Sunlight and water to produce kerosene: dream or reality?

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By Stéphane Amant – Senior Manager

A project funded by the EU and Switzerland has led to what may be a decisive breakthrough in the production of renewable jet fuel using sunlight, water, and CO2 [1]. This a project called SUN-to-LIQUID [2] follows on from a previous project, SOLAR-JET, who had developed the technology needed to produce the very first batch of solar kerosene in a laboratory. Researchers have scaled up the technology to a more industrial level and thus installed a power plant a solar concentrator that is unique in the world, at the IMDEA Energy Institute in Spain, to enable the first synthesis of solar kerosene outside the laboratory. How does it work? A field of heliostats that track the sun concentrates the sunlight by a factor of 2,500 (which is three times more than the current concentrated solar power plants used for electricity generation, such as those in Andalusia, for example), toward a reactor located at the top of a tower containing a mixture of water and CO2. The intense solar flux, which allows reaction temperatures to exceed 1,500°C, triggers thermochemical reactions that convert the initial mixture into synthesis gas, a mixture of hydrogen and carbon monoxide (see schematic diagram below). This synthesis gas is then processed by a conventional Fischer-Tropsch process for converting gas to liquid, by extending the carbon chains. The synthetic hydrocarbons produced as the end product are naphtha (a kind of gasoline), from the diesel and the jet fuel, in proportions that may vary depending on the settings chosen for the Fischer-Tropsch conversion. The project partners claim to have achieved a 90% reduction in net CO2 emissions compared to conventional jet fuel derived from fossil fuels.

Given the abundance of raw materials that do not compete with food production (water and CO2), The theoretical potential of this solution is immense, which clearly wins him favor. But as the saying goes, it’s easier said than done, and there are still significant obstacleschallenges that must be overcome for this solution to become a meaningful part of the aviation energy mix. While this list is by no means exhaustive, we can note, for example, that the CO2 must be captured upstream, which requires capture technologies that may be costly, especially if the CO2 is highly diluted (as it is in the atmosphere). This actually raises the question of the overall economic equation, which researchers have not yet addressed (which is not surprising in itself). For example, the overall energy conversion efficiency between incoming solar flux and the resulting liquid fuels is a key factor in reducing production costs: the project’s leaders have stated that the next steps will now focus in particular on improving the economic competitiveness of this solution, while working toward further industrialization of the process. Given the climate emergency we are facing, and knowing the considerable challenges involved in decarbonizing air travel, Perhaps public authorities will be called upon to subsidize this type of synthetic fuel in one way or another in the future. Then perhaps we'll have an interesting discussion about who will have to bear the additional cost (air travelers? the community as a whole?) and for which flights (The social benefit can vary greatly depending on the flight.) Check back in a few years for more concrete details!

Sources: [1] Greenaironline [2] Sun-to-Liquid