Cyclades Interconnection Phase D : Milos - Folegandros

Greek press and IPTO communications show that the high‑voltage submarine cable interconnections Milos–Folegandros and Folegandros–Thira had been fully laid by February 2025. Since cable laying must have started before completion and no separate start date is published, we treat this milestone as having been achieved by February 2025, using that month as an approximate start timeframe.

In September 2023, IPTO signed the contracts for the high‑voltage substations on Folegandros, Milos and Serifos, assets that form part of Phase D of the Cyclades interconnection which includes the Milos–Folegandros 150 kV AC submarine and underground cable link. The operator stated that signing these substation contracts put the entire Phase D project into the construction phase, marking the start of onshore construction activities associated with the Milos–Folegandros segment and the wider Southwest Cyclades interconnection.

IPTO awarded turnkey contracts in early February 2023 for the new 150 kV/MT GIS substations serving the Cyclades Phase D interconnection, including the substations on Milos and Folegandros that form part of the Milos–Folegandros link. The contracts, covering "SECTION A: GIS Substation 150kV/MT of Folegandros and Milos" and "SECTION B: GIS Substation 150kV/MT of Serifos", were awarded to TERNA S.A. and the NARI Technology–ELECTROMEC consortium, providing full study, equipment supply and installation for these substations.

On 16 December 2022, the European Investment Bank signed a €157 million own-resources loan with Greece’s Independent Power Transmission Operator (IPTO) to co-finance the fourth phase of the Cyclades interconnection, which links Santorini, Folegandros, Milos and Serifos to the mainland grid, including the 150 kV AC submarine and land cable section between Milos and Folegandros and the associated GIS substations.

IPTO (Independent Power Transmission Operator) awarded a contract on 18 November 2022 for the study, supply and installation of 150 kV underground and submarine XLPE cables for several Cyclades Phase D links, including the Milos–Folegandros section. The contract, awarded to Fulgor and Prysmian Powerlink, covers the Milos–Folegandros and Folegandros–Thira transmission lines, with Prysmian later describing an approximately €150 million turnkey scope to link Milos, Folegandros and Santorini under Phase D of the Cyclades interconnection project.

On 4 August 2022, via Government Gazette No. 494, the Cyclades interconnection project — including Phase D that links Santorini, Folegandros, Milos and Serifos to the mainland grid and incorporates the 150 kV Milos–Folegandros submarine cable section — was formally characterised as a project of general importance for the Greek economy, supporting its priority treatment and co‑financing under the Recovery and Resilience Fund 'Greece 2.0'.

On 3 February 2022, the Greek Regulatory Authority for Energy (RAE) approved and published Decision No. 611/2021 in the Official Journal, endorsing the Hellenic Electricity Transmission System development plan for 2021‑2030. This plan confirms implementation and completion in the second half of 2023 of Cyclades Interconnection Phase D, which includes the 150 kV AC submarine transmission line between Milos and Folegandros (about 55.2 km) with associated underground 150 kV links and new GIS substations on each island as part of the Lavrio–Serifos–Milos–Folegandros–Thira–Naxos corridor.

Between 2018 and 2021, preliminary development activities for the Cyclades Phase D interconnection, including the 150 kV AC Milos–Folegandros submarine and land cable section and associated new GIS substations on Milos and Folegandros, were carried out. According to the European Investment Bank, these early works covered design, permitting and part of the required land acquisition for the overall project linking Santorini, Folegandros, Milos and Serifos to the Hellenic Electricity Transmission System, enabling subsequent construction phases to proceed.

The European Investment Bank’s project page for IPTO Cyclades Interconnection Phase 4 records that the project’s Environmental Impact Assessment was approved by the Greek Ministry of Environment and Energy on 7 June 2021. This EIA approval, granted with specific prescriptions, covers the Phase D works of the Cyclades Interconnection, including the Milos–Folegandros link.

For Greek TSO-operated island interconnection projects, there is no separate Final Investment Decision in the commercial sense. The Greek state, through the Ministry of Environment and Energy and the National Recovery and Resilience Plan (Greece 2.0), commits public and EU funding for construction. IPTO/ADMIE, as the regulated transmission system operator, is obligated to develop the interconnection once environmental terms are approved, the project is included in the national development plan, and financing is secured. The EIA approval on 7 June 2021 by the Greek Ministry of Environment and Energy, combined with subsequent inclusion in the RRF and EIB financing, effectively constitutes the investment decision. This event is recorded as fid_financial_close because the planning consent and funding approval together serve the same function as a commercial FID.

For Greek TSO-operated island interconnection projects, the Environmental Impact Assessment approval by the Ministry of Environment and Energy serves as the de facto planning consent. Once the EIA is approved, the project has the regulatory authorisation to proceed with construction. This event is recorded as planning_consent_awarded alongside eia_approved because the Greek EIA approval serves both the environmental clearance and the project-level development consent functions.

In December 2020, IPTO issued a call for tenders for the Cyclades Phase D electrical interconnection, covering the submarine 150 kV AC cable links between Santorini, Folegandros, Milos and Serifos, which includes the Milos–Folegandros section. This tender marked the launch of procurement for Phase D of the Cyclades interconnection project.

On 9 October 2020, the Directorate of Environmental Permitting (DIPA) of the Greek Ministry of Environment and Energy transmitted the Environmental Impact Assessment (Μελέτη Περιβαλλοντικών Επιπτώσεων) for Phase D of the Cyclades electrical interconnection—covering the interconnection of the southern Cyclades islands, including Milos and Folegandros with the Greek interconnected transmission system—to the Attica Regional Council for approval of the project’s environmental terms.