Browsing by Author "Okullo, Willy"

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An experimental comparison of two receiver geometries for domestic thermal processes, suitable for high solar radiation African regions
(Scientific African, 2026-06-09) Rukaaya, Musa; Abedigamba, Oyirwoth P.; Mawire, Ashmore; Okullo, Willy
The study presents an experimental evaluation of two receiver configurations (zigzag and circular) integrated with a packed-bed TES system for domestic thermal processes, particularly cooking and drying. The research addresses a critical gap by examining how receiver geometry influences thermal performance in packed-bed TES systems, offering a potential solution to Africa’s energy storage challenges. The zigzag design achieves a higher average thermal efficiency of 8.30 ± 0.4 % compared to 6.52 ± 0.3 % for the circular design. It also obtained a higher maximum stored energy of 0.91 ± 0.005 MJ than the circular receiver, which reached 0.74 ± 0.004 MJ, over a 4-hour charging period under identical operating conditions. Notably, we performed experiments in a controlled environment and performance on local conditions will be assessed through outdoor testing. Additionally, we fabricated the receivers using locally sourced materials (copper and aluminum), making the technology more accessible and affordable, thus supporting a transition from non-renewable biomass fuel (firewood and charcoal) towards cleaner and more sustainable cooking solutions.
Feasibility of combined solar cookers and dryers for dual cooking and drying: A systematic review
(Solar Compass, 2026-02-12) Rukaaya, Musa; Abedigamba, Oyirwoth P.; Mawire, Ashmore; Okullo, Willy
Dual-purpose cooking and drying systems offer a promising solution for sustainable food preparation and preservation, particularly in regions with abundant solar radiation. This systematic review assesses the current state of technology and knowledge gaps in solar cooker cum dryers, focusing on design configuration, thermal performance, and sustainability relevance. A comprehensive search of the databases yielded 13 studies that met the inclusion criteria. The review highlights the strengths and weaknesses of the design configurations. The findings revealed that these systems can achieve temperatures up to 150 °C, making them suitable for cooking and drying applications, which reduces fuel costs and lowers carbon emissions. Limited work has been done on combined solar cookers and dryers, and most studies use the same unit for both cooking and drying, and very few have separate units. All reviewed studies on solar cookers combined with dryers have employed flat plate collectors with no work on concentrating systems, and most studies are experimental with limited numerical work. Most studies employed the natural convection mode of air circulation, with only a few focusing on forced convection. Additionally, most solar cookers combined with dryers lack energy storage systems, and there is limited work that has been reported on the economic analysis of the combined systems. These findings inform future research and development for sustainable energy solutions, providing insights for policymakers, researchers, and practitioners. This review aims to contribute to the development of efficient and effective combined solar cookers and dryers, ultimately enhancing food security and reducing reliance on fossil fuels.
Green synthesis of zinc oxide nanoparticles using Plectranthus cyaneus leaf extract for ethanol sensing
(Next Materials, 2026-07-15) Kawuki, Joseph; Mushebo, Emmanuel; Inyalot, Jude Tadeo; Okullo, Willy; Mukhokosi, Emma Panzi
In this work, zinc oxide (ZnO) nanoparticles (NPs) were green-synthesized using Plectranthus cyaneus leaf plant extract as a reducing agent. The synthesized ZnO NPs were characterized using X-ray Diffractometer (XRD), Scanning Electron Microscope (SEM), and Ultraviolet-Visible spectrophotometer. The XRD confirmed the crystal as a hexagonal wurtzite crystal structure with space group P63mc. The crystallite size was determined and found to increase with calcination temperature from 37.80 nm at 300 ◦C to 49.5 nm at 700 ◦C. The crystalline strain and dislocation density decreased from 1.538 × 10− 4 to 1.144 × 10− 4 and from 3.386 × 10− 2 nm− 2 to 2.919 × 10− 2 nm-− 2 respectively. The SEM images of the ZnO NPs reveal fine spherical particles with less agglomeration at higher temperature, thus enhancing surface area. The optical band gap decreased with an increase in temperature from 3.26 eV at 500 ◦C to 3.22 eV at 700 ℃. The synthesized ZnO NPs were used to fabricate an ethanol gas sensor on an interdigitated Indium doped tin oxide (ITO) coated glass substrate, which was exposed to various concentrations of ethanol, isopropanol, acetone, and methanol. The fabricated sensor exhibited high sensitivities of 27.6%, 10.7%, 9.9%, and 8.2% for ethanol, isopropanol, acetone, and methanol, respectively, at a working temperature of 200 ℃. The sensor exhibited fast response and recovery times of 17.90 s and 21.12 s for ethanol, respectively. The sensors’ selectivity of ethanol in the presence of other analyte were 36.16%, 38.77%, and 29.57% for isopropanol, methanol, and acetone, respectively. Therefore, our study provides a green route for synthesizing ZnO nanostructures as potential candidate for ethanol gas sensing.