Enhancing solar drying systems through integrated thermal energy storage and solar-assisted heat pump technologies: A pathway to sustainable food processing

Abstract

The growing global demand for sustainable and energy-efficient food preservation technologies has accelerated research into solar drying systems, particularly for remote and energy-constrained regions. While solar dryers offer significant environmental and economic benefits, their performance is often constrained by the intermittent nature of solar radiation, leading to reduced energy efficiency, inconsistent drying rates, and potential quality degradation of end products. This review synthesises recent advancements in integrating thermal energy storage (TES) and solar-assisted heat pump (SAHP) technologies into various solar dryer configurations—direct, indirect, mixed-mode, and hybrid systems. Special emphasis is placed on the selection and performance evaluation of sensible heat materials, phase change materials (PCMs), and thermochemical storage media, assessed based on thermal stability, storage capacity, cost-effectiveness, and adaptability to diverse climatic conditions. The role of SAHP integration is examined for its ability to maintain optimal drying temperatures and relative humidity, thereby extending drying periods and improving product quality retention. Comparative analyses from literature indicate that TES–SAHP hybrid systems can improve overall system efficiency by up to 35 % and reduce drying time by 20–40 %, depending on design and operating conditions. Furthermore, the review explores advancements in hybrid system optimisation, and techno-economic feasibility, highlighting applications for high-value agricultural and food products. Finally, the paper identifies key challenges—such as system complexity, initial investment costs, and material degradation—and outlines future research directions to enable the large-scale deployment of next-generation solar drying technologies in sustainable food processing.