Development and Thermal Evaluation of a Cocoa Solar Roaster Using a Dual-Axis Parabolic Cylinder Collector (PCC)

This study presents the design, construction, and thermal evaluation of a solar-powered cocoa roaster based on a Parabolic Cylinder Collector (PCC) with dual-axis solar tracking. The system integrates three functional subsystems: the cylindrical-parabolic reflecting surface, the stainless-steel absorber tube, and a microcontroller-based tracking mechanism. The prototype enables continuous acquisition of key thermal variables (solar irradiance, ambient temperature, absorber surface temperature, and bean temperature), allowing a detailed characterization of heat transfer processes during roasting. Roasting experiments were conducted at controlled durations of 40, 55, and 70 min between 10:00 and 14:00 h. Maximum roasting temperatures of 125°C–137°C were reached under average irradiance levels of 685.7–930.5 W m⁻². The lowest final moisture content was 2.19%, within the recommended range for high-quality cocoa. Longer roasting durations promoted thermal energy accumulation within the absorber tube, enhancing convective and radiative heat transfer to the bean mass even under fluctuating irradiance. The experimental trends reveal a strong coupling between irradiance variability, absorber temperature, and internal air-beam heat transfer. Comparison with reference parabolic trough collector studies indicate that, although the process-level roasting efficiency (3.83%–7.45%) is lower than conventional collector-level thermal efficiencies, the operating temperatures and moisture-reduction rates align with the thermal requirements of food-processing systems rather than high-enthalpy solar applications. These results also demonstrate the potential of coupling PCC-based solar concentration with low-temperature convective–radiative roasting processes. Overall, the findings confirm the feasibility of implementing PCC-based roasting technologies in rural or off-grid regions, where solar-driven heat transfer offers a sustainable, low-cost alternative to fossil-fuel-based roasting systems, enabling a controlled thermophysical environment for cocoa transformation.