The contracted works comprise specifically residual excavation for the headrace pressure tunnel – shallow section I (ODF I), the headrace pressure shaft, headrace pressure tunnel – shallow section II (ODF II), the headrace distributor pipe, tailrace distributor pipe, tailrace pressure tunnel, the intake/outlet structure in Lake Räterichsboden, the cavern powerhouse and various access, utility, and construction logistics tunnels. The waterway between the two reservoirs, Grimselsee and Räterichsbodensee, follows a direct alignment.
The route was optimized to minimize the length of the waterway. The total horizontal length of just under 1.2 km makes it possible to dispense with surge tanks on both the headrace and tailrace sides without incurring significant operational limitations. Thanks to the short distance between the two lakes and the availability of existing infrastructure, Grimsel 4 offers a commercially attractive solution.
In addition to the aforementioned reservoirs, the project utilizes other existing infrastructure such as the access and utility systems of the existing Grimsel power plants, as well as the Grimselsee intake structure and butterfly valve chamber (a Grimsel 4 advance investment) that were already constructed in conjunction with the replacement of the Spitallamm dam.
KWO received a construction permit in January 2026, and its board approved the CHF 300 million (US$374 million) investment in March 2026. Voith Hydro was awarded a contract in April 2026 for the supply of two 70 MW variable-speed pump turbines. With a design flow rate of 70 m³/s, the future power plant is designed to eliminate an existing hydraulic bottleneck between Lake Grimsel and Lake Räterichsboden to balance the broader KWO power complex.
In addition, the plant will facilitate reservoir and inflow management, thereby preventing water losses during high-water events and making a significant contribution to flood protection. Thanks to its flexible operating mode, Grimsel 4 will be able to respond to short-term grid fluctuations and cover peak loads during cycling operations. Grimsel 4 will also be capable of operating in “short-circuit” mode, where part of the pumped water is immediately passed through the turbines without completing the full storage cycle. This mode of operation allows for a rapid response to changing grid conditions without interrupting pumping operations. This significantly enhances the plant’s responsiveness, making it an invaluable asset in modern grid operations. Grimsel 4 will, in addition, provide system services such as primary, secondary, and tertiary frequency control.
The project is scheduled for commissioning in February 2032. The procurement notice can be viewed on the TED procurement website at: https://ted.europa.eu/en/notice/-/detail/549491-2026.
Procurement documents can be accessed at: https://www.simap.ch/de/project-detail/7fe1fc94-040e-4683-ad61-1b947f9148d0?lot-id=null. The entire tender must be submitted in German in two paper copies and in a single copy in PDF format on a USB stick. The required tender documents must be submitted in a sealed envelope marked “Bitte nicht öffnen – Angebotsunterlagen Bauhauptlos PSW Grimsel 4” to the below-mentioned address by 16.00 hours Eastern European Time, on 9 October 2026.
For further information, contact: Kraftwerke Oberhasli AG, Procurement Dept., Grimselstrasse 19, Innertkirchen 3862, Bern/Berne; Switzerland; E-mail: einkauf@kwo.ch; Tel.: +41 339822011.
