Could we use solar power to purify drinking water?

UniSA

The experimental desalination device used for outdoor sea-water evaporation testing (left) and an envisaged ocean-borne version.

There has been significant recent research into the possibility of desalination using photo-thermal evaporators powered only by sunlight. The problem has been achieving an efficiency high enough to make such devices practical.

Scientists at the University of South Australia (UniSA) think they have a solution. As in other experiments, they ised photothermal materials (PTMs) with excellent solar light absorption, floated on a water surface. Heat from the PTMs is concentrated at the surface causing evaporation and the generation of steam, which is free of salt or other pllutants and can then be harvested as drinking water.

One issue is that the water at the point of evaporation increases, and loses energy to  both the environment and the water bulk below via radiation and convection respectively.

The UniSA team focused on ways to actually reverse the conductive heat loss by adding a cold evaporation surface between the surface being heated and and the bulk of the water. They found that the conductive heat loss could can be fully absorbed by the cold evaporation surface and used for cold evaporation before it reaches the water bulk. Further, once the area of the cold surface was increased beyond a critical value, energy could be extracted from the bulk water to enhance the overall solar evaporation.

The scientists estimate that in this way a 1m2 surface area of salt water or contaminated water could provide enough clean water for a family of four.

USING THE SUN TO CREATE DRINKING WATER

Raising efficiency: The UniSA team improved efficiency of their solar steam generation to a practical level by optimising the energy flows during solar steam generation.

Remote locations: A viable water purifier could provide clean water where existing methods are too expensive, such as in disadvantaged or vulnerable communities and remote locations.

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