In a new twist to the quest to harness the power of the sun, Rice University scientists are using sun power to produce steam from icy cold water. The solar steam method, from Rice’s Laboratory for Nanophotonics, uses light-capturing nanoparticles to convert the sunlight into heat.

The inventors of solar steam see the first use of their new technology as being in the sanitation and water purification sector, but believe that it will also have implications for the renewable energy generation sector – especially in the field of solar thermal power.

Compared with photovoltaic solar panels, which have an overall energy efficiency of around 15 percent, the solar steam method has an overall energy efficiency of 24 percent.

The nanoparticles are the key to the solar steam method. When they are submerged in water and exposed to sunlight, they heat up quickly – rising to above 212 degrees Fahrenheit – and instantly vaporize the water to create steam.

“We’re going from heating water on the macro scale to heating it at the nanoscale,” said lead scientist Naomi Halas.

Ms. Halas, who is also the director of the Laboratory for Nanophotonics, noted that the particles used in the solar steam method are smaller than even 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,” she said.

“Solar steam is remarkable because of its efficiency,” said Rice graduate student Oara Neumann. “It does not require acres of mirrors or solar panels. In fact, the footprint can be very small.

As an example, Ms. Neumann cited a solar steam-powered autoclave that has already been created by Rice engineering undergraduates to sterilize medical and dental instruments.

“The light window in our demonstration autoclave was just a few square centimeters,” she pointed out.

Steam is one of the world’s most-used industrial fluids and it is also used in sterilization, food preparation and water purification. Steam, through steam driven turbines, also produces about 90 percent of the world’s electricity.

Most industrial steam however is produced in large boilers, because of its efficiency; solar steam can be more economical on a smaller scale.

Ms. Halas will be working to create an ultra-small-scale system for treating human waste in areas without sewer systems or electricity for the Bill and Melinda Gates Foundation as the winner of a Grand Challenges grant. – K.R. Jalbuena