Super-Efficient solar-Energy Technology


Rice unveils super-efficient solar-energy technology

‘Solar steam’ so effective it can make steam from icy cold water

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 way.”

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 centimeters.”

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 Foundation.

VIDEO is available at:

http://youtu.be/ved0K5CtmsU

A copy of the ACS Nano paper is available at:

http://dx.doi.org/10.1021/nn304948h

High-resolution images are available for download:

http://news.rice.edu/wp-content/uploads/2012/11/SOLAR-3-WEB.jpg

New solar steam technology developed at Rice University uses nanoparticles so effective at turning sunlight into heat that it can produce steam from icy-cold water. (Credit: Jeff Fitlow/Rice University)

http://news.rice.edu/wp-content/uploads/2012/11/SOLAR-2-WEB.jpg

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. (Credit: Jeff Fitlow/Rice University)

http://news.rice.edu/wp-content/uploads/2012/11/SOLAR-1-WEB.jpg

Rice University graduate student Oara Neumann and scientist Naomi Halas are co-authors of new research on a highly efficient method of turning sunlight into heat. They expect their technology to have an initial impact as an ultra-small-scale system to treat human waste in developing nations without sewer systems or electricity. (Credit: Jeff Fitlow/Rice University)

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Nanoparticles convert solar energy directly to steam


Houston, TXA new technology that uses nanoparticles to convert solar energydirectly into steam has been developed by Rice University scientists. This new “solar steam” method from Rice’s Laboratory for Nanophotonics (LANP) is so effective it can even produce steam from icy cold water. Published online in ACS Nano, the technology has an overall energy efficiency of 24%–even better than solar photovoltaic panels. Initially, however, the inventors of the solar steam technology say it will be initially used for sanitation and water purification in developing countries rather than for energy generation.

“This is about a lot more than electricity,” said LANP director Naomi Halas, lead scientist on the project. “With this technology, we are beginning to think about solar thermal power in a completely different way.” 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.” 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 and about 90% 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.

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. For 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.

SOURCE: Rice University; http://news.rice.edu/2012/11/19/rice-unveils-super-efficient-solar-energy-technology/

IMAGE: Rice University graduate student Oara Neumann and scientist Naomi Halas are co-authors of new research on a highly efficient method of turning sunlight into heat. They expect their technology to have an initial impact as an ultra-small-scale system to treat human waste in developing nations without sewer systems or electricity. (Courtesy Jeff Fitlow/Rice University)

Rice University graduate student Oara Neumann and scientist Naomi Halas are co-authors of new research on a highly efficient method of turning sunlight into heat. They expect their technology to have an initial impact as an ultra-small-scale system to treat human waste in developing nations without sewer systems or electricity. (Courtesy Jeff Fitlow/Rice University)

Light might prompt graphene devices on demand


MIKE WILLIAMS

 – OCTOBER 10, 2012

Rice University researchers find plasmonics show promise for optically induced electronics

Rice University researchers are doping graphene with light in a way that could lead to the more efficient design and manufacture of electronics, as well as novel security and cryptography devices.

Graphene circuitry

Nanoscale plasmonic antennas called nonamers placed on graphene have the potential to create electronic circuits by hitting them with light at particular frequencies, according to researchers at Rice University. The positively and negatively doped graphene can be prompted to form phantom circuits on demand.

Manufacturers chemically dope silicon to adjust its semiconducting properties. But the breakthrough reported in the American Chemical Society journal ACS Nano details a novel concept: plasmon-induced doping of graphene, the ultrastrong, highly conductive, single-atom-thick form of carbon.

That could facilitate the instant creation of circuitry – optically induced electronics – on graphene patterned with plasmonic antennas that can manipulate light and inject electrons into the material to affect its conductivity.

The research incorporates both theoretical and experimental work to show the potential for making simple, graphene-based diodes and transistors on demand. The work was done by Rice scientists Naomi Halas, Stanley C. Moore Professor in Electrical and Computer Engineering, a professor of biomedical engineering, chemistry, physics and astronomy and director of the Laboratory for Nanophotonics; and Peter Nordlander, professor of physics and astronomy and of electrical and computer engineering; physicist Frank Koppens of the Institute of Photonic Sciences in Barcelona, Spain; lead author Zheyu Fang, a postdoctoral researcher at Rice; and their colleagues.

“One of the major justifications for graphene research has always been about the electronics,” Nordlander said. “People who know silicon understand that electronics are only possible because it can be p- and n-doped (positive and negative), and we’re learning how this can be done on graphene.

“The doping of graphene is a key parameter in the development of graphene electronics,” he said. “You can’t buy graphene-based electronic devices now, but there’s no question that manufacturers are putting a lot of effort into it because of its potential high speed.”

Researchers have investigated many strategies for doping graphene, including attaching organic or metallic molecules to its hexagonal lattice. Making it selectively – and reversibly – amenable to doping would be like having a graphene blackboard upon which circuitry can be written and erased at will, depending on the colors, angles or polarization of the light hitting it.

Nonamers

Nonamers in the drawings at top and in the photos at bottom are arrays of nine gold nanoparticles deposited on graphene and tuned to particular frequencies of light. When illuminated, the plasmonic particles pump electrons into the graphene, according to researchers at Rice University who say the technology may lead to the creation of on-demand circuitry for electronic devices.

The ability to attach plasmonic nanoantennas to graphene affords just such a possibility. Halas and Nordlander have considerable expertise in the manipulation of the quasiparticles known as plasmons, which can be prompted to oscillate on the surface of a metal. In earlier work, they succeeded in depositing plasmonic nanoparticles that act as photodetectors on graphene.

These metal particles don’t so much reflect light as redirect its energy; the plasmons that flow in waves across the surface when excited emit light or can create “hot electrons” at particular, controllable wavelengths. Adjacent plasmonic particles can interact with each other in ways that are also tunable.

That effect can easily be seen in graphs of the material’s Fano resonance, where the plasmonic antennas called nonamers, each a little more than 300 nanometers across, clearly scatter light from a laser source except at the specific wavelength to which the antennas are tuned. For the Rice experiment, those nonamers – eight nanoscale gold discs arrayed around one larger disc – were deposited onto a sheet of graphene through electron-beam lithography. The nonamers were tuned to scatter light between 500 and 1,250 nanometers, but with destructive interference at about 825 nanometers.

At the point of destructive interference, most of the incident light energy is converted into hot electrons that transfer directly to the graphene sheet and change portions of the sheet from a conductor to an n-doped semiconductor.

Arrays of antennas can be affected in various ways and allow phantom circuits to materialize under the influence of light. “Quantum dot and plasmonic nanoparticle antennas can be tuned to respond to pretty much any color in the visible spectrum,” Nordlander said. “We can even tune them to different polarization states, or the shape of a wavefront.

“That’s the magic of plasmonics,” he said. “We can tune the plasmon resonance any way we want. In this case, we decided to do it at 825 nanometers because that is in the middle of the spectral range of our available light sources. We wanted to know that we could send light at different colors and see no effect, and at that particular color see a big effect.”

Nordlander said he foresees a day when, instead of using a key, people might wave a flashlight in a particular pattern to open a door by inducing the circuitry of a lock on demand. “Opening a lock becomes a direct event because we are sending the right lights toward the substrate and creating the integrated circuits. It will only answer to my call,” he said.

Rice co-authors of the paper are graduate students Yumin Wang and Andrea Schlather, research scientist Zheng Liu, and Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry.

The research was supported by the Robert A. Welch Foundation, the Office of Naval Research, the Department of Defense National Security Science and Engineering Faculty Fellows program and Fundacio Cellex Barcelona.