WiSo Engineering builds battery parks of European significance

In ensuring the stability and security of supply of the European energy system, large battery parks are becoming increasingly critical forms of infrastructure. In Estonia, the key player in this field is WiSo Engineering, which has the most experience in the region in constructing large-scale battery parks.

Under WiSo Engineering’s lead, Estonia’s largest battery storage park, Hertz 1, has now been completed, with a capacity of 100 MW and a storage volume of 200 MWh. Located in Kiisa, Hertz 1 is merely the first stage in an ongoing project: as early as this spring, a second battery park of the same size and capacity, Hertz 2, will be completed alongside it. Together, the two parks will form a 200 MW and 400 MWh whole – one of the largest battery park complexes in continental Europe.

WiSo Engineering carried out the construction and electrical work for the Kiisa battery park as a turnkey solution, from the drafting of building and electrical plans to construction, the installation of equipment and its integration into the electricity grid.

The ability of battery parks to react within milliseconds makes them a cornerstone of grid stability: they provide reserve capacity, regulate frequency and voltage, reduce price peaks and enable more renewable energy to be integrated into the grid. The synchronisation of the Baltic States with the electricity grid of continental Europe has significantly increased the importance of battery parks.

Hertz 1: Thousands of battery modules and complex electrical works

The construction of Hertz 1 was the most ambitious project in WiSo Engineering’s history – building Estonia’s largest battery park at a pace that left no room for error. Nothing of this scale or complexity had previously been undertaken in the country.

A challenge of its own was the installation of the battery technology. All 2328 battery modules – each weighing nearly 670 kg – had to be installed in containers on site. The intensive five-week installation cycle required the careful planning of logistics, precise lifting operations and flawless cooperation across the team.

“A total of 54 battery containers, 27 transformers and four medium-voltage distribution points were installed in a very short space of time,” explained WiSo Engineering CEO Risto Virveste. “That meant large-scale deliveries, complex electrical works and strict quality control, all happening simultaneously. The project tested the full range of our engineering capabilities, but this is exactly the sort of thing we exist for.” Virveste added that construction of the Hertz 1 battery park is now fully complete and that the site has been handed over to the client.

Hertz 2: Same scale, greater experience

The Hertz 2 battery park in Aruküla has also reached the final stage of construction: only the last cables remain to be connected, with the complex due for completion this spring. The scope of the undertaking is equally ambitious, with design, construction and installation of energy storage systems being provided as a turnkey solution. This time, however, WiSo already had the successful construction of Estonia’s largest battery park behind it – experience that allows every process to be carried out more efficiently.

The combined effect of the two parks means that the complex in Kiisa represents one of the highest levels of capacity and storage volume in continental Europe. “Energy storage on this scale fundamentally changes how the region’s electricity system functions, from frequency regulation to renewable energy integration,” Virveste noted. “We are no longer talking about individual parks, but integrated energy infrastructure that affects the Baltic grid as a whole.”

In addition to battery parks, WiSo Engineering’s portfolio includes numerous solar parks. One of these, completed in October 2024, is in Kirikmäe: at the time, it was the largest solar park in the Baltic States, with a generation capacity of more than 77 MW.

A strong, professional team

The battery park complex clearly shows that Estonia has the know-how and the ability to build energy facilities on a European scale. “We are constructing engineering solutions that boost the energy security of Estonia and the Baltic Sea region,” said Virveste. “Large-scale battery parks are technically complex, time-critical and require serious levels of competence. We have shaped our team for exactly those sorts of projects.”

According to Virveste, the success of any large project depends first and foremost on the professionalism of the people working on it. “Kudos to our chief engineer Jano Aunbaum, whose technical meticulousness was the unshakeable foundation of the entire project, and to our project manager Rünno Nemvalts, who always kept us on track and the lines of communication open,” he said. “But it was teamwork through and through – everyone knew what was expected of them, and they gave their all. That is our strength: people who are amazing at what they do and who you can always rely on.”

Smooth cooperation between developers and builders

The battery park complex is being developed through the joint venture Baltic Storage Platform (BSP) by the leading regional renewable energy developer Evecon, the French independent power producer Corsica Sole and the international investment fund Mirova.

Evecon CEO Karl-Joonatan Kvell says that building battery storage parks requires a first-rate construction partner. “It is not just about erecting facilities, but creating a comprehensive and reliable energy system in which every detail matters,” he remarked. “Throughout the project, WiSo Engineering has demonstrated an outstanding level of professionalism, successfully delivering the work in complex conditions, within a short space of time and meeting some very demanding quality requirements. That sort of competence and reliable cooperation is crucial if we want to build storage solutions that are strategic not only to Baltic energy systems, but to European ones as well.”