On April 28th, the Iberian Peninsula was hit by a widespread power outage that brought critical infrastructure across Spain and Portugal to a standstill. Investigations are currently underway to determine the root cause of the blackout, which lasted up to 15 hours in some regions. Red Eléctrica de España, Spain's grid operator, has ruled out cyber attacks despite ongoing speculation as authorities work to understand the systemic failure that left millions affected and raised urgent questions about the country’s grid resilience.
The loss of electricity began just after 12:30 pm CEST, when nearly 15 GW of demand was shed in a matter of seconds. The figure below illustrates the sudden drop on system load, where a phased-in restart was required to get the country’s generators back online.
There was no reported anomaly that could immediately explain the collapse, as grid conditions before the event appeared stable. However, large-scale blackouts like this often stem from a cascading failure following an initial disturbance. In such scenarios, if the balance between generation and demand is not quickly restored, frequency deviations can occur, triggering protective shutdowns across the grid. The rapid drop in load suggests an unexpected system separation or failure of major transmission infrastructure, which can quickly propagate across interconnected systems without sufficient inertia or corrective action.
In the hours leading up to the outage, solar power accounted for a significant share of generation, nearly 58% of the mix at its peak, making its sudden disappearance especially impactful. Following the blackout, black start-capable units played a critical role in restoring power, as these plants can initiate operations independently of the grid. Thermal and hydroelectric resources ramped up rapidly during the recovery. Nuclear facilities, which typically require longer restart procedures to ensure safe operating conditions, remained offline for several days.
Though rare, the blackout highlights a critical challenge for the energy transition: the need to maintain sufficient black-start capacity and flexible, load-following resources. Most renewables, such as wind and solar, are connected through grid-following inverters. These technologies depend on an existing frequency signal to operate and cannot independently restart the grid or provide ancillary services on their own. Pairing them with battery storage could enable grid-forming capabilities, but storage deployment and integration remain limited in Spain’s market today.
As Spain and other countries transition toward clean energy, much of the generation capable of providing black-start services are being phased out. In the past five years alone, Spain has added more than 55 GW of renewable capacity and retired 7.4 GW of coal. By 2030, renewables are expected to supply over 80% of the country’s electricity. While this marks meaningful progress toward decarbonization, it also introduces technical challenges in managing a grid with fewer stabilizing assets.
Spain’s recent blackout highlights the importance of ensuring power-system resilience in an evolving energy landscape. While the precise cause of the outage remains unknown, the event illustrates the operational challenges that can emerge in any complex grid, especially one with a growing share of variable renewable energy. As countries’ generation mixes continue to shift, it’s essential to maintain a foundation of flexible, dispatchable resources, such as gas-fired plants and battery storage, that can respond quickly to disturbances and help stabilize frequency.
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