Convergence and Diversification of Electricity-Generation Structures in the EU-27, 1990–2024

The European Union’s common climate and energy framework—the Renewable Energy Directives and the European Green Deal—seeks to align national energy systems, yet whether electricity-generation structures converge remains underexplored. Using Eurostat data (SIEC classification), we examine the generation mix of the 27 EU member states over 1990–2024, measured as unweighted country-level source shares, with generation-weighted EU aggregates reported as a complement. We assess diversification (normalized Shannon entropy, the Herfindahl–Hirschman index and the effective number of sources) and convergence (σ- and β-convergence and source-by-source Phillips–Sul log-t club tests computed on source shares, with log-ratio balances used as a robustness check). Mix diversification rises (mean normalized entropy from 0.41 to 0.62) and, as measured by entropy, its levels converge to a single club. Convergence across sources is selective: the shares of the contracting carriers—coal, oil, nuclear and hydro—display σ-convergence, whereas wind, solar and bioenergy form single all-country convergence clubs in relative terms, even as their cross-country dispersion widens. The fossil–nuclear base remains structurally divided: coal fragments into multiple clubs with a divergent group that includes Poland, and nuclear separates member states into nuclear and non-nuclear groups. These patterns emerged during the development of the common EU policy framework; identifying the causal contribution of specific instruments is left for future work. The findings carry implications for security of supply, as exposed during the 2022 energy crisis.