Switzerland – Hydro-electric plant construction work – Pumpspeicherwerk Grimsel 4 - Bauhauptlos

The PSW Grimsel 4 utilises two turbine groups without additional impounded water to exploit the existing potential between the two existing reservoirs, Grimsel and Räterichsbodensee. Due to the short distance between the two lakes and the existing plant components, an economically attractive power plant can be realised with the PSW Grimsel 4. In addition to the mentioned reservoirs, the project utilises further existing plant components, in particular the access and supply systems of the existing power plants at the Grimsel, as well as the intake structure Grimselsee with throttle valve chamber (pre-investment Grimsel 4) already realised in connection with the replacement of the Spitallamm dam. The new structures to be created generally comprise the continuation of the headwater-side penstock system from the throttle valve chamber with flat section and pressure shaft, the cavern powerhouse, the tailwater-side penstock system with tailwater tunnel and outlet structure, as well as additional access tunnels. The new power plant has a total capacity of 150 MW at a design flow rate of 70 m3/s and closes the existing bottleneck in the hydraulic system between Grimsel and Räterichsbodensee. In addition, the power plant also serves for lake and inflow management, which can avoid water losses in the event of high water and make a significant contribution to flood protection. Thanks to its flexible mode of operation, the PSW Grimsel 4 can react to short-term grid fluctuations and cover peak loads in circulating mode. In times of excess capacity in the grid, excess energy can be absorbed and stored. In times of need, the stored energy is available as peak power. In this way, Grimsel 4 supports not only the smoothing of load profiles but also the stabilisation of voltage and frequency in the transmission grid. The PSW Grimsel 4 is also able to operate in so-called hydraulic short circuit. In this mode, part of the pumped water is immediately turbinated again without completely passing through the storage cycle. This mode of operation allows for a very rapid response to changing grid conditions without having to interrupt the pumping operation. This significantly increases the reactivity of the power plant and makes it an extremely valuable tool in modern grid operation. In addition to energy production, the PSW Grimsel 4 also provides system services such as primary, secondary and tertiary control. The high flexibility of the pumped storage power plant enables it to provide control energy at very short notice, which is a decisive advantage in view of the increasing volatility of the power markets. With these properties, the PSW Grimsel 4 plays a central role in the energy transition and makes a significant contribution to supply security and the efficient use of hydropower resources.

Scope of work / main quantities

The following structures are to be newly created as part of the main construction contract for the PSW Grimsel 4:

- Penstock system with

- Remaining excavation headwater pressure tunnel flat section I (ODF I)

- Headwater pressure shaft (ODS)

- Headwater pressure tunnel flat section II (ODF II)

- Headwater distribution line (VOW)

- Tailwater distribution line (VUW)

- Tailwater pressure tunnel (UDS)

- Intake and outlet structure in Räterichsbodensee (ABR), excl. pre-cut (ETR)

- Cavern powerhouse (ZGR4)

- Various access, supply and construction logistics tunnels

The penstock route between the two reservoirs, Grimsel and Räterichsbodensee, runs in a straight line. The route was optimised with a view to a minimum length of the penstock route. The short overall horizontal length of only just over 1.2 km allows for the omission of a water lock in both the headwater (OW) and the tailwater (UW) without having to accept major operational restrictions.