A unified 4E framework for porous–PCM integrated solar stills: Synergistic enhancement of energy, exergy, economic, and environmental performance

Water scarcity in arid regions, such as Kabul, presents a critical challenge, further complicated by the inherent thermodynamic inefficiencies and high production costs of conventional single-basin solar desalination systems. These systems frequently experience significant exergy destruction and thermal instability, which hinder their practical deployment. To address these limitations, this study evaluates the Energy, Exergy, Exergoeconomic, and Environmental (4E) performance of a single-slope solar still enhanced with a porous wool layer and a phase-change material (PCM). Four configurations—Base, Porous, PCM, and the hybrid porous–PCM design—were analyzed to determine their capacity for performance improvement. The results demonstrate that the hybrid porous–PCM configuration provides the most effective performance. The cumulative thermal efficiency increased from 68.54% (Base) to 83.52% (hybrid), while exergy efficiency improved from 4.66% to 5.81%. Daily distilled water production rose from 4.22 L/m 2 to 5.91 L/m 2 , representing a 40.1% enhancement. From an economic perspective, the specific cost of freshwater decreased from 0.019 USD/L in the Base system to 0.013 USD/L in the hybrid design, a 31.6% reduction. Environmentally, avoided CO 2 emissions increased from 1.98 kg/m 2 ·day to 3.00 kg/m 2 ·day (a 51.5% improvement). These findings confirm that the combined porous–PCM architecture significantly mitigates exergy destruction and enhances cost-effectiveness, characterizing the integrated 4E framework as a viable approach for sustainable solar desalination in resource-constrained environments.