ENTSO-E final report: Iberia's 2025 blackout was triggered by over-voltage, not solar share

Summary

ENTSO-E released its final report on 20 March 2026 into the 28 April 2025 Spain-Portugal blackout, the worst in Europe in two decades, leaving 50+ million without power for up to 16 hours. The panel concluded the trigger was excessive voltage, not a supply shortage: it was "the first known blackout caused by over-voltage." Causes interacted , voltage oscillations, reactive-power-control gaps, divergent regulation practices between operators, rapid output reductions and generator disconnections in Spain, and uneven stabilisation. The findings reject the "too much solar" narrative; the report notes too few thermal plants were online to provide voltage control, and some renewable generation tripped as the system destabilised.

By the numbers

• 28 April 2025, the blackout; 20 March 2026, final report release.
• 50+ million, people who lost power.
• Up to 16 hours, longest restoration time in parts of Spain (12 in Portugal).
• First, over-voltage-triggered blackout of this scale on record.

Why it matters

The verdict reframes the policy fight: the risk in renewable-heavy grids is not generation share but the loss of voltage and reactive-power services as synchronous thermal units retire. It pushes operators toward grid-forming inverters, synchronous condensers and tighter cross-border voltage coordination.

What to watch

• Regulatory mandates for voltage/reactive-power services from inverter-based resources.
• Whether other high-renewable grids (CAISO, Australia) tighten voltage rules.
• Spanish and Portuguese operator-coordination reforms.