The Iberian Peninsula’s widespread blackout raises questions about the resilience of the electric power infrastructure in the two countries — and to an extent, the rest of Europe.

While it may be tempting to blame the unprecedented power outage that hit the Iberian peninsula this week on the rapid growth of wind and solar power in Spain, reliance on renewables is not to blame.

Solar energy was powering the grid in Spain and Portugal on Monday—until it wasn’t, leaving tens of millions without electricity.