Rice University scientists have unveiled a revolutionary new technology that uses nanoparticles to convert solar energy directly into steam. The technology’s inventors said they expect it will first be used in sanitation and water-purification applications in the developing world.
Maybe – the team has tested the technology with distillation experiments and found that solar steam is about two-and-a-half times more efficient than existing distillation columns – that’s music to the alcohol production crowd.
Or the steam could be used to sterilize medical waste and surgical instruments, to prepare food and to purify water. Engineered properly the solar steam’s efficiency could allow steam to become economical on a much smaller scale for industrial heat and generating electricity.
The key in the research is the technology has an overall energy efficiency of 24 percent. Photovoltaic solar panels, by comparison, typically have an overall energy efficiency around 15 percent. Bear in mind that about half of the solar energy arriving to earth’s surface is in the infrared range. Halas’ team 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.
Naomi Halas, a Director at Rice’s Laboratory for Nanophotonics (LANP) and the lead scientist on the project said, “This is about a lot more than electricity. With this technology, we are beginning to think about solar thermal power in a completely different way.”
The efficiency of the solar steam technology 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. The nanoparticles are so effective they can even produce steam from icy cold water. Halas said the solar steam’s overall energy efficiency can probably be increased as the technology is refined.
The technology is going to be on a very different scale. Halas explains, “We’re going from heating water on the macro scale to heating it at the nanoscale. 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 counter intuitive.”
To show just how counter intuitive, 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 at larges sale in large boilers, but solar steam’s efficiency could allow steam to become economical on a much smaller scale.
The Rice team believes people in developing countries will be among the first to see the benefits of solar steam. Engineering undergraduates have already created a solar steam-powered autoclave that’s capable of sterilizing medical and dental instruments at clinics that lack electricity.
Details of the solar steam method were published online yesterday in ACS Nano. The private circulation of the research impact is already underway – Halas has already 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.
Neumann, the lead co-author on the paper offers an overview by an analogy, “Solar steam is remarkable because of its efficiency. 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.”
Steam at economical small scales light up imaginations. 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.
This breakthrough merits close attention. Halas is the Stanley C. Moore Professor in Electrical and Computer Engineering, a professor of physics, professor of chemistry and professor of biomedical engineering, and is one of the world’s most-cited chemists. Her lab specializes in creating and studying light-activated particles.
A recent creation, gold nanoshells are the subject of several clinical trials for cancer treatment.
Team members and 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.
Quite a group with quite a result!