Renewables

Agios Efstratios becomes Greece’s first energy-autonomous island

Agios Efstratios Greece first energy autonomous island

Photo: Terna Energy

Published

August 22, 2025

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Published:

August 22, 2025

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A hybrid energy project transforming Agios Efstratios into the first energy-autonomous island in Greece is in trial operation. The system consists of a wind turbine, solar power plant, batteries, electric boilers and a district heating network.

It is a benchmark for the non-interconnected islands that won’t be connected to the mainland grid with undersea power cables.

Agios Efstratios is no longer renowned only for its history and natural beauty. It is an example of energy autonomy and sustainability. The island, also known as Ai Stratis, became the first non-interconnected Greek island with a 100% electricity supply from renewables. And more.

A pioneering energy complex is in trial operation. Agios Efstratios, which has only some 250 permanent residents, is in a group of small islands undergoing transformation through projects launched at the national level and benefiting from European Union funding.

Terna Energy completed hybrid energy system in Agios Efstratios

The Centre for Renewable Energy Sources and Saving (CRES or KAPE), an independent public entity, is responsible for the endeavor, on behalf of the Municipality of Agios Efstratios. Terna Energy, owned by Masdar, is the contractor for the works in the small North Aegean island.

The new hybrid energy system includes a 900 kW Enercon E44 wind turbine and a solar power unit of 225 kW. Their combined annual output is estimated at above 3 GWh.

Excess electricity is stored. One unit is a Tesla Megapack battery energy storage system (BESS) of 1.25 MW in operating power and a two-hour duration. It means the capacity is 2.5 MWh. There is also an electric boiler facility of 1 MW with hot water storage tanks that can hold 500 cubic meters of water at 120 degrees Celsius. It corresponds to 25 MWh.

The district heating network in Agios Efstratios is four kilometers long. It will be tested in the winter.

An oil-fired generator operated by state-controlled Public Power Corp. (PPC) remains as backup. It can work alongside the hybrid power plant.

Greece is connecting many islands to mainland power grid

The solutions from Agios Efstratios can be applied in other islands or in microgrids, CRES noted and said residents are getting cheaper energy.

The government launched its Islands Decarbonization Fund last year, with financing from the European Investment Bank (EIB). Together they aim to provide at least EUR 1.6 billion, and mobilize total investments of EUR 3 billion to EUR 5 billion.

In the hot summer months, there are many non-interconnected islands that can’t meet their power demand, especially because of the tourist season. Some are also struggling with water supply, prompting the need for desalination, which requires electricity. They rely on fuel oil generators.

The country’s Independent Power Transmission Operator (IPTO or, in Greek, Admie) is investing in major interconnection projects. A link to the mainland grid has improved the living conditions in the Cyclades islands of Syros, Paros and Mykonos. Together with a project for the western part of the archipelago, the transmission system operator is planning subsea cables to the Dodecanese and the Northeast Aegean.

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