Productivity improvement of hemispherical solar stills using thermal energy storage techniques: A focused review

Access to clean drinking water remains a global challenge, especially in arid and remote regions. Solar desalination using hemispherical solar stills offers a sustainable solution due to its low cost and eco-friendliness, but performance is limited by intermittent solar input and low nighttime productivity. This review is the first focused work that exclusively examines productivity enhancement hemispherical solar stills through thermal energy storage. These strategies are categorized into sensible storage like sand and gravel, and latent storage like paraffin wax, with both showing significant gains. Sensible materials have achieved productivity improvements of up to 75 %, while latent storage—particularly nanoparticle-enhanced phase change materials—has yielded increases exceeding 200 %. Overall, reported performance improvements include 30–245 % higher productivity, thermal efficiencies up to 78.1 %, and cost reductions as low as 0.00389 $/L. Hybrid systems combining thermal energy storage with reflectors, wicks, or condensers amplify these gains further. Despite these advances, challenges remain. Key gaps include the absence of long-term durability studies, limited performance testing beyond arid climates, and the lack of standardized metrics for comparative analysis. Addressing these issues is essential for scaling thermal energy storage-enhanced hemispherical solar stills to real-world applications.