In this paper, we propose a model-based system architecture for an interoperable blockchain-based local energy market for prosumers in a residential microgrid setting. Based on the Smart Grid Architecture Model our analysis deduced 21 organizational, informational, technical and blockchain requirements for a local energy market and its underlying information system. These are evaluated in the Landau Microgrid case study. We derive, that a clear value proposition for the key stakeholders, standardization of data exchange and communication, and a suitable physical implementation are the major challenges.