Solar fuels could solve one of the most pressing energy-related issues of the present time: the switch to a renewable energy base in the transportation sector. Especially aviation and heavy-duty transport will mostly rely on liquid fuels, which makes solar fuels an enabling technology for future mobility. Here, an analysis of the solar thermochemical fuel pathway that converts CO₂ and H₂O into liquid “drop-in”-capable fuels is presented, taking into account its life-cycle, economic, environmental and social performance. For a baseline plant layout in Morocco, nominal production costs of 1.97 € per litre of jet fuel are estimated, with greenhouse gas emission savings of 80% with respect to conventional fuel. Social concerns such as child labour or forced labour arise mostly through the import of materials and components from other developing countries. Alternative production locations are analysed, finding that in Chile – the country with the highest solar irradiation – nominal production costs of 1.72 € per L could be attained at an improved environmental life-cycle performance but at a higher risk of permitting child labour. The potential use of fossil CO₂ (instead of CO₂ directly captured from the air) is discussed and it is found that it cannot be used for the production of solar fuels with significantly lower emissions than conventional fuels. Regarding the potential use of grid electricity (instead of on-site concentrated solar power), the specific carbon intensity should be lower than 0.15 kg CO₂ eq. per kW h to meet the EU RED II targets. Overall, the solar thermochemical fuel pathway using both renewable energy and CO₂ has the potential to supply sustainable fuels to aviation in principally unlimited amounts.

The energy mix transition has accelerated the need for more accurate emissions reporting throughout the petroleum supply chain. Despite increasing environmental regulations and pressure for emissions disclosure, the low resolution of existing carbon footprint assessment does not account for the complexity of crude oil trading. The lack of source crude traceability has led to poor visibility into the “well-to-refinery-entrance” carbon intensities at the level of granular pathways between producers and destination markets. Using high-fidelity datasets, optimization algorithms to facilitate supply chain traceability and bottom-up, physics-based emission estimators, we show that the variability in global “well-to-refinery-entrance” carbon intensities at the level of crude trade pathways is significant: 4.2–214.1 kg-CO₂-equivalent/barrel with a volume-weighted average of 50.5 kg-CO₂-equivalent/barrel. Coupled with oil supply forecasts under 1.5 °C scenarios up to 2050, this variability translates to additional CO₂-equivalent savings of 1.5–6.1 Gigatons that could be realized solely by prioritizing low-carbon supply chain pathways without other capital-intensive mitigation measures.