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Towards Efficient Production of Sustainable Solar Fuels

Periodic Reporting for period 1 - ECLIPSE (Towards Efficient Production of Sustainable Solar Fuels)

Reporting period: 2019-09-01 to 2021-08-31

With more energy from the sun striking the earth's surface in an hour than is consumed annually by fossil fuels, solar energy has the potential to provide a significant part of the required global energy, in addition to substantially reducing the emissions of greenhouse gases, a critical goal in overcoming the challenges posed by the climate change. Two of the most severe limiting factors of using solar energy are the inconsistency of the power output, due to the day/night cycle and weather conditions, and the transportation issues due to geographical location. Solar fuels, produced by combining concentrated solar energy with thermochemical processes, are a promising concept to overcome both limitations. These fuels, acting as chemical energy carriers, can be generated at suitable sites and easily transported worldwide, where they can be stored and used upon demand. Current methods for carbon-neutral solar fuels generation are based on a 2-step reduction-oxidation cycle, with each step at different pressure and temperature, thus creating technological difficulties. Moreover, the solar-to-fuel energy conversion efficiency of the best process to date is less than 6%. The main goal of this research is to develop a novel method for the solar thermochemical splitting of CO2 and H2O, achieving high solar-to-fuel energy efficiency. To do so, a unique approach utilizing high-temperature heat recovery methods was investigated. The research work included rigorous modeling of the physics, detailed characterization, and experimental work. A novel high-temperature heat recovery method was developed for the solar redox reactor, the "dual-storage solar reactor" concept. Modeling work was validated by an experimental setup that was developed and tested in a high-flux solar simulator, demonstrating heat extraction at temperatures over 1250 deg. C and with heat extraction effectiveness over 80%. This work is a significant improvement over the state-of-the-art and is paving the new for further improvement, testing, and development of new high-temperature heat recovery methods.
In this project, a novel high-temperature heat recovery method for a solar reactor has been developed and investigated, both numerically and experimentally. We have performed an analysis of various potential heat recovery schemes that could be incorporated with state-of-the-art solar reactors. It was discovered that the most promising method is to use direct heat recovery, using an inert heat transfer fluid, to extract the heat from the reactor after the reduction step. This approach allows us to store the recovered heat and utilize it in the next cycle, another reactor, or in a different industrial process. Following this approach, several numerical CFD models have been developed, allowing us to perform a detailed analysis of the system and its potential. We could also utilize this to perform a parametric analysis prior to the design of the complex experimental setup and to identify key parameters and potential challenges. By following the insights provided, a novel method, called the dual-storage solar reactor system, has been developed. This system, consisting of two thermal energy storage units and a solar reactor, was designed, fabricated, and tested in the high-flux solar simulator. At the end of the experimental campaign, heat extraction effectiveness of over 80% was achieved, with heat transfer fluid temperatures of up to 1250 deg. C. Moreover, the combined experimental-numerical approach allowed us to validate the models, which can now be used for a scale-up study.
The project experimentally demonstrated for the first time a high-temperature heat recovery process from a volumetric solar reactor. In addition to the clear impact on the study of solar-driven thermochemical processes, this can also have a high impact on other industries where high-temperature processes are involved. The progress made in this work is contributing to the larger goal of transitioning to sustainable aviation and marine transportation. Since these sectors require hydrocarbon fuels as the energy source due to the high specific energy (which batteries are unable to provide to date), the development of solar fuels can help in providing the needed energy source in an environmental-friendly way. All the scientific insights gained in this project will be exploited and disseminated to the scientific community, as well as to the general public.