Principia has announced the completion of its first Battery Energy Storage System (BESS) unit — commercially named “Themelio” — in the Vouno area of Chalkidiki, near Polygyros. As one of the first grid-scale BESS installations in Greece, the project represents a major milestone for the company and contributes significantly to the country’s clean energy transition.
A New Foundation for Innovation
The project name “Themelio” (Greek for “foundation”) reflects Principia’s strategic shift beyond renewable energy generation into energy storage, advanced technology, and sustainable infrastructure. Themelio serves as a cornerstone for Principia’s long-term goal: to maximise the value of renewable energy sources and improve grid reliability through innovation.
Project Overview and Technical Highlights
Construction of the project began in April 2025 and was completed in October 2025. Commercial operation is expected to commence in December 2025. The system has a power capacity of 49 MW and an installed energy capacity of 127.04 MWh, with a guaranteed deliverable capacity of 98 MWh over two hours.
The storage system includes 26 battery containers provided by Sungrow, each with a maximum capacity of 5,015 kWh and using CALB 314 Ah battery cells. Additionally, 13 Sungrow power substations with 5,140 kW transformers and 33 kV medium-voltage switchgear support the infrastructure, along with two medium-voltage terminal substations that ensure a stable grid connection.
Over 20,000 labour hours were completed without a single accident, underlining Principia’s high health and safety standards.
The project has a total investment value of €28 million, financed equally by project finance through Eurobank and Principia’s own equity.
Strategic and System Benefits
Themelio enhances the flexibility of the Greek energy system by absorbing excess renewable energy and injecting it back into the grid when needed, particularly in congested network areas. This reduces curtailments of wind and solar power, increases renewable energy utilisation, and strengthens overall grid stability during peak demand periods.
The unit’s location near renewable generation sites supports energy decentralisation and contributes to the development of a smarter, more resilient energy network.
Supporting Greece’s National Energy Strategy
The project aligns with Greece’s national energy strategy, which targets the deployment of 3.55 GW of standalone BESS capacity. Recent regulatory shifts favour unsubsidised development models, prioritising guaranteed grid access to accelerate the deployment of energy storage technologies.
Themelio stands out as one of the first merchant BESS projects to be completed under this new regulatory framework, demonstrating both technical feasibility and investor confidence.
Looking Ahead
Themelio is the first step in Principia’s broader commitment to energy storage and grid innovation. The company aims to develop additional storage units across Greece, integrate advanced energy management systems, and support policies that ease deployment barriers and boost system value.
“Themelio marks the beginning of a new era,” said a Principia executive told The Voice of Renewables. “We are committed to expanding the frontier between renewable generation and system flexibility. This is how we will help shape a clean, resilient, and decentralised energy future — in Greece and beyond.”
