Development and performance evaluation of tube-type direct solar oven for baking bread

Solar ovens are not widely used for baking bread. There are some attempts to bake bread using solar energy and obtained a promising result. The aim of this research was to develop and test a tube type direct solar oven that a potential to be easily fabricated and largely produced at a low cost locally in the developing world. The developed solar oven has an overall dimension of (diameter and length) 0.1 m × 1 m and the height of the parabola is 0.35 m. Simulation of the design to obtain the focal point and bread baking process was done using SOLTRACE and COMSOL soft wares, respectively. Both simulation and experiments revealed that almost all the rays fall over the trough. Similarly, COMSOL software showed the baking process which was verified through experimental work. The prototype took 67 min s to reach its stagnation temperature of 127 °C, with an F1 of 0.32. Three WBT tests were taken at different days and the result showed that the direct tube solar oven overall thermal efficiency of 43.9%, 42.1% and 38.3% at an average solar isolation of 305 W/m², 259 W/m² and 232 W/m², respectively. The tube type direct solar oven has better efficiency compared to most of the direct type solar cookers. This is due to the air tight cover around the oven which reduces the thermal loss of the oven to ambient air, which is also a cause for the oven's good performance under low solar isolation. Further bread baking test showed that the solar oven has an overall utilization efficiency of 35.0% at an average solar isolation of 396 W/m². The time taken for baking is 16 min longer than its COMSOL analysis. This is due to the difference in design and prototype, especially while producing an air tight cover locally. Addressing this and other performance improvement issues, the solar oven could be disseminated to the wider community especially for people living in the rural parts of the developing world.