A solar mini refinery has been built on the roof of ETH Zurich in the middle of the city over the past few months. Sunlight is used there to produce synthetic fuel from carbon dioxide and the water in the air to power ship engines, for example. Only as much CO2 is released during combustion as was previously extracted from the air.

The facility’s process chain comprises three thermochemical conversion processes: the first step separates CO2 and water from the air by means of an adsorption-desorption process. The solar radiation is then concentrated 3000 times by a parabolic mirror and converted in a reactor into process heat with a temperature of 1,500 degrees Celsius. The cerium oxide inside the reactor is used to split water and CO2 in a two-stage reaction. Methanol or Fischer-Tropsch synthesis is then used to produce liquid fuel from the resulting hydrogen and carbon monoxide.

The scientists are currently planning the construction of a larger facility near Madrid as part of the EU Sun-to-Liquid project. According to their calculations, a solar facility with an area of about one square kilometer could produce around 20,000 liters of kerosene per day.