Solar electricity and solar fuels: status and perspectives in the context of the energy transition

The energy transition from fossil fuels to renewables is already ongoing, but it will be a long, complex and difficult process to carry out, since the global energy system is a gigantic and complex machine. Key renewable energy production data will be discussed, which show the remarkable growth of solar electricity technologies and indicate that crystalline silicon PV and wind turbines are the workhorse of the first wave of renewable energy deployment on the TW scale around the globe. The PV market alternatives along with other less mature options under intensive research will be briefly presented, along with the perspectives of concentrated solar power options. As far as fuels are concerned, the situation is significantly more complex because making chemicals with sunshine is far more complicated than generating electric current. The prime solar artificial fuel is molecular hydrogen, which is characterized by an excellent combination of chemical and physical properties. The routes to make it via solar energy and then synthetic liquid fuels are presented. The interconversion between electricity and hydrogen, two energy carriers directly produced by sunlight, will be a key tool to distribute renewable energies with the highest flexibility. However, the full integration of solar hydrogen in the world energy system can be achieved only in the long term. Two parameters and concepts that are often neglected in the scientific energy debate will be highlighted: the EROI (Energy Return On Investment) and the fact that the energy transition will not be limited by the availability of photons, but by the availability of natural resources - particularly minerals - which are needed to manufacture energy converters and storage devices on a multi-TW scale.