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SUNlight-to-LIQUID: Integrated solar-thermochemical synthesis of liquid hydrocarbon fuels

Periodic Reporting for period 3 - SUN-to-LIQUID (SUNlight-to-LIQUID: Integrated solar-thermochemical synthesis of liquid hydrocarbon fuels)

Reporting period: 2018-07-01 to 2019-12-31

Decarbonising the transport sector is a major societal challenge. In the long-term future, electrification or hydrogen can provide solutions, but certain sub-sectors such as aviation will still rely on liquid hydrocarbon fuels. As the sustainable production potential of biofuels is limited, radically different non-biomass non-fossil fuel production pathways must be developed. The SUN-to-LIQUID technology has the potential to meet future renewable fuel demand with a high greenhouse gas emission reduction. SUN-to-LIQUID hydrocarbon fuel is produced from the abundant feedstock H2O, CO2 and solar energy without the conflict of using arable land. Thus, in the long term it may have a profound positive impact on energy supply security worldwide, on minimizing the carbon footprint of e.g. aviation and also on the socio-economic development of economically challenged regions with arid non-arable land, and high levels of solar radiation.
The core conversion technology is a thermochemical redox cycle based on metal oxide material, driven by concentrated solar radiation. The primary objectives of SUN-to-LIQUID were the scale-up from the laboratory to the field at a pre-commercial scale and the experimental validation of the complete production chain to solar liquid hydrocarbon fuels at an increase of productivity by a factor of 30.
The unique solar fuel research facility at IMDEA Energía in Móstoles, Madrid, Spain (Figure 1) achieved a new record of > 5% in solar-to-syngas energy conversion efficiency and a pioneering long-term routine operation of > 100 cycles. It demonstrated
1) the tracking performance of the high-flux solar concentrating subsystem
2) the stability and performance of advanced redox materials in the up-scaled solar thermochemical reactor subsystem, and
3) the full integration of the gas-to-liquid (GtL) conversion subsystem for on-site solar fuel production.
A field of 169 sun-tracking heliostats delivered 50 kW of concentrated solar radiative power to the solar reactor positioned on top of the solar tower, driving the thermochemical co-splitting of H2O and CO2 via a redox thermochemical cycle at temperatures of 1500°C, and producing high-quality syngas which was further processed to kerosene. The system performance under realistic field conditions represents a pioneering achievement and demonstrates the technical feasibility of the solar technology for producing drop-in fuels at an industrial scale.
The solar reactor, designed and fabricated by ETH Zürich consisted of a cavity-receiver containing a porous redox structure directly exposed to the incoming concentrated solar radiation. Balance of plant and control instrumentation were implemented for the execution and evaluation of the solar redox cycles. The solar flux characterization a flux distribution measurement system was contributed by DLR, and also a calorimeter of identical aperture was integrated at the platform as well. The Fischer-Tropsch GtL subsystem from HyGear collected and converted the solar syngas to hydrocarbon fuel.
Advanced material development at ETH Zürich achieved superior porous structures made of ceria – the redox material with fast redox kinetics. The thermodynamic properties of undoped and doped ceria were determined and their redox performance were evaluated, and reticulated and hierarchically ordered porous structures were experimentally assessed for their ability to volumetrically absorb high-flux solar irradiation. Advanced heat management and heat recovery concepts were analysed with CFD modelling. Materials for a heat accumulator were experimentally tested by Abengoa.
For future development directions, Abengoa and DLR led a MW-scale plant study that investigated the receiver-reactor performance for a wide set of operational and design parameters. As a result of the analysis, several key factors for high-performance systems were identified: implementation of advanced redox structures, solid heat recovery, coherent optimization of the solar concentration system in combination with the actual receiver-reactor array design and operational strategy.
The techno-economic and environmental performance analyses of future commercial plants showed an emission reduction potential of 80% compared to conventional jet fuel, at estimated production costs of 2.0 €/L in the baseline case and of 1.2 €/L under favorable conditions.
The objectives of the project were fully reached. Solar fuels from H2O and CO2 were successfully produced in a solar tower and the highest solar-to-fuel energy efficiency for a thermochemical fuel plant of this kind was shown in June 2019. The joint press release of the consortium resulted in widespread visibility through media coverage with over 100 news articles and TV coverage in leading news channels. Social media activities complemented the project events. The project results were presented at conferences and published in high-impact refereed journals to set the scientific background for future R&D work. The SUN-to-LIQUID technology now stands for European leadership in this field at the time of completion of the project.
The high-flux solar concentration facility and the solar reactor developments represent significant progress beyond the state of the art. The compact concentration facility with 169 focusing prototype mirrors is capable of delivering a peak flux of 3000 kW/m2. This technology may be exploited in future high-flux concentration facilities. The 50-kW solar reactor outperformed previous solar reactor designs and exhibited stable cyclic redox operation on a daily basis: The fully integrated solar tower, solar reactor, and gas-to-liquid unit demonstrated the first-ever solar thermochemical fuel operation at an industrially-relevant scale.
Hierarchically-ordered porous structures featured porosity gradient for efficient radiative penetration and volumetric absorption, and thus has the potential for a higher specific solar fuel output per unit volume and, consequently, higher solar-to-fuel energy efficiency. Numerical investigation of solid-solid heat recovery concepts showed the high energy efficiency improvement potential of such systems at a large scale.
The unique research infrastructure for high-flux solar thermochemistry and the capabilities developed by all partners strengthens Europe’s competitive position in attracting best researchers worldwide and in pioneering innovations in solar fuel technology.
In the long term, the potential socio-economic impact of large-scale solar fuel production is two-fold: energy supply security and job creation from local fuel production. This is a strong driver for high-insolation regions with vast areas of arid non-arable land such as in southern Europe, Africa and Australia.
This technology has the potential to create new regional industries, while also strengthening existing ones through increasing demand. Country-specific input-output analyses to quantify the impact of plant investments provided insights on added value and job creation. This analysis also showed that attention must be given to preclude forced and child labor associated with imports from countries with lower social standards. On the positive side, the construction of a solar fuel plant with its necessary infrastructure investments for water provision, transport, etc. could support the development of surplus fresh water for the local population and agriculture with a profound and sustainable socio-economic impact.
SUN-to-LIQUID integrated solar-thermochemical plant at IMDEA Energía in Móstoles, Spain in operation