AN ANALYSIS OF EU POWER SYSTEM FLEXIBILITY: STORAGE CAPACITY NEEDS UNDER INCREASING VARIABLE RENEWABLE ENERGY SOURCES (VRES) PENETRATION

The increasing penetration of variable renewable energy sources in the energy mix plays a key role in the energy transition but it also poses serious challenges in terms of grid scheduling, regulation, management, and resilience. To cope with the non-programmable nature of renewables, increased generation reserves, ramp rates and curtailments are required to meet the electricity demand with an increasingly uncertain supply and to provide flexibility services to the grid. To avoid excessive operational costs and mounting inefficiencies, the grid calls for higher flexibility requirements from the electricity system. Currently, this can be provided only by conventional generators (such as thermoelectric or hydro-electric), by demand shifting (mainly by industrial loads) or by energy storage systems, whose current limited adoption is still insufficient for such objective. The definition of such flexibility requirements is still an open topic in the literature, with few analyses available targeting the problem in a quantitative fashion, especially when future energy scenarios are considered. For these reasons, this study provides insights into the historical trends of flexibility parameters in three representative EU members (Italy, Germany and Hungary). These parameters are discussed separately for each country and compared among countries through a novel visualization mode which traces their temporal evolution and seasonal patterns and allows comparison between electrical grids with varying power levels. Furthermore, the study anticipates diverse future scenarios for the Italian power system, considering increased variable renewables penetration. Each scenario is analyzed for renewable generation curtailments and seasonal variations in renewable energy supply. The assessment of different storage needs in terms of capacity and duration provides a quantitative foundation for addressing the evolving flexibility requirements in the face of future energy scenarios. Particularly, future scenarios for Italy highlight the potential need for short-term energy storage systems, such as batteries, with a capacity between 10 and 110 TWh/year to avoid renewable curtailment levels ranging from 5% to 40%. Alternatively, by expanding the potential for use to sectors other than electricity generation, the same curtailment levels could be used to generate green hydrogen, between 0.2-1.9 million tons per year. The results underscore the importance of balanced increases in wind and solar capacities to optimize flexibility and reduce seasonal storage demands, showcasing the study's relevance in shaping informed energy transition strategies.