A year after Spain and Portugal plunged into darkness, a final report reveals how ENTSO-e grid policies left the Iberian Peninsula dangerously exposed. The comprehensive analysis shows that a combination of voltage oscillations and overly narrow operating margins triggered the collapse of the entire electrical grid.

Investigators traced the blackout to two key oscillations: one a known grid-wide phenomenon, the other originating from a single inverter fault near the Spanish-Portuguese border. While these oscillations didn't directly cause the blackout, they pushed voltages to extremes where hardware began disconnecting. The grid's reactive power management system, designed to dampen oscillations, inadvertently raised transmission line voltages beyond safe thresholds.

The report identifies multiple systemic failures. Spain's grid policy assigned fixed reactive power values to renewable sources, eliminating flexibility when conditions changed. Manual operation of critical shunt reactors meant two-thirds remained unused as the crisis unfolded. Most critically, the five-kilovolt safety margin between normal operation and disconnection thresholds proved insufficient, with some hardware disconnecting prematurely or failing to respond properly to voltage warnings.