Energy, exergy, and environmental performance of a solar dryer for orange slices across tray levels and thicknesses

Abstract

Abstract This research introduces the development of an automated forced and natural solar dryer (AFNSD) equipped with a photovoltaic-powered IoT technology, temperature-responsive control system that seamlessly alternates between natural and forced convection to improve efficiency and minimize energy consumption. In contrast to traditional fixed systems, it avoids both over-drying and product spoilage. The affordable, solar-driven design makes it ideal for off-grid communities. By combining drying kinetics analysis with economic and environmental evaluations, the system aligns with and promotes sustainability objectives. The thermodynamic performance and sustainability indicators were also evaluated. The developed AFNSD was used for drying orange slices at different tray positions (lower, middle, and upper), and three slice thicknesses (4, 6, and 8 mm). the obtained results showed that thinner orange slices (4 mm) placed on the lower trays reached the equilibrium moisture content more quickly, with an average drying time of about 13 h. In contrast, thicker slices (8 mm) positioned on the upper trays required the longest drying time, averaging around 25 h to reach the equilibrium moisture content. The thermodynamic analysis showed that the maximum energy efficiency of the solar collector (SC) ( $$\:{\eta\:}_{en,\:\:SC})\:$$ was about 70.98%. And the maximum exergy efficiency of the SC ( $$\:{\eta\:}_{ex,\:\:SC})\:$$ and the drying chamber (DCh) ( $$\:{\eta\:}_{ex,\:\:DCh}$$ ) were about 21.93% and 43.64%, respectively. additionally, the sustainable indicators of both SC and DCh of the developed AFNSD, showed that the improved potential (IP) was in the range of 2.03 to 12.61 W in the SC and from 0.03 to 1.85 W in the DCh. The average waste energy ratio (WER) was 0.9 for the SC and 0.7 for the DCh. And the sustainability index (SI) ranged from 1.02 to 1.28 in the SC and from 1.2 to 1.77 in the DCh.