The results of a power flows and dynamic feasibility study confirmed that the Harmony Link onshore AC electricity interconnector between Lithuania and Poland can be a viable technical alternative to an offshore HVDC link. The study was carried out by the Institute of Power Engineering, Gdansk Division, Poland, on behalf of the Lithuanian, Polish, Latvian and Estonian transmission system operators (TSOs).
In April 2023, Litgrid and PSE, the Lithuanian and Polish TSOs, cancelled the procurement of the planned offshore Harmony Link HVDC interconnector due to a significant increase in cable and converter station prices. Immediately after this decision, the Polish and Lithuanian TSOs started the process of preparing for new tenders and considering various technical solutions that could reduce costs and be implemented in the shortest possible time.
One of the technical solutions considered by Litgrid and PSE was an onshore AC interconnector. This method of project implementation was initially assessed as a way to reduce the project budget and to implement the project faster.
The first phase of the commissioned study assessed the technical feasibility of the double circuit 220 kilovolts (kV) AC Harmony Link overland (cable and overhead) link and its impact on the stability of both the Baltic and Continental European power systems. The results of the calculations show that the implementation of the Harmony Link as an onshore technical solution provides comparable stability of the interconnected systems and can be considered to perform at least at the same level or better than the offshore interconnector.
The onshore link would consist of a transmission line between the reconstructed substations Gižai (in Lithuania) and Ełk (in Poland). The overland line would potentially partly use existing and planned road and rail infrastructure between Poland and Lithuania.
A decision on the specific technical approach for implementation of the Harmony Link interconnector is expected by the end of 2024.