Abstract
Water scarcity is a pressing concern in arid regions, and Morocco is no exception. Solar stills offer a low-cost off-grid desalination option, but their output is limited by poor thermal retention after peak solar hours. This study builds a six-node transient model for a single-slope solar still and compares four configurations — CSS, SWR, SWPCM, and SWR-PCM — under real Rabat meteorological data (14 July 2023). The model is validated against published experimental data and an analytical solution. SWR-PCM achieves the highest productivity (6.1 kg/m²/day, +66% vs CSS), the highest latent efficiency (48%), and the highest exergy efficiency (ηex = 3.2%). The resistance heats the basin to 72°C in the morning while the PCM (Tm = 56°C) extends evaporation into the evening. The PCM contributes more to exergy improvement (+0.7 pp) than the resistance alone (+0.5 pp), confirming the thermodynamic advantage of passive thermal storage. These results demonstrate the synergistic benefit of combining active heating with PCM storage for solar desalination in water-stressed regions.