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Sunlight instantly turns ice water to steam using nanoparticles

Image of solar steam device
The solar steam device developed at Rice University has an overall energy efficiency of 24 percent, far surpassing that of photovoltaic solar panels. It may first be used in sanitation and water-purification applications in the developing world.Jeff Fitlow / Rice University

Sunlight and itsy bitsy flecks of metal or carbon are all that’s required to quickly vaporize icy-cold water, according to researchers who recently unveiled a new steam-generating process that could revolutionize industrial practices without the hangover of greenhouse gas emissions.

Steam is used throughout our world. It spins turbines to generate electricity and heats kettles used to brew beer. It is used to sterilize medical equipment and distill alcohol

But, generating steam typically requires tons of energy to heat and boil water. The most common sources of energy are coal, oil, and natural gas — fossil fuels that when burned emit carbon dioxide, the greenhouse gas that’s building up in the atmosphere and causing the planet’s climate to change.

Researchers at Rice University unveiled a method that uses light-absorbing nanoparticles submerged in water to convert solar energy directly into piping hot steam. It is so effective that it can even produce the steam from ice water.

The tiny particles heat up so quickly that they instantly vaporize water, rather than dissipating the heat into the surrounding fluid. Precisely how this works is a bit of a mystery, according to Naomi Halas,  director of the nanophotonics laboratory at Rice University.

“There seems to be some nanoscale thermal barrier, because it is clearly making steam like crazy,” she told Technology Review.

The process has an overall efficiency of 24 percent, compared to about 15 percent efficiency for solar panels such as those on your neighbor’s roof. But generating electricity is unlikely the first application of the new technology, which was developed with funding from the Bill and Melinda Gates Foundation

Rather, it will be used for sanitation and water purification in developing countries, helping to stem the spread of disease. To that end, the Rice University team has already created a solar steam-powered autoclave to sterilize medical and dental instruments at clinics without access to electricity.

The technology could, however, also improve the efficiency and lower the cost of large-scale solar thermal energy generating plants, which use sunlight to warm up oil that is then used to heat water and generate steam to spin turbines. 

Generating steam directly with the nanoparticles would be 3 to 5 percent more efficient and result in a cost savings of about 10 percent due to the less complex design, Todd Otanicar, a mechanical engineer at the University of Tulsa, told Technology Review. 

For more information, check out the video below. A paper on the process was published Nov. 19 in the journal ACS Nano

 — via Technology Review and Rice University 

John Roach is a contributing writer for NBC News Digital. To learn more about him, check out his website. For more of our Future of Technology series, watch the featured video below.