Synergistic integration of PCM-filled coil fins and smart water depth control in solar stills: A comprehensive energy, exergy, and environmental analysis

Freshwater scarcity remains a critical global challenge, necessitating sustainable desalination solutions. This study investigates the performance enhancement of a double-slope solar still (SS) through the integration of hollow copper coil fins (HCCFs), phase change material (PCM), and an Arduino-based water depth control system. Three configurations were tested: conventional (Case I), fin-modified (Case II), and PCM-fin with smart control (Case III). Experimental results demonstrated that Case III achieved the highest productivity, yielding 1.81 L/m²/day, a 166 % improvement over the conventional still (0.68 L/m²/day) and 14 % higher than Case II (1.59 L/m²/day). Thermal analysis revealed peak energy and exergy efficiencies of 38.9 % and 4.31 %, respectively, for Case III, significantly surpassing Cases I (23.1 %, 1.45 %) and II (28.3 %, 3.45 %). The intelligent water depth modulation (20–35 mm) optimized heat transfer, while PCM extended post-sunset distillation. Economic and environmental assessments showed a payback period of 295 days and 4.8 tons of CO₂ mitigation over the system’s lifetime, with potential carbon credits of $190. This work establishes a novel, scalable approach for sustainable solar desalination.