Blackouts
How to avoid them and how to recover from them
On Friday, the final report on the April 2025 Iberian blackout was published. This is a good opportunity for reflecting about blackouts - how to protect the power system and yourself from blackouts, and how a post-blackout recovery looks like.
Protect yourself: batteries
From an individual perspective there’s a few options. The Polish government recently sent out a security leaflet to all citizens with some hints. But the section on blackouts was a bit underwhelming and featured a diesel generator. I have one and it’s horrible in every way… Fortunately, there’s an alternative.
It’s batteries, that have, unsurprisingly, boomed in Spain following the blackout. In fact in 2025, Spain doubled battery storage capacity, and is on track to do it again in 2026, if the projects currently in construction are deployed by end of year.
The surge in battery expansion is related to Spain’s grid resilience package, introduced after the April 2025 blackout. The Royal Decree set ambitious storage targets (22.5 GW by 2030), streamlining permitting, prioritizing hybrid power plants, cleaning up the connection queue. Stricter voltage control is being pursued as well.
With battery costs falling rapidly (20% a year on average, over the last decade) and oil going up, it’s quite hard to justify diesel generators these days.
Protect the system: interconnectors
Batteries - home and grid-scale, are a key new technology for grid stability and recovery. The other one is interconnectors. In fact, in a recent post-blackout report, the Spanish regulator called for more interconnection.
Here's a story of a blackout actually prevented by cross-border links.
On May 17, 2021, during a scheduled maintenance operation at the high-voltage substation Rogowiec, Poland, a human error disconnected several lines that feed power from the largest power plant in the country – Bełchatów, into the Polish grid. Around 3.5 GW of capacity was instantly removed, leading to a 158 mHz frequency drop, just shy of the 200 mHz buffer that would put the system in an emergency state.
The Continental Europe Synchronous Area (so the European grid) absorbed the frequency deviation by ramping up flows from neighboring countries. These flows instantly reached 4.5 GW – 2.3 GW more than allowed, putting pressure on the grid in Western Poland. But Polish and German transmission system operators (TSOs) managed to restore the frequency to nominal value within 30 minutes.
It was a close call, but thanks to interconnectors, the frequency drop was contained, avoiding the tripping of generators and cascading failures.
Recover
Even with protective measures, a blackout is possible. At that point, you need to restart the power system, which is not easy. Reading the ENTSO-E Iberian blackout report, I was fascinated by the restoration process. So I built a little animation showing how the Spanish grid was re-energized.
The restoration started with a few hydro power plants, plus interconnectors with France and Morocco. Once the hydro plants were running, they were used to start up other power plants - including gas and nuclear. Even though it’s simplified, the animation illustrates a few important points:
Without interconnections with France and Morocco, the restart would've been much more difficult
Not all black-starts succeed so you need a lot of redundancy. Several hydro plants were black-started to create electrical islands, but you'll notice in the animation that some frequency islands disappear. Plus there were 3 more attempts that aren't shown on the map because the islands never propagated.
Hydro power was key in the restoration process. Countries without hydro need a good alternative.
On the two last points, the ENTSO-E Expert Panel recommends adding battery storage to black-start tests. This would provide an additional safety layer in case some restart attempts fail / if there is limited hydro availability. Which nicely brings us back to the conclusions from the first section of this post - we need more battery storage.
Disclaimer: the visualization is simplified. I manually extracted the ~hourly snapshots from the raster graphics in ENTSO-E’s final report (so the node locations are not ideal), and then added approximate transitions because full minute data wasn’t disclosed. Which means some line and node renderings in between the snapshots will be inaccurate.
Data sources:
Power grid: Xiong, B., Fioriti, D., Neumann, F., Riepin, I., & Brown, T. (2026). Prebuilt Electricity Network for PyPSA-Eur based on OpenStreetMap Data (0.7) [Data set]. Zenodo
ENTSO-E, Final report of the Expert Panel on the 28 April 2025 blackout in continental Spain and Portugal
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Having a household battery unfortunately isn't sufficient, depending on where you live. Australia for example has anti-islanding rules (to protect equipment and the safety of people repairing the grid) which means you need a grid-forming inverter with the capability to island your house from the grid in a blackout.
I think some people get solar/battery then get disappointed when they can't use it during a blackout, which is fair.