Aviation and shipping currently contribute approximately 8% of total anthropogenic CO2 emissions, with growth in tourism and global trade projected to increase this contribution further1,2,3. 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 travel4. A promising solution are drop-in fuels (synthetic alternatives for petroleum-derived liquid hydrocarbon fuels such as kerosene, gasoline or diesel) made from H2O and CO2 by solar-driven processes5,6,7. 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 efficiencies8, and can deliver truly carbon-neutral fuels if the required CO2 is obtained directly from atmospheric air9. If H2O is also extracted from air10, 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 H2O and CO2 captured directly from ambient air to the synthesis of drop-in transportation fuels (for example, methanol and kerosene), with a modular 5 kWthermal 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.
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Grewe, V. et al. Evaluating the climate impact of aviation emission scenarios towards the Paris agreement including COVID-19 effects. Nat. Commun. 12, 3841 (2021).
Chen, J. et al. The relationship between the development of global maritime fleets and GHG emission from shipping. J. Environ. Manage. 242, 31–39 (2019).
World Demand by Product Groups, 2018–2019 (International Energy Agency, 2021); https://www.iea.org/data-and-statistics/charts/world-demand-by-product-groups-2018-2019
Schäfer, A. et al. Technological, economic and environmental prospects of all-electric aircraft. Nat. Energy. 4, 160–166 (2019).
Lewis, N. S., & Nocera, D. G. Powering the planet: chemical challenges in solar energy utilization. Proc. Natl Acad. Sci. USA. 103, 15729–15735 (2006).
Ozin, G. A. Throwing new light on the reduction of CO2. Adv. Mater. 27, 1957–1963 (2015).
Detz, R. J. et al. The future of solar fuels: when could they become competitive? Energy Environ. Sci. 11, 1653–1669 (2018).
Romero, M. & Steinfeld, A. Concentrating solar thermal power and thermochemical fuels. Energy Environ. Sci. 5, 9234–9245 (2012).
Zeman, F. S., & Keith, D. W. Carbon neutral hydrocarbons. Phil. Trans. R. Soc. A. 366, 3901–3918 (2008).
Wurzbacher, J. et al. Concurrent separation of CO2 and H2O from air by a temperature-vacuum swing adsorption/desorption cycle. Environ. Sci. Technol. 46, 9191–9198 (2012).
Brady, C. et al. Integration of thermochemical water splitting with CO2 direct air capture. Proc. Natl Acad. Sci. USA. 116, 25001–25007 (2019).
Jia, J. et al. Solar water splitting by photovoltaic-electrolysis with a solar-to-hydrogen efficiency over 30%. Nat. Commun. 7, 13237 (2016).
Chalmin, A. Direct air capture: recent developments and future plans. Geoengineering Monitor https://www.geoengineeringmonitor.org/2019/07/direct-air-capture-recent-developments-and-future-plans/ (2019).
Roeb, M. et al. Test operation of a 100 kW pilot plant for solar hydrogen production from water on a solar tower. Sol. Energy. 85, 634–644 (2011).
Vázquez, F. V. et al. Power-to-X technology using renewable electricity and carbon dioxide from ambient air: SOLETAIR proof-of-concept and improved process concept. J. CO2 Util. 28, 235–246 (2018).
Chueh, W. C. & Haile, S. M. A thermochemical study of ceria: exploiting an old material for new modes of energy conversion and CO2 mitigation. Phil. Trans. R. Soc. A. 368, 3269–3294 (2010).
Abanades, S. & Flamant, G. Thermochemical hydrogen production from a two-step solar-driven water-splitting cycle based on cerium oxides. Sol. Energy. 80, 1611–1623 (2006).
Madhusudhan, J. et al. Reversible phase transformations in novel Ce-substituted perovskite oxide composites for solar thermochemical redox splitting of CO2. Adv. Energy Mater. 11, 2003532 (2021).
McDaniel, A. H. et al. Sr- and Mn-doped LaAlO3-δ for solar thermochemical H2 and CO production. Energy Environ. Sci. 6, 2424–2428 (2013).
Muhich, C. L. et al. Efficient generation of H2 by splitting water with an isothermal redox cycle. Science. 341, 540–542 (2013).
Bayon, A. et al. Operational limits of redox metal oxides performing thermochemical water splitting. Energy Technol. https://doi.org/10.1002/ente.202100222 (2021).
Ermanoski, I. et al. Efficiency maximization in solar-thermochemical fuel production: challenging the concept of isothermal water splitting. Phys. Chem. Chem. Phys. 16, 8418–8427 (2014).
Abanades, S. et al., Synthesis and thermochemical redox cycling of porous ceria microspheres for renewable fuels production from solar-aided water-splitting and CO2 utilization. Appl. Phys. Lett. 119, 023902 (2021).
Chueh, W. C. et al. High-flux solar-driven thermochemical dissociation of CO2 and H2O using nonstoichiometric ceria. Science. 330, 1797–1801 (2010).
Marxer, D. et al. Solar thermochemical splitting of CO2 into separate streams of CO and O2 with high selectivity, stability, conversion, and efficiency. Energy Environ. Sci. 10, 1142–1149 (2017).
Furler, P. et al. Thermochemical CO2 splitting via redox cycling of ceria reticulated foam structures with dual-scale porosities. Phys. Chem. Chem. Phys. 16, 10503–10511 (2014).
Dähler, F. et al. Optical design and experimental characterization of a solar concentrating dish system for fuel production via thermochemical redox cycles. Sol. Energy. 170, 568–575 (2018).
Furler, P. et al. Syngas production by simultaneous splitting of H2O and CO2 via ceria redox reactions in a high-temperature solar reactor. Energy Environ. Sci. 5, 6098–6103 (2012).
Schäppi, R. et al. Solar thermochemical splitting of CO2 in a modular solar dish-reactor system. In Proc. ISES-SWC2019 Solar World Congress (2019); https://doi.org/10.18086/swc.2019.24.08.
Marxer, D. et al. Demonstration of the entire production chain to renewable kerosene via solar thermochemical splitting of H2O and CO2. Energy Fuels. 29, 3241–3250 (2015).
Zoller, S. A 50 kW Solar Thermochemical Reactor for Syngas Production Utilizing Porous Ceria Structures. Dissertation ETH No. 26451, ETH Zurich (2020).
Romero, R. et al. Solar-driven thermochemical production of sustainable liquid fuels from H2O and CO2 in a heliostat field. Proc. ISES-SWC2019 Solar World Congress (2019); https://doi.org/10.18086/swc.2019.23.02.
Corporan, E. et al. Emissions characteristics of a turbine engine and research combustor burning a Fischer-Tropsch jet fuel. Energy Fuels. 21, 2615–2626 (2007).
SolarPILOT software v.2015.10.5 (National Renewable Energy Laboratory, 2015); https://www.nrel.gov/csp/solarpilot.html.
Geissbühler, L. Thermocline Thermal Energy Storage: Advances and Applications to CSP, Compressed Air Energy Storage, and Solar Fuels. Dissertation ETH No. 24555, ETH Zurich (2017).
Scheffe, J. R. & Steinfeld, A. Thermodynamic analysis of cerium-based oxides for solar thermochemical fuel production. Energy Fuels. 26, 1928–1936 (2012).
Lapp, J. et al. Efficiency of two-step solar thermochemical non-stoichiometric redox cycles with heat recovery. Energy. 37, 591–600 (2012).
Hoes, M. et al. Additive-manufactured ordered porous structures made of ceria for concentrating solar applications. Energy Technol. 7, 1900484 (2019).
Wim, H. & Geerlings, H. Efficient production of solar fuel using existing large scale production technologies. Environ. Sci. Technol. 45, 8609–8610 (2011).
Kim, J. et al. Fuel production from CO2 using solar-thermal energy: system level analysis. Energy Environ. Sci. 5, 8417–8429 (2012).
Falter, C. et al. Geographical potential of solar thermochemical jet fuel production. Energies. 13, 802 (2020).
Falter, C. et al. An integrated techno-economic, environmental and social assessment of the solar thermochemical fuel pathway. Sustain. Energy Fuels. 4, 3992–4002 (2020).
Sutherland, B. R. Pricing CO2 direct air capture. Joule. 3, 1571–1573 (2019).
Perner, J. & Bothe, D. International Aspects of a Power-to-X Roadmap (Frontier Economics, 2018).
Patt, A. & Lilliestam, J. The case against carbon prices. Joule. 2, 2494–2498 (2018).
Rosenbloom, D. et al. Why carbon pricing is not sufficient to mitigate climate change – and how “sustainability transition policy” can help. Proc. Natl Acad. Sci. USA. 117, 8664–8668 (2020).
Lilliestam, J. et al. The near- to mid-term outlook for concentrating solar power: mostly cloudy, chance of sun. Energ. Source. B. https://doi.org/10.1080/15567249.2020.1773580 (2020).
Lilliestam, J. et al. Empirically observed learning rates for concentrating solar power and their responses to regime change. Nat. Energy. 2, 17094 (2017).
Villasmil, W., Meier, A. & Steinfeld, A. Dynamic modeling of a solar reactor for zinc oxide thermal dissociation and experimental validation using IR thermography. J. Sol. Energy Eng. 136, 010901 (2014).
Haring, H. W. Industrial Gases Processing (Wiley-VCH, 2008).
Haeussler, A. et al. Solar thermochemical fuel production from H2O and CO2 splitting via two-step redox cycling of reticulated porous ceria structures integrated in a monolithic cavity-type reactor. Energy. 201, 117649 (2020).
Ash-Kurlander, U. et al. Impact of daily startup-shutdown conditions on the production of solar methanol over a commercial Cu-ZnO-Al2O3 catalyst. Energy Technol. 4, 565–572 (2016).
Mehos, M. et al. Concentrating Solar Power Best Practices Study NREL/TP-5500-75763 (National Renewable Energy Laboratory, 2020); https://www.nrel.gov/docs/fy20osti/75763.pdf.
Malhotra, A. & Schmidt, T. Accelerating low-carbon innovation. Joule. 4, 2259–2267 (2020).
Trancik, J. Renewable energy: back the renewables boom. Nature. 507, 300–302 (2014).
Ferioli, F. et al. Use and limitations of learning curves for energy technology policy: a component-learning hypothesis. Energy Policy. 37, 2525–2535 (2009).
Nordhaus, W. The Climate Casino (Yale Univ. Press, 2013).
Patt, A. et al. Will policies to promote energy efficiency help or hinder achieving a 1.5 °C climate target? Energ. Effic. 12, 551–565 (2019).
Nemet, G. Beyond the learning curve: factors influencing cost reductions in photovoltaics. Energy Policy. 34, 3218–3232 (2006).
Haas, R. et al. A historical review of promotion strategies for electricity from renewable energy sources in EU countries. Renew. Sustain. Energy Rev. 15, 1003–1034 (2011).
Lilliestam, J. et al. The effect of carbon pricing on technological change for full decarbonization: a review of ex-post evidence. Wiley Interdiscip. Rev. Clim. Change. 12, e681 (2021).
Eskeland, G. et al. in Making Climate Change Work Dor Us: European Perspectives on Adaptation and Mitigation Strategies (eds Hulme, M. & Neufeldt, H.) 165–199 (Cambridge Univ. Press, 2010).
Kunreuther, H. et al. in Climate Change 2014: Mitigation of Climate Change (eds Edenhofer, O. et al.) 151–205 (IPCC, Cambridge Univ. Press, 2014).
Battke, B. et al. Internal or external spillovers ‒ which kind of knowledge is more likely to flow within or across technologies. Res. Policy. 45, 27–41 (2016).
Patt, A. Transforming Energy: Solving Climate Change With Technology Policy (Cambridge Univ. Press, 2015).
This work was funded in part by the Swiss Federal Office of Energy (grant no. SI/501213-01), the Swiss National Science Foundation (grant no. 200021-162435) and the European Research Council under the European Union’s ERC Advanced Grant (SUNFUELS, grant no. 320541) and ERC Starting Grant (TRIPOD, grant no. 715132). We thank P. Basler, T. Cooper, Y. Gracia, P. Good, G. Ambrosetti, A. Pedretti, D. Rast, M. Schmitz, N. Tzouganatos and M. Wild for their contributions to the technology development.
ETH Zurich has license agreements with its spinoff companies Climeworks and Synhelion, and owns the following patents: EP 09007467.5, WO2010/091831: Gebald, C., Wurzbacher, J. & Steinfeld, A., Amine containing fibrous structure for CO2 capture; PCT/EP2014/001082: Steinfeld, A., Scheffe, J., Furler, P., Vogt, U. & Gorbar, M., Open-cell materials for use in thermochemical fuel production processes; EP16194074, WO2018/073049: Steinfeld, A., Furler, P., Haselbacher, A. & Geissbühler, L., A thermochemical reactor system for a temperature swing cyclic process with integrated heat recovery; EP18195213.68: Ackermann, S., Dieringer, P., Furler, P., Steinfeld, A. & Bulfin, B., Process for the production of syngas. P.F. is the CTO of Synhelion; P.F. and A.S. are shareholders of Synhelion.
Peer review information Nature thanks Albert Harvey, Christian Sattler and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data figures and tables
a) The solar redox unit, comprising the primary sun-tracking solar paraboloidal concentrator coupled to a secondary planar rotating reflector, and the two solar reactors at the foci. b) The two solar reactors, water-cooled calorimeter, and Lambertian target for solar radiative power measurements (seen via the secondary reflector).
Extended Data Fig. 2 Representative solar redox cycle producing syngas with composition suitable for methanol synthesis.
a) Temporal variation of the nominal cavity temperature, total pressure, and outlet gas flow rates during a single redox cycle. b) Temporal variation of the cumulative species concentration and yield of solar syngas collected during the oxidation step. Operation conditions − During the reduction step: Qsolar = 5.1 kW, inlet flow 0.5 L/min Ar, Treduction-end = 1450 °C, total pressure ≤ 25 mbar. During the oxidation step: Qsolar = 0 kW, inlet flows 0.4 L/min CO2 + 9.8 g/min H2O, Toxidation-start = 900 °C, total pressure = 1 bar.
Extended Data Fig. 3 Representative solar redox cycle producing syngas with composition suitable for FT synthesis.
a) Temporal variation of the nominal cavity temperature, total pressure, and outlet gas flow rates during a single redox cycle. b) Temporal variation of the cumulative species concentration and yield of solar syngas collected during the oxidation step. Operation conditions − During the reduction step: Qsolar = 4.1 kW, inlet flow 0.5 L/min Ar, Treduction-end = 1450 °C, total pressure ≤ 50 mbar. During the oxidation step: Qsolar = 0 kW, inlet flows 0.2 L/min CO2 + 9.8 g/min H2O, Toxidation-start = 800 °C, total pressure = 1 bar.
Extended Data Fig. 4 Syngas yield (H2 in orange, CO in green, CO2 in black) for each of the 152 consecutive solar redox cycles.
L denotes standard liters.
Extended Data Fig. 6 Simplified layout of a commercial-scale solar fuel plant with ten solar towers, each for 100 MWthermal.
DAC: Direct Air Capture; GTL: Gas-to-Liquid.
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Schäppi, R., Rutz, D., Dähler, F. et al. Drop-in fuels from sunlight and air. Nature 601, 63–68 (2022). https://doi.org/10.1038/s41586-021-04174-y
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