Researchers from ETH Zurich have developed a novel technology that produces liquid hydrocarbon fuels exclusively from sunlight and air and have demonstrated the entire thermochemical process chain under real field conditions. Their new solar mini-refinery is located on the roof of ETH’s Machine Laboratory building in Zurich.

CO₂ and water are extracted directly from ambient air via an adsorption/desorption process. Both are then fed into the solar reactor at the focus of a parabolic reflector. Solar radiation is concentrated by a factor of 3,000, generating process heat at a temperature of 1,500 degrees Celsius inside the solar reactor.

At the heart of the solar reactor is a ceramic structure made of cerium oxide, which enables a two-step reaction—the redox cycle—to split water and CO₂ into syngas. This mixture of hydrogen and carbon monoxide can then be processed into liquid hydrocarbon fuels through conventional methanol or Fischer–Tropsch synthesis.

Carbon-neutral fuels are crucial for making aviation and maritime transport sustainable. ETH researchers have developed a solar plant to produce synthetic liquid fuels that release as much CO₂ during their combustion as previously extracted from the air for their production.

Aldo Steinfeld, Professor of Renewable Energy Carriers at ETH Zurich, and his research group developed the technology.

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

—Aldo Steinfeld

The solar mini-refinery on the roof of ETH Zurich shows that the technology is feasible, even under the climate conditions prevalent in Zurich. It produces around one deciliter of fuel per day. Steinfeld and his group are already working on a large-scale test of their solar reactor in a solar tower near Madrid, which is carried out within the scope of the EU project Sun-To-Liquid.

The next project goal is to scale the technology for industrial implementation and to make it economically competitive.

A solar plant spanning an area of one square kilometer could produce 20,000 liters of kerosene a day. Theoretically, a plant the size of Switzerland—or a third of the Californian Mojave Desert—could cover the kerosene needs of the entire aviation industry. Our goal for the future is to efficiently produce sustainable fuels with our technology and thereby mitigate global CO₂ emissions.

—,Philipp Furler, Director (CTO) of Synhelion and a former doctoral student in Steinfeld’s group

Two spin-offs already emerged from Aldo Steinfeld’s research group: Synhelion, founded in 2016, commercializes the solar fuel production technology. Climeworks, founded in 2010, commercializes the technology for CO₂ capture from air.