Experimental optimization of metallic wire cylinder-coils for enhancing the performance of hemispherical solar stills: A 4E analysis

Hemispherical solar stills (HSSs) offer a sustainable approach to decentralized desalination; however, their practical application is limited by low efficiency. This study introduces and systematically evaluates metallic wire cylinder-coils (MWCCs), a novel porous heat-storage medium, as a first-of-its-kind enhancement for HSS performance. To the best of our knowledge, this is the first experimental optimization of MWCC integration in HSSs, assessing the effect of coil number on thermal and economic performance. Four configurations were tested under identical climatic conditions in El Oued, Algeria, during June 2025: a reference traditional HSS (THSS) and modified HSSs incorporating two, four, and six coils (HSS-MWCC2, HSS-MWCC4, HSS-MWCC6). Results showed that MWCC integration substantially increased freshwater yield and efficiency. The HSS-MWCC6 achieved the highest productivity of 5.69 L/m²/day, a 49 % improvement over THSS (3.82 L/m²/day), while HSS-MWCC2 and HSS-MWCC4 improved yields by 25 % and 38 %, respectively. Peak thermal and exergy efficiencies for HSS-MWCC6 reached 80 % and 12 %. Economic analysis revealed a water cost of $0.043/L and a payback period of 27 days, whereas environmental evaluation projected 3.13 tons of CO₂ mitigation and $94.04 carbon credit revenue over a 10-year lifespan. These findings confirm MWCCs as a pioneering, cost-effective, and eco-friendly innovation for advancing solar desalination, offering scalable potential for deployment in water-scarce regions.