Solar Funnels Convert Sun into Hydrogen

Joanna Schroeder

According to a new article published by a team of researchers from CalTech and the Swiss Federal Institute of Technology there may be a new way to harness the energy of solar even when the sun is not shining. Led by Sossina Haile, she along with her colleagues are looking at ways to produce hydrogen and syngasses by using solar funnels.

In an article, “High-Flux Solar-Driven Thermochemical Dissociation of CO2 and H2O Using Nonstoichiometric Ceria,” published in the December 24, 2010 edition of Science magazine, the research team has developed a device that is able concentrate solar radiation and heat it up to 1,600 degrees Celsius. In simple terms, the heat that results from this process is then used to split water or carbon dioxide into hydrogen.

As described in an article in Clean Energy, the device consists of a quartz lens that focuses the solar radiation on a reaction chamber that is internally reflective and captures most of the photons that enter and converts them to heat. The device heats up at a rate of 140 degrees Celsius a minute until it reaches about 1,250 degrees Celsius, and stabilizing at more than 1,400 degrees Celsius. Through a two-step process, the device’s catalyst ceria (cerium dioxide) converts CO2 or water into its constituent elements.

Haile said in an interview, “Ceria is a metal oxide, what that material will do when heated is it will release oxygen.…It happens at high temperatures, when we cool it back down it wants to absorb oxygen.  “The ceria replaces the oxygen by stripping it from the supplied material, carbon dioxide or water, thereby creating carbon monoxide—used for syngas, or hydrogen—which can be used directly. Either resulting fuel could be used to store the sun’s energy for use in power generation.”

The funnels can be small, but they’re not nano-sized. “It’s like a sponge it’s porous and the gasses flow through it,” Haile said. But “it’s not nano because these temperatures are too high for nano-structures.”

According to Haile, the funnels are not efficient enough for commercial use and to date, only convert around 0.7 percent to 0.8 percent of the solar energy in the funnel into fuel. With further research she hopes this will improve dramatically.

“We calculated efficiency should be between 15 percent and 19 percent. We’re working with University of Minnesota on that. Right now it’s limited by the thermal design of the reactor. We need a better thermal design,” Haile concluded.

Hydrogen, Solar