The solar reactor that turns CO2 into clean fuel: Here’s how it works

Imagine a metallic tower wrapped in the reflections of thousands of mirrors tracking the sun like technological sunflowers. At its peak, a gleaming cylinder gathers all that energy to capture carbon dioxide from the air and transform it into clean fuel. It’s real. And it’s happening.

It may sound like magic, but it’s pure science. Thanks to this cutting-edge technology, we can dream of a world where CO_₂ becomes raw material to power planes, ships, and heavy machinery.

Developed by the Swiss Federal Institute of Technology in Zurich (ETH Zurich), this innovation shows that the sun’s energy can do more than just generate electricity —it can regenerate the air we breathe and drive sustainable mobility, even in sectors that today seem nearly impossible to decarbonise. But what exactly is a solar reactor?

What is a solar reactor, and how does it produce clean fuel?

A solar reactor is not a conventional solar plant or thermal facility. It’s a system that harnesses extreme, concentrated solar heat through a field of heliostats (sun-tracking mirrors) to trigger a controlled chemical reaction inside.

The process converts CO_₂ and water vapour (H_₂O) into a mixture of gases known as syngas, composed of hydrogen (H_₂) and carbon monoxide (CO). This syngas is the base material used to produce sustainable liquid fuels, such as synthetic kerosene for aviation.

A design with both visual and climate impact

The Swiss prototype is only a few meters tall. However, its architecture is reminiscent of facilities like the Daguangshan solar plant in China, where advanced thermochemical technologies have also been tested.

Such reactors could be integrated into existing facilities or developed as part of large-scale solar parks, turning sun-drenched regions into hubs for clean liquid fuel production.

From CO_₂ to kerosene: The step-by-step chemical process

1. Direct air capture

The system begins by absorbing air from the atmosphere using a direct CO₂ capture unit. This technology is already being applied in other fields, such as in Iceland, where CO_₂ is injected underground. Still, it serves here as the feedstock for the solar reactor.

2. Solar concentration and heat generation

Sunlight, redirected by thousands of heliostats, is focused into the reactor chamber. Inside, temperatures reach up to 1,500 °C, high enough to trigger thermochemical reactions.

3. Reaction with metal oxides

Within the reactor, a ceramic material —typically ceria (cerium oxide)— acts as a catalyst. When heated, the oxide releases oxygen. As it cools in the presence of CO₂ and H₂O, it reacts with them to produce syngas.

4. Liquid fuel synthesis

This syngas is processed through the Fischer-Tropsch synthesis, producing liquid hydrocarbons such as synthetic kerosene, synthetic diesel, or synthetic gasoline. Key point: These fuels are fully compatible with existing infrastructure. Their use emits only the CO₂ that was previously captured, effectively closing the cycle.