Knowing for sure what caused the massive blackout on April 28 last year, which left the entire Iberian Peninsula in darkness for hours, will be difficult. Several investigations have been carried out so far. Red Eléctrica, ENTSO-E (the European group of system operator companies), the National Commission for Markets and Competition (CNMC), the Ministry for Ecological Transition, and others have conducted them. All indicate that there was a combination of circumstances that led to the blackout, but without pointing to anyone in particular.