A new solar-powered evaporator could soon bring freshwater to millions of needy people

19 April 2021

One in five people around the world lack regular access to freshwater, which makes up just 3% of the world’s water sources. Most of the 1.5 billion or so people who need to go without freshwater, however, live in arid areas where there’s another natural resource in abundance: sunshine.

And so a team of researchers at the University of Southern Australia has decided to harness the power of the sun for creating freshwater. They have done this by fine-tuning a process to derive freshwater from seawater or polluted water through highly efficient solar evaporation.

Their technique allows a family of four to get enough fresh drinking water daily from just one square meter of seawater, brackish water or contaminated water, as the case may be.

The new system, which can be produced from inexpensive materials, is based on a photothermal structure placed on the surface of a water source to convert sunlight to heat and aid in the evaporation of the top layer of the liquid, which can then be harnessed as freshwater.

Although similar photothermal technologies have been designed before, the Australian team’s new version is far more efficient, according to its creators. That is thanks to the new design’s three-dimensional heatsink-like evaporator, which is shaped like a fin.

The design “shifts surplus heat away from the evaporator’s top surfaces, distributing heat to the fin surface for water evaporation, thus cooling the top evaporation surface and realising zero energy loss during solar evaporation,” explain the scientists, who describe the technique in a new paper.

“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,” they add.

The method makes it possible to derive anywhere between 10 liters and 20 liters of fresh water per each square meter of water each day.

“Previously many of the experimental photothermal evaporators were basically two dimensional; they were just a flat surface, and they could lose 10 to 20 per cent of solar energy to the bulk water and the surrounding environment,” explains Haolan Xu, an associate professor at the university who led the research.

“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 per cent efficiency for the solar input and draws up to another 170 per cent energy from the water and environment,” Xu adds.

Importantly, the system is inexpensive and it is also easy to construct and deploy. In addition, it is easy to maintain as the design of the photothermal structure prevents salt and other contaminants building up on the evaporator surface, the scientists say.

As a result, the new technology can provide a low-cost alterative to more expensive desalination techniques because it can easily be set up and run. “[B]ecause it is so simple and requires virtually no maintenance, there is no technical expertise needed to keep it running and upkeep costs are minimal,” Xu says.

“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,” he stresses.

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