According to some sources, steam-driven turbines still account for between 80 and 90 percent of the electricity generated in the world. Of course, the method for producing that steam can vary from nuclear power to burning fossil fuels.
Now researchers at Rice University believe that they have found a completely new way for generating steam by placing light-absorbing nanoparticles in water and focusing sunlight on the water so that steam is produced without actually boiling the water.
In this new method not only is it not necessary to boil the water, but the Rice researchers have also demonstrated that steam can be produced in water that remains near the freezing point with this sunlight/nanoparticle combination. According to the researchers, the steam is produced at very high efficiency in which 80 to 90 percent of the energy absorbed from the sun is actually converted to steam.
When these figures are translated into the energy conversion measurements used for photovoltaics it has an overall energy efficiency of 24 percent, significantly higher than photovoltaics that typically measure around 15 percent energy conversion efficiency.
A video demonstrating and describing the technology can be seen below:
The research, which was published in the journal ACS Nano (“Solar Vapor Generation Enabled by Nanoparticles") , made use of a range of materials including metallic and carbon nanoparticles. The key feature for all of them was that they needed to absorb light. When dispersed into water, these nanoparticles direct most of the energy into creating steam rather than heating up the water.
“We’re going from heating water on the macro scale to heating it at the nanoscale,” says Naomi Halas, the lead scientist on the project, in a press release. “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.”
While the technology is a tantalizing alternative to the way most industrial steam is produced in large boilers, the first prototypes of the technology have taken on a more modest scale.
Funded by a Grand Challenges grant from the Bill and Melinda Gates Foundation, the research team built a small-scale system for treating human waste in areas without sewer systems or electricity. The Rice team have also created a system based on the technology that could sterilize medical and dental instruments in places lacking electricity.
A small-is-beautiful approach to this technology may be the way to proceed initially, but the big hope certainly has to be that it could make large-scale electricity production cheaper and more efficient.
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.