The corresponding questions include: How can gas and heating networks contribute to making the electricity grid more flexible? What impact does a disruption to the gas network have on a coupled electricity network? Where in the heating network are bottlenecks expected as energy supply becomes decarbonised? How does the electricity network behave at distribution level in the event of bidirectional power flows due to energy supply and use at low voltage? The TransiEnt Library provides tools to explore such questions. It is an open-source library based on the Modelica modelling language. Using acausal, equation-based programming, the library implements differential algebraic equation systems for components of sector-coupled energy systems, enabling multi-physical modelling and analysis. Users can model coupled networks with existing models and investigate dynamic behaviour under current and future scenarios.
In 2013, the TransiEnt.EE research project (‘Transient simulation of complex energy systems with a high proportion of renewable energies’) was launched by three institutes at the Hamburg University of Technology (TUHH), marking the foundation of the project. Initially, the analyses focused on economic efficiency and environmental compatibility. A follow-up project expanded the consideration of energy systems to include resilience. In 2021, the TransiEnt Library consortium was expanded to include three new partners: the Fraunhofer Institute UMSICHT, the Gas- und Wärme Institut Essen e.V., and XRG Simulation GmbH. These partners contributed their own models to the library. The latest library release in September 2025 focused on simulating large networks (Gillner et al. 2025). A new approach to modelling heating networks through the strategic use of mass flow states and the avoidance of implicit equations enabled the simulation of networks with more than 2,167 transfer stations and a length of 140 km. The authors are not aware of any larger model with a comparable level of detail in another Modelica library (Westphal et al., 2025). Similarly, the development of prosumer models (i.e. models representing heat pumps, battery storage, photovoltaics, electric vehicles, etc.) in the electrical grid, as well as numerical improvements, have enabled the simulation of large distribution networks (Steffen et al., 2024; Wiegel et al., 2025). These further developments are strengthening the library's position in the simulation of coupled and large energy systems.
Consortium of the TransiEnt library:
- Institut of Engineering Thermodynamics, TUHH
- Institute of Electrical Power and Energy Technology, TUHH
- Fraunhofer UMSICHT
- Gas- und Wärme-Institut Essen e.V.
- XRG Simulation GmbH
Further reading:
- Website: https://www.tuhh.de/transient-ee
- Github: https://github.com/TransiEnt-official/transient-lib/releases
Bibliography:
Gillner, Markus et al. (2025). "Status of the transient library: Transient simulation of complex integrated energy systems." In Proceedings of the 16th International Modelica&FMI Conference.
Steffen, Tom, et al. (2024). "Impacts of Distribution Grid Congestion Management on Charging Efficiency of Private Electric Vehicles." In: NEIS 2024; Conference on Sustainable Energy Supply and Energy Storage Systems. VDE.
Westphal, Jan, Johannes Brunnemann, and Arne Speerforck. (2025). "Enabling the dynamic simulation of an unaggregated, meshed district heating network with several thousand substations." In Energy 322 (2025): 135434.
Wiegel, Béla, et al. (2023). "Towards a more comprehensive open-source model for interdisciplinary smart integrated energy systems." In: 2023 11th Workshop on Modelling and Simulation of Cyber-Physical Energy Systems (MSCPES), Texas, USA.
Wiegel, Bela, et al. (2025) "Real-Time Flexibility Allocation among Distributed Energy Resources: A Digital Twin-Driven Dynamic Optimization Approach." In ETG Kongress 2025; Voller Energie–heute und morgen. VDE, 2025.
Authors:
Prof. Arne Speerforck, Head of the Institute of Engineering Thermodynamics (Tel.: +49 40 30601 3244, arne.speerforck@tuhh.de)
Prof. Christian Becker, Head of the Institute of Electrical Power and Energy Technology (Tel.: +49 40 30601 3113, c.becker@tuhh.de)
Markus Gillner, M.Sc., research associate (Tel.: +49 40 30601 2866, markus.gillner@tuhh.de)
Béla Wiegel, M.Sc., research associate (Tel.: +49 40 30601 2240, bela.wiegel@tuhh.de)
