Assessing the operational impact of hydropower over-simplification in national energy system models

Modeling energy systems with a large share of cascaded hydropower requires an adequate representation of reservoir and plant interactions within a national power system. However, many energy system models rely on simplified or aggregated hydropower representations that neglect hydraulic interconnections, affecting operational results. This study quantifies the compound impact of hydropower cascade simplification, comprising hydraulic topology, inflow representation, and parameters aggregation, on national power system modeling. A hydropower cascade formulation is integrated into the open-source Dispa-SET unit commitment and economic dispatch model and compared with two simplified formulations with different levels of hydraulic detail, typically applied in mid and long-term energy system models. The analysis is applied to the Bolivian power system, where hydropower represents a significant share of electricity generation. The results show that simplified formulations significantly impact system operation. Hydropower generation is overestimated during the wet season and underestimated during the dry season. This leads to operational cost underestimation of 7% and up to 28.9% during the wet season depending on the formulation, and affects key operational indicators, including transmission congestion, reservoir operation, and the detection of shed load events. These findings highlight the importance of explicitly representing hydropower cascade dynamics when assessing the operation of hydro-dominated national power systems.