Performance evaluation of a latitude adaptive dual collector solar dryer

Solar drying provides an energy-efficient, low-carbon route for agricultural produce preservation and contributes to multiple UN Sustainable Development Goals (SDGs 2, 7, 12 and 13). Among available technologies, mixed-mode solar dryers are attractive because they combine direct solar heating with preheated airflow from a solar collector. However, in low-latitude regions, high solar altitude reduces effective solar irradiance on conventional south-facing collectors, lowering overall thermal efficiency. To address this limitation, a dual-collector mixed-mode dryer was developed by integrating solar air collectors on the north and south sides of a hemispherical drying chamber. The collector tilt was adjustable from 6° to 37° to enable latitude adaptability. A 20 kg batch capacity system was experimentally evaluated at CSIR-CSMCRI, Bhavnagar (21.76° N) using white onion as the primary test crop, with additional trials on garlic, tomato, green grapes, ginger, and green chillies. Compared to open sun drying, the system reduced white onion drying time by 63 %, and achieved an overall thermal efficiency of 23 % with energy-weighted collector efficiency of 52 %. The no-load performance and dryer performance indices were 1.447 and 1.097, respectively, confirming stable thermal performance. Eight thin-layer drying models were evaluated with the Midilli–Kucuk model best describing the drying behaviour. Sustainability assessment showed an energy payback duration of 2.78 years and CO 2 mitigation of 31.30 tonnes. The techno-economic analysis showed a payback period of 1.01 years, highlighting economic viability for rural deployment. Overall, the modular latitude-adjustable dual-collector dryer offers a practical and scalable solution for rural agro-processing.