Abstract:
Like most developing countries, Ethiopia's residential energy sector relies heavily on burning biomass, and cooking accounts for over 90% of the total energy used, with baking injera consuming 37% of this energy. Injera, a pan-cake-like bread consumed by most of the population, demands a temperature of 180–220 °C to be well baked. The widely spread injera baking stoves, an open-fire three-stone and electric injera baking stove, are energy inefficient; besides, for the biomass stove, the kitchen environment is highly polluted with soot and smoke that affect the health of household inhabitants. This thesis presents a new technology designed to address these challenges by utilizing an indirect solar stove for injera baking. The system incorporates an evacuated tube solar collector with a 0.52 m² absorbing area, two well-insulated heat transfer fluid (HTF) storage units, a rectangular stainless steel heat absorber tube, and three shut-off valves. Temperature is monitored using K-type thermocouples, and heat transfer is facilitated through natural circulation, driven by density variations between the receiver and stove. To optimize solar collection, V-shaped reflectors having a size (length × aperture width) of 190 cm by 18.74 cm are used to address the issue of areas of the tube that do not face the sun. The system also includes a shut-off valve to control the flow of sunflower oil (HTF), heated to 300 °C, which reaches to the bottom surface of the baking pan. The technology was developed and tested at the Bahir Dar Institute of Technology, achieving a header tank temperature of up to 325 °C, an oil temperature of 282 °C in the baking compartment, and a baking pan top surface temperature of 184 °C under clear sky conditions. For the baking performance test, two rounds of injera were successfully baked. Additionally, the economic and environmental impact analyses yielded encouraging results. Overall, the solar thermal baking system demonstrated an efficiency of 38.3%. However, challenges such as HTF smokes and direct thermal-based baking models suggest that there is room for performance improvement. The adoption of the technology could be significantly enhanced by integrating refined mineral oils as HTFs and incorporating a heat storage mechanism. In conclusion, the analytical and experimental results confirm the feasibility of indirect baking of injera, a process that has not been successfully demonstrated in previous efforts.
Keywords: solar collector; evacuated tube; reflector; GHGs; injera baking stove.