Multifunctional passive enhancement of solar desalination using natural materials in an inverted Pyramid Basin: Thermal and 4E performance analysis

This study introduces a novel solar still configuration that integrates multiple natural materials within a geometry-optimized inverted pyramid aluminium basin and presents the first systematic evaluation of their combined thermal behavior using a comprehensive 4E framework encompassing energy, exergy, economic, and environmental criteria. Although previous work has investigated individual natural materials, the synergistic influence of stones, a cotton wick, and luffa on heat transfer dynamics, evaporation behavior, and overall system efficiency has not been examined, particularly within an optimized basin geometry. The present design couples geometric solar intensification with material-driven thermal enhancement to create a low-cost and energy-efficient desalination system. Experimental findings showed that the integrated configuration delivered the highest performance among all tested cases: stones provided thermal storage to stabilize temperature, the wick promoted capillary-driven thin-film evaporation, and luffa facilitated uniform water distribution while reducing thermal losses due to its porous structure. The inverted pyramid geometry further improved solar energy concentration and reduced convective heat losses, strengthening thermal utilization. Under identical operating conditions, the optimal configuration achieved a maximum daily distilled yield of 4.18 kg/m 2 , corresponding to a 58.3% enhancement over the reference still. Thermal efficiency increased from 26.1%to 41.3% (58.2%improvement), and exergy efficiency rose from 2.03% to 2.92% (43.8% increase). The cost of desalinated water decreased from 0.020 to 0.014 USD per liter, a reduction of 30%, while annual CO₂ mitigation increased from 6.01 to 9.52 tons, indicating a 58.4%improvement. The 4E analysis further revealed a 29.1% reduction in embodied energy and a marked improvement in energy payback time. These results confirm the effectiveness of integrating multifunctional natural materials within an optimized basin as a practical and sustainable pathway for decentralized solar desalination.