spain

Spanish blackout report: Power plants meant to stabilize voltage didn’t

electricity, Energy, grid stability, Portugal, Science, spain / Kris Guyer / June 19, 2025

The blackout that took down the Iberian grid serving Spain and Portugal in April was the result of a number of smaller interacting problems, according to an investigation by the Spanish government. The report concludes that several steps meant to address a small instability made matters worse, eventually leading to a self-reinforcing cascade where high voltages caused power plants to drop off the grid, thereby increasing the voltage further. Critically, the report suggests that the Spanish grid operator had an unusually low number of plants on call to stabilize matters, and some of the ones it did have responded poorly.

The full report will be available later today; however, the government released a summary ahead of its release. The document includes a timeline of the events that triggered the blackout, as well as an analysis of why grid management failed to keep it in check. It also notes that a parallel investigation checked for indications of a cyberattack and found none.

Oscillations and a cascade

The document notes that for several days prior to the blackout, the Iberian grid had been experiencing voltage fluctuations—products of a mismatch between supply and demand—that had been managed without incident. These continued through the morning of April 28 until shortly after noon, when an unusual frequency oscillation occurred. This oscillation has been traced back to a single facility on the grid, but the report doesn’t identify it or even indicate its type, simply referring to it as an “instalación.”

The grid operators responded in a way that suppressed the oscillations but increased the voltages on the grid. About 15 minutes later, a weakened version of this oscillation occurred again, followed shortly thereafter by oscillations at a different frequency, this one with properties that are commonly seen on European grids. That prompted the grid operators to take corrective steps again, which increased the voltages on the grid.

The Iberian grid is capable of handling this sort of thing. But the grid operator only scheduled 10 power plants to handle voltage regulation on the 28th, which the report notes is the lowest total it had committed to in all of 2025 up to that point. The report found that a number of those plants failed to respond properly to the grid operators, and a few even responded in a way that contributed to the surging voltages.

Spanish blackout report: Power plants meant to stabilize voltage didn’t Read More »

Spain is about to face the challenge of a “black start”

Local conditions

While the grids in Spain and Portugal are connected to each other, they have limited connections to elsewhere. The only sources of external power to the grid come from France and Morocco, which are small connections, but they could be used to help black start some plants. Both blacked-out countries have significant hydropower, with Spain seeing it cover 10 percent of its demand and Portugal 25 percent. That’s useful because hydro plants need very little in the way of an external power supply to start operating.

Beyond that, both countries have invested heavily in renewables, with Portugal supplying about half of its power from wind and hydro, having closed its last coal plant in 2021. Spain receives about 40 percent of its power from renewables at present.

Solar is not an ideal power source for black-starting the grid, given that it’s unavailable for a significant chunk of the day. But solar panels produce direct current, with electronic systems matching it to the alternating current of the grid. With the right electronics, it can play a key role in keeping frequencies stable as grid segments are repowered. In productive areas, wind can provide black start power to other plants, and doesn’t need much external power to begin operations. It’s unclear, however, whether the local wind hardware is equipped for black starts, or if the local weather will cooperate (a quick check of the weather in various cities suggests it’s relatively calm there).

Batteries have the potential to be incredibly helpful, since they also provide direct current that can be converted to any frequency needed, and so used for both starting up power plants or for frequency stabilization as segments of the grid are brought back online. Unfortunately, neither country has installed much grid-scale battery hardware yet. That’s expected to change over the next few years in parallel with dramatically expanded solar power. But, at the moment, batteries will not be a huge help.

Regardless of how precisely the grid operators manage to handle this task in Spain and Portugal, they face a monumental challenge at the moment. If you’re seeing estimates of several days for the restoration of power, it’s because failing to meet this challenge will leave things back in the state they’re in now.