal Energy Storage System for Drying of Agricultural Products

Passive solar dryers play a crucial role in reducing postharvest losses in fruits and vegetables, especially in regions like sub-Saharan Africa with low electrification rates and limited financial resources. However, the intermittent nature of solar energy presents a significant challenge for these dryers. Passive solar dryers integrated with thermal energy storage (TES) can reduce intermittence and improve the drying efficiency. Currently, phase change materials (PCMs) are popular heat storage materials in dryers, and paraffin wax dominates. The main problem with the use of PCMs is that it is necessary to closely constrain the temperature range of the process during charging and discharging. This can be a difficult condition to meet in simple solar dryers due to the variable availability of solar radiation. Instead, solid-phase materials, such as sand and rocks, are often used. Soapstone is one of the natural rocks with good thermal properties, but it has yet to be used as a TES material in solar dryers for drying agricultural products. Therefore, the main objective of the present study was to develop a novel solar dryer integrated with soapstone as a TES material and evaluate its performance. The proximate analysis to examine the quality of dried products using the developed technology was also carried out. The comparative experiments for the developed dryer were conducted in two modes: dryer with TES materials and without TES materials, and the results were compared with open sun drying (OSD) by drying 50 kg of fresh pineapple and carrot at different times. The drying times for pineapples in the dryer with TES, without TES, and OSD were 13, 24, and 52 h, respectively. However, the drying times for carrots in the dryer with TES, without TES, and OSD were 12, 23, and 50 h, respectively. Notably, the dryer integrated with TES materials could supply heat for around 3-4 h after sunset. The thermal efficiency of the dryer, collector efficiency, and storage efficiency of TES materials were calculated and found to be 45, 43, and 74.5%, respectively. Proximate analysis indicated that the dryer integrated with TES materials effectively maintained the quality of the dried products compared to OSD. Solar dryer integrated with soapstone showed great promise as sustainable and efficient solutions for reducing postharvest losses and enhancing food security in resource-constrained regions like sub-Saharan Africa.