Consortium by ETH Zürich, IMDEA Energía, Bauhaus Luftfahrt, DLR, HyGear, Abengoa and ARTTIC.

With the Project:
SUN-to-LIQUID (SUNlight-to-LIQUID: Integrated solar-thermochemical synthesis of liquid hydrocarbon fuels)

The SUN-to-LIQUID project developed the technology to produce renewable drop-in fuels that have the potential to minimize the carbon footprint of the aviation sector at a global scale. It uses abundant feedstocks - water, CO2 and solar energy without conflict with arable land. The core conversion technology is a thermochemical redox cycle driven by concentrated solar energy, utilizing the entire solar spectrum and operating at thermodynamically efficient high temperatures, to co-split water and CO2 into high-quality syngas that is further processed to clean hydrocarbon fuels. Following laboratory-scale experiments, this technology was advanced with approximately a 10-fold increase of solar radiative power and a 3-fold improvement in solar-to-syngas energy efficiency. Solar fuel plants are expected to provide local jobs in rural areas and increase energy security, as already proved with concentrated solar power plants.


Two particularly important challenges and targets in the global agenda are: First, the Paris Agreement, concerning the limitation of global warming to 1.5°C, which according to the IPCC 2018 Special Report requires the implementation of renewable energy and technologies for deep de-carbonization. Second, the aviation industry has set a target of 50% reduction of CO2 emission in 2050 compared to 2005 and complete global de-carbonization by 2060. These ambitious targets of the aviation sector are also a driver for the future development of technologies to produce drop-in-capable renewable aviation fuel in the order of 500 Mt/year by 2050. While rail, road, or maritime transport may utilize electricity or renewable hydrogen for propulsion, aviation is expected to rely on high-energy-dense liquid hydrocarbon fuels for many decades to come. Today, civil aviation is almost exclusively dependent on fossil-crude-oil-derived jet fuel with significant CO2 release.


Biofuels have been introduced as alternative jet fuels, but the biofuel technology does not meet sustainability and availability requirements at the scale of future global fuel demand. The advent of synthetic solar jet fuels offers a truly sustainable perspective as they can be synthesized from water and CO2, using concentrated solar energy. These are most efficiently and competitively produced in desert regions with high direct normal solar irradiation. Thus, there is no land competition with food or feed production. The future global fuel demand can be met by utilizing less than 1% of the global arid land. The motivation of this project was the development of the scientific and technological basis for renewable fuels. Its main objective was the demonstration of the feasibility and scalability of the entire production path.


The main innovation is the enhancement of the solar-to-fuel energy conversion efficiency and the scaling-up of the technology from the laboratory to a pioneering scale: SUN-to-LIQUID demonstrated this technology with on-sun operation in the field with a 30-fold increase in specific yield, thereby developing key innovations such as an advanced high-flux ultra-modular solar heliostat field, a 50 kW solar reactor, and optimized redox materials to produce synthesis gas that was subsequently processed on-site to liquid hydrocarbon fuels. The integration and stable operation of all subsystems into a pioneering solar fuel facility represents a unique research facility for high-flux solar thermochemistry that demonstrated further innovation potential towards a technology and a future of replicable stand-alone solar chemical plants to supply the global demand of sustainable aviation fuel from water, CO2 and sunlight. This and the capabilities developed by all partners are the first significant steps towards pioneering innovations in the solar fuel technology which has a significant greenhouse gas reduction potential.



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