The research plant on the roof of Zurich. Source: ETH Zurich/Alessandro Della BellaA solar mini-refinery on the roof of ETH Zurich is demonstrating the production of hydrocarbon fuels from sunlight and air under field conditions. The thermochemical conversion system extracts carbon dioxide and water from ambient air and uses solar energy to convert these into syngas, which can be further processed into methanol, kerosene and other drop-in transportation fuels.

Water and CO₂ are split into kerosene with the aid of a cerium oxide ceramic at the focus of a parabolic reflector, where solar radiation is concentrated by a factor of 3,000 and process heat attains a temperature of 1,500° C.

The current demonstration system produces about one deciliter of fuel per day, and a larger-scale test of the solar reactor is planned for a solar tower facility near Madrid. The researchers theorized that a solar plant covering 1 km² could produce 20,000 litres of kerosene per day.