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Greece ADMIE's Transmission Investments Plan [free access]

December 8, 2021

Greece, much like other European countries, is focusing on carrying out a smooth energy transition and becoming a climate neutral economy by 2050. The objectives set by the country’s National Plan for Energy and Climate for 2030 and the Long-Term Energy Planning for 2050 require integration of renewable energy sources (RES) on a big scale. The installed RES capacity is projected to more than double from the present 9.2 GW (including 3.7 GW of large hydropower projects) to 19 GW in 2030. In 2020, RES accounted for 20 per cent of the country's final energy consumption, which was aligned with the European Union (EU) target for the year but was higher than the initial national target of 18 per cent. Going forward, integration of huge amounts of RES will require commensurate investments in electricity transmission, which makes the role of the country’s independent power transmission operator (IPTO), Anexartitos Diacheiristis MetaforasIlektrikis Energeias (ADMIE), all the more crucial.


ADMIE’s draft Ten-Year Development Plan (TYNDP) 2022–2031, released in January 2021, mirrors these energy transition targets. As per the plan, ADMIE proposes to invest EUR4.1 billion in its electricity transmission network up to 2031 including in new international interconnections, upgrades to the national transmission system at high voltage (150 kV) and ultra-high voltage (400 kV) and new compensation projects throughout the system to improve reliability. In particular, ADMIE plans to develop the 400 kV voltage network as the backbone of its system, which is ADMIE’s first priority for safe operations. The development of interconnections of the non-interconnected islands (NIIs) is a key focus for ADMIE, as harnessing the wind potential of the country’s seas and islands depends on these interconnections. The IPTO’s long-term strategy includes plans in low greenhouse emission technologies, efficient load balancing, ancillary services, storage systems, strategic expansion of offshore transmission and cross-border interconnections, and energy system digitisation.


Demand forecasts

The draft TYNDP 2022–31 lays out two different demand scenarios for the upcoming decade, namely, the energy and climate plan scenario and the increased demand scenario. Both scenarios take into account the scheduling of electricity on the interconnected islands, which would lead to an increase in power demand in the country. However, the target is to implement initiatives such as energy efficiency and savings to eventually lower energy consumption, leading to a relatively small increase in demand. The projected electricity demand under the energy and climate plan scenario is based on the assumptions of the National Long-Term Strategy for 2050 whereas that under the increased demand scenario has been formulated with estimates based on available historical data on demand and published forecasts prepared by other competent authorities.


Under the energy and climate plan scenario, electricity demand is expected to register a compound annual growth rate (CAGR) of 1.23 per cent and increase from 54,320 GWh in 2021 to 61,400 GWh in 2031, while under the increased demand scenario, demand is likely to register a CAGR of 1.72 per cent, increasing from 56,310 GWh to 66,780 GWh in the corresponding years.


Network expansion

Island interconnections

The NII interconnection projects constitute the most important part of the draft TYNDP accounting for over 80 per cent of planned investment. These interconnections have significant environmental benefits as the expansion of existing thermal power plants (TPPs) on the islands will no longer be required. Further, it would make it possible to gradually place those TPPs in cold reserve. Moreover, it will result in annual savings through elimination of the public service obligations (PSOs) of electricity supply met by high-cost oil-fired units, amounting to EUR300 million and EUR50 million for Crete and the Cyclades respectively.


One of the major and most anticipated island interconnection projects for Greece is the Crete interconnection, which is being implemented in two phases. Phase I of the project, known as the Crete–Peloponnese interconnection, was completed in April 2021 and entailed the construction of two 135-km, 150 kV alternating current (AC) undersea cables (USC) between landing points in southeast Peloponnese (near Neapoli) and west Crete at a cost of EUR356.4 million. Phase II of the project, involving the Crete–Attica interconnection, is currently under implementation by Ariadne Interconnection, a 100 per cent subsidiary of ADMIE, and is scheduled for completion in 2023. The 500 kV high voltage direct current (HVDC) submarine cable with a transmission capacity of 1 GW will significantly expand the margin to transfer clean energy between the islands and the mainland. The EUR1 billion interconnector project is deemed as urgent to avert electricity shortages on Greece’s largest island, Crete.


Another key project is the Cyclades interconnection, which involves four phases, three of which have been completed. Phase A was completed in 2018 and included the connection of Syros with Lavrio, as well as with the Islands of Paros, Mykonos and Tinos. The Phase B interconnection was completed in September 2020 and included the connection of Paros–Naxos–Mykonos and the construction of a new gas-insulated switchgear (GIS) substation in Naxos. Phase C, completed in October 2020, involved the launch of the second cable between Lavrio and Syros, as well as of the required connection works (shunt reactors and bays) in Lavrio and Syros. The fourth phase (Phase D) of the interconnection, which is currently under implementation, entails an investment of EUR386 million and will interconnect the islands of Thira, Milos, Folegandros and Serifos with the mainland national electricity transmission system. It is scheduled for completion in 2024.


Further, ADMIE has also planned an interconnection of the Aegean Islands with the mainland system along with the interconnection of the Dodecanese Islands. The main objectives behind the interconnection of the Aegean Islands include system stability with improved security of supply for the islands’ electricity system; drastic reduction of electricity generation costs in the islands; substitution of oil units with renewable energy plants and imports from the mainland; several environmental benefits; and renewable energy enhancement as the majority of the energy needs will be met by renewable energy, while the rest will be imported from the mainland.


ADMIE is also undertaking the expansion of the 400 kV system to Megalopolis (with the subsequent creation of a 400 kV Patras–Megalopolis–Corinth loop), the Sporades Island Complex Interconnection, and high voltage substations and related projects (at Koumoundourou, Patra, Rouf) among others.


Cross-border interconnections

Greece is also involved in developing cross-border interconnections with its neighbours, the most recent one being the EU-backed EuroAfrica Interconnector. In October 2021, a trilateral agreement was signed between Greece, Egypt and Cyprus to link the electricity power networks of the three east Mediterranean countries through a subsea transmission cable with a capacity of 2 GW. Some of the other cross-border projects under various stages of development are the EuroAsia Interconnector to link the transmission systems of Greece–Cyprus and Israel with direct current (DC) connections; a new 151-km-long, 400 kV AC Maritsa East 1 (Bulgaria)−Nea Santa (Greece) line; and a 400 kV interconnector between the south transmission system of Albania and the Greek power system. The implementation of the new interconnections with Italy, Turkey, North Macedonia and Albania is estimated to contribute to an increase of 500 MW in the net transmission capacity of the Hellenic electricity transmission system.


Investments in system compensation and energy storage

High levels of RES penetration, scattered production with operation of small and medium-sized units, limited participation of high-power thermal units along with short circuit-level limitations have created the need for ADMIE to increase its transmission system compensation. Hence, the IPTO is implementing a five-year pilot project that includes comprehensive measures and projects to better prepare its systems to address these conditions. Under this, ADMIE has installed two static VAR compensator (SVC) systems at the Syros and Platanistos substations for voltage regulation in the Cyclades and at the interconnection network of wind farm stations of the Kafireas project. Based on the operation of these projects, the IPTO will evaluate the possibility of continuous automatic control of the voltage of the whole Cyclades. The installation of ±60 MVAr static synchronous compensator (STATCOM) at the Heraklion III substation in Crete has also entered the final phase.


With the interconnection of almost all the Greek islands as well as large RES penetration, the IPTO plans to invest in energy storage that can enhance the much-needed flexibility in the system. With technological advancements and electricity market reforms, storage systems can contribute to efficient network development with less investment and increase the efficiency of the existing networks through better grid congestion management and system support in high RES penetration scenarios.


The IPTO has planned a pilot accumulator system project in the existing Naxos substation with 7-10 MW batteries having a four-hour storage capacity. Similar pilots will be implemented in other islands to provide reserves and to aid the construction of new wind farms on the islands. The project is scheduled for integration by 2022 and will help cover emergencies in case of the failure of the Cyclades interconnection. ADMIE is also in the process of preparing a feasibility study for the integration of a pilot battery station in central Greece for local congestion management in conditions of high-RES penetration. 


Separately, ADMIE plans to implement the New Regional Energy Control Center of Crete in Heraklion, Crete, along with installation of phasor measurement units (PMUs) for the monitoring of the AC connection of Phase A of the Crete interconnection.


Focus on offshore wind transmission

Given its extensive coastline, Greece has significant offshore wind potential, something that it is planning to develop on a massive scale. There are currently no offshore wind farms in Greece, but the expansion of the interconnected transmission system to the island areas makes it a feasible option. This, in addition to the recent technological and regulatory developments, will give the much needed push for offshore wind farms in the Greek sea area. ADMIE is actively participating in discussions for the formulation of the offshore wind-specific framework. One of the key issues that needs to be addressed is ADMIE’s role in the design, construction and financing of the necessary grid expansion and reinforcement works as well as the inclusion of any offshore transmission projects in ADMIE’s development plan.


The way forward

Clean energy is poised to support energy resources diversification. During the 2019 UN Climate Action Summit, the Greek government had announced that Greece would decommission its entire lignite plant fleet (of 4,337 MW) by 2023; the only exception to this was the under-construction 610 MW Ptolemaida V lignite plant. Such a massive transition of the energy system to a new lower carbon system would involve major structural changes in the sector. Moreover, the mass development of renewable energy will require a focus on the safe transmission of the generated power from the transmission system and the safe and stable operations of the system. Providing access to an ever-increasing volume of RES generation may also result in network saturation and congestion. Although IPTO has planned reinforcement projects to increase the capacity of these networks, many of these projects have been delayed. Therefore, future planned projects must be implemented in a timely manner to ensure the grid is ready to handle the expected massive RES penetration that will support the country’s climate neutrality goals.


Figure 1: ADMIE’s 400 kV transmission lines and interconnections with the islands and neighbouring countries

Note: The international interconnections relate to those with Italy, Albania, Northern Macedonia, Bulgaria and Turkey.

Map accessed as on November 23, 2021

Source: ADMIE


Table1: Key planned cross-border interconnections as per ADMIE’s draft TYNDP2022-31 


Project scope

Scheduled commissioning

Second Greece–Bulgaria interconnection


Construction of a new 151-km, 400 kV interconnection line between Maritsa East (Bulgaria) and Nea Santa (Greece). Of this, 30 km will be in Greek territory and 121 km in Bulgarian territory.

June 2022

Second connection between Greece and Italy

Studies underway for a new undersea power interconnector with up to 1 GW capacity.


EuroAsia Interconnector

Implementation of the interconnection of the transmission systems of Greece, Cyprus and Israel with DC connections.


EuroAfrica Interconnector

This will link the electricity power networks of the three east Mediterranean countries through a subsea transmission cable with 2 GW capacity.


Upgrade of Greece–Northern Macedonia interconnection

The feasibility of implementing this interface will be considered in a joint IPTO and MEPSO working group set up for this purpose.


Second Greece–Albania interconnection


A new 400 kV interconnector between the south transmission system of Albania and the Greek power system.


Second Greece–Turkey interconnection

A new 400 kV interconnector between Greece and Turkey.



Note: DC – direct current; MEPSO – Electricity Transmission System Operator of Macedonia; NA – not available

Source: ADMIE; Global Transmission Research


Table 2: Greece's key island interconnection projects (EUR million)


Voltage (kV)

Line length (km)

Investment (EUR million)

Planned completion

Cyclades interconnection Phase D 

(interconnection of Santorini, Milos, Folegandros and Serifos islands with the Continental



353.2 km (submarine AC cables); 19.6 km (underground AC cables)



Crete interconnection (Phase B) Ariadne interconnection 

[between Crete and mainland Greece (Attica region)]

± 500 kV HVDC




Skiathos island interconnection 






High voltage substations and related projects (Koumoundourou, Patra, Rouf)





Corridor B to Peloponnese (Megalopolis–Corinth–Koumoundourou)





Dodecanese interconnection 

(Karpathos, Rhodes, Symi, Kos–Kalymnos, Patmos and Arkioi systems with mainland Greece)





North Aegean interconnection

(Santas–Lemnos, Lemnos– Lesvos, Lesvos–Chios, Lesvos–Skyros, Aliveri–Skyros, Chios–Samos, Samos–Kos)





Note: NA – not applicable

Source: ADMIE; Global Transmission Research