Baltic Storage Platform (BSP) — a joint venture between the Baltic region's leading renewable energy developer Evecon, the French independent solar power producer Corsica Sole and the sustainable investment manager Mirova — today officially opens the Hertz 1 battery energy storage system (BESS) at Kiisa.
The opening marks a historic turning point for the Baltic energy sector. With its substantial storage capacity of 200 MWh, Hertz 1 is the first of two strategic projects (Hertz 1 and Hertz 2 are 100 MW/200 MWh each) intended to stabilise the regional power system following the Baltic states' synchronisation with the continental European grid.
The project was made possible by a significant financing package of 85.6 million euros, provided at the end of 2025 by the European Bank for Reconstruction and Development (EBRD), the Nordic Investment Bank (NIB) and Edmond de Rothschild Asset Management.
Strategic impact on national security
Bringing Hertz 1 into operation is a major step forward for Estonia's energy independence and grid stability. By providing fast-response frequency regulation services, the facility ensures that the electricity grid remains resilient even during fluctuations in renewable generation or unforeseen disturbances.
Flexible services for grid stability
The facility is designed to operate across a wide range of electricity and ancillary services markets, including frequency containment reserves (FCR), automatic and manual frequency restoration reserves (aFRR and mFRR), as well as intraday and day-ahead markets, providing flexible and responsive support to the power system.
By participating in several electricity and ancillary services markets, Hertz 1 has been designed as a flexible, market-oriented asset capable of responding to the system's needs in real time. This operational flexibility allows the project to support grid stability, market efficiency and the integration of renewables, while contributing to the overall reliability of the electricity market.
Reducing price volatility for consumers
Beyond grid stability, large-scale battery storage also plays an increasingly important role in dampening electricity price swings. By storing electricity when production costs are low and releasing it during periods of high demand, Hertz 1 helps to soften the extreme price fluctuations that consumers have faced ever more frequently in recent years, while supporting a more efficient balance between electricity generation and consumption.
Large-scale battery storage is also a key factor in enabling the integration of low-cost renewables into the electricity system. By capturing surplus renewable energy when availability is high and prices are low, and making that energy available when demand rises, Hertz 1 helps to maximise the value of renewable generation while supporting a more efficient and reliable power system.
The Estonian Minister of Energy and the Environment, Andres Sutt, said the project proves two things. First, private investors are both able and willing to back large energy projects in Estonia. Second, the future is here. Ten years ago this would have been the largest lithium-ion battery park in the world; thirty years ago it would have been science fiction.
From today, Estonia's energy security is considerably stronger. Our electricity grid is now as robust as if we had added a large new power station to the system, said Karl-Joonatan Kvell, chief executive of Evecon. Hertz 1 is a critical piece of infrastructure that allows us to manage our energy sovereignty with confidence, while accelerating the transition to clean, renewable energy.
Technological innovation
Hertz 1, located just 25 km from Tallinn, brings a notable technical first to Estonia: a high-voltage connection to the 330 kV transmission grid via an underground cable. This development improves the physical resilience of the connection and sets a new standard for integrating large-scale storage into the national grid.
The BESS facility is based on a containerised design, with 54 containers holding a total of 2,328 battery modules. Each container integrates battery racks together with cooling, fire safety and monitoring systems, forming a safe and self-contained energy storage unit. This modular approach allows the system to store and deliver electricity efficiently while ensuring reliable operation throughout its service life.
The project would not have been possible without the strong support and close cooperation of TSO Elering. Their expertise, engagement and collaboration have been essential to the successful development and integration of the BESS facility and its long-term contribution to the power system.
Industrial delivery and strategic partnerships
The successful delivery of Hertz 1 also reflects the project's industrial execution strength and close cooperation with key technology and engineering partners, including Yuso, Connecto, Energel and Nidec Conversion. Thanks to strong coordination across the engineering, systems integration and commissioning phases, the project was delivered to an ambitious timetable and in line with the highest technical and operational standards required for large-scale battery storage infrastructure.
Corsica Sole chief executive Michael Coudyser added: Hertz 1 demonstrates Corsica Sole's ability to deliver complex, large-scale battery storage solutions in a highly demanding technical environment and to an ambitious, tightly managed project schedule. Drawing on our international experience in engineering, grid integration and battery system operation, we are proud to help strengthen Estonia's energy resilience and to support the Baltic region's sustainable integration into the European electricity grid.
The service life of the BESS facility will be communicated transparently. As owner and operator, we are fully committed, throughout its 15 years of operation, to ensuring that the system reliably delivers essential services to the grid for the whole of its working life.
Comments from the partners
Raphaël Lance, global head of private assets at Mirova, commented: Now that the Baltic states are synchronised with the continental European grid, storage is the critical link. Hertz 1 shows that grid-scale storage is bankable at scale. As the partnership's first investor, we are mobilising long-term capital alongside local developers and local teams to deliver clean, reliable energy and stronger security of supply for the region.
As renewable generation continues to grow rapidly across the European Union, energy storage has become a strategic challenge for securing energy independence and maintaining grid stability. Large-scale battery storage systems such as Hertz 1 are essential to balancing intermittent renewable generation with consumption needs, while supporting Europe's transition to a more resilient, low-carbon electricity system.
Looking ahead
While Hertz 1 enters full operation today, Baltic Storage Platform has already begun construction of its sister project, Hertz 2, at Aruküla. Once both are complete by the end of 2026, their combined capacity will reach 200 MW / 400 MWh, forming one of the most powerful battery complexes in continental Europe.