A systematic review of design and thermal modification techniques for solar still performance enhancement

Abstract

Global freshwater scarcity remains a major challenge, particularly in arid and developing regions where conventional desalination technologies may be costly or difficult to deploy. Solar stills provide a simple, decentralised, renewable-energy-based approach for producing potable water, although their relatively low productivity remains a significant limitation. This systematic review examines design and thermal modification strategies for improving solar still performance, focusing on phase change materials (PCMs), fin and extended-surface configurations, and basin water-depth variation. Following the PRISMA 2020 framework, 66 peer-reviewed studies published between 2000 and 2025 were systematically identified, screened, and critically analysed using Scopus, Web of Science, ScienceDirect, and Google Scholar. PCM integration improves thermal energy availability by storing heat during high solar irradiation and releasing it during reduced solar input, while fins enhance heat-transfer area and thermal interaction within the basin. Basin water depth influences thermal inertia, with shallow water generally promoting faster heating and evaporation. However, the critical synthesis reveals considerable variation in reported performance due to differences in solar still geometry, material properties, climatic conditions, operating parameters, experimental duration, and reference configurations. Consequently, no single enhancement technique can be considered universally superior. The findings highlight the need for standardised performance reporting, long-term validation, climate-specific optimisation, and systematic investigation of interaction effects among thermal storage, heat-transfer enhancement, and basin water depth. Future research should focus on integrated and practically scalable solar still designs that combine these complementary mechanisms to achieve reliable and sustainable freshwater production.