The sun is a clean and inexhaustible source of energy, with the potential to provide a sustainable answer to all future energy supply demands. The sun’s energy is already being harnessed in various ways: whilst photovoltaic cells convert sun light into electricity, solar thermal installations use the vast thermal energy of the sun for purposes such as heating fluids to a high temperature. There’s just one outstanding problem: the sun doesn’t always shine and its energy is hard to store. For the first time, researchers at the Paul Scherrer Institute PSI and the ETH Zurich have unveiled a chemical process that uses the sun’s thermal energy to convert carbon dioxide and water directly into high-energy fuels: a procedure developed on the basis of a new material combination of cerium oxide and rhodium. This discovery marks a significant step towards the chemical storage of solar energy. The new approach is based on a similar principle to that used by solar power plants. The researchers use heat in order to trigger certain chemical processes that only take place at very high temperatures above 1000 °C. Advances in solar technology will soon enable such temperatures to be achieved using sun light.