The probe by the Upper House -- controlled by the opposition People's Party (PP) -- is the first to assign responsibility for the power failure that plunged much of Spain and Portugal into darkness for up to 16 hours on April 28, 2025.
The nine-month investigation concluded that the blackout was not an unforeseeable accident, but rather the result of long-standing structural weaknesses that were already known.
"The blackout was the result of a known vulnerability, of a system that had been giving warnings for some time, and of a failure to act with the required diligence," PP Senator Alicia García told reporters.
The preliminary report cited repeated voltage oscillations in the weeks and months leading up to the blackout as evidence of growing problems within the electrical system.
The Senate committee held Red Eléctrica, a subsidiary of Redeia, and the Ministry for the Ecological Transition primarily responsible for the outage, while criticizing the CNMC, the energy and antitrust regulator, for what it described as regulatory and supervisory inaction.
The investigation gathered testimony from dozens of witnesses, including the Minister for the Ecological Transition, Sara Aagesen, the Chairwoman of Redeia, Beatriz Corredor, and the Chairwoman of the CNMC, Cani Fernández.
The final report will be published this week, although no changes to the preliminary findings are expected.
(Reporting by Emma Pinedo and Pietro Lombardi; editing by David Latona; English translation by [Agency Name])
