The Iberian Blackout - On That Day
There has been a ton written on the Iberian Peninsula Blackout, I won’t add to all the pundits and point at a single thing and say that it is the smoking gun. First off, system collapses are always more complex than just one thing, it’s usually a group of unfortunate events that gets you in trouble. Let’s just talk about where things were and what we know right now.
In the days leading up to 04/28/25, Red Electra had been enjoying a boon of renewable output, so much so that energy prices were negative, Red Electra was paying to export power. At the time of the blackout prices were slightly negative, about 870MW was being exported to France. It was also spring outage season, the “shoulder months” are a popular time to take powerplant maintenance outages. About 50% of the Red Electra nuclear fleet was out of service for spring outages.
The synchronous Transmission tie to France from the Iberian Peninsula is considered quite weak, it consists of a few 400kV and 200kV lines. Much of the power transfer capability is DC, which does not strengthen the synchronous connection.
Reports place the energy supply to the Red Electra system at somewhere between 65% to 75% renewable at the time of the blackout. It was an unusually warm day on the Iberian Peninsula, so the load was higher than normal. Red Electra has almost no battery storage, so the majority of the load was serviced by Inverter Based Resources (IBRs) that provided no system inertia. Red Electra has significant pumped storage capacity, but it was all offline, and 3GW was in pump mode.
Red Electra had been under considerable political pressure to advance the use of renewables after the nation received accolades for 100% renewable service shortly before the outage.
While Red Electra has been ordering flywheel-equipped synchronous condensers for the DC connected island territories, it does not appear that Red Electra had seen the need to add them to the mainland system.
There were signs that there was trouble, there was intermittent but persistent oscillations that kept appearing between the Iberian Power system and the rest of Europe with the Iberian system swinging over the relatively weak AC ties. The full nature of the swings is difficult to examine because there are relatively few synchrophasor Phasor Measurement Units (PMUs) deployed in the area. It does not appear that Europe uses Power System Stabilizer (PSS) technology. (see Power Systems – Where are My Controls Part 2 to learn more about PSS) If you reference the recent IBR based Level 3 NERC Alert, it is clear that IBRs can create forced oscillations, but the phenomenon is poorly understood at this point. Systems with good inertia can dampen out these oscillations in a few cycles, but Red Electra was incredibly short on inertia the day of the blackout. The Iberian system would behave much like a kite with no tale on the end of the weak transmission string. These periods of oscillation had been happening for several years.
Red Electra adopted the European Interconnection standards for IBRs that are quite similar to the NERC standards that are in place here in the USA. The include fault ride through, reactive power support, and active power recovery. Regardless of these standards, IBRs still show a troublesome tendency to shut down when exposed to rapidly changing or abnormal power system conditions. In heavy IBR implementation, this can lead to an IBR cascade where IBRs in a region shut down as the disturbance created by IBRs shutting down expands. A number of the event reports linked in the NERC Alert detail these types of events.
This is the Iberian Blackout Sequence of Events as we know them now, we will begin with the pre-event oscillations:
First oscillation: Around 10:05 UTC (12:05 CET), this oscillation was most dominant in northern Portugal.
Second, stronger oscillation: Followed at approximately 10:20 UTC (12:20 CET), with a major focus in southern Spain. This oscillation was also notably pronounced in the Baltic region, suggesting a systemic coupling across the continental European network. This concurs with other reports of oscillations between the Iberian Peninsula and Latvia. These Baltic Nations just synchronized to the EU Interconnection on 2/9/25. One note, swings with Norway, Sweden and Finland are impossible as they have asynchronous ties to the mainland EU system. There is a report that Red Electra Operators took action to quell this oscillation, but the type of action has not been released.
EU Interconnection Starting at 12:32:57 CET and within 20 seconds afterwards, presumably a series of different generation trips were registered in the south of Spain, accounting to an initially estimated total of 2200 MW. No generation trips were observed in Portugal and France. As a result of these events the frequency decreased, and a voltage increase was observed in Spain and Portugal. This is the initiating event.
Between 12:33:18 and 12:33:21 CET, the frequency of the Iberian Peninsula power system continued decreasing and reached 48.0 Hz. The automatic load shedding defense plans of Spain and Portugal were activated. This load shedding was likely designed to coordinate with large high inertia thermal generation. A large regional loss of renewable generation was not expected and had not been studied. The load shedding scheme was insufficient and did not remove enough load to save the system.
At 12:33:21 CET, the AC overhead lines between France and Spain were disconnected by protection devices against loss of synchronism. This statement means the Iberian Peninsula went out of step and lost synchronism with France. Out of step protection tripped the lines.
My personal conclusions are that we don’t have all the facts so those that say they know what happened are selling papers. I am much more careful in pointing to the blame. But let’s list a few glaring problems:
The oscillations! Come on guys, your power system is talking to you, it says I don’t feel good. The system was apparently talking to you for years, but like that leaky steam pipe telling you there is a weak weld, if you ignore it, it just becomes noise, until …. Here is an oscillation trend from the EU system.
Here is a trend of a massive voltage oscillation on the Iberian power system that just continues to grow until the system collapses. I have seen one post on this and no one is talking about it. But this is extremely nasty.
With little synchronous generation online, no batteries, and no synchronous condensers, one must ask what the reactive reserve looked like. Did they have enough resources to control voltage?
I think there is little doubt that the initiating cause is a cascading inverter trip in the South of the system that left Red Electra generation deficient beyond the system's ability to survive. I do not believe reports blaming the collapse on some unnamed line trip in the Southern Region, that dog don’t hunt. If a line had tripped that data would be easy to identify on the Red Electra EMS system
The oscillations, one 13 minutes before the trip and one 28 minutes, before the trip show an eerily familiar pattern of a developing oscillation that isn’t going to go away. 13 minutes seems like the perfect time for that oscillation to return, with vengeance. Notice that 13 minutes before the heart of the oscillation was in the Southern Region, right where the collapse started. I am strongly suspicious that there was something created on the system by an oscillation that was outside the ability of the area IBRs to follow or manage, so they shutdown. This created a local generation deficiency and a frequency well that quickly expanded to consume the whole system. Because frequency and voltage were changing so rapidly, it would have exceeded many of the IBRs ability to follow and they would have abandoned ship early.
So that’s my two cents, I am not claiming to know more than anyone else, but let’s draw some conclusions;
It was all the renewables fault! Well, was it really, or was it the fault of the System to not prepare for the realities of what they were doing? You will notice I have used the word renewable very little, and talked about IBRs, it’s the IBR technology combined with most renewables sources lack of inertia that caused much of the problem.
However, there are things that can be done to mitigate what happened, they are all expensive, so are they worth it? That is ultimately up to the utility. These are suggestions if a utility wants to pursue a major integration of IBRs.
Strategic and extensive use of flywheel equipped synchronous condensers (SCs). Properly placed SCs with inertia would have helped slow the rate of frequency change which may have kept some IBRs in operation. Also properly placed SCs in the Southern region would have depressed the sudden voltage rise, which also may have helped. SCs with inertia are capable of using PSS technology to suppress oscillations.
Strategically placed grid scale battery installations to provide instantaneous frequency support on a major IBR loss. It’s important that part of that capacity is designated emergency only to assure batteries are not depleted when needed. Batteries with advanced programing IBRs that can provide synthetic inertia and PSS support.
A massively expanded underfrequency load shedding program starting at 49.5 Hz with at least eight steps ahead of generation load shedding. Such a system may need to shed 50 to 75% of system load to keep the bulk energy system intact.
An underlying network of fast start peaking gas turbines to be available to provide rotating inertia and system support as needed. The network needs to be sufficient to move enough of the system from IBR to rotating mass when system conditions require stability. Peaking turbines can provide enhanced PSS support against their inertia during periods of instability.
Widespread application of PMUs so system phase angles can be monitored. With widely applied PMUs an out of tune IBR that is generating forced oscillations can be identified and removed from service until repaired.
If one does not already exist, an IBR level 2 registration program similar to what has been implemented by NERC to assure IBR compliance to system standards.
The above certainly is not a guarantee of zero blackouts on an IBR rich system, but it should go a long way to isolate issues to local regions instead of system wide collapse. By preserving the backbone of the bulk system, recovery is usually fairly quick. The reality is, if you are going to run on a renewable heavy system, you may have to accept that outages will be more common.
For the moment Red Electra has decided to return to a traditional generation rich format and curtail renewable generation. This is the proper conservative approach after a system collapse. They will want to complete their root cause analysis and initiate any recommended changes before risking another system wide collapse.
That about covers my thoughts, what do you think? Anyone have anything to add? I plan to take a short break and come back to talk about IBRs. As always, I hope you enjoyed it. Thank you for reading my Substack!
Additional reading on the subject;
The Electric Grandma; The Switches in Spain
Gordian Knot News: The Cost of Grid Inertia
Steve’s Substack; What Caused The Blackout On The Iberian Peninsular? It’s Complicated.
ENTSO-E expert panel initiates the investigation into the causes of Iberian blackout
Energy Bad Boys: El Blackout , in addition I want to express my gratitude for the Energy Bad Boys continued support of my little Substack, much of my success is credited to them.
An excellent blow-by-blow account of the day of the Spanish blackouts. From a VERY knowledgeable grid specialist.
Really outstanding review and analysis; thank you.
Your previous 2-part post on power system control and analysis was superb.