Introducing MEGO and PDC: Novel Indicators for Quantifying Market Rigidity and Cross-Border Price Divergence in Central European Electricity Markets

The massive integration of variable renewable energy sources (vRES) in Central Europe is fundamentally transforming electricity price formation and straining transmission grids. However, existing academic metrics, such as the RES Capture Price, offer only a static view of investor revenues and fail to capture dynamic market rigidity and systemic risks during periods of high instantaneous vRES penetration. This study addresses this literature gap by introducing two novel and transparent methodological parameters: Market Exposure to Green Overproduction (MEGO) and the Price Divergence Coefficient (PDC). Formulated as conditional non-parametric indicators, the MEGO index quantifies the conditional probability of price collapse and the loss of market elasticity during hours when vRES penetration exceeds critical thresholds (α = 0.50 to 0.80) of systemic load. Conversely, the PDC index measures the frequency of substantial price non-convergence across neighbouring bidding zones (CZ, PL, FR) relative to the German reference market (DE). Based on an extensive dataset spanning from 2015 to mid-2026—capturing the transition to 15 min market time units— the empirical results reveal a distinct change in market behaviour. While the frequency of price collapse during high-vRES periods was lower in earlier years and temporarily reduced during the 2022 energy crisis, the post-crisis period (2024–2026) exhibits substantially higher MEGO values, with periods in which wind and solar generation exceeded 80% of instantaneous system load being associated with prices at or below 0 EUR/MWh in up to 60% of the evaluated intervals. Concurrently, the PDC analysis reveals persistent spatial price non-convergence, particularly in France and Poland. These patterns coincided with major changes in European electricity-market conditions, including the implementation of Core Flow-Based Market Coupling, variations in nuclear availability and evolving cross-border network conditions; however, the PDC indicator alone does not permit causal attribution to any individual factor. The proposed MEGO and PDC parameters provide policymakers, transmission system operators (TSOs), and investors with an intuitive diagnostic framework for dimensioning grid flexibility, energy storage, and cross-border infrastructure in the decarbonization era.