The increasing share of variable renewable energy such as wind and solar in the power systems creates challenges for operational flexibility. Long-term energy system planning tools, such as OSeMOSYS (Open Source energy Modelling System) are widely used to study capacity expansion pathways. However, they lack the temporal resolution and the constraints in the operational scale needed to consider the flexibility of the optimized energy mix. IRENA FlexTool provides the capability for detailed sub-hourly operational flexibility modelling.

This paper presents a framework for the coupling of OSeMOSYS with IRENA FlexTool, bridging the gap between long-term planning and short-term operational analysis. This allows the evaluation of the long-term investment decisions to the short-term operability needs, which is more essential with high shares of wind and solar. The framework is independent of the model input data to facilitate broader use.

This coupling consists of five parts: First, the IRENA FlexTool input is created automatically from the OSeMOSYS input by transferring it through the INES (Interoperable Energy System) specification with the parts of the system and constraints that exist in both models. This ensures that the two inputs are compatible, and it decreases the workload for the user to write two sets of inputs. Second, the long-term investment optimization is made with OSeMOSYS. Third, the generation mix and the invested capacities are passed to the IRENA FlexTool inputs. Fourth, the feasibility and the flexibility of the proposed system are assessed and the potential issues such as reserve inadequacy and ramping limitations are revealed. Fifth, a feedback loop allows iterative refining of long-term planning until a reasonable short-term flexibility is achieved.

This integrated approach allows easy addition of flexibility considerations to existing and new long-term energy system planning studies to provide better insights into future infrastructure investments.