Near-Perfect Purifier

Water purifier with solar still

New solar still could help make clean water available to all.

The idea of using energy from the sun to evaporate and purify water goes back at least 2,000 years, to the days of Aristotle.

Now, University at Buffalo researchers are bringing this technology into the modern age, producing drinking water at record-breaking rates and with near-perfect efficiency, says Qiaoqiang Gan, associate professor of electrical engineering at the UB School of Engineering and Applied Sciences.

Modernizing an age-old technology

Solar stills have been around for a long time. They use the sun’s heat to evaporate water, leaving salt, bacteria and dirt behind. Then, the water vapor cools and returns to a liquid state, at which point it’s collected in a clean container.

The technique has many advantages. It’s simple, and the power source—the sun—is available just about everywhere. But even the latest solar still models are somewhat inefficient at vaporizing water.

Gan’s team addressed this challenge through a neat, counterintuitive trick: They increased the efficiency of their evaporation system by cooling it down.

A central component of their technology is a sheet of carbon-dipped paper that is folded into an upside-down “V” shape, like the roof of a birdhouse. The bottom edges of the paper hang in a pool of water, soaking up the fluid like a napkin. At the same time, the carbon coating absorbs solar energy and transforms it into heat for evaporation.

Low cost, high gain

“Most groups working on solar evaporation technologies are trying to develop advanced materials, such as metallic plasmonic and carbon-based nanomaterials,” Gan says. “We focused on using extremely low-cost materials and were still able to realize record-breaking performance.”

The inexpensive technology could provide drinking water in regions where resources are scarce or where natural disasters have struck. Gan’s team estimates that, using their technology, a solar still the size of a mini fridge could generate five to 10 liters of clean water a day.