Due to the energy transition, the traditional power grid turns from a centralised grid, with single big power plants, into a heterogeneous one, with many unpredictable and volatile electricity producers and consumers. Moreover in the future, common households not only consume energy, but also feed their own energy with photovoltaic plants, batteries or heat pumps, into the grid. This creates a demand for a management system which allows forecasting, planning and tracing electricity usage from producers to consumers and is extendible to the participants' needs. Utilising blockchain technology allows one way of mapping the heterogeneous and decentralised characteristics of the future power grid into a suitable decentralised energy management system. This work analyses possible decentralised concepts and already existing blockchain solutions in order to propose a generic architecture solution for a decentralised energy management system. In addition, the doability of the proposed architecture is shown with a possible implementation, using the Ethereum platform. Furthermore, the implementation is realised in a minimal prototype. Conclusively, the architecture and its implementation are evaluated against possible requirements of a decentralised energy management system, which verifies their suitability for the given problem. This work is not only proposing a solution for an energy-related problem, but also shall help to find the true benefits of the blockchain technology and its current ecosystem.