LondonA new solar still achieved 278% apparent thermal efficiency, researchers report.
Reed-structured microchannels synchronize water supply, vapor escape, and salt rejection — the bottleneck that defeated previous passive designs.
The system runs stably in 15% saline without crystallization; researchers say it scales for off-grid arid deployment.
Sources: Nature
THE ENERGY FLOOR
Evaporating one liter of water requires roughly 2,260 kJ — the latent heat of vaporization. Sunlight at peak delivers about 1 kW per square meter. Physics sets a hard ceiling on how much fresh water a passive solar still can produce per square meter per day.
THE SALT REJECTION PROBLEM
As water evaporates, salt concentrates in whatever's left. Crystals form on wicks and surfaces, blocking capillary flow and reflecting sunlight. Every passive desalination design lives or dies on whether brine can be flushed continuously without external pumps.
WHY REEDS
Juncus effusus — the soft rush — evolved hollow stem channels that move water and air between roots and atmosphere. The same multiphase plumbing that lets a wetland plant breathe through saturated mud is what synchronizes liquid intake and vapor escape in a still.
THE GULF CONTRAST
The Persian Gulf is already among the saltiest seas on Earth, and Gulf states meet most of their water demand through industrial multi-stage flash and reverse osmosis plants — gigawatts of fossil-fueled capacity. A passive solar still trades throughput for zero operating energy, which is the right tradeoff only off-grid.
WHO NEEDS THIS
Roughly 2 billion people lack reliably safe drinking water. The bottleneck is rarely absolute scarcity — it's grid access, fuel cost, and capital for centralized plants. A device that runs on sunlight, tolerates brackish input, and rejects its own salt collapses three of those constraints at once.