The sweeping power outage that hit Spain and Portugal this week has raised questions about the electricity grid in a region not normally known for blackouts

It was the second serious European power outage in less than six weeks after a March 20 fire shut down Heathrow Airport in the U.K.

Millions were plunged into darkness in Europe on Monday as a massive power outage impacted parts of Spain, France and Portugal. The blackout wreaked havoc on travel across the three countries, and the impacts extended beyond there, too.