NGEN Doubles One of Austria's Largest Battery Storage in Arnoldstein

NGEN commissioned the facility at Arnoldstein-Gailitz in Carinthia in September 2023. Eight Tesla Megapack units delivered 10.3 MW and 20.6 MWh, the largest battery storage system in Austria at the time. In 2025 six Megapack 2 XL units were added, taking the site to 14 units, 22 MW and 44 MWh. The expanded plant returned to the grid in June 2025 and was officially inaugurated on 17 October 2025.

The battery stands alone on an industrial site and connects to the Austrian transmission grid through the Gailitz substation, 300 metres away. Austrian Power Grid is the customer. The plant takes a signal from APG roughly every two seconds telling it whether to absorb or release, so in practice it follows the balance of the Austrian control area continuously rather than running to a schedule.

Hardware is one part of the project. Which market Arnoldstein serves in a given period, and at what price, is decided by NGEN's software, the same platform that runs the company's European fleet.

Wind and solar take a rising share of the Austrian mix and of the connected European grid. That puts pressure on the transmission operator to hold frequency and to manage congestion, and it changes the kind of capacity the system needs. Less of it has to be running in order to be ready; more of it has to be committed and released at short notice.

Austria is not short of storage in general. Carinthia alone holds the country's largest pumped-storage complex. Batteries do not replace that fleet. They cover the fastest end of the range, where the response has to be immediate and the commitment short, and they can be sited where the network needs them rather than where the topography allows. Arnoldstein was built to add exactly that.

Being built and connected is only the entry condition. From there the capacity has to be offered, priced and delivered in every quarter-hour of the year. No control room does that by hand, which is why the operating question on a project like this is a software question.

Arnoldstein is a standalone battery on the transmission grid. The hardware sets the envelope: 22 MW held for two hours. Everything above that envelope is a decision about which product to serve and when.

The platform tracks grid conditions and market prices continuously, forecasts where the system is heading, and positions the asset accordingly. It moves capacity between balancing products and short-term energy trading as prices and system needs change, rather than committing the same megawatts to several products at once.

The site delivers into Austrian Power Grid's control area, and APG in turn participates in the European balancing platforms: PICASSO for automatic frequency restoration reserve, which APG joined in June 2022, and MARI for manually activated reserve. Those platforms operate between transmission operators, not between operators and individual plants. The practical effect for Arnoldstein is that capacity offered in Carinthia can end up correcting a deviation elsewhere in the synchronous area.

The asset is supervised around the clock from NGEN's dispatch centre in Žirovnica, Slovenia, which runs the European fleet as one system. On the hardware side, the container architecture is what made the 2025 expansion straightforward: six more units on the same land, behind the same connection, with nothing rebuilt.

Doubled without a new site

Six additional Megapack 2 XL units took the plant from 10.3 MW to 22 MW on the same land and the same connection point.

Balancing capacity for APG

Capacity delivered to Austrian Power Grid, following a signal updated roughly every two seconds.

Flexibility that crosses borders

Because APG participates in PICASSO and MARI, capacity offered in Carinthia can be activated for deviations elsewhere in the synchronous area.

Austria's largest at inauguration

At 44 MWh, the largest battery storage facility in the country when the expanded plant was inaugurated in October 2025.