Attica-Crete (Ariadne)

Overview

The Attica-Crete high-voltage direct-current link represents the largest energy transmission investment in Greece, designed to end Crete’s long-standing “electrical isolation” by integrating the island into the mainland grid with a capacity of one gigawatt. Its completion marks a turning point in Greek energy infrastructure, combining cutting-edge technology, deep-sea engineering and significant environmental and economic benefits.

Background and Rationale

Crete has historically relied on fossil-fuelled power plants to meet its growing electricity needs, particularly during peak summer tourism months. Aging thermal units faced mandatory decommissioning by late 2022, prompting IPTO (the independent power transmission operator) to launch a submarine interconnection to secure reliable supply and enable the island to tap mainland renewable energy sources. The project also aligns with Greece’s decarbonization and grid-stability objectives.

Technical Specifications

Operated at ±500 kV using voltage-source converter (VSC) technology—the first application of advanced VSC in the Mediterranean—the interconnector comprises two bipolar submarine cable circuits, each rated for 500 MW, delivering a total transmission capacity of 1,000 MW. The subsea route spans approximately 335 km reaching depths up to 1,200 meters.

Route and Infrastructure

Starting at the Koumoundourou converter station in Attica, the scheme dispatches two underground HVDC cables to the Megara coast at Pachi. At this landing point, the cables transition to the seabed, traversing the Aegean Sea to the Korakia landing near Heraklion. From Korakia, the link continues by underground cables to the Damasta converter station, where the DC power is converted back to AC and fed into Crete’s GIS substation for distribution. Two dedicated electrode stations—one on the islet of Stachtoroi off Attica and another at Korakia—ensure reliable grounding for the bipolar system.

Implementation and Project Partners

Ariadne Interconnection S.p.s.a., a wholly owned IPTO subsidiary, led the project. Key turnkey contracts were awarded in June 2020 to a consortium of Siemens Energy and TERNA for the design, supply and installation of the ±500 kV, 1,000 MW converter stations and related gas-insulated switchgear on Crete. Major cable supply and installation responsibilities were entrusted to Prysmian, Nexans, NKT-Hellenic Cables and Hellenic Cables, with GEK TERNA managing civil works and onshore HV distribution.

Construction Timeline

Marine surveys to chart the optimal subsea route concluded in spring 2021, following which cable laying, converter-station construction and associated infrastructure advanced toward a late-2024 completion date. Despite initial projections for mid-2023 commissioning, the interconnector successfully entered trial operation on 24 May 2025, transmitting DC power through its full system and initiating a summer-long testing phase before full commercial service.

Economic and Environmental Impact

By interlinking Crete with the mainland grid, the project is estimated to deliver annual consumer savings of approximately €550 million in utility charges, projected to grow to €1 billion by 2030. Environmental benefits include a reduction of around 500,000 tons of CO₂ in the first full year of operation, elimination of pollutants from local thermal plants and strengthened integration of renewable resources. Socially, the scheme generated numerous construction-phase jobs and improved power-supply resilience for residents and the tourism sector.