The study was carried out to evaluate the performance of a continuous solar roaster for the roasting of soybeans. The system comprises a 10 m2 fixed focus concentrator coupled with the continuous solar roasting system which is designed for decentralized processing of agricultural products in medium to high temperature range. The independent variables of roasting time (10–30 min) and temperature (140–160°C) were optimized for soybean roasting using response surface methodology. The optimized roasting conditions were found to be 29 min and 160°C at which urease activity was decreased to 0.09 ΔpH, protein solubility decreased to 80.76% and protein dispersibility index decreased to 28.53%, which inferred quite satisfactory performance for continuous solar roaster for soybean roasting in terms of quality. Moreover, moisture and fat contents were reduced by 86.3 and 29.9%, respectively whereas protein, fiber, carbohydrate and ash contents were increased by 12.9, 10.6, 8.1, and 14.1%, respectively after roasting. It was also concluded that 100 kg soybean can be roasted successfully on a sunny day with average direct normal irradiance ranging between 600 and 800 W m−2. The payback period of continuous solar roaster was estimated to be 1.3 years in terms of fuel savings. Practical applications Roasting of perishable agricultural products by concentrating solar power is a novel research area of solar thermal energy utilization in medium to high temperature range agricultural processing. A prototype of a continuous solar roaster (CSR) was developed that was fitted with a 10 m2 elliptical fixed focus concentrator and a copper coil heat receiver coupled with the roasting unit. The CSR can generate a temperature >200°C for roasting with available direct normal irradiance (DNI) of 600–800 Wm−2 during the peak hours on a sunny day, thus capable of roasting a variety of agricultural products between 150 and 220°C. The farmers can install CSR at farm‐gate level for commercialized value addition as it is completely independent from fossil fuel based energy supplies for thermal and electric energy generation. Significant socio‐economic benefits could be realized for small to medium scale rural farming communities with this decentralized and eco‐friendly technology particularly in developing countries.

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The current research has been conducted to investigate the capacity of an indigenously developed thermal oil based continuous solar roaster (CSR) for groundnuts roasting. A 10 m2 standing Scheffler fixed focus concentrator is used to target the incoming direct normal irradiance at casted aluminum surface of a heat receiver which transfers this heat energy to the roasting unit by means of thermal oil circulation. The roasting unit comprises a cylindrical shell (2000 mm in length and 450 mm in diameter) attached beneath a semi-circular oil flow jacket and equipped with a ribbon type screw conveyer with 6 mm thick paddles. Optimizing for maximum energy utilization and feeding capacity using response surface methodology, roasting time for light, medium and dark quality was found to be 14 + 0.1, 20 + 0.1 and 29 + 0.1 min respectively. In terms of roasting quality, CSR has shown quite satisfactory results. The study revealed that continuous solar roaster has the capability to roast 140 to 288 kg groundnuts per day subjected to dark to light roasting quality with average direct normal irradiance ranging from 650–800 Wm−2. The overall thermal efficiency of the system was found to be 37.8%. The payback period of CSR was estimated to be 2450–5250 useful working hours.

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.