The Simplest Desalinator
The solar still is the oldest and simplest desalination technology — a shallow basin of saltwater under a tilted glass cover. Sunlight passes through the glass, heats the dark basin, and evaporates water. Vapor rises, contacts the cooler glass surface, condenses into droplets, and gravity pulls them down the tilted surface into a collection channel. The process requires no electricity, no membranes, no pumps — only sunlight and a transparent cover.
Thermal Balance
Solar still performance is governed by heat balance: incoming solar radiation must overcome reflection losses, heat basin water, drive evaporation, and compensate for thermal losses through the glass and basin walls. Only the fraction that drives evaporation produces freshwater. Thermal efficiency (evaporative energy / solar input) typically reaches 30–45% for a simple single-basin design. The rest is lost to convection, radiation, and ground conduction.
Design Optimization
Water depth is the most impactful design parameter. Shallow basins (2–5 cm) heat rapidly, reaching temperatures 20–40°C above ambient and maximizing the vapor pressure difference that drives evaporation. The glass angle affects both solar transmission and condensate drainage — 15° is typical. Black basin liners maximize solar absorption. Adding internal or external condensers, vacuum operation, or wicking materials can significantly enhance yield beyond the simple design.
Where Simplicity Wins
Solar stills are impractical for cities but transformative for isolated communities, disaster relief, and off-grid households. A 2 m² still produces enough drinking water for one person in sunny climates, at zero operating cost and near-zero maintenance. In arid coastal developing regions, solar stills provide a resilient, decentralized water supply that requires no infrastructure, no fuel, and no technical expertise to operate.