A review of innovative materials and techniques in solar stills: A focus on heat localization and thin film evaporation

Freshwater scarcity is becoming a worldwide problem, more so in remote locations. Solar stills are a promising technology for desalination, leveraging solar energy; however, their productivity requires significant enhancement. This review focuses on recent efforts to improve the efficiency of solar stills based on thin-film evaporation and heat localization, which benefit from combinations of advanced materials, structural modifications, and energy management. Various configurations including single slope, flat, double slope, pyramid, tubular, and hemispherical solar stills are discussed. It is found that the application of nanocomposites, wicks, and nanoparticles increases solar radiation absorption and heat retention, significantly increasing water productivity and thermal efficiency. Also, wicks, nanoparticles, solar tracking, and advanced basin designs are highlighted as promising ways to maximize evaporations and minimize thermal losses. Modified designs increased water productivity by over 300 % and yields by 368.5 %. Advanced setups using materials such as CuO, TiO₂, and graphene attained a thermal efficiency of 86.78 % and improved solar absorption and productivity by 161.5 %. Innovations such as rotating wicks and drums increased thin-film evaporation by 400 %, while phase change materials provided continuous evaporation, increasing freshwater production by more than 240 %. The production costs were also reduced by up to 66.2 %, yielding a minimum freshwater cost of 0.0042 $/L. A bibliometric analysis, using VOSviewer, of trends in thin-film evaporation and heat localization techniques for scaling up SS technologies for sustainable freshwater globally.