Testing fault at 100 MW battery disrupts Estonia–Finland power link

On January 20, a disturbance in Estonia’s power system caused both EstLink connections between Estonia and Finland to shut down. This led to a loss of roughly 1,000 MW of power, equivalent to about 20% of the Baltic region’s winter electricity load. The shortfall was initially covered by support from the continental European grid, as the 500 MW AC connection between Poland and Lithuania operated at double its rated capacity to compensate. Later, reserve capacity within the Baltic states was deployed.

The oscillations were triggered by a 100 MW/200 MWh battery energy storage system in Kiisa, just south of Tallinn, one of the largest battery storage systems in the Baltics. The incident occurred during final grid connection testing, which caused the DC cables to trip.

The €100 million facility, developed by Estonian company Evecon in partnership with French firms Corsica Sole and Mirova, features 54 battery containers supplied by Nidec Conversion. Construction began in mid‑2024, with Kiisa’s batteries expected to be connected to the grid by Q3 2025, and full market services projected for early 2026.

The park connects to the Estonian transmission network (Elering) via a 330 kV underground AC cable – the first of its kind in Estonia at this voltage. A major milestone during construction was the delivery and installation of a 126-ton transformer.

Estonia’s electricity and gas transmission system operator, Elering, described the event as a significant learning experience for the Baltic region following desynchronization from the Russian power grid, particularly as the number of inverter-based devices connected to the network continues to grow.

While Elering did not initially identify the Kiisa project, it confirmed that the oscillation was caused by a device connected to the main grid in Estonia whose behavior did not comply with network requirements.

Reigo Kebja, member of the management board and head of asset management at Elering, said: “Elering continues to analyze the incident and is assessing additional measures to reduce the impact of similar events on the electricity system in the future. It is crucial to increase awareness among market participants about the potential effects of such incidents on the entire system.”

However, Evecon CEO Karl-Joonatan Kvell confirmed in a written response to Delfi Ärileht that the device referenced by Elering belongs to the Kiisa battery park.

Kvell emphasized that the fault occurred during the configuration and testing period, not regular operations. He noted that the battery park is designed to meet all applicable standards and that compliance tests are intended to validate the system under real-world conditions.

He added that the primary responsibility for the incident lies with technology provider Nidec Conversion.

“The ongoing testing phase is being carried out by the system manufacturer, who remains responsible until the system’s final commissioning, which will take place after testing concludes,” he said.

Evecon previously announced plans to officially open the Kiisa battery park on February 3.