Research on diversification and resilience of the energy mix to ensure energy transition

Purpose. The purpose of this study is to examine the structure of the energy mix as a prerequisite for diversifying energy resources, which determines the resilience of the energy system to external shocks and shapes its internal energy supply potential, and to assess this structure empirically through a comparative analysis of Ukraine and Poland. Methodology. The assessment of energy mix diversification and resilience is based on the integrated application of entropy-based and concentration-based indices, which are widely used in contemporary energy system studies. Shannon entropy is employed to evaluate the degree of structural diversity and balance of the energy mix, reflecting the level of dependence on dominant energy sources. An increase in entropy values indicates a reduction in concentration risks and an improvement in the structural resilience of the energy mix under energy transition conditions. The Herfindahl–Hirschman Index (HHI) is applied as a complementary indicator to validate and interpret the results of the entropy analysis. The consistent dynamics of increasing Shannon entropy and decreasing HHI values confirm a stable trend toward energy mix diversification and reduced concentration risks. Findings. Using the cases of Ukraine and Poland, the study substantiates the structural characteristics and dynamics of the energy mix over the period 2013–2024. The analysis identifies key trends in energy supply transformation and highlights critical turning points that significantly influenced structural changes in the energy mix. The main constraints and drivers of energy resource diversification that determine the resilience of the energy mix under energy transition conditions are identified, providing an analytical basis for energy policy design and managerial decision-making. Originality. The proposed analytical framework, combining Shannon entropy with the Herfindahl–Hirschman concentration index, enables a systematic assessment not only of the structure and evolution of the energy mix but also of the risks associated with excessive reliance on dominant energy sources, accounting for their advantages and limitations. Practical value. The study identifies key directions for energy policy transformation in Ukraine and Poland during 2013–2024, and substantiates the effectiveness of energy resource diversification in enhancing the resilience of the energy mix. The results may support strategic planning and evidence-based management in the energy sector.