The Bornholm power outage that left the Danish Baltic Sea island without electricity on 21 January 2026 was triggered by a technical fault in the local grid operator’s control systems, which allowed an unusually high current to build up and forced the Sweden–Bornholm undersea interconnector to disconnect. Power was restored island-wide within about four hours, and both Energinet and TREFOR El-net Øst said there was no damage to the sea cable itself.
Timeline of the outage on 21 January
At 10:16 CET, electricity went out across Bornholm after the interconnector supplying the island from Sweden disconnected. TREFOR El-net Øst said the disconnection happened because the cable tripped on overcurrent. Energinet, which operates the undersea cable, said the cable continued to function and that the priority was getting power to flow safely to consumers again.
According to TREFOR, the sea cable was reconnected shortly after 11:10 CET. Supply then returned gradually as grid equipment was checked across the island: some customers regained power around 12:30 CET, and all consumers were back online by about 14:00 CET.
What failed in TREFOR’s grid control system
In an updated explanation published on 22 January, TREFOR said the outage was caused by a fault in a system designed to limit current levels on Bornholm. The company said the primary limiting system malfunctioned and that an additional backup safeguard also failed to activate.
As a result, the extraordinary current level overloaded the interconnector and caused it to disconnect, cutting supply to the whole island. TREFOR said it is still investigating why the backup system did not step in.
Why Energinet said the sea cable was not damaged
Early reports focused on a “cable fault”, but Energinet clarified that there was no fault on the undersea cable itself. The company said Bornholm was ready to be supplied from Sweden again and that restoration depended on coordination with the local distribution network to re-energise the system safely.
This distinction matters because a cable failure would usually imply physical damage and a potentially longer repair timeline. In this case, both operators described the event as an operational trip caused by overcurrent, followed by re-synchronisation and step-by-step restoration.
How critical services were managed
During the outage, authorities warned the disruption could affect water supply, which depends on electricity for pumping and treatment. Reports from Danish media said emergency services also started up a power plant in Rønne to support the restoration effort.
The disruption highlighted a practical reality for islands: even short outages can cascade into challenges for water, heating and communications if backup systems are not available or fuel supplies are limited.
What comes next for Bornholm’s power resilience
TREFOR said it is continuing to investigate the malfunction and the failure of the backup safeguard. The incident is also likely to feed into a broader Nordic and Baltic discussion about grid resilience, especially for geographically exposed areas that rely on single interconnectors.
For Bornholm, the key question is not only what triggered the trip, but whether protective systems and operational procedures can be strengthened to reduce the risk of another island-wide outage—particularly during winter demand peaks.
