The SOLAR-JET partners and advisors (ETH Zürich, Bauhaus Luftfahrt, Deutsches Zentrum für Luft- und Raumfahrt (DLR), ARTTIC and Shell Global Solutions) are optimizing a two-step solar-driven thermochemical cycle based on ceria redox reactions to produce the syngas, achieving higher solar-to-fuel energy conversion efficiency over current bio and solar fuel processes.

The H₂:CO molar ratio of the syngas can be controlled in a range from 0.25 to 2.34 by adjusting the feedstock H₂O:CO₂ molar ratio from 0.8 to 7.7.

The solar reactor consists of a cavity-receiver containing a porous monolithic ceria cylinder. Concentrated solar radiation enters through a windowed aperture and impinges on the ceria inner walls. Reacting gases flow radially across the porous ceria, while product gases exit the cavity through an axial outlet port.

The solar-to-fuel energy conversion efficiency, defined as the ratio of the calorific value of CO (fuel) produced to the solar radiative energy input through the reactor’s aperture and the energy penalty for using inert gas was 1.73% averaged over the whole cycle. The demonstrated efficiency is roughly four times greater than the next highest reported value to date for a solar-driven device. Additionally, the fuel (CO) yield per cycle was increased by nearly 17 times compared to that obtained with optically thick ceria felt because of deeper penetration and volumetric absorption of high-flux solar irradiation.

The solar reactor technology features enhanced radiative heat transfer and fast reaction kinetics, which are crucial for maximizing the solar-to-fuel energy conversion efficiency.

—Professor Aldo Steinfeld, ETH Zürich.

Although the solar-driven redox cycle for syngas production is still at an early stage of development, the processing of syngas to kerosene is already being deployed by companies, including Shell, on a global scale. This combined approach has the potential to provide a secure, sustainable and scalable supply of renewable aviation fuel and more generally for transport applications, the partners said. Moreover, Fischer-Tropsch derived kerosene is already approved for commercial aviation.

This is potentially a very interesting novel pathway to liquid hydrocarbon fuels using focussed solar power. Although the individual steps of the process have previously been demonstrated at various scales, no attempt had been made previously to integrate the end-to-end system. We look forward to working with the project partners to drive forward research and development in the next phase of the project on such an ambitious emerging technology.

— Professor Hans Geerlings, Shell

The €3.1-million (US$4.3-million), four-year SOLAR-JET project was launched in June 2011 and is receiving financial support (€2.2 million / US$3.0 million) from the European Union within the 7^th Framework Programme for a duration of four years. In the next phase of the project, the partners will optimize the solar reactor and assess the techno-economic potential of industrial scale implementation.

Resources

• Furler P., Scheffe J.R., Steinfeld A. (2012) “Syngas production by simultaneous splitting of H₂O and CO₂ via ceria redox reactions in a high-temperature solar reactor,” Energy & Environmental Science, Vol. 5, pp. 6098-6103 doi: 10.1039/c1ee02620h