Iberian Peninsula Blackout

The Iberian Peninsula operates as an integrated power system serving Spain and Portugal through two national transmission operators: Red Eléctrica de España (REE) and Redes Energéticas Nacionais (REN). The region is characterized as an "energy island" with minimal interconnection to Continental Europe—only 3.4% interconnection capacity versus EU targets of 10-15%.

Both countries have aggressive renewable energy targets: Spain aims for 81% renewable electricity by 2030, while Portugal targets 85%. At the time of the blackout, solar generation accounted for 59% of Spain's electricity mix.

The system relies on conventional power plants (natural gas, coal, nuclear, hydropower) to provide critical grid services including voltage control, frequency regulation, and system inertia—functions that inverter-based renewable resources cannot fully provide without advanced grid-forming capabilities.

Power grids must continuously maintain voltage and frequency within tight tolerances across the entire network. Voltage control is distinct from frequency control and requires continuous adjustment by generation sources.

Conventional thermal and hydro plants provide voltage support through their synchronous generators, which can dynamically adjust reactive power output. This capability is essential during system perturbations.

Grid operators must forecast and manage the energy mix to ensure adequate voltage control capacity is available, particularly during high renewable penetration when fewer conventional generators are online.

On April 28, 2025, at 12:03 CEST, grid operators detected an atypical oscillation in the power system. Standard control procedures were implemented, including reducing electricity exports to France via the limited interconnection.

While these actions successfully mitigated the oscillation, they created a secondary effect: voltage began increasing across the grid. At 12:33 CEST, voltage levels exceeded safe operating thresholds.

The voltage surge triggered protection systems in generation plants, causing them to disconnect from the grid. This created a cascading failure—as each plant disconnected, remaining plants had to carry more load, further destabilizing voltage control.

The Spanish government investigation concluded that REE miscalculated the required energy mix, resulting in insufficient conventional generation capacity available for voltage control on April 28.

Multiple conventional power plants that were expected to provide voltage support failed to respond properly when needed. Some plants did not have adequate voltage control settings configured. Others disconnected prematurely rather than providing support.

REE disputed the government findings, asserting they had planned adequate voltage support based on their calculations. However, both parties agreed that certain conventional plants failed to perform their expected voltage control functions.

With 59% solar generation at the time of the event, the grid had limited electrical inertia—the stabilizing effect of large rotating masses in conventional generators. Inverter-based resources like solar and wind do not inherently provide this inertia.

Modern advanced inverters can simulate inertia (synthetic inertia) and provide voltage support, but Spain had installed only 25 MW of battery storage versus a 500 MW target. The rapid renewable transition had outpaced the deployment of grid-support technologies.

Critically: Both investigations ruled out renewable energy as the cause. The system had operated successfully with similar renewable penetration levels before. The failure was in conventional plant response, not renewable generation.

Within minutes of the first plant disconnections, approximately 15 gigawatts of generation capacity went offline—60% of Spain's total generation. This massive loss triggered frequency and voltage collapse across both Spain and Portugal.

A complete blackout occurred at 12:33 CEST, affecting the entire Iberian Peninsula and a small area of southern France near the Spanish border. The event lasted nearly 10 hours in most areas.

The rest of Continental Europe experienced no significant disturbance, demonstrating that the limited interconnection which contributed to the problem also prevented contagion to the broader European grid.

System restoration was achieved through coordinated efforts by REE, REN, and RTE (France). Black-start capability—the ability to restart generation without external power—was essential.

Spain used interconnections with France and Morocco to help energize the grid. Portugal initially relied on black-start from two power plants, then received support from Spain through a 220 kV interconnection.

By Tuesday morning, nearly all demand had been restored in Spain. In Portugal, 85 of 89 substations were restored by late Monday evening. The successful rapid restoration demonstrated operational preparedness despite the unprecedented nature of the event.

This was the first blackout in Continental Europe's synchronous area where a cascading series of generation disconnections combined with voltage increases led to complete system collapse. Previous blackouts involved different failure mechanisms.

The incident occurred during a period of high renewable penetration, raising questions about voltage management strategies as grids transition away from conventional generation. However, the root cause was conventional plant failure, not renewable generation.

The event exposed a gap between assumed and actual performance of conventional plants. Grid planning relied on these plants to provide voltage support, but operational reality did not match planning assumptions.

ENTSO-E (the European network of transmission system operators) established an Expert Panel in May 2025 to investigate the incident. The panel includes TSO experts, regulators (ACER), and national authorities.

The investigation follows a two-phase approach: Phase 1 produced a factual report (released October 2025) detailing the sequence of events. Phase 2 will analyze root causes and produce recommendations expected in Q1 2026.

Parties found responsible may be liable for losses incurred during the outage. Both the Spanish government and grid operator have committed to measures strengthening voltage control and improving European grid integration.

As grids integrate higher levels of inverter-based renewable resources, the role of conventional generation shifts from energy supply to grid services provision. This transition requires explicit planning and new operating procedures.

Assumed capabilities of generation assets must be regularly tested under realistic operating conditions. Paper compliance with voltage control requirements does not guarantee operational performance during system stress.

Grid operators need enhanced tools and frameworks to manage voltage stability in systems with reduced synchronous inertia. Advanced inverters, battery storage with grid-forming capabilities, and real-time monitoring are essential.

Limited interconnection creates both vulnerability (less mutual support) and resilience (prevents cascade to neighboring systems). The optimal interconnection level depends on relative reliability of connected systems.

This pattern appears wherever renewable penetration increases rapidly without corresponding deployment of grid-support technologies and updated operational procedures for conventional plants.