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Wehr underground hydropower plant - Energy deep within the mountain

Wehr pumped-storage power plant is the most powerful of its kind in Germany. The four hydroelectric sets generate around one billion kilowatt-hours of power annually.

In a process not dependent on the weather, state-of-the-art technology moves huge masses of water in a closed circuit between Wehra reservoir and Hornberg reservoir, which lies roughly 600 metres higher up. From there, the water passes along a steel-plated pressure shaft 1,385 meters long and 5.5 meters in diameter to the machine hall within the cavern, where it drives huge turbines, making it possible to generate electricity within a matter of seconds if required.

In a reverse process, high-power pumps are used here to pump water from Wehra reservoir up to Hornberg reservoir to relieve the pressure on the power grid, depending on what the power grids need at the time.

One key feature is the additional and independent machine with black-start capability, which, with its output of around four megawatts, can be the starting point for restoring the system following a power grid collapse in Germany.

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 period1968 to 1976
Underwater tunnel1,502 metres long with a diameter of 7 metres
Average drop height in metres625
Generator output in megawatts (average):910
Pump output in megawatts (average):980
Upper reservoirHornberg reservoir
Lower reservoirWehra reservoir

Facts and figures

  • Cavern: 219 metres long, 19 metres wide and 35 metres high
  • Wehra reservoir capacity: 4.3 million cubic metres of water; Hornberg reservoir: 4.4 million cubic metres of water (enough to generate power at full load for around seven hours)
  • Maximum turbine flow rate: 180 cubic metres of water per second
  • Maximum pump flow rate: 144 cubic metres of water per second
Pumpspeicherkraftwerk WehrWehr pumped-storage power plant
HornbergbeckenHornberg reservoir
DruckschachtPressure shaft
ZufahrtsstollenAccess tunnel
WasserschlossSurge tank
BetriebsgebäudePlant building
UnterwasserstollenUnderwater tunnel
EnergieableitungsstollenEnergy diversion tunnel
WehrabeckenWehra reservoir
FreileitungOverhead lines
WehrastollenWehra tunnel
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