Sunlight can produce energy and clean water at the same time

Engineers have constructed a device that not only generates electricity from the sun, but also distills freshwater from seawater. Solar farms that install such two-for-one systems could help meet the increasing global demand for drinking water while cranking out useful power. 

Peng Wang, Wenbin Wang and Yusuf Shi have applied for a patent on the new concept. They are part of an 11-member team that developed the new device. All work at King Abdullah University of Science and Technology in Thuwal, Saudi Arabia. They described their new device online July 9 in Nature Communications.

A solar cell forms the heart of the new system. Such cells harvest sunlight to make electricity. Some of the incoming light, however, will turn into heat. The new system harvests this waste heat to drive the evaporation of seawater. That water vapor wafts through a porous membrane made from plastic. This filters out contaminants, including salt. As such, this is a desalination system. So the liquid that condenses out on the other side will be clean freshwater. 

The removal of salt from the water “doesn’t affect the electricity production by the [solar cell],” explains Peng Wang. He’s an engineer and lead author of the new study.  “At the same time,” he adds, this system “gives you bonus freshwater.” 

Such tackling of two big challenges at once “is a great idea,” says Jun Zhou. He’s a materials scientist at Huazhong University of Science and Technology in Wuhan, China. Zhou was not involved in the new project.

The system’s prospects

So far, the King Abdullah researchers have reported on lab tests using a prototype, or early experimental version of the device. They exposed it to a lamp whose light mimics that of the sun. The new system converted about 11 percent of the light it received into electricity. That’s not bad. Solar cells sold today typically transform some 10 to 20 percent of the sunlight they soak up into usable energy. 

Wang’s team also tested how well their system cleaned up water. They fed it saltwater and dirty water that contained toxic heavy metals. Their findings suggest that a device about a meter (39 inches) across could pump out about 1.7 kilograms (3.7 pounds) of clean water per hour. For perspective, a gallon (3.8 liters) of water weighs 8.4 lbs (3.8 kg).

“It’s really good engineering work,” says George Ni of the project. He’s an engineer who was not involved in the new study. He did, however, work on water desalination while a graduate student at the Massachusetts Institute of Technology. 

“The next step is, how are you going to deploy this?” says Ni. “Is it going to be on a roof? If so, how do you get a source of water to it? If it’s going to be [floating] in the ocean, how do you keep it steady” so that it isn’t toppled by waves? Such practical issues would need to be figured out before the device could enter real-world use.