Silicon as energy carrier—Facts and perspectives

Due to the diminishing reserves of carbon based primary energy carriers and the need to reduce carbon dioxide (CO2) emissions worldwide, an alternative energy concept was developed using elemental silicon as secondary energy carrier. Starting from sand, silicon can be accessible on a carbon/carbon dioxide free route in a process cycle using cost-effective—at best renewable—energy anywhere in the world. The reduction process sand→silicon, just as the generation of every synthetic secondary energy carrier, requires a significant amount of energy, which then is partially stored in the metal. Using existing technology, silicon can be transported and stored without any risk. Reactions of silicon with oxygen or nitrogen are exothermic and result in the release of thermal energy as well as formation of economically valuable products—instead of CO2. From silicon nitride, ammonia is obtained as a feed stock for the fertilizer industry as well as for hydrogen production. Alternatively, hydrogen is produced from silicon directly by simple reactions with water or alcohols, giving sand or silicon-based compounds as byproducts. These are available for a variety of different technical applications and, if required, can be recycled easily.