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.

Spain experienced a widespread power outage that left millions without electricity for nearly a full 24 hours. While power has largely been restored, the cause of the failure is still under investigation.

Spain suffered several power glitches and industry officials sounded repeated warnings about the instability of its power grid in the build up to its catastrophic blackout on Monday.