Down to tenths of a second: why a renewable grid can be more reliable than a fossil-fuelled one

The panel that opened RENMAD UsefulAI 2026 began with a yes-or-no question, which the moderator framed as the reason for holding the event. Can a 100% renewable grid, managed with artificial intelligence, become as reliable as a fossil-fuelled one? All four speakers said yes. Josep Maria Salas, a board member of the CNMC, Spain's competition and energy regulator, corrected the question before answering it: "Not equal, but more reliable". When the moderator asked the room for a show of hands, she saw "a lot of people convinced".

That answer has a technical basis.

What the blackout report concludes

The expert panel of ENTSO-E, the association of Europe's transmission system operators, published its final report on 20 March 2026 and concluded that the blackout of 28 April 2025 was the result of multiple interacting factors. The sequence it describes begins with voltage fluctuations and oscillatory phenomena. Widespread generation disconnections in Spain follow, "particularly inverter-based resources", meaning equipment that connects to the grid through an electronic converter. Then comes a cascade of overvoltage disconnections, and finally the Iberian system is separated from the Continental Europe Synchronous Area.

The report's technical analyses put the rapid rise in voltage down to a combination of factors "which unfolded over very short timescales, leaving limited time for effective operational response".

Check the clock. Between 12:33:18 and 12:33:21 the voltage in the south of Spain rose sharply, and the overvoltage set off a cascade of generation losses. At 535 milliseconds past 12:33:21, protection devices tripped the overhead lines between France and Spain, and by 960 milliseconds past 12:33:23 the separation of the Iberian system was complete. In between, the automatic load-shedding plans, which disconnect demand to hold the system up, were activated, and so was the defence plan. None of it prevented the collapse.

The report's root cause tree adds two boxes. One records that voltage control support from conventional generators was not effective. The other records that the shunt reactors, the devices that bring voltage down when the grid has too much of it, were operated manually, which requires decision-making and processing time. The correction depended on someone giving the order.

Why speed leaves the human operator out of the loop

Salas framed the problem as one of speed. His starting point was the European energy union, which means interconnecting every country. From there, "a frequency problem in Poland can blow up on you in Cádiz in tenths of a second".

He reasoned it through: "when you take operating decisions because of a frequency variation 6,000 kilometres away, you have to act in tenths of a second". And so, "there is simply no time, physically, for you to take the decision". Then he widened the point. "More and more the power system, the main technical challenge from an engineering point of view, isn't the phenomena that happen, but the speed at which they happen."

In Salas's estimate, a voltage variation that used to play out over a given timescale in a fossil-fuelled system now plays out two or three orders of magnitude faster, that is, between a hundred and a thousand times. If the phenomenon is compressed that much and the chain of measuring, deciding and giving the order is not, control-room expertise loses ground to the way the equipment is set. If you work in a control centre, the box on manually operated reactors is already telling you so.

Salas also distinguished three dimensions. "One is energy, I think there's no problem. Another is power, here a problem does appear. And the other is quality of service and here problems appear too." Energy is how much electricity there is over the day, power is how much there is at the instant you ask for it, and quality of service means voltage that holds steady. Reliability lives in the last two. That is why a grid with a lot of renewables and a good control layer can beat a fossil-fuelled one with slow control.

Where the fast response has to sit

In the tenths-of-a-second layer there is no time for an instruction, so the response has to come built into the equipment you buy. That is where grid forming comes in. Whereas a conventional converter locks on to the voltage that is already there and follows it, a grid-forming converter imposes its own. ENTSO-E defined the capability in its 2020 technical report. To provide instant power to loads that change suddenly, the equipment needs "a voltage source characteristic", and that capability does not wait for anyone to measure, decide and give the order.

The blackout report's recommendations take a different route: automating the voltage resources already installed. Grid forming does not appear in any of them. One asks transmission system operators to explore, as appropriate, automatic control of shunt reactors. Another asks them to explore the possibility of centralised or zonal voltage regulation, with setpoints "automatically calculated based on real-time voltage measurements in reference nodes". These are the voltage or reactive power values each generator has to hold, worked out here by the machine. A third calls for automatic oscillation detection, with a caveat written into the report: automated corrective actions should be applied selectively.

That layer depends on hardware. Javier Pemán of NVIDIA said that digital twin simulations work. "The problem is that there are no physical devices that make that possible." The investment needed is enormous, he added, and it lies in the devices that can react in real time to whatever the AI recommends.

What this layer asks of the machine is boring. Francisco Balboa, founder of Logixs Digital, described himself as "super sceptical" about the idea of an all-knowing oracle. He said that "we can't live with even that 1% of hallucination". He wants "ecosystems in which, in the end, we're looking for determinism, not something random that can fail you that 0.1% of the time". If your asset is going to provide a service in this layer, you will be required to show behaviour that is repeatable and measurable.

What is already being built in Spain

The layer that works in minutes already has a market. In mid-February 2026 the CNMC counted 365 applications for qualification to provide voltage control. In March, Red Eléctrica, Spain's transmission system operator, reported that more than a hundred generating units had met the technical requirements and more than fifty installations were already providing the service. And on 30 June 2026 the CNMC approved a resolution amending operating procedures 7.4 and 14.4 to encourage the dynamic provision of the voltage control service. It was published on 10 July in the BOE, Spain's official gazette.

Look closely at the timings in that resolution, because they tell you where you stand. For real-time voltage setpoint tracking, the response time, which the resolution defines as the time the provider takes to deliver 90% of the reactive power required, must be under two minutes. Two minutes and a few tenths of a second sit on very different scales: two layers, two different jobs. If your plant is already qualified, you are in the minutes layer, the one dispatched from a control centre. The tenths-of-a-second layer is bought in the converter and in the protection settings, which the ENTSO-E report wants validated.

If you are connecting a large load, this lands on you directly. Salas warned that the technical connection requirements for data centres "are very unusual and are very new", and that speed comes back into play in how they respond to voltage variations. In his view, data centres "are not industry, they are infrastructure", and connecting one is nothing like connecting a traditional machine.

The report describes 28 April as the most severe and unprecedented incident in the European power system for more than twenty years. It groups its twenty-one new recommendations under voltage control, oscillations, disconnections, the system defence plan and restoration. None asks for a lower share of renewables, and several ask inverter-connected installations to behave differently on voltage. That leaves Spain well placed, because the system that lived through the incident is the one that already has the dynamic voltage control service up and running.

The moderator had said as much at the start of the panel, when Salas argued that AI will be disruptive in spite of regulation. "I love that the regulator is the aggressive one. […] And that the vendor is the conservative one. This is the world turned upside down."

Reliability will be won or lost in the tenths-of-a-second layer, and that layer is bought in equipment and in settings. The calls you make this year on converters, protection and qualification are already part of the outcome.

Opening panel, RENMAD UsefulAI 2026, Madrid, 2 June 2026.