Scientists from the Rice University in Houston, Texas, have developed a new technology that uses nanoparticles to convert solar energy directly into steam with an overall energy efficiency of 24 percent. The research was published in ACS Nano.
The team from Rice’s Laboratory for Nanophotonics (LANP) used light-capturing nanoparticles to convert sunlight into heat. By submerging the light-capturing nanoparticles in water and exposing them to sunlight, the particles heat up so quickly they instantly vaporize water and create steam. So it doesn’t require boiling water. The method, the scientists refer to as “solar-steam””, works in a different way than conventional solar thermal panels, that can only heat up water slowly.
The solar steams’ overall efficiency of the 24 percent is quite high compared to the efficiency of photovoltaic solar panels, which have an overall energy efficiency of around 15 percent. The LANP – team says the overall energy efficiency can probably be increased as the technology is refined.
On Rice University’s website LANP Director Naomi Halas, the lead scientist on the project, explains why they managed to achieve such high efficiency: “We’re going from heating water on the macro scale to heating it at the nano-scale ” 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 counter-intuitive.”
The solar steam method is apparently so effective, it can even produce steam from icy cold water. This video shows how the LANP-team creates steam from almost frozen water. Water with added nanoparticles sits in an ice bag, a lens is used to concentrate sunlight onto the near-freezing mixture in the tube. The nanoparticles heat up and produce steam. The technology converts about 80 to 90 percent of the energy coming from the sun into steam.
According to the researchers, the technology can play an important part in low-cost sanitation, water purification and human waste treatment for the developing world. Although its not the initial intended use , it could be very interesting exploring this technique for the generation of electricity by using steam. Perhaps with a steam turbine as a converter?