In a development that is being called “revolutionary”, Rice University engineers at the Laboratory for Nanophotonics (LANP) have unveiled a new technology for converting solar energy “directly into steam” (that is, without requiring heating of the entire fluid volume).
And unlike current macroscale, solar-to-steam methods, the new “solar steam”: technology uses nanoparticles. The particles — measured in billionths of a meter in size — are so effective that they can nearly instantly produce steam from even ice-cold water.
They are also “super-efficient”, producing an overall efficiency of 24%, as compared to photovoltaic solar panels, which typically have an overall energy efficiency of about 15 percent.
“We’re just boiling water in a radically different way.” Naomi Halas, LANP
How it Works
The efficiency of the solar steam method is due to the light-capturing capacity of the carbon-metal nanoparticles. The particles were designed to interact with a broader spectrum of light waves (as compared to those used in medical therapeutics) that includes both visible and non-visible wavelengths.
Once submerged in water and exposed to sunlight, the nanoparticles are able to heat up so rapidly that they “instantly” convert the surrounding water into steam. Thus, a much smaller fraction of solar energy is required in heating of the fluid.
The team believes that even greater efficiencies will be achieved as the new tech is refined — perhaps through combining this tech with existing, low-cost, solar-concentrating technologies.
Lead scientist and LANP Director Naomi Halas elaborates:
“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 counterintuitive.”
Indeed, so counter intuitive that graduate student Oara Neumann decided to make a video demonstrating the efficacy of the nanoparticle reaction — one that does not even require the particles to make direct contact with water. particles were added to a test tube of water which was then submerged in a larger tank of ice water. Using a lens to concentrate sunlight on the (nearly frozen) test tube mixture, they were able to generated steam in a matter of seconds.
First Uses for the New Tech
Despite this breakthrough and its potential for the renewable energy industry, the scientists state that its first use will most likely be for water purification in developing world nations which lack proper water sanitation systems.
Steam is perhaps the most useful industrial fluid produced.World-wide, nearly 90% of electricity is generated via steam. Steam is also critical for sterilization in the medical industry.
But most of this industrial steam is produced in large boilers, making them impractical for wide-scale adoption in impoverished communities around the globe.
The Rice team believes that solar stream efficiency — and its effectiveness over a much smaller surface area — could make steam generation more economical on much smaller operational scales.
According to the published paper abstract, the tech could be used to generate other fuel sources too. “Sunlight-illuminated particles can also drive H2O-ethanol distillation, yielding fractions significantly richer in ethanol content than simple thermal distillation.”
Previously, Rice engineering students had created a solar steam-powered autoclave that can sterilize medical equipment at clinics that lack electricity. Additionally, lead scientist Halas 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.” [source: Rice press release]
“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,” said Halas.
Details of the solar steam method were published online today in ACS Nano.
Top photo: 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