Context and ambition


The European Commission aims to eliminate net greenhouse gas emissions by mid-century. The transportation sector will play an important role in the transition to a carbon neutral society.

Two key challenges towards achieving this target relate to:

  • an increased feedstock basis for renewable fuel production
  • the development of longer-term renewable fuel technologies for specific transportation sectors like aviation

Electrification, and likely also hydrogen, will play a major role in the decarbonization of transportation. Nevertheless, there will be a continued need for liquid hydrocarbon fuels, especially for aviation and shipping. First-generation biofuels cannot meet the required volumes, due to availability and sustainability constraints. Thus, scalable technologies will be required to meet the longer-term needs for renewable fuels in energy and transport.



The overall ambition of SUN-to-LIQUID II is the significant advancement of energy conversion efficiency and robustness of the solar thermochemical fuel pathway and its integrated demonstration.

It is the aim of SUN-to-LIQUID II to advance the state of the art by the introduction of novel 3D-printed structured materials to the reactor, effective heat recuperation, a step forward in focus accuracy and stability of the solar concentrator, and in conversion efficiency of the gas-to-liquid facility, as well as to ensure sustainability and circularity by recycling of ceria and reducing water consumption. The aim of the project is to achieve 15% efficiency in the solar reactor and stable operation throughout the day. This will enable reliable long-term campaigns at significantly higher efficiency than today, producing significant amounts of liquid fuels.

This represents a significant multiple increase in efficiency from the current state of the art, which current experimental record value is 4.1% for the solar co-splitting of CO2 and H2O to syngas (demonstrated in the H2020 project SUN-to-LIQUID).

SUN-to-LIQUID II aims for the production on 20 consecutive sunny working days with an integrated and optimized parameter setting, which corresponds to about 200 cycles and an estimated production of 750 L of syngas per sunny day (vs. 102 cycles in the current state of the art).


SUN-to-LIQUID II concept

Solar radiation is the most scalable form of renewable energy. SUN-to-LIQUID II will develop a set of versatile technologies for solar fuel production from CO2 and H2O, this comprises in particular:

  • An improved high-flux solar concentration system for applications using high-temperature process heat
  • The development of efficient solar thermochemical fuel conversion using novel 3D printed redox materials
  • Heat exchange concepts to further improve the efficiency of high-temperature energy technologies

The combination of these technologies will enable efficient solar synthesis gas production in the long-term, ranging from solar H2 generation, over solar syngas at adjustable H2:CO ratio, to pure CO2 splitting. SUN-to-LIQUID II will specifically focus on a synthesis gas with H2:CO ratio of about 2 that is suitable for solar jet fuel production via Fischer-Tropsch synthesis.

The project will build on the preceding EU-funded H2020 project SUN-to-LIQUID, which successfully demonstrated on-sun solar thermochemical fuel production on a 50-kW scale.

The SUN-to-LIQUID II project consortium is convinced that enabling cost-effective fuel production from sustainable and abundantly available feedstock is the key to leverage relevant and long-term impact.

By aiming for this ambitious impact, the project also contributes to 6 of the 17 Sustainable Development Goals (SDG) of the United Nations for a more sustainable future for all (2030 Agenda):