DEVELOPMENT OF A PASSIVE HYBRID SOLAR DRYER FOR COCOA BEAN

Abstract

A passive hybrid solar dryer was designed, fabricated and evaluated for cocoa bean drying, integrating solar and biomass energy sources to enhance drying efficiency under varying insolation conditions. The system comprises a solar collector, a drying chamber, and a biomass-fueled briquette chamber. The solar collector features a 3 mm thick acrylic cover, optimizing solar energy absorption. The drying chamber consists of two compartments for cocoa bean placement, while the lower chamber extends to accommodate an auxiliary heat source for uninterrupted drying. Briquettes derived from cocoa pod husks were utilized as an alternative energy source during periods of low or no solar radiation. Post-fabrication, a no-load test was conducted to assess baseline thermal performance, followed by experimental drying trials using fermented cocoa beans. The drying experiments were carried out between October and November, 2022, when the ambient temperature and relative humidity were within the ranges of 25.8-31.3℃ and 58.7-89.0%, respectively. The cocoa beans achieved the desired moisture content in three days under solar drying alone, two days under hybrid drying, and within one day using only the biomass heat source. The average drying rates for solar, briquette and hybrid heat sources were 0.06, 0.3 and 0.35 kg/h, respectively while their temperature levels were within the ranges of 30.9-59.2, 30.4-56.4 and 29.5-61.5℃, respectively. However, it took a longer time for the heat to build up when solar radiation was used as the only heat source, resulting in the extended drying period. The developed hybrid system demonstrated a significant reduction in drying time, ensuring continuous and efficient drying, and thereby improving post-harvest processing of cocoa beans