Improving Solar Still Operation for Water Purification: A Review of Vertical Wick Distillers

ABSTRACT

Freshwater scarcity remains one of the most pressing humanitarian and environmental challenges of the 21st century, driving urgent demand for decentralized, low‐energy purification technologies. Among passive solar desalination systems, solar stills have attracted sustained research attention; however, their characteristically low distillate yield has long constrained practical adoption. Vertical wick integration—encompassing both standard vertical wick solar stills (VWSS) and the more advanced vertical corrugated wick solar still (VCWSS)—has emerged as a transformative design strategy that simultaneously amplifies evaporation surface area, exploits capillary‐driven feedwater transport, and feeds pre‐heated brine into a coupled primary still, creating a synergistic thermal cascade. This review critically analyses 10 experimental investigations spanning eight distinct still geometries—conventional, coiled, pyramid, stepped, tray, hemispherical, spherical, tubular, and concave—each augmented with vertical wick subsystems and evaluated alongside co‐applied enhancements such as silver nanoparticle‐enriched phase change materials (Ag‐PCM), corrugated absorbers, internal reflectors, extended fins, and magnetic field application. The results are striking: VCWSS‐integrated configurations consistently outperform their VWSS counterparts, with the fully optimized concave‐VCWSS‐Ag‐PCM system achieving a peak daily productivity of 13,650 mL/m ² /day—a 326% gain over a conventional baseline—and a thermal efficiency ceiling of 76.4%, the highest recorded across all reviewed configurations. Even the most modest wick‐integrated hybrid, a pyramid still coupled with VWSS and nanocomposite PCM, delivered an 84% productivity uplift and reduced water production cost from USD 0.019 to USD 0.0142 per liter, underscoring the economic accessibility of wick‐based retrofits across still geometries. Across the full dataset, freshwater production costs span USD 0.0048 to USD 0.012 per liter—competitive with many decentralized purification alternatives—while annual avoided CO ₂ emissions reach up to 29.3 tons per installation, affirming meaningful environmental co‐benefits. Isolated performance attribution reveals that the vertical wick subsystem alone contributes 107%–117% incremental yield gains beyond the improvements already achieved by geometric and material modifications, confirming its role as the dominant driver of hybrid system performance. Despite these advances, the review identifies four persistent research gaps: the restriction of nearly all studies to single‐day, lab‐scale experiments; the absence of long‐term wick durability and salt‐fouling data beyond bi‐annual maintenance cycles; insufficient investigation of real industrial or agricultural wastewater feeds; and limited interdisciplinary coupling with photovoltaic, wind, or adsorption‐based energy subsystems. To bridge these gaps, future work is directed toward machine‐learning‐assisted multi‐variable optimization, CFD‐guided wick geometry refinement, next‐generation metamorphic fabric absorbers, and pilot‐scale field deployment targeting 8–10 L/m ² /day in arid regions at a capital cost below USD 50/m ² . By consolidating quantitative performance evidence, economic benchmarks, and a forward‐looking research roadmap, this review provides a definitive reference for engineers and scientists advancing scalable, sustainable solar desalination.