Cyclades Interconnection Phase D : Thira - Naxos

In 2023, the European Investment Bank and Greece’s Independent Power Transmission Operator (IPTO) signed a €108 million long-term loan agreement using Recovery and Resilience Facility (RRF) funds to co-finance construction of the fourth phase of the Cyclades interconnection, including the Thira (Santorini)–Naxos link, complementing an earlier €157 million EIB own-resources loan for the same €524 million project.

On 16 December 2022, the European Investment Bank (EIB) signed a €157 million long-term loan from its own resources with Greece’s Independent Power Transmission Operator (IPTO) to co-finance construction of the Cyclades interconnection Phase 4 project, which links the western and southern Cyclades islands, including the Thira–Naxos section, to the mainland grid.

The Cyclades electrical interconnection Phase D, which includes the Santorini (Thira)–Naxos segment linking Santorini, Folegandros, Milos and Serifos to the Hellenic Electricity Transmission System, was designated as a project of broader/general importance for the national economy by the Greek authorities, as formalised in Government Gazette No. Δ' 494/4.8.2022 and later referenced in IPTO’s financial reports.

During the summer of 2022, the submarine 150 kV high‑voltage cable between Santorini (Thira) and Naxos was successfully laid, completing installation of the first segment’s interconnector cable for Cyclades Phase D. IPTO’s subsequent 2025 financial reports describe the laying of the cable between the two islands as having been completed in summer 2022, while associated substation works on Santorini continued.

On 9 May 2022, IPTO announced that the Santorini–Naxos electrical interconnection, the first section of Cyclades Interconnection Phase D, is being implemented under Greece’s National Recovery and Resilience Plan "Greece 2.0" with funding from the European Union’s NextGenerationEU instrument amounting to EUR 164.5 million. This grant co-finances Phase IV of the Cyclades electrical interconnection and provides non‑repayable capital support for the Thira–Naxos HV 150 kV subsea and associated onshore works.

On 9 May 2022, IPTO launched onshore construction for the Santorini–Naxos (Thira–Naxos) interconnection by laying the foundation stone of the new 150 kV GIS High Voltage Substation at Monolithos on Santorini. The ceremony, attended by IPTO’s Chairman and CEO along with representatives of Damco Energy and Hellenic Cables, marked the formal start of substation works that will host the high‑voltage cable linking Santorini to Naxos under Cyclades Phase D.

On 1 October 2021, IPTO awarded a turnkey contract to the consortium DAMCO ENERGY S.A. – Xian Electric Engineering Co. Ltd for the study, supply of equipment and installation of the new 150 kV/medium-voltage GIS substation at Thira and a Static VAR Compensator (SVC) with a capacity of -100/+50 MVAR, providing the onshore substation and reactive power compensation needed for the Naxos–Thira interconnection.

On 10 August 2021, ADMIE (IPTO) Holding announced that its affiliate ADMIE (IPTO) SA had successfully completed the tender for the Santorini–Naxos cable section of the Cyclades Interconnection Phase D. Hellenic Cables was named the temporary contractor and underbidder for the subsea cable project, with an initial budget of EUR 100 million and a bid price of EUR 79.5 million, while the final contractor appointment was to be confirmed in the following days in line with legal procedures.

The Environmental Impact Assessment (EIA) for the IPTO Cyclades Interconnection Phase 4 project, which includes the Thira–Naxos link, was approved with conditions by the Greek Ministry of the Environment and Energy on 07/06/2021, confirming that with specified mitigation measures the project would not have significant adverse environmental effects or harm the integrity of Natura 2000 sites along the route.

For Greek TSO-operated island interconnection projects, the EIA approval by the Ministry of Environment and Energy serves as the de facto planning consent.

In December 2020, IPTO launched procurement for the Santorini (Thira)–Naxos electrical interconnection by issuing the call for tenders, marking the start of Phase D of the Cyclades electrical interconnection and initiating the tender process for the 150 kV AC subsea cable link between Naxos and Thira.

Phase D of the Cyclades electrical interconnection was launched when IPTO issued a call for tenders in December 2020 for the Naxos–Santorini (Thira) interconnection, initiating the first sub‑project that will radially meet the main energy demand of the islands to be interconnected and pave the way for completion of the wider Phase D works.

A multi-agency committee comprising representatives from RAE, IPTO, HEDNO and DESFA completed research into alternative power supply options for the Non‑Interconnected Islands, concluding that the Cyclades Phase D interconnection— including the Naxos–Thira link—was the optimal financial and technical solution and using these findings as the basis for the project’s design.