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Witznau power plant - Idyllically nestled middle level

Wonderfully situated on the lower course of the Schwarza, Witznau pumped-storage power plant looks like something out of a fairy tale. State-of-the-art technology is at work behind the 47-metre-high power plant walls (37 metres of which are visible), which also serve as the dam wall of Witznau reservoir. As the middle level of the Schluchsee Group, Witznau power plant forms an important part of the storage and generation cascade between Waldshut and the High Rhine.

The power plant is fed by water from Schwarza reservoir, which flows along a 9.2-kilometre-long pressure tunnel. Together with Mettma reservoir to the west, Schwarza reservoir serves as the upper reservoir for Witznau power plant. The lower reservoir is Witznau reservoir.

From here, once the work is done, the water either continues flowing along a 9.4-kilometre-long underground tunnel into Waldshut power plant or – depending on requirements – is pumped back up into Schwarza or Mettma reservoirs.

Energy transition

Being able to store electricity in large quantities and generate it within seconds when needed is now more important than ever. The sun and the wind have long been playing their part in generating electricity in Germany and are producing an ever increasing share. Yet these generation sources fluctuate depending on the weather and are unreliable. Pumped-storage power plants come into play when too much electricity overloads the grid or a lack of electricity threatens the supply. They work within seconds, produce zero emissions and generate outputs that rank them among the best of all available storage technologies.

How pumped-storage power plants work

Pumped-storage plants consist of an upper and lower basin. Between them are power plants, which pump water uphill if there is excess electricity and allow it to flow down again through turbines to generate electricity when power is needed. They are precisely tailored to meet the needs of the grid at all times. As such, they help to secure the supply – cleanly, effectively and reliably.

Schluchseewerk AG

With its five pumped-storage power plants, Schluchseewerk AG is one of Germany’s largest suppliers and leading experts. As a partner to its shareholders, it oversees the safe and reliable operation of all its facilities, thereby helping to stabilise the power grid and playing its part in safeguarding the energy supply for today and tomorrow. Schluchseewerk – we are driven by water!

Technical data:

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Construction period:1942 to 1951
Tunnel length:9.4 kilometres (Rhine Valley Tunnel)
Average drop height:160 metres
Average output in turbine mode:150 megawatts
Average output in pump mode:80 megawatts
Upper reservoirWitznau reservoir
Lower reservoirReservoirs in the High Rhine and the Aubecken reservoir in Dogern

Facts and figures

  • Average annual generation: approx. 220 million kilowatt-hours of power (enough to cover the annual needs of around 60,000 three-person households)
  • Pressure equalisation structure: Berau surge tank (height 75 metres, diameter 12 metres)
  • Turbine flow rate at full load: 132 cubic metres of water per second (this could fill about 1,100 bathtubs every second); pump flow rate at full load: 40 cubic metres of water per second
  • Storage capacity of the reservoirs (in cubic metres): Witznau 1.35 million; Schwarza 1.29 million; Mettma 1.57 million
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