Increasing water productivity in hemispherical distillers using nanoparticle-coated egg-shaped metal basins filled with half-eggshells, eggshell powder, and sand grains as natural and corrugated thermal storage materials

To mitigate the drinking water crisis, it is imperative to enhance the water productivity of solar stills, particularly in arid regions. This study presents the first application of eggshell halves filled with either white sand grains or processed eggshell powder as cost-effective natural energy storage and corrugation materials to improve the production of hemispherical solar stills. To investigate the proposed techniques, three identical hemispherical solar still were developed and evaluated under identical weather conditions. The configurations included: a conventional still with egg-shaped metal basin coated with nanoparticles (HSD-SET), a modified still with eggshell halves filled with white sand grains (MHSD-SET&ES_SG), and a modified still with eggshell halves filled with eggshell powder (MHSD-SET&ES_ESP). Additionally, the microstructure and morphological properties of eggshells were examined using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to ascertain their chemical composition. The findings showed a significant enhancement in water productivity, with increases of up to 51.94 % (9.64 kgm⁻²day⁻¹) and 85.64 % (11.87 kgm⁻²day⁻¹), for the MHSD-SET&ES_SG and MHSD-SET&ES_ESP configurations, respectively, compared to the conventional HSD-SET (6.35 kgm⁻²day⁻¹). It is noted that the productivity improvement for the MHSD-SET&ES_ESP was 22.18 % higher than that of MHSD-SET&ES_SG. Furthermore, the adoption of these modified configurations led to reductions in productivity cost by 48.81 % and 79.77 % and shortened the payback time by 32.85 % and 40.92 % respectively. Finally, the annual CO₂ emissions were reduced by 2.83 and 3.33 tons for the MHSD-SET&ES_SG and MHSD-SET&ES_ESP configurations, respectively.