Renewable energies have changed the energy paradigm in Spain and are doing so in almost the entire world. But the future, now, depends on storage. If renewables only generate energy when there is a resource –wind in the case of wind power, sun in the case of photovoltaics, or water in the case of hydropower– it is necessary to have systems to store the energy when these sources do not exist. Because one of the main requirements in the world of electricity is the security of supply.