Cyclades Interconnection Phase D : Lavrio - Serifos

Asso.subsea also completed the geotechnical survey campaign for the Lavrio–Serifos and Serifos–Milos submarine cable routes in Cyclades Phase D, delivering soil and seabed data to support seabed preparation, cable laying and protection works for the 150 kV Lavrio–Serifos interconnector.

IPTO/ADMIE reports that installation and laying of the 150 kV high‑voltage submarine cable for the Lavrio–Serifos interconnection, part of Cyclades Phase D linking the Lavrio GIS substation on the mainland to the new GIS substation on Serifos, was completed in February 2024.

In September 2023, contracts were signed for the high-voltage substations on Folegandros, Milos and Serifos, placing the Cyclades interconnection project, including the Lavrio–Serifos link which relies on the Serifos substation, into the construction phase. This milestone marked the start of onshore construction activities associated with the project’s island substations.

Hellenic Cables signed a turnkey contract with IPTO under the fourth phase of the Cyclades interconnection to supply and install 150 kV high‑voltage onshore and offshore cables for the Lavrio–Serifos and Serifos–Milos electrical interconnections, with a total length of about 170 km. The scope includes design, manufacturing, delivery, installation, protection, joints and terminations, and final testing, to integrate Milos and Serifos into the continental Electricity Transmission System within approximately 28 months.

On 9 March 2023, IPTO/ADMIE formally awarded the cable supply and installation contracts for the Cyclades Phase D interconnection to Hellenic Cables (cables segment of Cenergy Holdings), covering the Lavrio-Serifos and Serifos-Milos 150 kV submarine links. Per ADMIE's 2022 Annual Financial Report, cable lines Lavrio-Serifos, Serifos-Milos, Milos-Folegandros and Folegandros-Thira were signed in the first quarter of 2023 — marking the effective Final Investment Decision for the approximately EUR 490 million Phase D programme, co-financed by the EU Recovery and Resilience Fund. As with other TSO-led projects, IPTO does not have a traditional project-finance FID moment; the EPC contract signing commits the capital and functions as the effective financial close for this phase of the Cyclades interconnection.

On 16 December 2022, the European Investment Bank signed two loan tranches of EUR 65 million and EUR 250 million, totalling EUR 315 million, with Independent Power Transmission Operator SA (IPTO) to finance the IPTO Cyclades Interconnection Phase 4 project, which extends the mainland grid from Lavrio to the Cyclades islands including Serifos. The amortising EIB loan with a long tenor and substantial volume supports the project’s investment needs and diversifies IPTO’s funding sources, underpinning the interconnection of Western and Southern Cyclades with the Greek transmission network via Lavrio.

The Cyclades Phase D interconnection project, which includes the 150 kV Lavrio–Serifos submarine and underground link, was formally designated as a project of broader significance for the Greek national economy by Government Gazette No. Δ' 494/4.8.2022. This national classification underpins the strategic importance of completing the Cyclades interconnection, including the Lavrio–Serifos segment, and supports its co‑financing under the Greece 2.0 Recovery and Resilience Facility.

The Greek Ministry of Environment and Energy approved the environmental terms for Phase D of the Cyclades electrical interconnection with the mainland transmission system, which includes the Lavrio–Serifos link as part of the broader Naxos, Serifos, Milos, Folegandros and Santorini connections to Lavrio. This decision grants overarching development consent for the phase, enabling Independent Power Transmission Operator (ADMIE/IPTO) to proceed with implementation of the interconnection works, including the Lavrio–Serifos section.

RAE Decision 590/2021: the Greek Regulatory Authority for Energy (RAE, Rythmistiki Archi Energeias) issued Decision 590/2021 authorising the Cyclades Phase D interconnection programme, including the Lavrio-Serifos and Serifos-Milos 150 kV HVAC submarine links as well as the Milos-Folegandros and Folegandros-Thira segments. This regulatory decision establishes the project as a Major Project in the Greek transmission system planning framework and creates the legal basis for IPTO (ADMIE) to proceed with the investment. Date precision is year-only because the specific RAE decision date is not provided in available public sources; source is ADMIE's 2024 Sustainability Report (published November 2025) which references the decision number and year but not the specific issuance date.

By mid-2021, IPTO reported that the fourth and final phase of the Cyclades electrical interconnection—which includes the Lavrio–Serifos 150 kV AC submarine and underground link as part of the wider Serifos–Milos–Folegandros–Thira scheme—had been included in Greece’s National Recovery and Resilience Plan "Greece 2.0" and would receive approximately EUR 170 million of co‑financing from the EU’s Recovery and Resilience Facility / NextGeneration EU, with the remainder of the roughly EUR 386 million phase‑wide investment funded from national and IPTO resources. Later financial reports reconfirm that the Cyclades interconnection fourth phase, including the Lavrio–Serifos and Serifos–Milos submarine cables, is co‑financed by the Recovery and Resilience Facility.