The Building and Energy Simulation Optimization and Surrogate-modelling (BESOS) platform is a cloud-based portal that will make modular, reusable software components for integrated energy systems analysis available to researchers. Buildings, renewable energy generation and storage technologies and associated energy systems all pose complex, interacting design and operational challenges. Finding high-performing solutions to these problems requires a new generation of computational tools, blending aspects of simulation, optimization, machine learning and visualization.