New Technology Uses Nanoparticles to Convert Solar Energy Directly into Steam

Scientists at Rice University have unveiled a new solar technology using nanoparticles, which can directly convert solar energy into steam, without boiling the water, at an efficiency rate of about 24%.

The new technology, dubbed "solar steam", uses nanoparticles submerged in water to convert the sunlight into heat. The particles used in the system heat up so rapidly that the water is instantly vaporized into steam, as the particles can be activated by not just visible sunlight, but also by shorter wavelengths that are invisible to the human eye.

"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." - Naomi Halas, Director, Rice Laboratory for Nanophotonics (LANP)

The team believes that developing countries may be among the first to take advantage of the benefits of solar steam for sanitation and water purification, and in that vein, a group of engineering undergraduates at Rice have already built an autoclave using solar steam for sterilizing medical and dental instruments.

As steam is one of the world's most used industrial fluids, used to generate up to 90% of electricity, as well as for water purification and food preparation, this breakthrough could make a big difference in many areas of society:

"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." - Rice grad student Oara Neumann, lead co-author on the paper

The results of the project are documented at a paper published at ACS NANO: Solar Vapor Generation Enabled by Nanoparticles

"Solar illumination of broadly absorbing metal or carbon nanoparticles dispersed in a liquid produces vapor without the requirement of heating the fluid volume. When particles are dispersed in water at ambient temperature, energy is directed primarily to vaporization of water into steam, with a much smaller fraction resulting in heating of the fluid. Sunlight-illuminated particles can also drive H2O - ethanol distillation, yielding fractions significantly richer in ethanol content than simple thermal distillation. These phenomena can also enable important compact solar applications such as sterilization of waste and surgical instruments in resource-poor locations."

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