Drop-in fuels from sunlight and air.

Aviation and shipping currently contribute approximately 8% of total anthropogenic CO emissions, with growth in tourism and global trade projected to increase this contribution further. Carbon-neutral transportation is feasible with electric motors powered by rechargeable batteries, but is challenging, if not impossible, for long-haul commercial travel, particularly air travel. A promising solution are drop-in fuels (synthetic alternatives for petroleum-derived liquid hydrocarbon fuels such as kerosene, gasoline or diesel) made from HO and CO by solar-driven processes. 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, and can deliver truly carbon-neutral fuels if the required CO is obtained directly from atmospheric air. If HO is also extracted from air, feedstock sourcing and fuel production can be colocated in desert regions with high solar irradiation and limited access to water resources. While individual steps of such a scheme have been implemented, here we demonstrate the operation of the entire thermochemical solar fuel production chain, from HO and CO captured directly from ambient air to the synthesis of drop-in transportation fuels (for example, methanol and kerosene), with a modular 5 kW pilot-scale solar system operated under field conditions. We further identify the research and development efforts and discuss the economic viability and policies required to bring these solar fuels to market.