Scientists make carbon neutral fuel out of air and sunlight

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Researchers at ETH Zürich claim to have developed a new system that can create carbon-neutral fuels from sunlight and air.  

Led by Aldo Steinfeld, Professor of Renewable Energy Carriers at ETH Zürich, the team has been operating a solar mini-refinery on the roof of the university for the past two years. Using a multi-stage thermochemical process, the system produces liquid fuels, such as kerosene or methanol.

Read more: £15m sustainable aviation fuel contest launched in UK

What makes the new technology especially interesting is that it can be used under field conditions, as opposed to the specialised conditions created in a laboratory setting.

The rooftop solar mini-refinery is comprised of three parts - an air capture unit that removes water and CO2 from the air, a solar redox unit to turn those materials into syngas - a carbon monoxide/oxygen mix - using captured solar power, and a third gas-to-liquid synthesis unit that turns that syngas into a liquid to be used as a fuel. 

"This plant proves that carbon-neutral hydrocarbon fuels can be made from sunlight and air under real field conditions," said Steinfeld. "The thermochemical process utilises the entire solar spectrum and proceeds at high temperatures, enabling fast reactions and high efficiency."

The ultimate goal is to produce carbon-neutral fuels for some of the heavier polluting sectors like shipping and aviation, though the engineers behind the discovery noted that the technology still requires significant development, as well as upscaling.

Read more: Biomass and its role in the energy transition

In 2019, global aviation kerosene consumption was 414 billion litres. According to Steinfeld, upscaling to the point where global demand is met would require around 45,000 km² (17,375 miles²) of land - equivalent to 0.5% of the Sahara Desert.

The fuel would also initially be more expensive than kerosene, meaning that it would need to be accompanied by investment and policy support.

Around 8% of total global emissions come from flying and shipping and the new system is part of a broader push to reduce the two sector's carbon footprint. 

One proposed option is to produce drop-in fuels, which would replicate the effect of diesel or kerosene and are produced out of water and CO2 in a process powered by solar energy.

Read more: On The Crest Of A Green Wave – Decarbonising The Maritime Sector

However, thus far scientists have had limited success. While there has been some progress in making many of the individual parts of such a system, creating the full thing in a way that is workable in real-world conditions has so far proven difficult.

The research has been published in a new article in Nature entitled 'Drop-in Fuels from Sunlight and Air'.

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