Seasonal energy storage is one of the largest challenges of the energy turnaround. In the project HybridStock, the seasonal storage of renewable energy in aluminium is investigated. At times of high availability of electricity from renewable sources, this energy is converted to chemical energy and stored in elementary aluminium. In winter, chemical energy from the oxidation reaction of aluminium is used to produce heat and electricity. In this project the concept which was the subject of the feasibility study HePoStAl is further pursued through laboratory work and the construction of prototypes.