Performance investigation of a hybrid solar dryer with electric and biogas backup air heaters for chilli drying

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Solar drying is an efficient, low-cost, and environmentally-friendly post-harvesting process. This work presents the experimental investigation on drying of red chili using two different types of hybrid mode solar dryers: Electric Hybrid Mode Solar Dryer (EHMSD) and Biogas Hybrid Mode Solar Dryer (BHMSD). In both modes, a cabinet-type drying chamber is integrated with two different auxiliary backup air heaters that can operate with electricity and biogas. From initial no-load experiments, the optimized mass flow rate of the dryer was estimated as 0.03 kg/s. Then, red chilli was dried from an initial moisture content of 70.2% (w.b.) to a final moisture content of 17.7% (w.b.) within 16 hr in the EHMSD and 14 hr in the BHMSD. However, in Open Sun Drying (OSD) experiments, the red chilli samples reached only 40.2% (w.b.) requiring twice the drying time compared to the dryer. Moreover, the variation in drying rate and exergy were estimated for chilli drying in both the dryers. The maximum value of the effective moisture diffusivity (2.73 × 10−9 m2/s) was observed in BHMSD samples, which was four times higher than that of the OSD samples. Moreover, the efficiency of BHMSD was found to be 6% higher than that of EHMSD.The estimated exergy destruction in BHMSD and EHMSD was 26.7% and 30.8% of the net input exergy. BHMSD also offers energy savings by utilizing biogas as an auxiliary heating source instead of electricity. Therefore, the novel BHMSD can be an eco-efficient and sustainable alternative to the traditional EHMSD from the perspective of energy sustainability.