A year after the April 28, 2025 Iberian blackout that left Spain and Portugal without power for up to 12 hours, MIT Energy Initiative researcher Pablo Duenas-Martinez explains the technical chain of events. The outage was triggered by a voltage death spiral: oscillations on the grid, combined with insufficient conventional generators providing reactive power control in southern Spain, caused a cascade of automatic shutdowns starting with small solar installations. Five key lessons emerged: regional (not just national) generator ratios matter for reactive power; large solar and wind plants above 5 MW must now provide reactive power control; better coordination between transmission and distribution system operators is needed; Spain's upper voltage limit is dangerously high and should be lowered; and automated shunt reactors plus additional STATCOM devices are being deployed to enable faster voltage response.
