The day of the power outage, Spain "did not have sufficient voltage control capacity" due to a programming error, says the responsible minister Sara Aagesen to reporters after the causes were presented.
The overvoltage started a chain reaction where the protection system shut down parts of the power grid, which in turn caused the power outage.
Aagesen emphasizes that Spain's power grid is theoretically strong enough to handle such events and that necessary measures will now be proposed.
The power outage paralyzed large parts of Spain and to some extent also Portugal when, among other things, the mobile network, airports, local traffic, traffic lights, and shopping centers were shut down.