With transport being one of the main contributors to greenhouse gas (GHG) emissions, researchers are looking for low-carbon alternatives to replace the conventional fuels being used today. One such promising development took place at ETH Zurich, where researchers developed a technology that is capable of producing liquid hydrocarbon fuels from just air and sunlight. This was done at their solar mini-refinery and in doing so, their team became the first in the world to demonstrate the process under real-world conditions. The research group, led by Professor Aldo Steinfeld, believe that developing low-carbon alternatives is an essential part of the transition away from fossil fuels.

How Does This Technology Work?

The solar plant combines three thermochemical processes to create liquid fuels from sunlight and air. These include direct air capture, solar redox, and gas-to-liquid conversion. A Direct Air Capture unit first extracts CO2 and water from ambient air, which is fed into a solar reactor which generates heat of around 1,500℃ through the concentration of solar radiation. A ceramic structure made of cerium oxide inside the reactor enables a reaction that splits the water and COinto a mixture of hydrogen and carbon monoxide known as synthesis gas (syngas). The gas can then be processed into liquid hydrocarbon fuels like methanol or kerosene through the use of a gas-to-liquid unit. 

The great part about this process is that these carbon-neutral synthetic fuels release only as much CO2 during combustion as was previously extracted from the air. The fuels are also compatible with the worldwide existing infrastructures for fuel distribution, storage, and utilization, and can contribute to sustainable aviation and shipping.

Is It Viable?

The team has proven the feasibility of the technology on a small-scale through their mini-solar refinery on the roof of ETH Zurich. The refinery currently produces around one decalitre of fuel per day, even under Zurich’s climate conditions. But this, according to Steinfeld, proves that carbon-neutral hydrocarbon fuels can be made from sunlight and air under real field conditions.


However, the cost of production is too high at present. The next stage of this technology is the scaling up of the system for industrial implementation. The next step for the team is the large-scale testing of the solar reactor technology, which they are doing in a solar tower near Madrid, in the scope of the SUN-to-LIQUID European Union (EU) project. The tower successfully demonstrated the first synthesis of solar kerosene from CO2 and water in a demonstration on the 13th of July last year.

The Full-Scale Commercial Implementation 

Two spin-off companies have emerged from this research group. They are currently focused on making this technology commercially viable. Climeworks, which is commercialising the technology for CO2 capture from the air, and Synhelion, which is commercialising the solar fuel production technology. Synhelion hopes to launch the first full-size commercial system using this technology by 2025, with a production volume of ten million litres of methanol annually. They also say that a solar plant spanning an area of just one square kilometre could produce 20,000l of kerosene a day.  This could mean that a plant the size of Switzerland could cover the kerosene needs of the entire aviation industry.

The goal of these two companies is to effectively produce sustainable fuels with their technology and thereby mitigate global CO2 emissions. The Bloomberg New Energy Finance (BNEF) New Energy Outlook presentation on June 2019, described wind and solar energy as two most important renewable energy technologies, predicting that they would account for 50% of global energy by 2050. This means that solar and wind infrastructures can be enhanced to meet varying energy needs as well as pave the way for technology such as the solar refinery to be commercially viable in the near future.

Summarized from Future Power Technology and ETH Zurich.

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