Abstract
Solar radiation is undoubtedly the most abundant source of renewable energy on Earth. However, it is intermittent and unevenly distributed across the globe. Although photovoltaic technology enables it to be efficiently converted into electricity, the production of fuels, which store the energy collected in the form of chemical bonds, is the only way to envisage energy storage for renewable energies on a terajoule scale. A number of pilot projects are evaluating the coupling of photovoltaic technologies with water electrolysis to produce hydrogen (H2). This gas is a promising energy carrier, easily reconvertible into electricity thanks to fuel cell technologies. Hydrogen can also be used to produce methanol or methane from carbon dioxide. Alternatively, the development of technologies for the direct conversion of solar energy into fuels (without the intermediate production of electricity) would undoubtedly reduce costs, while enabling massive, sustainable storage of solar energy. In fact, this is the solution developed by the living world: during photosynthesis, plants use light to directly synthesize high-energy molecules such as sugars, by reducingCO2 and oxidizing water.
