The exact reasons behind the power loss remain uncertain.
Spanish Prime Minister Pedro Sánchez urged caution against misinformation.
Juanma Moreno, President of the Regional Government of Andalusia, said a cyberattack could be the cause, but this was quickly dismissed by officials close to the government.
Portugal’s electricity network, Redes Energéticas Nacionais (REN), cited a significant voltage fluctuation in the Spanish grid as a contributing factor, which affected Portugal while it was importing Spanish energy.
Such fluctuations could be triggered by rapid changes in temperature or wind speeds, but rarely have such a huge impact.
Could intermittent renewables be to blame?
Renewable energy sources, like wind and solar, are inherently intermittent due to their dependence on weather conditions.
The power failure began at 12:33pm local time according to Spanish Prime Minister Pedro Sánchez.