98 MWh Themelio battery project built in under six months, in boost to Greek grid

Greek renewable energy company Principia has completed the construction of its first battery energy storage system (BESS), known as Themelio. Located in the Vouno area of Chalkidiki, near Polygyros, the 49 MW / 98 MWh project has one or two quirks.

While the installation has nominal capacity of 127 MWh as one of the first wave of grid-scale BESS projects implemented in Greece, it has a guaranteed two-hour duration, which translates to the 98 MWh figure.

Themelio is equipped with Sungrow’s PowerTitan BESS product, and the Principia installation is listed as including 26 battery containers using CALB 314 Ah cells, each with a maximum capacity of 5.015 MWh, 13 Sungrow power stations with 5.140 MW transformers, 33 kV switchgear, and two main medium-voltage terminal substations.

Construction began in April 2025 and was completed in October 2025, as commercial operation is slated to begin in December 2025. Principia noted the six-month timeframe while also stating that “over 20,000 work-hours were completed with zero accidents” at Themelio.

The project had a €28 million budget with Principia contributing half of the budget using its own funds, while the other half was financed via Eurobank.  The Themelio project won support from the Greek government in 2024 ‘s second auction standalone energy storage systems via a contract for difference (CfD) arrangement.

Principia itself is co-owned as a joint venture between Enel in Italy, and Australian funds manager, Macquarie Asset Management.

In July 2025, Faria Renewables secured a €28 million loan from Attica Bank to finance a 49.9 MW / 134.16 MWh BESS in Greece.