Cyclades Interconnection Phase D : Serifos - Milos

In September 2023, contracts were signed for the High Voltage Substations on Folegandros, Milos and Serifos as part of the fourth and final phase of the Cyclades electrical interconnection, placing the overall project, including the onshore substation works on these islands, into the construction phase.

Independent Power Transmission Operator (IPTO) reported that in February 2023 it signed the cable contracts for the remaining three southwest Cyclades islands—Folegandros, Milos and Serifos—under Phase D of the Cyclades interconnection, which include the Lavrio–Serifos and Serifos–Milos 150 kV submarine links. Earlier tender coverage specified that Hellenic Cables was awarded the subsea cable package from Lavrio to Serifos and from Serifos to Milos, covering about 170 km of 150 kV AC cable and valued at €195 million, thereby establishing Hellenic Cables/Fulgor as the cable supplier for the Serifos–Milos interconnector segment.

On 16 December 2022, the European Investment Bank signed a €157 million own‑resources loan agreement with Greek TSO IPTO to co‑finance the fourth stage of the Cyclades interconnection, which includes the submarine and underground 150 kV links and new GIS substations connecting Santorini, Folegandros, Milos and Serifos to the mainland grid, including the Serifos–Milos segment. This development‑bank debt financing supports construction of about 350 km of cables for the Western and Southern Cyclades islands’ integration into the Hellenic Transmission System.

The Greek government formally designated the Cyclades interconnection Phase D project, which includes the 150 kV Serifos–Milos submarine link, as a project of broader/general significance for the national economy via Government Gazette No. Δ’ 494/4.8.2022, enabling its treatment as a nationally important infrastructure scheme and supporting its co-financing under the Greece 2.0 Recovery and Resilience Facility (NextGenerationEU).

Between 2018 and 2021, IPTO carried out preliminary development activities for the fourth stage of the Cyclades interconnection linking Santorini, Folegandros, Milos and Serifos, including project design, permitting and partial land acquisition, thereby preparing the Serifos–Milos 150 kV submarine interconnector segment for subsequent construction rollout.

The Ministry of the Environment and Energy of Greece approved the Environmental Impact Assessment for the IPTO Cyclades Interconnection Phase 4 project, which includes the Serifos–Milos section, on 7 June 2021, issuing an environmental permit with prescriptions. The permit and underlying EIA studies confirm that, with specified mitigation measures, the project is not expected to have significant adverse effects on the terrestrial or marine environment, including Natura 2000 sites along approximately 26 km of the route.

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 (typically a combination of state budget, EU Recovery and Resilience Facility funds, and EIB loans). The approval of environmental terms and subsequent inclusion in state funding programmes effectively constitutes the investment decision, as the TSO has no discretion to decline once the regulatory and financial framework is in place. This event is recorded as fid_financial_close because the planning consent and funding approval together serve the same function as a commercial FID: they authorise and obligate the TSO to invest in construction. The pattern is analogous to German TSO offshore grid connections where the BNetzA NEP confirmation serves as the de facto FID.

In December 2020, IPTO issued a call for tenders for the Naxos–Thira interconnection, which marked the launch of Phase D of the Cyclades electrical interconnection programme that includes the Serifos–Milos link.

Energypress reported that TERNA and a consortium of Nari and Electromec were named provisional winners of an IPTO tender to develop new high-voltage substations on Folegandros, Milos and Serifos, which form part of the fourth phase of the Cyclades interconnection and will host the terminations of the 150 kV links including the Serifos–Milos submarine cable. The article noted that interested parties had faced a 6 July 2022 bid deadline and that IPTO aimed to have the substation contracts signed by June following evaluation of the offers.