Recent Advances in Solar Still Technology: Design, Performance Enhancement, and Thermal Energy Storage.

Solar stills provide a simple approach for producing freshwater from saline or contaminated water by utilizing solar energy as the main thermal input. Their uncomplicated construction, low operating requirements, and suitability for decentralized applications have maintained research interest despite the relatively low productivity of conventional designs. This review examines recent developments in solar still technology with emphasis on the relationship between configuration, heat and mass transfer, and performance enhancement. The fundamental principles governing solar distillation are first discussed, followed by a critical overview of major solar still configurations, including single-slope, double-slope, pyramid, inclined, stepped, multi-basin, tubular, and hybrid systems. The principal operating and climatic parameters affecting evaporation and condensation are subsequently examined. Particular attention is given to passive and active enhancement approaches, thermal energy storage using phase change materials, nano-enhanced phase change materials, nanomaterials, absorber modifications, cover cooling, and hybrid renewable-energy integration. In addition to freshwater productivity, thermal and exergy efficiencies, economic feasibility, and environmental considerations are considered when evaluating the practical effectiveness of different technologies. The review also discusses limitations that restrict direct comparison among published studies, including differences in climatic conditions, water depth, basin geometry, measurement procedures, and operating periods. Finally, research gaps related to long-term stability, standardized testing, material durability, economic assessment, and the combined use of geometry and advanced thermal storage are identified. The review provides a structured basis for selecting and developing solar still configurations and enhancement techniques for future decentralized desalination applications.