A review of models for energy system flexibility requirements and potentials using the new FLEXBLOX taxonomy

Although there is large consensus regarding the significance of flexibility in power systems, there exists significant disparity in the definitions and models employed to describe flexibility. To structure existing flexibility descriptions, this work classifies the mathematical principles underlying the flexibility models and finds quality metrics, machine learning models, and flexibility envelopes to be the main higher-order classes, with envelopes being the most popular one. It finds that there is a significant degree of mathematical incompatibility among different flexibility models, even within the same class. This is primarily due to the utilization of distinct flexibility metrics. To address the ambiguities in flexibility definitions and terminology, this paper introduces FLEXBLOX, a formal flexibility taxonomy. FLEXBLOX encompasses three core building blocks: a power system’s flexibility requirements, the flexibility potentials provided by flexibility resources, and flexibility mediators that facilitate between the requirements and the potentials. An analysis of 49 flexibility models shows that three of them cover both flexibility requirements and potentials. However, only one of the three approaches also considers a flexibility mediator between them. Two models are generic enough to describe the flexibility potential of diverse flexibility resources, but certain resource characteristics are often excluded. To date, there is no flexibility model that addresses all three flexibility building blocks of the FLEXBLOX taxonomy coherently. This leaves room for future research directions that are suggested in this work.