IMPROVED (SPER) DESIGN WITH SOLAR-DRIVEN AIRFLOW AND CONTROLLED WATER CIRCULATION FOR REDUCED POSTHARVEST LOSSES IN SEMI-ARID OFF-GRID SETTINGS

Off-grid communities in Borno State face persistent challenges in preserving perishable food commodities due to high ambient temperatures, low relative humidity, and unreliable electricity supply. These constraints result in significant postharvest losses, weaken local food security, and limit the economic viability of smallholder farmers and informal food vendors. Conventional refrigeration systems, particularly vapor-compression technologies, are largely unsuitable in such contexts because of their high energy demand, dependence on continuous grid power, and environmental concerns associated with synthetic refrigerants. This study examines the viability and performance potential of a Solar-Powered Evaporative Refrigerator (SPER) as a sustainable cooling solution for off-grid environments. Constructed primarily from locally available, low-cost materials, the system was designed for autonomous operation, environmental sustainability, and scalability. Field testing under representative semi-arid conditions (ambient temperatures of 32–41 °C and relative humidity of 18–35%) demonstrated a maximum internal temperature reduction of up to 12 °C, alongside increased internal relative humidity suitable for fresh produce storage. Performance evaluation showed that the SPER reduced tomato spoilage by approximately 75% over a 72-hour storage period, significantly outperforming conventional non-insulated Zeer pots. Thermal analysis revealed that the combined effects of clay-based insulation, sustained fibre saturation, and solar-driven airflow were critical in stabilizing internal temperature and humidity levels, while maintaining low water and energy consumption. Overall, the findings confirm the SPER’s potential as a low-energy, decentralized refrigeration technology for resource-limited, off-grid settings. Its adaptability to tomatoes and other perishable commodities offers a practical pathway to reducing postharvest losses, improving food security, and promoting environmentally friendly cooling solutions in semi-arid regions.