Experimental investigation and thermo-economic performance analysis of silver energized phase change material integrated solar still system

Transparent covered slope solar stills have gained significant attention for clean water production; however, their widespread adoption is limited by low productivity, high heat losses, and operation restricted to daylight hours. To address these challenges, this study proposes an innovative integration of silver-enhanced phase change materials (AgePCM) into a solar still (SS) system. The thermophysical properties of AgePCM at varying nanoparticle concentrations (0.2, 0.4, 0.6, 0.8, and 1.0 mass%) were systematically characterized, including morphology, chemical stability, optical performance, thermal conductivity, energy storage capacity, and thermal reliability. A dimensionless figure of merit (FOM) was introduced to enable standardized comparison of nanoenhanced PCMs. Although AgePCM-5 exhibited the highest FOM, AgePCM-4 was identified as the optimal formulation due to its superior thermal conductivity and balanced thermophysical performance. Experimental results revealed that the optimized AgePCM-4 sample achieved a 73.82% increase in thermal conductivity, a 6.02% enhancement in melting enthalpy, and a 62.85% reduction in light transmittance compared to the base PCM. A three-criterion parametric sensitivity analysis identified thermal conductivity as the dominant factor governing productivity enhancement, contributing 49.81% of the total logarithmic gain, followed by optical absorbance (44.93%) and melting enthalpy (5.27%). The AgePCM-integrated solar still (SS-AgePCM) system demonstrated significant improvements, with water temperature and distillate production increasing by 5.0% and 89.7%, respectively. Economic analysis indicated a reduced freshwater production cost of ₹2.4 per liter and a payback period of 6.9 months. These findings demonstrate the effectiveness, scalability, and economic viability of the proposed system for sustainable water production in water-scarce regions.