A big fat energy zero
The Spanish periodical El Economista has published some fascinating – and alarming – transcripts of recordings of conversations among country’s grid operators in the days and weeks before the 2025 blackout. This post is a lightly edited machine translation to give Anglophone readers a chance to understand the implications.
At 10:59 in the morning on April 28, 2025, about an hour and a half before the Iberian Peninsula suffered one of the largest electrical blackouts in its recent history, talk in the control centers already featured a mixture of resignation, stress and fear. "I think we're going to see a fat zero", said one of the operators in a telephone conversation with the grid operator Red Eléctrica de España (REE). It was not a casual turn of phrase. It was a raw summary of weeks – and, other recordings reveal, months – of oscillations, voltage problems, emergency manoeuvres and an growing feeling that the system was losing stability.
The audio recordings of these exchanges capture something exceptional: the language of the system before the collapse. On the other end of the phone there is no retrospective analysis or institutional explanation. There are operators talking in real time about "crazy" voltages, emergency manoeuvres, a lack of stable generation and a risk that, in private, was already beginning to be verbalized bluntly.
The scene on April 28 begins with a direct question from Seville: "What is happening with the voltages? They are crazy today". The response that comes from REE does not encourage any peace of mind. "I would like to know that too", responds the supervisor. From there, the conversation describes an operation marked by urgency: open and close the reactors [control mechanisms on the substations], wait for the system to stabilize "a little" and intervene again. It was minute-by-minute management of a network that wouldn’t stabilise.
In that same exchange a diagnosis is seen to emerge. The REE technician recognises that in the south there were only two groups [of synchronous generation] capable of cushioning the oscillations —Arcos and Almaraz— and admits that "we would have to have more groups involved". What's more it specifies the kind of support was missing: "more 'fat' generation, thermal", [emphasis added] which provides stability to the system. The warning is not issued a posteriori, but in real time, when the network was still operational but was already showing signs of fatigue.
The tone of the conversation hardens as you go. "We will destroy something and everything", says one of the interlocutors. Another tries to downplay the prediction. But the phrase that summarizes the situation ends up prevailing: "I think we are going to see a 'fat' zero". The scenario of a total collapse was no longer a remote hypothesis, but a possibility that operators were beginning to assume would happen. About an hour and a half later, that scenario materialized.
A problem that came from behind
The audios show that the fragility of the system did not arise on the day of the blackout. On January 31, 2025, almost three months earlier, a conversation between the Endesa control center in Barcelona and REE was already reflecting a severe disturbance. After a divergence of up to 1,000 MW in grid flows, operators detected a sudden drop in voltage. [System operator] REE pointed to a massive dropout of photovoltaic generation and the episode is described as "a very very brutal oscillation".
The technician himself admits that it was not an isolated event. "Things like this have happened many times", he points out, although he acknowledges that that the current episode was been especially intense. He also anticipates that the incident would require further analysis: "There will be meetings about this (...), they’ll produce a report or something". The conversation introduces one of the recurring themes in the rest of the audio recordings: the difficulty of managing renewable generation that comes and goes abruptly, with no way to manage it.
Lack of inertia and out-of-control voltage
On April 7, just three weeks before the collapse, these concerns were already explicit. In a call from Seville, operators warned of a "brutal problem", with voltages well below the limits in several provinces. The response from REE pointed directly to the root of the problem: "the interconnectors and little generation that gives inertia to the system".
Minutes later, another conversation from the same day reveals even more erratic behaviour. The voltages, they explain, "have gone up [for no reason] ". The system was beginning to exhibit volatility that was difficult to control even when there had been no direct operational changes. In that context, a structural concern also appears: the impact of nuclear closures. "If they dismantle the nuclear plants (...), it is going to be the turning point", warns an operator. The response from REE is conclusive: "You can't sustain this".
A network that is increasingly difficult to stabilize
Taken together, the recordings trace a clear sequence of events. First, isolated episodes of oscillations, which then begin to repeat themselves. Afterwards, an increasingly sensitive system, with less inertia and growing difficulties in controlling voltages. Finally, on the day of the blackout, operations affected by the sudden entries and exits of generators, with little support from conventional generation and with operators who were already openly contemplating the risk of "energy zero".
The audios do not in themselves constitute a definitive technical conclusion about the causes of the blackout, but they do provide a key element: they show that, at the operational level, concern existed and was growing. And when the collapse came, not everyone perceived it as a completely unexpected event.