On 7 July, the Hertz 2 battery energy storage system, with a capacity of 100 MW and 200 MWh, was officially opened in Arukila, Harju County, Estonia. Together with Hertz 1, opened in Kiisa in February, it forms one of the most powerful complexes of its kind in continental Europe, helping to ensure the stability of the Baltic states' power system.
This is already the second major Baltic Storage Platform project in Estonia. It is managed by renewable energy developer Evecon, French electricity producer Corsica Sole and international investment fund Mirova.
After Hertz 2's completion, the combined capacity of the two battery parks reaches 200 megawatts, and their storage capacity – 400 megawatt-hours, covering a significant share of the country's need for battery energy storage capacity. The Arukila battery park is connected to the transmission network operated by Elering and will provide services in several electricity markets.
Its main task is to provide rapid regulation of grid frequency. This has been particularly important for the stability of the Baltic power system since the region's grid was synchronised with the continental European frequency zone in February 2025. The system will also be used in the day-ahead and intraday electricity markets.
The largest private investment in Estonia's energy sector
Estonia's Minister for Energy and the Environment Andres Sutt (Andres Sutt) stressed that the Hertz 1 and Hertz 2 projects have demonstrated the appeal of Estonia's energy sector to international investors:
“Foreign investment is invaluable to the development of our economy, which is why we must protect it, so that new investment from friendly countries continues to reach us in future. At the same time, the Hertz 1 and Hertz 2 projects are significant for balancing the whole power system and for bringing more renewable electricity to market – Estonia needs precisely this kind of flexible capacity more and more at a time when the Baltic states maintain their own frequency. ”
Evecon CEO Karl-Joonatan Kvell (Karl-Joonatan Kvell) noted that Hertz 1 and Hertz 2 together represent the largest private-sector investment in Estonia's energy sector – a total of EUR 170 million. “It was a bold decision that we took together with our French partners at the end of 2023: we made the decision without relying on subsidies and taking on the full market risk, ” he said.
“With Hertz 2 now in operation, the complex, together with Hertz 1 in Kiisa, is working at full capacity and helping the Baltic power system to maintain frequency and curb price spikes, ” added K. J. Kvell.
“Following the completion of Hertz 1, Hertz 2 was also delivered quickly and smoothly, building on the same technical solution – for which we are grateful to our partners. Because the volume of the Baltic frequency market is limited, it is important that the state ensures equal conditions for all market participants. A predictable and fair market allows private investment to bring maximum benefit to the system, ” noted Corsica Sole CEO Michael Coudyser (Michael Coudyser).
“Hertz 2's completion is a new, significant milestone in Mirova's commitment to financing clean energy in Estonia. As one of the country's leading foreign investors, we believe that this battery system helps ensure the stability of the power system during its transition, while also demonstrating that Estonia's ecosystem is ready for such major projects, ” said Mirova Head of Private Assets Raphaël Lance (Raphaël Lance).
“Now that the batteries are already operating, what matters most to us is a stable legal environment and transparent operating conditions, so that investors can continue to confidently finance new businesses and infrastructure, ” he added.
Stabilising the grid in milliseconds
After the Baltic states disconnected from the Russian power grid in February 2025, they have had to maintain their own grid frequency. The Hertz 2 battery park also plays a significant role in this process – it responds to frequency fluctuations and other unforeseen disturbances within milliseconds, helping to maintain the balance between electricity production and consumption.
Large-scale battery storage plays an increasingly important role in bringing renewable energy to market and in reducing electricity price fluctuations. Hertz 2 stores electricity when market prices are low – which usually means that a large amount of renewable electricity is being generated at that time – and releases the stored energy back into the grid when prices and demand are high.
In this way, the storage facility both makes use of surplus renewable energy that would otherwise go unused and reduces the extreme price spikes that consumers have experienced in recent years.
Hertz 2, located in Arukila near Tallinn, is technically a copy of Hertz 1. The park is built on a containerised principle: a total of 2,328 battery modules are installed across 54 containers. Each container houses battery racks, along with cooling, fire safety and monitoring systems, so that each container operates as an autonomous and safe module.
The project was carried out in close cooperation with transmission system operator Elering and technology and engineering partners, including Yuso, Connecto and Energel. The electricity storage systems used in the park were supplied by Nidec Conversion, whose subcontractor in Estonia for the construction and electrical installation work on both Hertz parks was WiSo Engineering.
Hertz 1 and Hertz 2 construction was financed with an EUR 85.6 million loan granted by the European Bank for Reconstruction and Development (EBRD), the Nordic Investment Bank (NIB) and Edmond de Rothschild Asset Management. Legal advice on the transaction was provided by law firms Rask and Cobalt.
About Mirova
Mirova is a global asset management company specialising in sustainable investment and an affiliate of Natixis Investment Managers. Having held a leading position in sustainable finance for more than ten years, Mirova develops innovative investment solutions across all asset classes, seeking to combine long-term value creation with a positive impact on the environment and society.
Mirova is headquartered in Paris and offers a broad range of equity, fixed income, multi-asset, energy-transition infrastructure, natural capital and private equity solutions to institutional investors, distribution platforms and private investors in Europe, North America and the Asia-Pacific region. As at 31 March 2026, the assets under management of Mirova and its affiliates stood at EUR 34.2 billion.
Since 2020, Mirova has been a mission-led company (for more information – www.entreprisesamission.com), certified as a B Corp. Since 2006, the B Corp movement has been promoting business worldwide as a force for positive change, aiming to make business a force for good, and highlighting companies that combine profit (for profit) with public benefit (for purpose).
B Corp's aim is to certify companies that integrate social, community and environmental goals into their business models and operations. B Corp certification confirms that a company meets high, verified standards of performance, accountability and transparency across various areas – from employee well-being initiatives and donations to supply chain practices and the materials used.
Mirova, having obtained B Corp certification, reapplies for B Corp certification every three years, and the certification fee is EUR 30,000 (for more information – www.bcorporation.net/en-us/certification). Reference to the rating or the mark does not imply the future performance of any fund or its managers.
Portfolio management company – a French joint-stock company (RCS Paris No. 394 648 216, AMF accreditation No. GP 02-014), 59, Avenue Pierre Mendès-France, 75013, Paris. Mirova is an affiliate of Natixis Investment Managers. Website – www.mirova.com, LinkedIn – www.linkedin.com/company/mirova.
About Natixis Investment Managers
The Natixis Investment Managers affiliate model gives clients access to the independent investment approach and specialised expertise of more than 15 active managers. The company is one of the largest asset managers in the world: it ranked 20th in Investment & Pensions Europe's 2025 Top 500 Asset Managers ranking, compiled from surveys and publicly available data on assets under management as at 31 December 2024.
Natixis Investment Managers has more than USD 1.4 trillion (EUR 1.2 trillion) in assets under management. As at 31 March 2026, the assets under management of Natixis Investment Managers and its affiliates reached USD 1,452.8 billion (EUR 1,261.0 billion). The reported assets under management may include notional assets, assets under advisement, gross assets, assets of minority-owned affiliates and other non-regulated assets managed or serviced by companies affiliated with Natixis Investment Managers.
The company specialises in high-conviction active investment strategies, insurance and pension solutions, and private assets, and also offers a diverse range across various asset classes, styles and instruments. It works with clients to understand their individual needs and to provide valuable analytical insight and investment solutions tailored to their long-term goals.
Natixis Investment Managers is headquartered in Paris and Boston, and is part of Groupe BPCE – the second-largest banking group in France, which operates through the Banque Populaire and Caisse d'Epargne retail banking networks.
Investment management companies affiliated with Natixis Investment Managers: AEW; DNCA Investments (a brand of DNCA Finance); Flexstone Partners; Gateway Investment Advisers; Harris Oakmark; Investors Mutual Limited; Loomis, Sayles & Company; Mirova; Naxicap Partners; Ossiam; Ostrum Asset Management; Seventure Partners; Vauban Infrastructure Partners; Vaughan Nelson Investment Management; VEGA Investment Solutions and WCM Investment Management.
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