| Iberian blackout , six months on


margins. There are also reports that some units contracted or expected to provide dynamic voltage support did not respond as required in the crucial seconds, exacerbating the excursions and forcing the subsequent protection actions. Understanding the broader system context is essential: the Iberian system, particularly in Spain, has a high penetration of inverter- based resources and, at times, relatively limited synchronous short-circuit strength and inertia compared with historic norms.


That reduced pool of synchronous support constricts system behaviour under disturbance. Lower inertia removes counter-balancing capacity against power frequency oscillations, shortening the time available for corrective action after a fault or a sudden trip. It also renders some traditional, generator-level stabilising mechanisms, such as synchronous condensers and static compensators, less effective unless explicitly configured to operate in the new conditions.


In summary, the technical record available today points to a composite failure: low- frequency oscillations and voltage excursions that triggered protection actions, in a system operating with high renewable share and reduced synchronous support.


Are renewables to blame? What lessons should we take from the Iberian blackout of 2025?


Of course, very few people would argue that we should reverse course on renewable energy sources.


The progress made across Europe to increase the grid’s proportion of renewable electricity is one of the continent’s most impressive achievements in recent decades. The European Union’s Renewable Energy Directive commits to an overall energy mix with 42.5 per cent renewable energy by 2030, having reached 24.6 per cent in 2023.


However, there are structural-, operational- and equipment-level measures, relating to energy sources, inertia, excitation and reactive-power control, monitoring and protection design, that can increase system resilience.


Asynchronous vs synchronous generation


One plain fact is Spain’s reliance on asynchronous, inverter-based renewable generation. Wind and solar plants connect to the grid through power electronics, not direct electromagnetic coupling in synchronous rotating machines.


While inverters can provide some synthetic inertia and fast frequency response, they don’t inherently contribute synchronous inertia or short-circuit strength in the same way as conventional generators. This limits grids’ natural ability to damp oscillations or withstand sudden voltage swings.


Test input–output panel for generator excitation system (photo: Excitation & Engineering Services (EES))


Other countries benefit from a different mix. Norway, Austria and Iceland, for instance, have large proportions of synchronous renewable generation, chiefly hydro and geothermal. These resources behave akin to traditional fossil fuel units, inherently providing stabilising inertia and reactive power current. This gives operators wider margins to absorb shocks and time to intervene before disturbances escalate. Hydro power does feature in the two Iberian peninsula countries’ energy mix: seven per cent and 13 per cent for Portugal and Spain respectively. Additionally, nuclear power represented 20 per cent of Spain’s generation capacity in 2024. However, relative to some countries, hydro resources are more limited and VRE dominates.


The challenge for TSOs and power plant managers is to replicate those stabilising functions by other means. Already, asset owners are trialling grid-forming inverters to deliver synthetic inertia and fast frequency support, and installing synchronous condensers to bolster reactive power and fault strength.


Lessons to learn to prevent future large-scale blackouts


As national and interconnected international electrical grids adopt more asynchronous renewable generation capacity, the resilience to frequency oscillations provided by inertia and short-circuit contribution will decrease. For system operators, this means living up to the same expectations of a stable and healthy grid without some traditional tools.


In this context, real-time monitoring and visibility of system operating conditions becomes even more critical. Robust SCADA monitoring and control enable response within seconds of


disturbances arising. They also allow proactive management, adjusting generation dispatch, line flows or protection settings before small deviations cascade into a wider system separation.


As worsening climate change makes weather patterns more unpredictable, wind and PV solar energy generation will also become harder to forecast. Investment in advanced forecasting tools, such as AI-powered weather trend prediction solutions, can help operators bridge this gap and balance demand with supply. Technologies to support voltage regulation and overall system stability, like the reactive power compensation equipment mentioned earlier, will be non-negotiable upgrades to electrical grids targeting greater renewable penetration as we approach the EU’s 2030 deadline. From a synchronous machine manager’s perspective, well-maintained and optimised excitation systems that can cope with evolving grid conditions are a priority. AVRs and power- system stabilisers are essential components to dampen fluctuations in voltage and power frequency, thereby contributing to a more stable grid.


Ultimately, the power transmission and distribution community must recognise the continuing value of synchronous generation. Established electrical grids operate under assumptions and conditions originating from their fossil fired beginnings, that cannot be ignored.


While compensatory technology can help maintain stability, the phenomena of inertia and reactive power haven’t lost their importance. In fact, the future of our networks depend on resilient, well-monitored electrical infrastructure.


 read about our consultancy process here: https://excitationengineering.co.uk/consultancy/  


www.modernpowersystems.com | October 2025 | 23


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