[LINK] Rice unveils super-efficient solar-energy technology

stephen at melbpc.org.au stephen at melbpc.org.au
Tue Nov 20 23:10:35 AEDT 2012

Rice unveils super-efficient solar-energy technology

By Jade Boyd – November 19, 2012

HOUSTON — (Nov. 19, 2012) — Rice University scientists have unveiled a 
revolutionary new technology that uses nanoparticles to convert solar 
energy directly into steam. The new “solar steam” method from Rice’s 
Laboratory for Nanophotonics (LANP) is so effective it can even produce 
steam from icy cold water.

Details of the solar steam method were published online today in ACS 
Nano. The technology has an overall energy efficiency of 24 percent. 
Photovoltaic solar panels, by comparison, typically have an overall 
energy efficiency around 15 percent. However, the inventors of solar 
steam said they expect the first uses of the new technology will not be 
for electricity generation but rather for sanitation and water 
purification in developing countries.

“This is about a lot more than electricity,” said LANP Director Naomi 
Halas, the lead scientist on the project. “With this technology, we are 
beginning to think about solar thermal power in a completely different 

The efficiency of solar steam is due to the light-capturing nanoparticles 
that convert sunlight into heat. When submerged in water and exposed to 
sunlight, the particles heat up so quickly they instantly vaporize water 
and create steam. Halas said the solar steam’s overall energy efficiency 
can probably be increased as the technology is refined.

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

To show just how counterintuitive, Rice graduate student Oara Neumann 
videotaped a solar steam demonstration in which a test tube of water 
containing light-activated nanoparticles was submerged into a bath of ice 
water. Using a lens to concentrate sunlight onto the near-freezing 
mixture in the tube, Neumann showed she could create steam from nearly 
frozen water.

Steam is one of the world’s most-used industrial fluids. About 90 percent 
of electricity is produced from steam, and steam is also used to 
sterilize medical waste and surgical instruments, to prepare food and to 
purify water.

Most industrial steam is produced in large boilers, and Halas said solar 
steam’s efficiency could allow steam to become economical on a much 
smaller scale.

People in developing countries will be among the first to see the 
benefits of solar steam. Rice engineering undergraduates have already 
created a solar steam-powered autoclave that’s capable of sterilizing 
medical and dental instruments at clinics that lack electricity. Halas 
also won a Grand Challenges grant from the Bill and Melinda Gates 
Foundation to create an ultra-small-scale system for treating human waste 
in areas without sewer systems or electricity.

“Solar steam is remarkable because of its efficiency,” said Neumann, the 
lead co-author on the paper. “It does not require acres of mirrors or 
solar panels. In fact, the footprint can be very small. For example, the 
light window in our demonstration autoclave was just a few square 

Another potential use could be in powering hybrid air-conditioning and 
heating systems that run off of sunlight during the day and electricity 
at night. Halas, Neumann and colleagues have also conducted distillation 
experiments and found that solar steam is about two-and-a-half times more 
efficient than existing distillation columns.

Halas, the Stanley C. Moore Professor in Electrical and Computer 
Engineering, professor of physics, professor of chemistry and professor 
of biomedical engineering, is one of the world’s most-cited chemists. Her 
lab specializes in creating and studying light-activated particles. One 
of her creations, gold nanoshells, is the subject of several clinical 
trials for cancer treatment.

For the cancer treatment technology and many other applications, Halas’ 
team chooses particles that interact with just a few wavelengths of 
light. For the solar steam project, Halas and Neumann set out to design a 
particle that would interact with the widest possible spectrum of 
sunlight energy. Their new nanoparticles are activated by both visible 
sunlight and shorter wavelengths that humans cannot see.

“We’re not changing any of the laws of thermodynamics,” Halas 
said. “We’re just boiling water in a radically different way.”

Paper co-authors include Jared Day, graduate student; Alexander Urban, 
postdoctoral researcher; Surbhi Lal, research scientist and LANP 
executive director; and Peter Nordlander, professor of physics and 
astronomy and of electrical and computer engineering. The research was 
supported by the Welch Foundation and the Bill and Melinda Gates 


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