At 12:33 CEST on April 28, 2025, an outage cut power across continental Spain and Portugal and briefly affected a small area of southwest France. This was the first full blackout in the history of the Spanish system and its first loss of power event in history caused by overvoltage problems.
The event was not the simple story many first reached for. It was not a cyberattack. It was not a straightforward failure of solar or wind power plants. It was not solely caused by lack of spinning generation. It was a fast-moving voltage event in a system where generation, grid operation, protection settings, regulation and visibility did not move at the same speed as the energy transition.
Voltage control
Before delving into the consequences of the event and what they mean for Spain and for the wider European system, let’s start with the basics, what is voltage control. Everyone understands what a power shortage is, but what about reactive power? Voltage is the power grid equivalent of “pressure” in a gas-hydraulic network. A power system does not only need enough megawatts; it also needs megavars (reactive power) to stay within safe limits so equipment can operate correctly. If voltage rises or falls too far, generators, transformers and protection systems can disconnect to avoid damage, which can make a disturbance spread quickly.
