Comparative review of phase change materials for enhancing the thermal performance of solar desalination systems

Global water scarcity has intensified the need for sustainable freshwater production technologies. Solar stills offer a cost-effective desalination option, yet their limited productivity and dependence on daytime solar irradiance restrict deployment. Thermal energy storage using phase change materials (PCMs) has emerged as a promising strategy to extend freshwater production beyond daylight hours. However, existing reviews overlook systematic links between PCM properties and solar still operational constraints. This review compares eight PCM families — paraffins, fatty acids, alcohols, glycols, esters, hydrated salts, molten salts, and metallic alloys — against melting temperature compatibility with the 40–80 °C operating range, latent heat capacity, thermal conductivity, and long-term cycling stability, based on 167 peer-reviewed articles (2000–2024). Key findings: paraffins and fatty acids, with melting points of 6–71 °C and 47–70 °C and latent heats of 80–269 J g⁻¹, are the most viable PCMs for passive solar stills despite thermal conductivities below 0.35 W m⁻¹ K⁻¹; hydrated salts are suitable if phase segregation and supercooling are mitigated; molten salts and metallic alloys are thermally incompatible with conventional passive systems. A multi-criteria weighted decision matrix is proposed to guide PCM selection, with future research directions including nanocomposite PCMs, cascaded thermal storage, and pilot-scale validation.