Dimitrios Pantelakis

European electricity systems are transforming as renewable generation expands across national markets with different generation portfolios and operating conditions. This study assesses 25 European electricity systems over 2015–2025 using harmonised hourly ENTSO-E generation and load data, day-ahead electricity prices, and population indicators. The framework integrates hourly fixed-effects models, temporal renewable-penetration measures, population-normalised indicators, structural clustering, and a conditional outlook to 2030. Higher solar and wind generation is associated with lower contemporaneous fossil generation, but the magnitude varies across countries and should not be interpreted as a physical substitution rate or causal effect. Renewable penetration increased substantially, while higher variable-renewable shares were associated with a greater incidence of very-low and negative day-ahead prices. Population-normalised and clustering results indicate a broad transition toward higher renewable and lower fossil generation without convergence to a single European system configuration. A backtested multi-model ensemble extends the historical evidence to 2030 with uncertainty intervals and external scenario benchmarking. The contribution is integrative rather than methodological: operational, temporal, market, and structural dimensions are evaluated jointly to assess the consistency and heterogeneity of the European electricity transition.

European green-hydrogen assessments often infer conversion opportunity from annual renewable quantities even though electrolyser output depends on both electricity chronology and technology-specific operating constraints. This study develops a harmonised physical screening framework for 40 European countries that separates annual renewable-energy scale from hourly chronology and propagates uncertainty through alkaline (AEL), proton-exchange-membrane (PEM) and anion-exchange-membrane (AEM) electrolysis. The renewable-performance gap is defined as the positive difference between reference generation and generation associated with an empirical upper-performance benchmark derived from country- and technology-specific historical capacity factors. It is a counterfactual screening quantity rather than observed curtailment or market-available surplus electricity. For the 2024 baseline, 2025 hourly series are used exclusively as normalised chronology donors and contain no 2025 annual generation or capacity information. All positive-gap hours are converted through 5,000 aligned Monte Carlo simulations including electricity capture, sizing, availability, minimum load, specific electricity consumption and delivery losses. The descriptive European aggregate P50 is 1.919, 3.104 and 6.094 Mt H2 yr-1 in 2024, 2030 and 2050. A joint alternative specification yields medians 1.5– 6.3% below the central estimates while preserving country rankings (𝜌 > 0.99; unchanged top ten). A controlled common-engine factorial sensitivity shows that replacing the 2025 chronology with a 2019–2024 multi-year profile changes P50 by only 0.4–0.8%, whereas broadening the upper- performance benchmark changes it by 5.9–8.2%. Benchmark characterisation is therefore the larger source of specification sensitivity, while the broad spatial ordering remains stable.

This study examines the association between the formal (de jure) adoption of renewable energy source (RES) support instruments and observed RES deployment outcomes across 36 European countries. We assess whether broader legislative adoption—measured by a transparent breadth/coverage index (SIC/OIL) based on binary coding and equal sector weights—correlates with higher RES shares. The empirical design comprises three complementary steps: (i) hierarchical clustering (Ward’s method; Euclidean distance on standardised indicators) to classify countries by legislative adoption profiles; (ii) parallel clustering of countries by RES utilisation profiles using 10 z-score-standardised outcome indicators (total and sectoral RES shares and per capita RES use by source); and (iii) an integrated comparison of both typologies, followed by a cross-sectional regression test of the OIL–RES association. Legislative and utilisation clusters do not systematically coincide, and the baseline regression shows a weak, statistically insignificant association with very low explanatory power (R² = ≈ 0.015), supporting heterogeneity (H1) rather than a universal positive average relationship (H₂). Interpretation is conservative because SIC/OIL captures policy-mix coverage (not budgets, enforcement, or design stringency) and because some low/zero policy entries may reflect limited source coverage. Overall, the findings suggest that observed RES performance is primarily shaped by country-specific structural conditions (resource endowments, economic capacity, and sustained long-term investment), implying that context-sensitive instruments and stronger implementation capacities should complement formal policy adoption.

The increasing integration of renewable energy sources (RES) in Spain is leading to substantial amounts of surplus electricity, presenting a strategic opportunity for green hydrogen production as a key enabler of energy storage and decarbonisation. This study quantifies this untapped potential for 2024. Based on the difference between installed renewable capacity and actual generation, an economically viable surplus of 18,419 GWh was identified within an optimal 10-h operating window. The hydrogen production potential was modelled for three electrolysis technologies—Alkaline (AEL), Proton Exchange Membrane (PEM) and Anion Exchange Membrane (AEM)—using total energy consumption values of 57.40, 65.55 and 59.95 MWh/t H₂, respectively, including auxiliary systems. The estimated annual hydrogen production ranges from 280,999 t (PEM) to 320,897 t (AEL), with AEM yielding an intermediate value of 307,247 t. The analysis reveals a strong regional concentration, with more than 63% of the potential located in Castile and León, Andalusia, Castile-La Mancha and Extremadura. While this range represents an upper technical limit, it highlights the significant opportunity to valorise surplus renewable energy, contingent on targeted investment and a supportive regulatory framework.

This study presents a novel experimental method to determine the flammability limits and the minimum oxygen concentration in methane–hydrogen mixtures using the spark test apparatus (STA), by incorporating CO₂ as an inert compound. The proposed methodology allows for the more accurate and efficient assessment of the safety of these flammable mixtures, which is crucial for industrial applications where hydrogen-enriched fuels are used. When comparing the literature data, the differences between methods are not significant, although the procedure, apparatus, and test conditions influence the results. Then, the proposed method is experimentally validated in the STA. Methane is enriched with hydrogen at different concentrations (10, 20, 30, and 50%). The results in the STA show good alignment with the literature data. Furthermore, literature data analysis allows for the generation of an empirical curve that shows the influence of hydrogen addition in methane–air mixtures. The theoretical flammability intervals are also presented as a result. Such representations, after method validation, are the base of the flammability interval test in the STA. The capability of the STA to define flammability ranges in ternary diagrams provides an innovative graphical approach to control explosive atmospheres and facilitates its application in the prevention of industrial accidents.