Analysis of the April 28th Blackout in Spain

As the future of electric energy takes shape, many countries are accelerating the energy transi tion by promoting renewable technologies and pursuing ambitious targets that seek to combine economic competitiveness, rapid deployment, and deep decarbonization. The frequently questioned, yet inevitable, energy transition is being propelled by the rapid expansion of renewable energy sources, introducing operational challenges that are reshaping both, the technical, and economic foundations of modern power systems. As inverter-based renewable generation becomes increasingly predominant, system operators face a dual challenge: integrating large shares of intermittent, non-dispatchable resources into existing grids while ensuring security of supply in a context where cost-effective ancillary services still depend heavily on conventional synchronous generation. Historically, technologies such as gas, nuclear, and large hydropower plants have provided not only active power, but also essential non-energy services, which include inertia, frequency response, and dynamic voltage control, services that are now progressively diminishing as these units retreat from the generation mix. As Spain aims at a net-zero energy system by 2050, the potential role of traditional energy sources as nuclear energy and combined cycles remains highly debated. Many studies generally focus on the technologies themselves, e.g. carbon footprint, construction time, commissioning or payback period or individual wholesale prices, often aiming to demonstrate the advantages of fast and low-cost installation of renewable technologies. The share of renewable energy in the generation mix has grown continuously, delivering significant benefits such as lower prices, increased competitiveness, and progress in electrification. However, renewable deployment has been regionally uneven, leading to imbalances between regions. Moreover, because this growth has largely relied on replacing conventional generation, some areas now lack crucial synchronous generation, which has historically provided the services necessary to maintain system stability. Although the European grid expansion targets to address this problems, there are scenarios where the physical expansion of interconnections is constrained, problem usually found on the periphery of the Continental Europe Synchronous Area. This is worsened in the case of the Iberian Peninsula, due to the French reluctance to expand interconnection capacity aiming at shielding its centralized electricity market from the competitive pressure of the Iberian market. i In this cases, ensuring a stable power output and a reliable contribution to overall system perfor mance becomes a critical concern. Renewable technologies, while essential to decarbonization, present intrinsic limitations due to the mismatch between their nominal capacity and their effective system contribution. Furthermore, their limited inertia and controllability exacerbate the complexity of solving frequency and voltage events, incurring into higher ancillary services costs and renewables market share reduction. To address these challenges, technological innovation is indispensable. Advances such as syn thetic inertia, grid-forming converters, reactive power control and dynamic, agile grid operation to enable renewable and storage technologies to participate more actively in system stability and ancillary service provision. However, technological progress alone is insufficient without corresponding regulatory and market progression. The evolution toward high-renewable elec tricity systems demands a reframing of market design, from a primarily focused on energy transactions to one that systematically integrates resilience, flexibility, and the secure delivery of system services [1, 2] . These attributes must be recognized as fundamental components of cost-effective and sustainable decarbonization, as the electric system is the cornerstone of the energy transition and the electrification of industry and transport. The analysis of unprecedented events, as Spain’s April 28th blackout illustrates the critical importance of resilient system, highlighting vulnerabilities linked to the reliance on emergency balancing actions unable to compete with power electronics effects, and the need to still rely on intrinsically secure generation technologies, whose stability is based on physical principles, such as nuclear [3, 4], combined-cycle, and large hydro power