“We are now at the cavern and about 40 meters below Lake Traunsee,” says Klaus Höller, project manager at Energie AG. Some participants in the official first ascent with State Governor Thomas Stelzer, State Economics Councilor Markus Achleitner and Energie-AG board member Leonhard Schitter have an uneasy feeling – but the little water comes from the mountain. The Ebensee pumped storage power plant is being built here in Sonnstein, making it “the largest battery in Upper Austria,” as Stelzer and Achleitner unanimously call it.
After around six months of construction, the access tunnel to the cavern, where the pump turbine, generator and transformer will be located, is finished – it goes 460 meters deep into the limestone. Dusty air, the smell of explosions, huge construction machines and shotcrete everywhere on the walls for stabilization. The cavern is already being enlarged from above; in the end it will be 40 meters high (and as big as the Ebensee church). From here, the energy dissipation tunnel leads underground to the Kohlstatt district, where the energy then comes back into the network. The existing 110 kV line is used for this. At the same time, work and drilling is already underway on the vertical pressure tunnel (length: 560 m), where the water is pumped up to the reservoir.
Costs: 451.3 million euros
“At 451.3 million euros, it is the largest investment in our history,” says Energie AG boss Schitter. The pumped storage power plant will be an important compensation for photovoltaic peaks in the future – and crucial for Upper Austria’s energy supply. The pipes inside the mountain have a diameter of around 4.5 meters and the water will flow here at a speed of 30 to 40 cubic meters per second. “That’s the equivalent of a swimming pool,” says Höller.
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Image: Max Mayrhofer
The project is on budget and on schedule, said Technical Director Alexander Kirchner. It should go into operation as planned in 2027 and be able to supply or store 170 megawatts. In addition, the power plant also has economic significance: In total, more than 1,500 workers have been employed in five years, 130 on site in the tunnel every day, working in 10-hour shifts. And seven days a week, there is only no blasting at night (10 p.m. to 6 a.m.) and on weekends. The advance is an average of six meters per day. “The importance and size of the project is enormous – you can see that,” says Stelzer. For Achleitner it is a “milestone in the energy transition”.
The forest road takes you up to the Rumitzgraben towards Langbathsee – the upper water reservoir, which can also be seen from the Feuerkogel. “We are working on the 60 meter high dam, at the end it will be sealed with asphalt and can store 1.3 million cubic meters of water. That corresponds to around 45,000 pools,” says Norbert Rechberger (Energie AG Generation). The stored energy will soon be able to supply 280,000 households.
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