New lines of defence: how interconnectors keep the lights on

Interconnectors keep power flowing through disruptions

Without interconnectors, Europe could have experienced two additional major blackouts in the last five years, and the Iberian one could have been much more severe. 

Interconnectors help stabilise or restart grids after faults

Several examples show how interconnectors helped stabilise grids during incidents that could have otherwise had much more severe consequences.

European interconnectors made recent grid stress events less severe

While European power systems maintain excellent reliability standards, multiple events in the past have put grids to a test. In those moments, interconnectors played a key role in stabilising the power systems and preventing widespread power cuts, or restarting the system if a blackout did occur. 

Prevention: interconnectors helped avoid two potential blackouts in Poland

On 17th May 2021, a human error led to the malfunction of a high-voltage substation in Poland – Rogowiec. The substation feeds power from the largest power plant in the country – Bełchatów, into the Polish grid. The incident suddenly disconnected around 3.5 GW of capacity from the system and led 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 absorbed the frequency deviation by ramping up flows from neighbouring countries. These flows instantly reached 4.5 GW – 2.3 GW more than allowed. Significant load appeared on power lines in Western Poland – 5 lines were operating at above 100% capacity, two of them above 120%, posing a risk of overloading. These violations were resolved by the Polish and German transmission system operators (TSOs), who limited flows and restored the frequency to nominal value within 30 minutes.

Immediately after the incident, the Polish TSO requested emergency support from neighbouring countries to rebuild capacity reserves. Interconnectors were initially essential to prevent further frequency drops, the tripping of generators and cascading failures. Then they became key to rebuilding the system’s reserves while the grid malfunction was being removed.

Another stressful event happened in Poland on 22nd June 2020, when heavy rainfall damaged coal supply lines. This, along with several other random failures, led to a record unplanned generation loss of 5.7 GW, equivalent to a quarter of that day’s peak demand. The event wasn’t as sudden as the one in 2021, and the frequency was not disrupted, so the incident didn’t require a formal investigation.

However, the Polish TSO had to request emergency imports from neighbouring countries and deployed almost all coal plants available in “cold reserve” – plants used only in emergency situations. If interconnectors hadn’t provided 3 GW of power, a blackout would have been a real possibility. Only around 2 GW of coal and pumped-storage capacity was left in the system, meaning 1 GW of demand could not have been balanced, leading to voluntary or forced reductions.

Stability: interconnectors filled France’s generation gap throughout 2022

France has recently faced major generation gaps due to nuclear plant outages. Historically, the country was the biggest exporter of electricity in Europe. However, in 2022, the total electricity generation dropped from 550 TWh in 2021 to 468 TWh – a decrease of 15%. Flows switched from net exports of 42 TWh in 2021 to net imports of 17 TWh. Peak imports reached 11 GW – 75% of the total interconnector capacity. In certain moments, imports covered up to 17% of the country’s peak electricity demand. While French nuclear has rebounded since 2022, the fleet still experiences outages, especially during heatwaves. In those moments interconnectors continue filling the capacity gaps, reducing price spikes as well.

Recovery: interconnectors restarted the Iberian grid after the blackout

On 28th April 2025, Spain and Portugal were hit by the largest blackout in Europe’s modern history, leaving around 60 million people without electricity for hours. Multiple causes led to the incident, and a final report by the European Network of Transmission System Operators for Electricity (ENTSO-E) is due in October 2025. 

What is already certain is that, after the blackout, interconnectors were essential in restarting the Iberian power system. Just 10 minutes after the blackout, the first France-Spain power line was reenergised, soon joined by the interconnector with Morocco and other connections with France. With the help of hydro and gas units, a full restoration was achieved in Spain around 4 AM on 29th April, around 16 hours after the incident. 

The Iberian Peninsula is more vulnerable to blackout risks than other European countries due to limited connections to the continental grid. Following the blackout, Spain and Portugal urged the EU to back new interconnector projects, citing stronger links as essential to preventing future disruptions. 

The 2021 blackout in Texas offers a stark warning of what can happen if connectivity isn’t sufficient. In February 2021, severe cold weather left more than 4.5 million people without power for several days, causing 250 deaths. With peak demand above 70 GW but just 1 GW of interconnection, the state was unable to stabilise frequency deviations or replace the 34 GW of missing capacity through imports, leading to a quick collapse. Restarting the system after the blackout was difficult as well – with fossil gas generators rendered unavailable, interconnectors could not be used to resynchronise the system, as was the case after the Iberian blackout. This is why exploring additional interconnection was one of the recommendations of the Federal Energy Regulatory Commission that analysed the blackout.

Up to 55% of Europe’s power system has limited electricity import options, increasing the risk of blackouts 

The more cross-border capacity a country has, the more stability can be provided by neighbours during grid stress events. This can be measured by the ratio of interconnector capacity (in the import direction) and a country’s peak electricity demand.

This ratio varies from 12% in Poland, to almost 200% in Latvia – a country that has relatively small domestic demand, but supports electricity transits between Central Europe, the Baltics and the Nordics. However, there is no guarantee that imports from neighbours will be available instantly and at full capacity. That is why diversification is key: the more neighbours a country is connected to, the higher the chance that cross-border support can be provided on short notice.

Summing the peak electricity demand of countries with three or fewer import directions and an import potential ratio of 25% or lower, up to 55% of Europe’s power system can be considered at risk due to limited emergency import options. Three countries – Spain, Ireland and Finland – are particularly exposed, with very little support available from neighbours in case of grid incidents.

Interconnectors provide security in times of uncertainty and war

Being essential for Europe during Russia’s aggression, interconnectors have also become targets of sabotage.

Interconnectors helped when power systems were attacked

Interconnectors have a key role in stabilising power systems after a fault. But the past three years have also highlighted their other security feature – delivering stable electricity even during war.

Keeping the grid alive during Russia’s attacks on Ukraine’s infrastructure

Before 2022, Ukraine’s power system was connected to the Russian and Belarusian ones. On the day of the full-scale invasion, Ukraine requested an emergency synchronisation with the European power system. This was achieved in a record time of just 3 weeks. This proved to be a critical security move since Russia’s invasion of Ukraine included multiple attacks on energy infrastructure. 

By May 2024, about 70% of Ukraine’s thermal generation capacity was either occupied or damaged, compromising the country’s ability to meet domestic demand. Fortunately, up to 2.4 GW of import capacity was available for Ukraine – equivalent to 20% of the peak demand – including emergency response schemes by neighbouring grid operators.

Thanks to interconnectors, during the most severe attacks on Ukraine’s energy infrastructure in 2024, Ukraine imported over 800 GWh of electricity a month, though a capacity gap still remained, leading to local power cuts. Imports totalled 4 TWh in 2024, a striking shift from Ukraine’s historical role as an exporter of around 2 TWh of electricity a year in pre-war 2020 and 2021.

Stabilising Moldova ahead of parliamentary elections

Similarly to Ukraine, Moldova’s power system used to be synchronised with Russia and Belarus. In 2022 it also went through an emergency synchronisation process, using interconnectors with Romania – which again proved to be an effective security move. On 31st December 2024, Russia stopped supplying gas to Moldova’s largest power plant, in an effort to destabilise the country ahead of parliamentary elections. Moldova was forced to source up to 62% of electricity demand from Romania.

Fortunately, thanks to grid investments, Moldova’s energy security will soon be strengthened. A new interconnection, Vulcanesti – Chisinau, is due to be deployed by the end of 2025, providing up to 80-90% of Moldova’s peak demand in emergency situations and ensuring independence from Russia. Two other interconnectors are being constructed, Balti-Suceava, due in 2027, and Straseni-Gutinas, due in 2030, allowing for the full integration of Moldova with the European power grid.

Shielding Lithuania, Latvia and Estonia from Russia’s energy blackmail

Once reliant on Russia’s power grid, Lithuania, Latvia and Estonia were fully synchronised with Europe’s grid and decoupled from Russia on 9th February 2025. The Baltic Synchronisation was one of the EU’s biggest grid projects, receiving 1.2 billion EUR of support from the Connecting Europe Facility. The decoupling of Baltic States from Russia was made possible thanks to new cross-border connections between Poland and Lithuania (LitPol Link), and between Estonia and Latvia, as well as existing connections between Estonia and Finland (EstLink and EstLink 2), and Lithuania and Sweden (NordBalt). To further strengthen the energy security of the Baltics, a new interconnector between Lithuania and Poland is being planned: HarmonyLink, due in 2030.

Europe’s interconnectors need boosting and securing

Interconnectors are key in guaranteeing grid resilience, energy security and, more broadly, Europe’s safety. To continue providing stability against grid failures or geopolitical threats, two sets of actions need to be taken: the expansion of interconnector capacity and better security of existing infrastructure.

The upcoming European Grid Package presents a timely opportunity to strengthen political commitment around both areas.

European interconnection capacity is expected to almost double between 2024 and 2040, or even triple if all currently planned projects were delivered on time. Priority should be given to areas with limited connectivity and high exposure to potential disruption – such as the Iberian Peninsula, Eastern Europe and Finland. 

However, strategic investments will only happen with strong political commitment and cross-border collaboration. Worryingly, Poland, the EU’s fifth largest electricity market, has almost no interconnection expansion projects planned, despite recent near-blackout incidents and a high risk of sabotage. Yet, the country could benefit from new projects in the region: the Baltic Energy Hub and an Eastern European transmission highway that would secure Eastern Europe from Russia, and also enable the full integration of Ukraine, Moldova and the Western Balkans with the European power system.

Existing infrastructure needs to be secured as well. The European Commission recently proposed an Action Plan on Cable Security and a Hybrid Toolbox addressing hybrid warfare. Denmark is researching underwater drones that could capture and immobilise hostile underwater vehicles, NATO established a Critical Undersea Infrastructure teams in the UK and Belgium, and already deployed at least 20 drone boats in the Baltic Sea. But these reactive measures must be coupled with coordinated planning and permitting to accelerate grid investments – as more interconnections, lines and substations make the system more resilient if one of the elements is attacked.

In the case of cross-border and offshore projects, this requires more active steering by the European Commission, facilitating regional collaboration and mediating between governments and financing institutions such as EIB and EBRD. Grid enhancing technologies, including digital solutions, should be incentivised in EU funding, enhancing monitoring, maintenance and recovery of grid assets. Supply chain security is essential as well, with a priority for “made in Europe” components and digital systems. 

Finally, in both grid expansion and protection, collaboration and coordination is critical, given the group of stakeholders ranges from grid operators, through the EU, governments and financial institutions, to NATO and different branches of the military.

Supporting materials

Downloads

Download the full analysis PDF.

Additional materials

For more information about planned interconnection capacity expansion please consult Ember’s Interconnection data tool.

Acknowledgements

Contributors

Ember: Izabela Urbańska, Reynaldo Dizon, Elisabeth Cremona

We thank Caspar Hobhouse from the European Union Institute for Security Studies (ISS), Zuzanna Nowak from The Opportunity Institute for Foreign Affairs, and Isabelle Dupraz from the European Initiative for Energy Security (EIES) for their contributions.