A highly efficient water-evaporation method has been developed by researchers from the University of South Australia that can make a square meter source of water drinkable for a family of four.
The ‘world-first’ technique means that drinking water can be derived from seawater, brackish water or contaminated water. It offers a promising possibility for the challenge of accessible fresh drinking water in densely populated and vulnerable communities.
Currently, 1.42 billion people – including 450 million children – live in areas of high, or extremely high, water vulnerability, and that figure is expected to grow in coming decades.
Lead researcher and ARC Future Fellow Associate Professor Hoalan Xu said that his team is the first in the world to extract energy from the bulk water during solar evaporation and use it for evaporation.
“This has helped our process become efficient enough to deliver between 10 and 20 litres of fresh water per square metre per day,” A/Prof Xu said.
The innovation of the breakthrough is made all the more exciting because the research team have been able to keep it low-cost and virtually zero-maintenance. The technology could potentially be deployed in places where desalination and purification systems would have been too expensive to be viable.
“This technology really has the potential to provide a long-term clean water solution to people and communities who can’t afford other options, and these are the places such solutions are most needed,” A/Prof Xu said.
“In remote communities with small populations, the infrastructure cost of systems like reverse osmosis is simply too great to ever justify, but our technique could deliver a very low cost alternative that would be easy to set up and basically free to run.”
Using a photothermal structure that sits on the surface of a water source and converts sunlight to heat, the method focuses energy on the surface to rapidly evaporate the uppermost portion of the liquid.
According to A/Prof Xu, previous efforts to explore the use of similar technology were set back by problems with energy loss as heat passed into the source water and dissipated into the air above.
This new method overcomes traditional problems of solar energy loss because scientists developed a three-dimension, fin-shaped heatsink-like evaporator. The ‘heatsink’ design shifts surplus heat away from the water’s top surfaces, distributing heat to the fin surface for water evaporation, and cooling the top evaporation surface and realising zero energy loss during solar evaporation.
“Previously many of the experimental photothermal evaporators were basically two dimensional; they were just a flat surface, and they could lose 10% to 20% of solar energy to the bulk water and the surrounding environment,” A/Prof Xu explains.
“We have developed a technique that not only prevents any loss of solar energy, but actually draws additional energy from the bulk water and surrounding environment, meaning the system operates at 100% efficiency for the solar input and draws up to another 170% energy from the water and environment.”
This heatsink technique means all surfaces of the evaporator remain at a lower temperature than the surrounding water and air, so additional energy flows from the higher-energy external environment into the lower-energy evaporator.
The researchers from UniSA’s Future Industries Institute are also exploring industrial applications for the technology.
“There are a lot of potential ways to adapt the same technology, so we are really at the beginning of a very exciting journey,” A/Prof Xu says.
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