Applications of Natural Rocks as Heat-Storage Materials for Food Drying in Sub-Saharan Africa

Natural rocks are emerging as a viable solution for solar heat storage in Sub-Saharan Africa due to their low cost and accessibility, as well as their ability to reduce energy costs and reliance on solar energy. This study review research on applications of natural rocks as heat-storage materials for food drying in Sub-Saharan Africa. Findings of this study indicate that current research on the combination of drying systems with thermal energy storage systems using natural rocks as storage material focuses on indirect solar dryers (66.67%), mixed mode solar dryers (16.67%), and solar-assisted heat pump dryers (16.67%). These dryers perform admirably, particularly in extreme weather conditions and when there is no sunlight. The findings show that using natural rocks as a storage medium can increase the efficiency of dryers by up to 17.48%, reduce drying time by as much as 50%, and extend the drying operation by 2 to 4 hours after sunset. This study also identifies and proposes key areas for further research. In particular, more attention is needed to characterize the thermal properties of the storage materials used, as this aspect is often underexplored in African studies. Understanding these properties is essential for optimizing the performance of solar dryers and making informed choices about which materials to use. In addition, the techno-economic analysis of all these dryers is neglected, making it difficult to assess the economic impacts of these technologies and facilitate their adoption in communities. Exergoeconomic analysis should also be carried out in order to facilitate optimization and understand the actual efficiency of these dryers.