The interaction of wind, solar and hydropower

Located amidst the wonderful Alpine setting of Mölltal, a southern Austrian valley in the province of Carinthia, the redeveloped Reisseck II pumped storage plant is as innovative as it is ambitious. After six years of construction, this new facility creates a hydraulic connection between two groups of existing power stations, Malta and Reisseck-Kreuzeck. As such, it makes energy generation in the Alps even more efficient and sustainable. And it marks a real high point in the development of pumped storage hydropower plants. “From a technology point of view,” says Martin Nussmüller, a Voith project leader on Reisseck II, “we can say it is one of the most modern pumped storage plants in the world.”

Environmentally sound foundations

The original Reisseck-Kreuzeck system was created between 1948 and 1961, with Malta opening in 1978. This means that Reisseck II required no major additional environmental changes. Indeed, though up to 250 people, huge machinery and underground tunnels were integral to its completion, the landscape has been returned to its idyllic Alpine aesthetic. “Around €8 million has been spent on renaturalizing the area,” says Nussmüller.

Now complete and operational, Reisseck II increases the efficiency of the area’s energy generation system, ensuring that the installation is as environmentally friendly as possible. As a result, it is known by those who worked on the project by its nickname – the “green battery.” Whenever windpowered or solar energy sources are compromised because of local weather conditions, Reisseck II comes into its own: in double-quick time, the pumped storage plant can step in to supply power, and then be throttled back when wind or solar conditions improve.

“This was a great challenge,” says Anton Huber, also a Voith Project Manager on Reisseck II. “We had to go beyond the usual specifications, but we showed we could complete the project to a very high standard.” The central tenet of the design is that though the turbines are small, they provide a very high power output, which equates to exceptional efficiency, as stipulated by the customer, Verbund Hydro Power GmbH (the Austrian energy provider). Huber adds: “The pump turbines have been labeled ‘Grenzleistungsmaschinen,’ or ‘performance- limit machines.’ This refers to the fact that the power output of the turbines relative to their size is right at the limit of what is currently possible. Therefore, from an efficiency and technological viewpoint, they really are cutting-edge.”

The result: Reisseck II has an output of 430 MW in both pumping and turbine modes, and increases the overall output of the two power-plant-groups by 40%, from 1,029 MW to 1,459 MW. The beauty of the technology and the overall design is that energy generation can be adapted to the prevailing conditions almost instantaneously. And of course, as a pumped storage plant, Reisseck II can store energy for use whenever it is needed.

Like any other hydropower site in a remote region, the project was a complex undertaking. Construction at 1,600 meters above sea level and up to 200 meters deep inside a mountain presented considerable challenges, particularly in terms of transporting huge machinery to the right place. In addition, delays caused by avalanches and forest fires were always a risk. Nevertheless, nothing was allowed to endanger the completion of the project, as David Giefing, Project Manager for the Pump Turbine at Verbund Hydro Power GmbH, concludes: “Throughout the project, I always felt I had found a trustworthy partner in Voith. With our credo, ‘the technical solution always comes first,’ we were able to overcome every project challenge together.”