Thus the PowerPuff girls were born: Solar thermochemical fuels production

Principle Investigator: Wojciech Lipinski, University of Minnesota, collaboration with Caltech and Abengoa Solar

Water, carbon dioxide, and sunlight. Those are the only three ingredients University of Minnesota researchers are using to produce synthetic fuel for transportation and industry use. Working in collaboration with California Institute of Technology and Abengoa Solar, Inc. and funded by ARPA-E, the team is building a solar thermochemical reactor to efficiently produce fuel from sunlight.

Using heat from solar energy, “we can end up with chemicals that are of the same composition as fossil-derived fuels,” said Wojciech Lipinski of University of Minnesota and the principle investigator on the project. It means solar energy can be distributed and stored in a chemical form, using the existing infrastructure, he added.

Solar radiation captured and concentrated by solar towers and dishes is used to produce heat at temperatures of 1500 degrees Celsius, hot enough to melt steel. This heat is then used to split water and CO2 molecules into hydrogen and carbon monoxide, components of synthesis gas. Synthesis gas can be converted to synthetic hydrocarbon fuels such as gasoline, diesel, and kerosene.

The reactor is much more efficient than existing reactors, boasting a 10 percent conversion rate of solar energy to fuel, based on engineering models. That’s 10 times the rate of current solar fuel technologies.

In the solar reactor, a metal oxide is cycled between high and low temperature zones in order to react with water and CO2 to produce hydrogen and carbon monoxide.

“The studies up to date … did not explicitly consider recovery of heat internally in the cycle when the material is cycled between the high temperature and low temperature step, and vice versa,” Lipinski explained. In most designs this heat was inherently lost, which contributed to low efficiencies.

In the reactor designed by Lipinski along with his colleagues Jane Davidson and Thomas Chase at the University of Minnesota, a system is in place to recover more of this heat and increase efficiency. The development and use of ceria-based materials is the other main innovation to improve efficiency, which is being investigated by Sossina Haile from California Institute of Technology. Ceria is a compound derived from the rare earth metal cerium.

The project is still getting started, having officially begun in December 2011. Lipinski indicated that there are fundamental issues to solve, such as the development of ceria-based materials, but the 10 percent conversion rate has been proven. Another future challenge is the supply of CO2 required for the reactor.

“The one challenge associated with the production of solar fuel from water and CO2 is to provide a concentrated stream of input CO2,” Lipinski said, “and this input should, ideally, come from atmospheric air … There is a need to address the issue of atmospheric CO2 capture, and there are many groups working in this field as well.”

University of Minnesota is spearheading the project, with a focus on reactor design, building, and testing. Caltech researchers are involved in materials development, while Abengoa Solar, Inc. oversees the commercialization of the technology.

The project is funded by a $3.6 million ARPA-E grant.


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