Flexibility options and their representation in open energy modelling tools

To reach climate targets, future energy systems must rely heavily on variable renewable energy sources (VRES) such as wind and photovoltaic (PV). As the share of VRES increases, the topics of flexibility and the smart interplay of different flexibility options grow in importance. One way to analyse flexibility options and enhance the design of future energy systems is to use energy system modelling tools. Although a wide range of openly accessible models exist, there is no clear evaluation of how flexibility is represented in these tools. To bridge this gap, this paper extracts the key factors of flexibility representation and introduces a new classification for flexibility and influencing factors. To evaluate the current modelling landscape, a survey was sent to developers of open energy modelling tools and analysed with the newly introduced Open ESM Flexibility Evaluation Tool (OpFEl), an open source evaluation algorithm to assess the representation of different flexibility options in the tools. The results show a wide range of different tools covering most aspects of flexibility. A trend towards including sector coupling elements is visible. However, storage and network type flexibility, as well as aspects touching system operations, are still underrepresented in current models and should be included in more detail. No single model covers all categories of flexibility options to a high degree, but a combination of different models through soft coupling could serve as the basis for a holistic flexibility assessment. This, in turn, would allow for a detailed evaluation of energy systems based on VRES.