Performance enhancement of a solar still using thermal energy storage and innovative designs: recent progress, challenges, and future directions

Abstract

Solar distillation is an environmentally friendly method of producing freshwater, yet its use at large is constrained by low productivity (usually 3 L m−2 day−1) and reliance on the daytime solar radiation. Thermal energy storage (TES) materials, especially phase change materials (PCMs) and nanoparticle-enhanced PCMs (NePCMs), are promising solutions to extend operation into non-sunlight hours and improve thermal efficiency. The reviewed studies show that the use of TES can enhance productivity by 20–75%, and NePCMs can significantly improve thermal conductivity and heat retention. This review summarizes recent experimental and numerical advances in PCM- and NePCM-based solar stills including encapsulation techniques, material placement, and thermal performance under varying climatic conditions. It also examines novel designs such as multi-stage and wick-type solar stills, as well as hybrid systems that integrate auxiliary heating and geometric optimization to improve freshwater production and efficiency. Recent developments in PCM encapsulation have enhanced thermal stability and durability, while optimized integration of TES has improved energy storage, thermal management, and cost-effectiveness. This review highlights present challenges and future research directions for PCM-based TES systems that can enhance the competitiveness of solar desalination technologies while contributing to the SDGs 6 and 13 through sustainable and energy-efficient water purification.