Energy and exergy analysis of a solar coffee roaster using concentrating scheffler-reflector

Abstract

• An innovative solar coffee batch-type roasting system using a fixed-focus Scheffler reflector as a heat source. • Investigated thermal analysis of the solar roster unit based on energy and exergy. • Analysis provides clear insights into energy distribution and losses in the system. • The energy at the solar reflector was found to be 3680 W and out of which 66% (2449 W) was available for roasting coffee. • The integration of solar thermal energy into the roaster unit performs efficient decentralized roasting of coffee beans. The energy and exergy based thermal analysis was conducted on a newly developed solar coffee roasting system. The system is comprised of a rotating drum (diameter: 400 mm × length: 400 mm), electric motor with variable frequency drive, cooling tray (diameter: 500 mm × height: 100 mm), fan blower, and coupled with a heating source i.e., Scheffler fixed focus solar concentrator (8 m 2 ). Experiments were conducted using 2 kg coffee beans (variety Coffea arabica L .). The results revealed that the system is capable to process the complete batch in 21 ± 1 min at the temperature of 250 °C at corresponding solar radiations in the range of 800–850 W/m 2 . The specific product energy was calculated to be 1543 kJ/kg. The average exergy input, out, and loss of the solar roasting system were found to be 83.98, 47.58, and 36.40 kJ/kg, respectively. The results show that the average exergy efficiency and improvement potential factor of the solar roaster were 56.28% and 22.59 kJ/kg, respectively. Out of total available power (3680 W) at the solar reflector, 66% of energy was available for roasting coffee. The findings of this study show that the developed system could be a valuable tool for design and optimization of the energy distribution and losses at various components of the solar roasting system.