The energy system is currently facing several challenges, including grid stability problems, the curtailment of renewable energy (RE), security of supply and an imbalance between supply and demand in the RE generation. The aim of Siemens Gamesa Renewable Energy’s Electric Thermal Energy Storage (ETES) making it possible to increase the share of RE in total electricity generation is to counteract these challenges and thus to advance the energy transition. Due to the regionally uneven distribution of RE, an increased grid expansion is necessary. Energy storage enables base load capability of RE and increases grid stability. In times of high RE-generation, in which the grid reaches its capacity limits, RE are switched off, causing financial losses for the RE operator and/or for the end user. ETES reduces such financial losses storing electricity in periods of over-capacity and feeding it into the grid in times of RE production. In addition, ETES increases the flexibility of conventional steam-power-processes, but also the conversion of conventional power plants into emission-free energy storage systems, thus ensuring ETES future security of supply and gives conventional power plants a second life.