Aviation and shipping currently contribute approximately 8% of total anthropogenic CO 2 emissions, with growth in tourism and global trade projected to increase this contribution further 1-3 . Carbonneutral transportation is feasible with electric motors powered by rechargeable batteries, though challenging if not impossible for long-haul commercial travel, particularly air travel 4 . A promising solution are drop-in fuels (synthetic alternatives for petroleum-derived liquid hydrocarbon fuels such as kerosene, gasoline or diesel) made from H 2 O and CO 2 by solar-driven processes 5-7 . Among the many possible approaches, the thermochemical path using concentrated solar radiation as the source of high-temperature process heat offers potentially high production rates and efficiencies 8 and can deliver truly carbon-neutral fuels if the required CO 2 is obtained directly from atmospheric air 9 . If H 2 O is also co-extracted from air 10 , feedstock sourcing and fuel production can be co-located in desert regions with high solar irradiation and limited access to water resources. While individual steps of such a scheme have been implemented, we now demonstrate operation of the entire thermochemical solar fuel production chain, from H 2 O and CO 2 captured directly from ambient air to the synthesis of drop-in transportation fuels (e.g. methanol, kerosene), with a modular 5-kW thermal pilot-scale solar system operated under real field conditions. We further identify the R&D efforts and discuss the economic viability and policies required to bring these solar fuels to market. Solar fuel production using H 2 O and CO 2 obtained through direct air capture (DAC) has so far largely been limited to bench-top 11,12 or pilot-scale 13,14 demonstrations of individual steps. A combined PV-electrolysis system 15 produced solar fuels from water and captured CO 2 , but the set-up was not optimized and coupling of intermittent solar hydrogen production with continuous non-solar hydrocarbon synthesis necessitated the co-feeding of fossil-derived syngas.

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