2026-08-13 –, Room 6
We introduce the inner workings and use of ReSiE, a new package for the simulation of sector-coupled energy systems with complex non-linear control schemes on the scale of city districts. The package is based on a different mathematical approach than comparable tools in the field of energy system modelling, which typically use MILP. The strengths and weaknesses of this approach are discussed. Furthermore we present some "lessons learned" and how Julia was leveraged to implement the package.
The ReSiE package is the simulation engine of a larger collection of tools for the planning, modelling, simulation and analysis of sector-coupled energy systems on the scale of city districts. The typical use case of the package is the early planning stage of a project, when limited information is available, yet important decisions have to be made concerning which technologies to employ and how the energy system components are connected and controlled.
As an "engine", its chief concern is the calculation of power, heat and other energy flows for each timestep, as well as the necessary post-processing to perform economical analysis of results, which is required for optimisation and parameter variation studies. Using the engine therefore does benefit from additional tools to create the necessary input configuration, but does not require the user to program any code.
Comparable tools in the field of energy system modelling and simulation often make use of mathematical models of linear optimisation and mixed-integer linear programming (MILP). In contrast, ReSiE uses a different approach based on aspects of systems analysis, agent-based simulation and graph theory. This incurs several dis-/advantages compared to established tools:
* Optimisation is separated from simulation, however only black-box optimisation is possible
* No limitation on the complexity of the individual energy system component models. For example the ground-coupled heat storage model uses a finite-volume method to co-simulate heat transport into the ground.
* Complex non-linear control mechanisms involving the interaction of multiple components are possible, however new strategies have to be implemented as code
* Highly flexible system topology with no hard limitations on size and depth of the network, however edge cases can occur that require deliberation
Development of the package was the first major project using Julia of all involved developers, which lead to several stumbling blocks along the way. The most severe of these are discussed alongside which Julia-specific considerations were observed.
Etienne Ott works as researcher and software developer at siz energieplus. With 10 years of experience as software developer and a focus on software for mathematical modelling, simulation and technical monitoring in the field of energy systems and the built environment, he is involved in projects developing the tools for complex analyses of district energy systems and the performance of buildings.