The increasing integration of variable renewable energy sources (VRESs) into modern power systems presents significant challenges in ensuring operational flexibility, highlighting the need for robust methodologies to evaluate and ensure system reliability. The Insufficient Ramping Resource Expectation (IRRE) has emerged as a critical metric for quantifying the probability of ramping deficiencies in power systems. However, its traditional application, designed primarily for capacity-constrained systems, may not fully capture the operational dynamics of energy-constrained systems, such as those dominated by hydropower generation. This study analyzes the IRRE methodology and proposes enhancements to incorporate additional constraints, including seasonal and monthly hydrological variability and operational reserve requirements, to better reflect the flexibility limitations in energy-constrained systems. A case study of the Brazilian electricity system evaluates these modifications by comparing traditional and enhanced IRRE results across varying scenarios, including higher VRES penetration. Results reveal that, under stricter constraints, IRRE values increased by over 11 times for monthly hydrological limits in the Northeast subsystem, compared to the traditional IRRE. Additionally, combining these constraints with a 5% operational reserve requirement led to ramping deficits in up to 5% of the hours in a year for the same subsystem, highlighting the critical impact of operational constraints. Furthermore, scenarios with 30% and 100% VRES growth resulted in deficits increasing by 56 times and 418 occurrences, respectively, in certain subsystems. These findings demonstrate the enhanced IRRE’s effectiveness in evaluating flexibility challenges and its relevance for supporting planning and operational strategies in systems undergoing rapid renewable energy expansion.

The increasing integration of variable renewable energy sources (VRES) into modern power systems presents significant challenges in ensuring operational flexibility, highlighting the need for robust methodologies to evaluate and ensure system reliability. The Insufficient Ramping Resource Expectation (IRRE) has emerged as a critical metric for quantifying the probability of ramping deficiencies in power systems. However, its traditional application, designed primarily for capacity-constrained systems, may not fully capture the operational dynamics of energy-constrained systems, such as those dominated by hydropower generation. This study critically reviews the IRRE methodology and proposes enhancements to incorporate additional constraints, including seasonal and monthly hydrological variability and operational reserve requirements, to better reflect the flexibility limitations in energy-constrained systems. A case study of the Brazilian electricity system evaluates these modifications by comparing traditional and enhanced IRRE results across varying scenarios, including higher VRES penetration. The findings reveal significant increases in ramping insufficiencies when additional constraints are considered, particularly in subsystems with constrained hydropower resources. By integrating more realistic and specific operational constraints, this study advances IRRE's applicability as a planning tool and to guide policy decisions, ensuring enhanced system reliability in the face of escalating renewable energy integration specially into energy-constrained systems.