Development and Experiments on a Batch-Type Solar Roaster—An Innovative Decentralized System for Coffee Roasting

Faizan Majeed,Oliver Hensel,Ali Raza,Anjum Munir

doi:10.3390/su14042217

Abstract

About 70% of the harvested coffee is exported to the industrialized nations for value addition due to lack of processing and logistic facilities in developing coffee producer countries, thus leaving behind a marginal economic return for the growers. This research was conducted to investigate the roasting capacity of an innovatively developed batch-type directly solar radiated roasting system for the decentralized processing of coffee using solar energy. Central composite rotatable design (CCRD) was employed to design the experiments to optimize the coffee roasting process. Experimental results revealed that with an average solar direct normal irradiance (DNI) of 800 W/m2, the roaster was capable of roasting a batch of 2 kg coffee beans in 20, 23, and 25 min subjected to light roasts, medium roasts, and dark roasts, respectively at a drum speed of two revolutions per minute (rpm). The batch-type solar roaster has the capacity to roast 28.8–36 kg of coffee beans depending on dark to light roasting conditions on a clear sunny day with DNI ranging from 650 to 850 W/m2. The system thermal efficiency during coffee roasting was determined to be 62.2%, whereas the roasting efficiency at a corresponding light roast, medium roast, and dark roast was found to be 97.5%, 95.2%, and 91.3%, respectively. The payback period of the solar roaster unit was estimated to be 1038 working sunshine hours, making it viable for commercialization.

Highlights

Coffee (Coffea spp.) is widely cultivated throughout the tropical regions comprising more than 70 species, all of them originating from Africa
The pyranometer was fixed at the Scheffler reflector for continuously facing the sun through a black pipe of length 100 mm fixed on it for only allowing to record the direct normal irradiance (DNI)
The Scheffler concentrator was mounted with a daily tracking mechanism working on an automatic photovoltaic (PV) sun tracking system comprised of a PV-powered direct current (DC) gear motor and for the seasonal adjustments due to the sun declination angle throughout a year, the manually adjusted telescopic clamps were installed to precisely focus the DNI onto the roasting drum

Summary

Introduction

Coffee (Coffea spp.) is widely cultivated throughout the tropical regions comprising more than 70 species, all of them originating from Africa. The individual villages are small socioeconomic units but often underappreciated in centralized energy planning models due to the higher cost of infrastructure and transmission lines for scattered populations, which uplift the overall consumption of carbon-based fuels and lead to environmental degradation. This whole scenario overburdens the deprived farmers and indirectly enforces them to sell their perishable agricultural produce in the local markets without adding any remarkable value, returning them a meagre profit [4,5].

Methods

Results

Conclusion