Iberian Peninsula Blackout Report

In mid-June, the Spanish government and grid operator REE released reports on the April 28, 2025, midday blackout that affected Spain, Portugal, and a small part of southern France. These reports give a detailed breakdown of causative factors and recommendations to address them. More details are expected from the European Network of Transmission System Operators for Electricity (ENTSO-e) early in the fall.

During the event, no inclement weather stressed the grid, which was lightly loaded with sufficient capacity to meet projected demands. Over half of Spain’s 27 GW of electric demand came from wind and solar inverter-based resources (IBRs), a situation that occurs regularly in the Texas Interconnection.

Operator actions to dampen grid oscillations within the Spanish grid (and with the larger interconnected European grid) increased the amount of transmission in-service and reduced exports in the half-hour prior to the event. Light loading on the transmission system led to increasing grid voltage. This caused an overvoltage trip at a collector substation for multiple solar facilities; other generation losses followed due to still-rising voltage. In some instances, generator voltage ride-through settings led to unnecessary reductions when units had the capability to safely remain connected. Besides loss of generation, resources failed to provide dynamic voltage regulation to arrest the voltage rise. REE asserts that some synchronous generators did not meet their obligations. Spanish grid rules for renewables do not require them to provide dynamic voltage support. This combination of factors led to frequency decay even as voltages rose, to the point of activating automatic underfrequency load shed that came too late to arrest deteriorating conditions. Degradation reached the point where generation protection systems tripped due to loss of synchronism (referred to as being “out of step”); this also opened alternating-current tie lines to France and Morocco. The cascading losses blacked out the grid in 27 seconds. Restoration began immediately and fortunately the grid was restored within a day, aided by power imports from the French and Moroccan tie lines.

This event was a complex interplay of equipment characteristics, operational planning considerations, and regulatory decisions, not any single factor. Similarities exist between the European and North American grids, notably the significant share of generation from renewable IBRs and the presence of weak areas of the grid. There are also some key differences in how the Electric Reliability of Council of Texas (ERCOT) grid operates, though, which might have helped in Spain.

ERCOT-connected IBRs are required to contribute to voltage control to a much higher degree, with new rules governing ride-through performance from ERCOT and the North American Electric Reliability Corporation (NERC) that will further enhance capability and coordination. The Iberian grid operators might also benefit from the support of batteries and synchronous condensers like our Region’s grid has. Existing NERC standards, such as those for voltage support, provide assurance that synchronous generators and IBRs will contribute to grid operations in stressed periods. NERC Alerts, like the current Level 3 Alert on IBR Performance and Modeling, point out the need for additional work by both the generation and grid operators to understand equipment capability in our evolving grid.