(1) Impervious core
(3) Shell zone
(5) Solid ground
(6) Rock foundation
(7) Grout curtain
(8) Underground shielding construction
With a usable storage capacity of about 31 mio m³, the new Kühtai reservoir is about half the size of the existing Finstertal reservoir. The dam is designed as a natural rockfill dam with a central earth core and a height of 113 m from the original valley floor to the dam crest. The full reservoir level is at 2,140 m above sea-level. All of the material used for the rockfill dam is extracted on site from the future reservoir and the tunnel excavation.
Similar to the two existing dams, natural stone and structural elements will be used for the airside dam surface to blend in the structure with the natural surroundings in the best possible way.
The Kühtai 2 power station with its headrace tunnel – a tunnel 4.5 m in diameter – connects the new Kühtai reservoir with the existing Finstertal reservoir. The power station is built completely underground in a rock cavern and is designed for pumped storage operation. Two pump turbines form the heartpiece of the station. These turbines are reversible, meaning their function and direction of rotation can be turned around: in turbine operation, up to 90 m3/s of water are flowing in the headrace tunnel from the Finstertail reservoir to the Kühtai reservoir with the turbine driving the generator, causing the generator to feed electricity into the grid.
In pump operation, the generator turns into a motor that draws electricity from the grid. The turbine is now driven by the generator and acts as a pump, pumping water from the Kühtai reservoir up to the Finstertal reservoir.
This makes it possible to store water for electricity production later on, similar to a storage battery but in much larger quantities. A short underground 220 kV cable supplies electrical energy to the existing Kühtai power station which is already connected to the electricity grid. There is no need for a new high-voltage line to the Inntal valley. This is only one of many advantages of the location with its existing power stations and infrastructure.
erneuerbare+ Kühtai guarentees the energy supply for future generations
The collecting works – a tunnel 4.2 m in diameter and 25.5 km in length – with its 6 water intakes opens up an additional catchment area in the middle, eastern part of the Ötztal valley and the head of the Stubaital valley. The harnessed water is fed into the Kühtai reservoir at a slight gradient. Due to local conditions, two of the water intakes are situated slightly below the collecting works; a pumping station is used to raise the water drawn off there to the level of the collecting works.
As a general principle, the amount of water drawn off at the intakes conforms to ecologically compatible levels. Natural flow dynamics are maintained even if at a lower level. In the winter months no water is drawn off at all.