Arnoldstein 2, Austria - 11.6 MW / 23.2 MWh

Two years after the first containers were installed, NGEN added six Tesla Megapack units at Arnoldstein. The new units add around 11.6 MW and 23.2 MWh and take the site to 21.9 MW and 43.8 MWh, usually rounded to 22 MW and 44 MWh. The expanded plant went back on the grid in June 2025.

The official inauguration took place on 17 October 2025 in the Euronova industrial park, where the battery stands. At that point Arnoldstein was the largest and most powerful grid-serving battery storage system in Austria. Earlier in 2025, NGEN's Fürstenfeld battery had taken that position; the expansion brought it back to Carinthia.

The plant connects directly to a substation 300 metres away. Its customer is the transmission system operator Austrian Power Grid (APG).

Austria already meets more than 90 percent of its electricity demand from renewable sources. The difficulty is timing: solar and wind output peaks when demand does not, and the surplus has to go somewhere. The aim at Arnoldstein is to bring this variable generation under control and make electricity available where and when it is needed.

Carinthia is known for pumped storage. Malta-Reißeck, Austria's largest pumped-storage plant, is in the province. A battery does the same basic job but reacts far faster, ramping from zero to full output within seconds.

The quickest way to add more of that capability was at a site that already had it. Arnoldstein had an operating plant, an industrial location and a grid connection, so the expansion could go ahead without a new site.

The six new units are Tesla Megapack systems with lithium iron phosphate (LFP) cells, installed next to the original eight. With 14 units across both phases, the site can deliver its full output for about two hours.

Roughly every two seconds, the plant receives a signal from APG telling it whether to store or release electricity. The grid is checked continuously for overload or undersupply, and the battery responds accordingly.

NGEN's software markets the capacity. It provides balancing reserve to APG and optimises the remaining capacity on the intraday and day-ahead markets, moving between them as prices and system needs change.

The site is supervised around the clock from NGEN's dispatch centre in Žirovnica, Slovenia, just across the border from Arnoldstein.

More than doubled on the same site

Six additional Megapack units took the site from 10.3 MW to 22 MW and from 20.6 MWh to 44 MWh.

Austria's largest at inauguration

When it was inaugurated in October 2025, Arnoldstein was the largest and most powerful grid-serving battery in Austria.

Balancing reserve for APG

The plant follows APG's control signal, updated roughly every two seconds, and provides balancing reserve to the Austrian grid.

A step towards larger projects

At the inauguration, NGEN announced a plant four times the size in Upper Austria. That project, Wagenham, is now being built with 85 MW and 170 MWh.