On 7 July, the Hertz 2 battery energy storage system (BESS), with a capacity of 100 MW and a storage capacity of 200 MWh, was officially opened in Aruküla, Raasiku municipality, Harju County. It is the second large-scale project in Estonia by Baltic Storage Platform, the joint venture between Evecon — the region’s leading renewable energy developer — French power producer Corsica Sole, and international investment fund Mirova. Together with its sister project Hertz 1, opened in February in Kiisa, the two form one of the most powerful BESS complexes in Continental Europe.
With the completion of Hertz 2, the combined capacity of the two battery parks reaches 200 megawatts and their storage capacity 400 megawatt-hours, covering a large share of Estonia’s battery storage needs. The Aruküla BESS is connected to the electricity transmission grid operated by Elering and will participate in a range of electricity markets, including providing fast-responding frequency regulation services that have become critically important for ensuring the stability of the Baltic power system following the synchronisation of the grid with the Continental European frequency area in February 2025. The BESS will also take part in the conventional day-ahead and intraday electricity markets.
Minister of Energy and the Environment Andres Sutt said that the Hertz 1 and Hertz 2 BESS projects have proven the attractiveness of Estonia’s energy sector to international investors. “Foreign investment is of invaluable importance in developing our economy, and we must safeguard it so that new investments from friendly foreign countries keep coming our way in the future. At the same time, the Hertz 1 and Hertz 2 BESS projects are important for balancing the entire power system and for bringing more renewable electricity to the market — this is exactly the kind of flexible capacity that Estonia needs more and more at a time when the Baltic States maintain their own frequency.”
“Together, Hertz 1 and Hertz 2 represent the largest private-sector investment in Estonia’s energy sector — €170 million in total. It was a bold decision, which we took together with our French partners at the end of 2023: the investment decision was made 100% against the market, without any subsidies,” said Karl-Joonatan Kvell, CEO of Evecon. “With Hertz 2 now up and running, the BESS complex together with Kiisa Hertz 1 is operating at full scale and helps the Baltic power system maintain frequency and lower price peaks.”
“Following Hertz 1, Hertz 2 was completed quickly and smoothly on the basis of the same technical solution — we are grateful to our partners for that! As the volume of the Baltic frequency markets is limited, it is important that the state ensures equal playing field for all market participants. Predictable and fair market allows private investments to deliver maximum value to the system,” noted Michael Coudyser, CEO of Corsica Sole.
“The completion of Hertz 2 is a new milestone for Mirova in our commitment to finance clean energy in Estonia. As a key foreign investor in the country we believe this large battery can both fulfill a critical need in the energy system in its transition and show that Estonian ecosystem is ready for such large projects. Now that batteries are up and running, what is critical to us is the stability of the legal environment and the transparency in which we can operate them, so that investors remain confident to finance new companies and infrastructures,” said Raphaël Lance, Head of Private Assets at Mirova.
After leaving the Russian power grid, the Baltic States have, since February 2025, had to maintain the frequency of their own power system themselves. Hertz 2 contributes to this directly: the BESS responds within milliseconds to frequency fluctuations and unexpected disturbances, helping to keep production and consumption balance in the electricity grid.
Large-scale battery storage plays an increasingly important role in bringing renewable energy to the market and in easing electricity price volatility. Hertz 2 stores electricity when market prices are low — which usually means that plenty of renewable electricity is being generated at that moment — and feeds the stored energy back into the grid when prices and demand are high. In this way, the BESS both captures surplus renewable energy that would otherwise go unused and reduces the extreme price spikes that consumers have experienced in recent years.
Located near Tallinn in Aruküla, Hertz 2 is technically a replica of Hertz 1. The park is based on a containerised solution — 54 containers house a total of 2,328 battery modules. Each container holds battery racks together with cooling, fire-protection and monitoring systems, forming a safe and self-contained unit. The project was completed in close cooperation with transmission system operator Elering and with technology and engineering partners including Yuso, Connecto and Energel.
The battery storage systems used in the park were supplied by Nidec Conversion, whose subcontractor in Estonia for the both Hertz battery parks construction and electrical works was WiSo Engineering.
The construction of Hertz 1 and Hertz 2 was financed through an €85.6 million loan from the European Bank for Reconstruction and Development (EBRD), the Nordic Investment Bank (NIB) and Edmond de Rothschild Asset Management. The transaction was advised on legal matters by the law firms Rask and Cobalt.
About Mirova
Mirova is a global asset management company dedicated to sustainable investing and an affiliate of Natixis Investment Managers. At the forefront of sustainable finance for over a decade, Mirova has been developing innovative investment solutions across all asset classes, aiming to combine long term value creation with positive environmental and social impact. Headquartered in Paris, Mirova offers a broad range of equity, fixed income, multi-asset, energy transition infrastructure, natural capital and private equity solutions designed for institutional investors, distribution platforms and retail investors in Europe, North America, and Asia-Pacific. Mirova and its affiliates had €34.2 billion in assets under management as of March 31, 2026. Mirova is a mission-driven company*, labeled B Corp**.
The reference to a ranking or a label does not prejudge the future performance of the funds or its managers. *Mirova has been a mission-driven company since 2020. For more information: www.entreprisesamission.com. ** Since 2006, the B Corp movement has been promoting strong values of change worldwide to make businesses “a force for good” and to distinguish those that reconcile profit (for profit) and the common good (for purpose). The goal of B Corp is to certify companies that incorporate social, societal, and environmental objectives into their business models and operations. B Corp certification is a designation indicating that a company meets high standards of verified performance, accountability, and transparency on factors ranging from employee benefits and charitable donations to supply chain practices and input materials. Certified since 2020, Mirova submits a new B Corp certification application every three years. The certification fees amount to €30,000. For more information, please visit the B Corp website here: https://www.bcorporation.net/en-us/certification
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Mirova is an affiliate of Natixis Investment Managers.
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