An integrated techno-economic, environmental and social assessment of the solar thermochemical fuel pathway†
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.