The blackout that engulfed the Iberian Peninsula on Monday was chaotic and stressful for many. But it had a silver lining.

Electricity is pulsing through Spain and Portugal again after a massive outage knocked out power in both countries on Monday. So too are questions.

The Spanish power distributor calls it “exceptional and extraordinary.” Power went down just after noon and by nightfall only half of the power had been restored in Spain. The cause was not immediately clear Monday.