ISAaR – Integrated Simulation Model for Unit Dispatch and Expansion with Regionalization

What is ISAaR used for?

When we want to investigate the future energy system and how to get there, we use our energy system model “ISAaR”.

ISAaR (shortened from its German name “Integriertes Simulationsmodell zur Anlageneinsatz- und Ausbauplanung mit Regionalisierung” – or “Integrated Simulation Model for Plant Deployment and Expansion Planning with Regionalization” in English) is a linear optimization model that mathematically describes the European energy system. The model covers, among other things, the conventional power plant fleet, power generation from renewable energies depending on the respective generation potentials, energy consumption of the final energy sectors, and as the transmission grid – and this for 28 European countries. The following questions play an important role:

  • How do climate protection targets affect the energy system?
  • What role do storage and sector-coupling technologies play, or what opportunities do the flexibilities of the technologies offer?
  • What relevance does hydrogen have in the future energy system?
  • How will Germany’s export position change in the European network?
  • What are the repercussions of an increasing number of electric vehicles on the energy system?
  • What electricity prices can be expected in the future?
  • How will the full-load hours of different plant types develop in the future?

Scope of ISAaR

ISAaR balances the energy carriers electricity, methane, hydrogen, district heating, liquid hydrocarbons, CO2 as a feedstock, and biomass on its so-called energy carrier tracks. Consumption loads, generation plants, and, if applicable, storage facilities are assigned to each energy carrier track. In each case, one year is considered in hourly resolution. The consumption loads are calculated in advance in the final energy sector models of the industry, households, tertiary sector (trade, commerce, services), and transport sectors and transferred to ISAaR. Conversion technologies such as power-to-heat, power-to-gas, or electrolyzers serve as connections between energy carrier tracks (Figure 1). In addition to the plant deployment, the expansion of different technologies can also be calculated simultaneously.

Figure 1: Elements of the energy system and their coupling

The regional resolution of the model is flexible and depends on the input data. Energy can be transported between regions (e.g., European countries) in the form of the energy carriers electricity and hydrogen via pre-defined trading capacities. In addition to market calculations (exemplarily shown in Figure 2), more detailed considerations of the restrictions of the European power transmission network are also possible by network calculations using the PTDF approach (Power Transfer Distribution Factor) (see Figure 3).

Figure 2: Average electricity prices and grid model based on the net transmission capacities of the modeled countries for the solidEU scenario, year 2050 within the eXtremOS project.
Figure 3: Grid model

Non-European countries are not explicitly included in the modeling, but there is the option to import hydrogen or liquid hydrocarbons to Europe.

In order to map climate protection targets in ISAaR, annual greenhouse gas caps can be defined. In addition, different paths for the development of CO2 certificate costs can be specified. In this way, it is possible to investigate how different political demands affect the energy system under consideration.

Background and Functionality

ISAaR is a linear optimization (LP) model that optimizes plant deployment and expansion in terms of minimizing total system cost. The linear system of equations is built in MATLAB and solved with the solvers CPLEX or Gurobi. The input data, such as generation curves of renewable generation technologies or techno-economic parameters, are imported from FREM, the internal database of FfE. After successfully solving the optimization problem, the results are processed in MATLAB. The relevant optimization variables are exported back to FREM for further processing and visualization.

The modular design allows an easy exchange of the input parameters and thus the uncomplicated consideration of different calculation variations. For this purpose, the input data are compiled in different scenarios, which can be selected via a graphical user interface and, if necessary, additionally parameterized.

Two high-performance servers are available at the FfE for the calculations required to solve the optimization problem (see Figure 4).

Figure 4: Basic interrelationships of the technical implementation of ISAaR

The temporal resolution is defined separately in ISAaR for each energy carrier track, while the spatial resolution can be varied depending on the application. Possible options range from consideration of individual grid nodes to aggregation at the county or national level.

When calculating future optimization years, assumptions regarding the boundary conditions, such as the development of the electrical and thermal load or cost paths for generation technologies, are specified as scenarios. The modeling includes deployment planning for existing plants as well as expansion planning for future plants, such as the expansion of renewables, electrolyzer, or electricity storage. Depending on the focus of the research project, individual support years up to the target year are calculated, e.g. 5-year steps between 2020 and 2050 in the eXtremOS project.

The visualization of the results is done with the help of the web application “ISAaR-Charts“. The interactive displays make it possible to validate, compare and analyze the calculation results quickly and efficiently. This enables a deeper understanding of the interrelationships of the modeled energy system, based upon which conclusions can be drawn for the issues investigated.


Figure 5: Project history of ISAaR and its main topics

ISAaR was developed in 2012 in the MOS project (“Merit Order of Energy Storage 2030”) at the FfE. Since then, ISAaR has been used in various projects and has been constantly further developed to find answers to evolving research questions and to reflect current developments in the energy industry. The chronological order of the projects is shown in Figure 5.

In the MOS project, different storage and flexibility technologies were investigated to identify cost-optimized storage structures in Germany and Austria. The follow-up project MONA (“Merit Order Grid Expansion 2030”) investigated grid-optimizing measures, especially with high shares of renewable energies. For this purpose, ISAaR was extended to Europe for the energy carrier electricity. The PTDF approach for linearizing load flows was implemented to map grid restrictions.

In Dynamis, the decarbonization of the German energy system was analyzed. A primary focus was the repercussions of the application-side measures for GHG reduction (GHG: greenhouse gases) in the final energy sectors on the energy system. In the course of the project, the energy carriers hydrogen, methane, liquid hydrocarbons and biomass were included in the model (modeled in Germany only). For this purpose, the term “energy carrier track” was introduced in order to visually describe the energy balances of the energy carriers modeled in ISAaR. Furthermore, additional sector-coupling technologies were implemented. The addition of all generation plants was limited to Germany.

In C/sells it was investigated which system feedback effects can be observed when prosumers market their flexibility for grid optimization measures.

In eXtremOS, the energy carrier tracks and plant expansion were extended to 28 European countries. In addition, the energy carrier track “CO2 as a feedstock” was introduced. The focus of the project was the evaluation of flexibility in the context of European electricity market coupling under extreme technological, regulatory and societal developments.

In BDL, the bidirectional charging management of electric vehicles and their repercussions on the energy system are considered.

In all projects, the model has been continuously developed to reflect the latest developments in the energy industry in ISAaR. The continuous extension leads to a higher level of detail and allows a comprehensive consideration of the energy system.

Current projects

Currently, ISAaR is being used and further developed in the following major projects: