Same Destination, Different Paths? Trajectory Types of EU Electricity Generation Mixes and Their Structural Energy Security Exposure, 2000–2024

European Union countries can reach comparable electricity-generation mixes through transformations that differ in sequence, timing, and structural exposure. This study examines annual mixes for all 27 Member States in 2000–2024 as ten-part closed trajectories. The primary specification preserves reported zeros, applies a Hellinger transformation, compares trajectories by multivariate dynamic time warping with a four-year Sakoe–Chiba window, and clusters them using partitioning around medoids. Three conditional multi-country pathway types were identified among 26 countries: a diversifying fossil-to-renewables pathway, nuclear-renewables coexistence, and a concentrated island transition. Estonia was retained as a country-specific oil-shale profile outside the typology. Separation was moderate (mean silhouette = 0.2802), although bootstrap stability was high. Endpoint-only and full-trajectory partitions agreed only partly (Adjusted Rand Index = 0.4695), but a strict pairwise test found no extremely similar endpoints combined with extremely different paths. The representation of the mix reorganized the partition, whereas elastic time alignment changed only one assignment. Because imports, interconnection, flexibility, reliability, costs, and adaptive capacity lie outside the data, the typology does not measure overall energy-security risk. It shows instead that declining fossil shares redistribute rather than remove structural exposure, and it identifies where concentration, technology dependence, and substitution patterns warrant deeper assessment.