In the frame of national project sCO2 Efekt supported by Czech technological agency TAČR, Research Centre Rez (CVR) is developing an innovative, effective and flexible energy storage system. This system is based on the P2H2P (Power to Heat to Power) technology also called Carnot battery, with the utilization of a sCO2 Brayton cycle for heat to power conversion. In frame of the project, the key components of the storage system will be developed and experimentally verified. The key components are mainly the compressors and turbines and the storage tank. To be able to test the compressor and turbine, an experimental test facility called Sofia is also being developed. The main parameters of the Sofia facility are temperature up to 550°C, maximal test pressure of 25MPa and flow rate of about 25kg/s. The highest possible power of the turbine to be tested is up to 1.5MW electrical. In this paper, the conceptual design of the large scale experimental facility is described including its main components.