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Swiss lab's rooftop demo shows sunlight and air can make fuel

Proof of concept produces tiny volume of hydrocarbons, but makes a big point

Scientists in Switzerland claim to have proved it is possible to create fuel from air and sunlight in the first field experiment of its kind.

In a week where nations grapple with climate policy in an effort to curb the worst excesses of global warming at the COP26 summit, the pilot system demonstrates an important possible source of carbon-neutral fuel for industries struggling to decarbonise, such as aviation and shipping, which currently contribute around 8 per cent of total carbon dioxide emissions attributed to human activity.

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But, producing 32 millilitres of methanol in a typical seven-hour-day run, the current proof of concept will require investment and a policy shift to compete with fossil fuels.

The technique, described in a peer-reviewed early access version of the paper in science journal Nature earlier this month, captures carbon dioxide and water directly from ambient air. They are then fed into a solar redox unit which is heated to 1,500˚C using an umbrella-like parabolic sunlight collector. The inside of the reactor employs cerium oxide in a two-step thermochemical process. Firstly, cerium oxide is reduced, and oxygen is released. In the second step, CO2 and water are added to a mixture of hydrogen and carbon monoxide. The cerium oxide then absorbs oxygen, oxidizes and returns to its initial state, allowing the process to begin again.

The output mix – also known as syngas – is fed into a gas-to-liquid unit where it is converted to methanol, although such units can convert the gases into kerosene, gasoline, or other liquid fuels.

Given the high investment needed to scale such technology, the output would cost vastly more than commercial aviation fuel and would need policy support to be viable, according to the research group led by Professor Aldo Steinfeld of ETG Zurich.

"Bringing such solar fuels to the market will require substantial process optimization and upscaling, and this should be supported by policy schemes that enable market introduction at commercial scale," the paper said.

With investment, the researchers estimate that the technique could produce 95,000 litres of kerosene a day – enough to fuel an Airbus A350 carrying 325 passengers for a London-New York roundtrip – from a 3.8km2 field.

Co-sourcing water and CO2 from the air means the system could operate without a fresh water supply, making it suitable for desert locations, thus avoiding impact on agriculture, human population or areas rich in wildlife. Just half a per cent of the Sahara Desert could support the world's total aviation kerosene consumption of around 400 billion litres per year, for example, the researchers claim.

If only one could think of a cabal of space-obsessed tech billionaires looking to invest some spare change. ®

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