Co-funded by the EU and Switzerland, the European research project SUN-to-LIQUID II was launched on 1 November 2023. Leading partner institutions from academia and industry will demonstrate scalability and high efficiency in the production of sustainable hydrocarbon fuel from water, CO2 and concentrated sunlight via high-temperature chemical conversion. 

The European Commission (EC) aims to eliminate net greenhouse gas (GHG) emissions on the path to climate neutrality by mid-century. The transportation sector will play an important role in the transition to a society living on 100% renewable energy. Two key challenges towards achieving this target relate to (i) an increased feedstock basis for renewable fuel production and (ii) the long-term development of sustainable fuel technologies for aviation. While electrification, and likely also hydrogen, will play a major role in the decarbonization of transportation, there will still be a continued need for energy-dense liquid hydrocarbon fuels, especially for aviation and shipping. First-generation biofuels cannot meet the required volumes, due to availability and sustainability constraints. Hence, scalable technologies will be required to meet the longer-term fuel demand. Solar radiation is the most scalable form of renewable energy. 

SUN-to-LIQUID II will develop a set of versatile technologies for solar fuel production from water and CO2, such as: 

•  an improved high-flux solar concentration system for applications using high- temperature process heat; 

•  efficient “solar-thermochemical” fuel production, i.e. a sunlight-driven high- temperature chemical conversion process, using novel 3D-printed materials in the solar reactor for the reduction-oxidation processes; 

•  heat exchange and recovery concepts to further improve the efficiency of high- temperature conversion processes. 

The ultimate output will be a step-change technology advancement and a roadmap for a robust and sustainable conversion pathway to produce high-quality renewable liquid fuel from the inexhaustible potential of solar energy. 

SUN-to-LIQUID II taps into a virtually unlimited resource of sustainable fuel production by developing the technology and roadmap to produce high-quality renewable liquid fuel directly from water, CO2 and concentrated solar energy. The primary objective of SUN-to- LIQUID II is to increase the solar reactor energy efficiency to more than 15% by improving the effective radiative absorption using 3D-printed redox materials with optimized structure and by recovering sensible heat during the temperature swing redox process. It will bring key advancements from laboratory-scale research in redox material and heat recovery to validation in an industrially relevant environment. Besides, this project will provide evidence for cost-effective >80% GHG emission reduction especially for aviation, with technical scalability to production potentials beyond projected demand. The project is built on the preceding Horizon2020 project SUN-to-LIQUID which successfully demonstrated on-sun solar- thermochemical fuel production on a 50-kW scale.