Iberian blackout, six months on |
New ‘expert panel’ report: the what, but not the why
The 45 member legally mandated ‘expert panel’ set up by ENTSO-E (European Network of Transmission System Operators for Electricity) to investigate the 28 April Iberian blackout has released what it calls a “comprehensive factual report” on this unprecedented incident. It was the most significant power system event in Europe in over two decades, and the first ever of its kind (overvoltage)
440 430 420 410 400 390 380 370
Spain 435
420 10:30
Upper voltage limit in Spain: 435 kV
Portugal 390 375
in voltage, from 10:30 CEST
First voltage fluctuations observed in Spain (but “within normal range of operations”). Source: ENTSO-E
The new report, published 3 October, “ahead of the legal deadline”, presents a detailed account of system conditions on 28 April leading up to the blackout, the sequence of events, and the restoration process. It supersedes an earlier report from the expert panel (see MPS July/ August 2025, pp 8-10).
At 262 pages, the new document is described as the first major report of the expert panel and has been produced in line with EU regulations. But it is by no means the last word; its authors say it does not include analysis, consideration of root causes or suggestions as to how such blackouts might be avoided.
Work is already underway on preparation of the expert panel’s final report, which is expected to be released in Q1 2026. This will include a detailed root cause analysis and recommendations as to how to prevent similar events happening in the future.
The expert panel comments that in Portugal and France it has proved possible to collect the necessary data and transfer it in a timely manner to the panel, whereas in Spain significant difficulties arose in obtaining high quality data from “several DSOs and generating companies” and at the time of writing the report some of the information required from Spanish entities was still missing.
430 420 410 400 390 380 370 360 350
Time
Sines substation (SSN) Lower voltage limit
Recarei substation (SRR) Upper voltage limit
10:30
Upper voltage limit in Portugal: 420 kV
The expert panel notes that the morning hours of 28 April 2025 were characterised by increasing renewables generation, leading to decreasing prices on the day-ahead market and increasing exports from Spain, up to 5 GW in total. It was described as a typical spring day in south west
Spain - centre/south-west
600 400 200 0
-200 -400 -600
Qmeasured Qreference
Example of difference between reactive power provided (Qmeasured) and requested (Qreference) (central/south west Spain). Source: ENTSO-E
Qmeasured
Spain, with renewable infeed following usual patterns (as it had done on preceding days), with a high concentration of renewables in the south west of the country as of noon. From around 09:00, the variability of the voltage in Spain started increasing, albeit
20 | October 2025|
www.modernpowersystems.com
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9:00 9:15 9:30 9:45 10:00 10:15 10:30 10:25 11:00 11:15 11:30 11:45 12:00 12:15 12:30 9:00 9:30 10:00
11:30 12:00
kV
Mvar
Voltage [kV]
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