The transition from fossil to renewable fuels is one of the most important challenges of the future. The SUN-to-LIQUID project takes on this challenge by producing renewable transportation fuels from water and carbon dioxide with concentrated sunlight: The project, which is funded by the EU and Switzerland, has now successfully demonstrated the first synthesis of solar kerosene. “The SUN-to-LIQUID core solar technology and the integrated chemical plant were experimentally validated under real field conditions relevant to industrial implementation,” said Aldo Steinfeld of ETH Zurich, who leads the development of the solar thermochemical reactor. “This technological demonstration can have important implications for the transportation sectors, especially for the long-haul aviation and shipping sectors strongly dependent on drop-in hydrocarbon fuels,” announced project coordinator Andreas Sizmann of Bauhaus Luftfahrt, “we are now a step closer to living on a renewable ‘energy income’ instead of burning our fossil ‘energy heritage’. This is a necessary step to protect our environment.”
From the laboratory to the field
The preceding EU-project SOLAR-JET developed the technology and achieved the first-ever production of solar jet fuel in a laboratory environment. The SUN-to-LIQUID project scaled up this technology for on-sun testing at a solar tower. For that purpose, a unique solar concentrating plant was built at the IMDEA Energy Institute in Móstoles, Spain. “A sun-tracking field of heliostats concentrates sunlight by a factor of 2500 – three times greater than current solar tower plants used for electricity generation,” explains Manuel Romero of IMDEA Energy. This intense solar flux, verified by the flux measurement system developed by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) makes it possible to reach reaction temperatures of more than 1500 degrees Celsius within the solar reactor positioned at the top of the tower.
The solar reactor, developed by project partner ETH Zurich, produces synthesis gas, a mixture of hydrogen and carbon monoxide, from water and carbon dioxide via a thermochemical redox cycle. An on-site gas-to-liquid plant that was developed by the project partner HyGear processes this gas to kerosene.
DLR has many years of experience in the development of solar-thermal chemical processes and their components. In the SUN-to-LIQUID project, DLR was responsible for measuring the solar field and concentrated solar radiation, for developing concepts for optimised heat recovery and – as in the previous SOLAR-JET project – for computer simulations of the reactor and the entire plant. Researchers from the DLR Institute of Solar Research and the DLR Institute of Combustion Technology used virtual models to scale up the solar production of kerosene from the laboratory to a megawatt-scale plant and to optimise the design and operation of the plant. For SUN-to-LIQUID, DLR solar researchers developed a flux density measurement system that makes it possible to measure the intensity of highly concentrated solar radiation directly in front of the reactor with minimal interruption of its operation. This data is necessary to operate the plant safely and to determine the efficiency of the reactor.
Unlimited supply of sustainable fuel
Compared to conventional fossil-derived jet fuel, the net carbon dioxide emissions to the atmosphere can be reduced by more than 90 percent. Furthermore, since the solar energy-driven process relies on abundant feedstock and does not compete with food production, it can thus meet the future fuel demand at a global scale without the need to replace the existing worldwide infrastructure for fuel distribution, storage, and utilisation.
SUN-to-LIQUID is a four-year project supported by the European Union’s Horizon 2020 research and innovation programme and the Swiss State Secretariat for Education, Research and Innovation (SERI). It began in January 2016 and will end on 31 December 2019. SUN-to-LIQUID joins leading European research organisations and companies in the field of solar thermochemical fuel research, namely ETH Zurich, IMDEA Energy, DLR, Abengoa Energía and HyGear Technology & Services B.V. The coordinator Bauhaus Luftfahrt e.V. is also responsible for technology and system analyses. ARTTIC supports the Research Consortium with project management and communication.