Stochastic Assessment of Availability Factors: The Case of Spain

Following the massive power cut in Spain on 28 April 2025, questions have been raised about the reliability of energy generation infrastructure in the face of the variability of renewable energy sources. On the other hand, the market penetration of electric vehicles and their charging requirements implies the need for knowledge about the availability of electric generation technologies. This research work presents a macro-level analysis of the availability factor of electricity generation mix, applied to the case of Spain and based on data collected between 2019 and 2024. Using hourly generation and installed capacity data, a methodology is developed to estimate the seasonal and daily availability of the main generation technologies: photovoltaic, solar thermal, wind, hydroelectric, nuclear, combined cycle, coal and others. The analysis reveals that conventional sources, such as nuclear and combined cycles, exhibit low variability, with daily fluctuation of less than 1%. In contrast, renewable sources show significant variability. Photovoltaic availability increases from 22.6% ± 1.3% in the early morning to 57.8% ± 0.6% during summer afternoons, while solar thermal energy reaches a maximum of 78.5% ± 1.3% under the same conditions. The results highlight the uncertainty generated by the high penetration of renewable energy and the challenges posed by balancing generation with demand, particularly given new consumption patterns influenced, for example, by electric vehicles, battery storage and green hydrogen, among others. The integration of probabilistic planning frameworks into infrastructure development and the extension of this analysis to the provincial level, together with the incorporation of restriction and self-consumption scenarios involving constraints and self-consumption, will help to ensure the robust operation of the grid in the future.