For the past two years, researchers led by Aldo Steinfeld, Professor of Renewable Energy Carriers at ETH Zurich, have been operating a solar mini-​refinery on the roof of the Machine Laboratory in the centre of Zurich.

This unique system captures carbon dioxide and water from the atmosphere and uses solar energy to convert it into syngas, which is then converted into liquid fuel that’s essentially carbon neutral.

Aldo Steinfeld said: “This is no science fiction; it is based on pure thermodynamics. The solar refinery consists of three thermochemical conversion units integrated in series: First, the direct air capture unit, which co-​extracts CO₂ and H₂O directly from ambient air. Second, the solar redox unit, which converts CO₂ and H₂O into a specific mixture of CO and H₂ so-​called syngas. And third, the gas-​to-liquid synthesis unit, which finally converts the syngas into liquid hydrocarbons.”

The researchers set up a small 5-kW pilot system on the roof of a building. Running for seven hours a day in intermittent sunlight, the device was able to produce 32 ml (1.1 oz) of methanol each day.

It is easy to point out that 32 ml is a very small amount and even the authors of the study point out to cover the entire demand of kerosene in aviation, it would require 17,375 sq miles of solar plants, an area about the size of Estonia. This would cost considerably more than the fuel they are replacing.

But Anthony Patt, co-author of the study, said: “Our analysis of policy instruments shows a need for technology support similar to what has existed for solar and wind energy. Both of these used to cost roughly ten times as much to build and operate as fossil generators, back when governments first started to support them. The current price ratio for solar kerosene compared to fossil is of the same order. A comparison with other renewable energy technologies shows that with a similar support mechanism, it ought to be possible to bring the cost of solar kerosene down to the current cost of fossil aviation fuel.”

The research was published in the journal Nature.