Solar distillation technology is being increasingly deployed worldwide to provide freshwater for industrial and potable purposes. Despite its promise, solar-driven evaporation/condensation systems are marked by low and slow water production rates. To remedy this, a faster and lower cost approach to solar desalination has been developed by researchers from Ural Federal University (Russia) and Northern Technical University (Iraq).

The solar distillation process was modified to increase evaporation efficiency by inclusion of a rotating hollow steel cylinder in a rectangular basin with a hinged transparent cover.

Inside the water-filled basin, the cylinder is slowly rotated by a solar-powered DC motor. As the hollow cylinder turns, a thin film of water is continuously formed on its surface, absorbing heat and evaporating much faster than in more commonly used systems. As with a traditional solar still, the resulting condensation travels down the inside of the cover into an aluminum trough, which in turn channels it into a separate vessel.

A prototype was tested on a rooftop in the Russian city of Ekaterinburg during the summer of 2019, with the cylinder turning at a rate of 0.5 rpm. The system was documented to be up to 400% more effective at producing drinking water compared with a conventional solar still.

The researchers note that system productivity can be further increased by expanding the surface area for absorption and evaporation in the cylinder with a fin or surface corrugation.

A paper on this development is published in Case Studies in Thermal Engineering.