How to boil water using only sunlight

Boiled water has many uses. It produces steam, which be used for energy. It can also be used for sanitation or desalination. But as anyone who has left a pot of water outside knows, sunlight alone is not enough to boil water.

Or is it? Researchers at Rice University have devised a way to boil water using only sunlight - and small carbon or metal particles, which are smaller than a wavelength of light, which reflect the sun’s rays and heat the water. The particles’ heat is concentrated near the water’s surface, creating a vapor bubble - and producing steam. In this way, only a small portion of a container of water must be heated in order for the liquid to boil - a small enough portion that sunlight alone can do the trick. The notion is a radical departure from traditional boiling, which requires that the entire container be heated.

“We’re going from heating water on the macro scale to heating it at the nanoscale,” said Naomi Halas, the director of Rice University’s Laboratory for Nanophotonics and the lead scientist on the project. “Our particles are very small — even smaller than a wavelength of light — which means they have an extremely small surface area to dissipate heat. This intense heating allows us to generate steam locally, right at the surface of the particle, and the idea of generating steam locally is really counterintuitive.”

Students are already at work on potential applications of the technology, including a steam-powered autoclave, used to sterilize medical and dental instruments, and small-scale system for treating human waste in areas without access to sewage systems or electricity. Future applications could include powering hybrid air-conditioning and heating systems.

“This is about a lot more than electricity,” Halas said. “With this technology, we are beginning to think about solar thermal power in a completely different way.”

See a video produced by Rice University here.

Photo: Flickr/Jalal Hameed Bhatti

via [Fast Company]