Experimental and numerical investigation of single-slope solar still performance enhanced by porous absorbing materials: thermal, economic, and environmental assessments.

Low freshwater productivity and poor thermal efficiency remain key limitations of conventional single-slope solar stills. In this study, porous absorbing materials are investigated as passive performance-enhancement strategies for small-scale solar desalination. A combined experimental and numerical analysis was conducted on a traditional solar still (TSS) and two modified configurations incorporating melamine sponge (MSSS) and pumice stone (VPSSS), operated under real climatic conditions in Karbala, Iraq. The results demonstrate that the MSSS achieved the highest daily freshwater yield of 1347 mL/day, corresponding to a 56.9% increase compared with the TSS, alongside an average thermal efficiency of 49.3%. The VPSSS produced 1055 mL/day, representing a 22.9% improvement and a thermal efficiency of 38.2%. Economic analysis indicates that, under optimal operating conditions, the MSSS reduced the water production cost to 0.07569 USD/L with a payback period of approximately 2.5 years. The energy payback period ranged from 0.55 to 0.86 years, whereas the exergy recovery period remained considerably longer (28–35 years), highlighting inherent thermodynamic limitations. In addition, the MSSS configuration achieved an annual CO2 emission reduction of approximately 1612 kg, corresponding to a cost saving of 17.36 USD. Overall, the findings suggest that porous absorbing materials, particularly melamine sponge, offer an effective and economically feasible approach for enhancing solar still performance in arid and remote regions.