OptiFlow: A flexible network flow modelling framework for energy systems analysis and beyond

With a global move towards more renewable energy sources in the energy system and increased sector-coupling, a good spatiotemporal resolution and representation of related transport networks become increasingly important. Existing energy system models are, however, often built for specific purposes with limited flexibility for modification. Modelling future energy systems calls for flexible and adaptable tools that can represent the complexity of integrated energy systems. This article introduces the OptiFlow framework, which is a bottom-up, open-source optimisation model based on network graphic theory. OptiFlow can represent linear movements of flows across processes and across spatial and temporal dimensions, such as processes for transport or inter-temporal storage or processes with time delay. The framework can represent network topologies, including energy carriers or feedstocks related to the energy system. OptiFlow can be used as stand-alone or it can be soft- or hard-linked to established energy system models such as Balmorel. OptiFlow has been applied to a wide range of use cases, including waste management, biomass utilisation, renewable fuel production, Power-to-X, and cascading hydropower, including interactions with the surrounding energy system. This article presents an overview of the OptiFlow framework, focusing on network design, spatiotemporal dimensions, and integration with other energy system models. Furthermore, the article presents a simple case study where OptiFlow is hard-linked with Balmorel to optimise the production of renewable maritime fuels. Overall, OptiFlow seek to reduce the future need for purpose-built model development with a flexible framework for modelling any process or set of processes interacting with the energy sectors.