Rotating-part solar stills: A review of configurations, mathematical modelling, and efficiency analysis

Conventional solar stills have long been used for water desalination, but their productivity and efficiency remain limited due to the challenges associated with low evaporation and condensation rates. To address these limitations, recent research has focused on enhancing solar still performance through the integration of rotating components, such as wicks, drums/cylinders, discs, and other innovative elements. This review addresses the low productivity and efficiency of conventional solar stills by examining the systematic integration of rotating components, including wicks, drums/cylinders, discs, and other innovative elements, to enhance evaporation and condensation rates. Experimental and theoretical studies published between 2017 and 2026 are analysed, with innovations classified by the type of rotating element employed. Key performance parameters are evaluated, including rotational speed, material selection (e.g., jute versus cotton wicks), incorporation of nanofluids and phase change materials (PCMs), external condensers, and auxiliary enhancements such as solar tracking and reflectors. The findings demonstrate substantial productivity improvements: rotating wick systems achieved yield increases of up to 660.45% with efficiencies reaching 88%, rotating drum and cylinder configurations reported gains up to 431.1% with efficiencies of 84.05%, and rotating disc systems attained productivity enhancements up to 617.4% with efficiencies of 77.2%. Other rotating concepts, including spherical balls and adaptive evaporators, demonstrated improvements up to 189.38%. Economic analyses confirm strong feasibility, with the cost of distilled water reduced to as low as 0.005 USD/L. Overall, the review identifies rotating-part solar stills as a promising and scalable solution for increasing freshwater production while improving energy efficiency, cost-effectiveness, and environmental sustainability.