Engineers upgrade ancient, sun-powered tech to purify water with near-perfect efficiency

The new water purification technique involves draping a sheet of carbon-dipped paper in an upside-down “V.” The paper’s bottom edges soak up water, while the carbon coating absorbs solar energy and transforms it into heat for evaporation. Credit: Huaxiu Chen

Low-cost device — shaped like a birdhouse — could help provide drinking water to people affected by natural disasters

Left to right: Researchers Qiaoqiang Gan, Zongmin Bei and Haomin Song were among the authors of the new study in Advanced Science. The three engineers and their colleagues are working to bring the solar still to people who need it through their startup company, Sunny Clean Water. Credit: Douglas Levere / University at Buffalo

A central component of the new technology is a sheet of carbon-dipped paper folded into an upside-down “V.” The paper’s sloped geometry keeps it cool by weakening the intensity of light illuminating it. (A flat surface would be hit directly by the sun.) This novel, slanted architecture helped to speed vapor and water generation in experiments. Credit: Youhai Liu

BUFFALO, N.Y. — The idea of using energy from the sun to evaporate and purify water is ancient. The Greek philosopher Aristotle reportedly described such a process more than 2,000 years ago.

Now, researchers are bringing this technology into the modern age, using it to sanitize water at what they report to be record-breaking rates.

By draping black, carbon-dipped paper in a triangular shape and using it to both absorb and vaporize water, they have developed a method for using sunlight to generate clean water with near-perfect efficiency.

“Our technique is able to produce drinking water at a faster pace than is theoretically calculated under natural sunlight,” says lead researcher Qiaoqiang Gan, PhD, associate professor of electrical engineering in the University at Buffalo School of Engineering and Applied Sciences.

As Gan explains, “Usually, when solar energy is used to evaporate water, some of the energy is wasted as heat is lost to the surrounding environment. This makes the process less than 100 percent efficient. Our system has a way of drawing heat in from the surrounding environment, allowing us to achieve near-perfect efficiency.”

The low-cost technology could provide drinking water in regions where resources are scarce, or where natural disasters have struck. The advancements are described in a study published on May 3 in the journal Advanced Science.

The project, funded by the National Science Foundation (NSF), was a collaboration between UB, Fudan University in China and the University of Wisconsin-Madison. UB electrical engineering PhD graduate Haomin Song and PhD candidate Youhai Liu were the study’s first authors.

Gan, Song and other colleagues have launched a startup, Sunny Clean Water, to bring the invention to people who need it. With support from the NSF Small Business Innovation Research program, the company is integrating the new evaporation system into a prototype of a solar still, a sun-powered water purifier.

“When you talk to government officials or nonprofits working in disaster zones, they want to know: ‘How much water can you generate every day?’ We have a strategy to boost daily performance,” Song says. “With a solar still the size of a mini fridge, we estimate that we can generate 10 to 20 liters of clean water every single day.”