COMPASsCO2 aims to integrate solar energy into highly efficient supercritical CO2 Brayton power cycles for electricity production. Concentrated solar radiation is absorbed and stored in solid particles and then transferred to the s-CO2. In COMPASsCO2, the key component for such an endeavor shall be validated in a relevant environment: the particle-s-CO2 heat exchanger. To reach this goal, the consortium will produce, test, model and validate tailored particle-alloy combinations that meet the extreme operating conditions in terms of temperature, pressure, abrasion and hot oxidation/carburization of the heat exchanger tubes and the particles moving around/across them.