METLEN, a Greece-based industrial and energy group, and its partner Karatzis Group of Companies have inaugurated the largest standalone BESS in Greece. The plant, which stands in Thessaly, Greece, is rated at 330 MW and 790 MWh. It was opened on 14 October 2026 at a ceremony that was attended by the Prime Minister, Kyriakos Mitsotakis, and by the Minister of Environment and Energy, Stavros Papastavrou.

The two groups own the project through a joint investment vehicle, in which METLEN holds 49% and Karatzis Group holds 51%. METLEN was responsible for the construction of the facility, and it has also taken on its operation and maintenance. The joint venture agreement for the plant had been announced on 9 October 2025, and the investment has since been carried out with loan support from the Recovery and Resilience Facility of the EU, which forms a part of NextGenerationEU.

According to the partners, the plant is the largest standalone energy storage facility in Eastern Europe, and it is also one of the largest in the EU. It has been designed to make the energy system more flexible and resilient, so that the renewable power which is generated in Greece can be used with greater efficiency. In the view of the partners, storage, grid works and interconnections are essential preconditions for attracting investment and for strengthening the production base of both Greece and Europe.

Evangelos Mytilineos, the Executive Chairman of METLEN, said that storage, "alongside grids and interconnections, is essential if we are to use the clean energy we generate with efficiency and provide businesses and consumers with a more reliable and predictable energy supply." For his part, Antonis Karatzis, the Chairman and CEO of Karatzis Group of Companies, said, "Our participation in a storage project of this scale reflects our strategic choice to invest in infrastructure with a long-term horizon and a meaningful value for the Greek economy."

The Prime Minister, in his speech at the ceremony, described the facility as an important step towards building the Greece of the future. He also highlighted the contribution that the investment would make to the energy security and the competitiveness of the country, and he congratulated both groups on the completion of the project.

METLEN is an industrial and energy group which is based in Greece and listed in London and Athens. Its partner, Karatzis Group of Companies, is a Greek industrial group with its base in Heraklion, Crete.