Terra Firma Energy – 18 June 2025

A government investigation has found that programming errors by Spain’s transmission system operator (TSO), Red Eléctrica, and the improper disconnection of generating units were key factors behind the widespread blackout that struck the Iberian Peninsula on 28 April.

Speaking after a Council of Ministers meeting, Spain’s Vice-President and Minister for Ecological Transition, Sara Aagesen, presented the findings and confirmed that poor voltage control planning contributed significantly to the outage.

The day before the blackout, Red Eléctrica requested that ten thermal power plants remain available for voltage stability support. Although these plants were not expected to be active under normal market conditions, they were part of the TSO’s contingency planning framework. However, when one plant withdrew availability at 8:00 pm local time on 27 April, the TSO opted not to replace it.

According to Aagesen, this decision meant the grid entered 28 April with insufficient voltage control resources during key afternoon hours, despite forecasts indicating a need for support.

During the event, some power units disconnected from the grid automatically to protect themselves from voltage irregularities. But the report highlights that several units may have disconnected unnecessarily, triggering a wider over-voltage wave that intensified the blackout.

The generation shortfall initially believed to be concentrated in Badajoz, Granada, and Sevilla was later found to also affect Caceres, Huelva, and Segovia. The cascading failures unfolded in just 21 seconds.

The government has ruled out any cyberattack or external interference as a cause of the incident.