Efficiency potential of solarthermochemical fuel production
With its widespread availability, solar energy forms a cornerstone of the transition of the energy sector from a fossil to a renewable base. Regarding the production of renewable fuels for aviation, the use of sunlight in a thermochemical cycle promises a particularly high energy conversion efficiency. Carbon dioxide and water are split into carbon monoxide and hydrogen in a solar reactor using a metal oxide, for example cerium dioxide. The yielded gas mixture is then converted into liquid hydrocarbon fuels.
As was shown by researchers at Bauhaus Luftfahrt, the conversion efficiency of the solar reactor has a decisive influence on the economic and ecological performance of the produced fuels, as it defines the required size of the solar concentrator1. As part of the engagement of Bauhaus Luftfahrt in the assessment of the fundamental innovation potential of solar fuel technology, a generic and modular model for the description of a large number of possible reactor concepts has been developed2.
Application of this model showed that heat recuperation from the reactive material is essential for the achievement of high efficiencies, with novel solid-state counter-flow heat exchangers potentially reaching about 80 % recuperation efficiency. The developed model also enables optimisation of the reactor geometry for a given set of operating parameters.
The outcomes represent an important contribution to R&D efforts on reactor technologies, such as performed in “SUN-to-LIQUID”3, to utilise sunlight cost-efficiently for sustainable large-scale production of aviation fuels.
1C. Falter, V. Batteiger, A. Sizmann, Environmental Science and Technology, 50 1 (2016)
2C. Falter, A. Sizmann, R. Pitz-Paal, Solar Energy, 122 (2015)
3The research leading to these results has received funding from the European Union Horizon 2020 research and innovation programme under grant agreement no. 654408.
- Thermochemical energy conversion efficiency as a function of heat recuperation: Thermochemical solar-to-fuel energy conversion efficiency depends strongly on heat recuperation in the heat exchanger.
- Generic reactor model: Schematic of the developed generic reactor model including chambers for reduction and oxidation of the redox material as well as intermediate heat exchange (highlighted)