The Nant de Drance project is a 900MW pumped-storage hydroelectric power station under construction in the Valais municipality of Switzerland.

The project is being developed by Nant de Drance SA, a consortium of Alpiq (39%), Swiss Railway Company SBB (36%), Industrielle Werke Basel (IWB) (15%), and Valais Electricity Company Forces Motrices Valaisannes (FMV) (10%) with an estimated investment of approximately £1.67bn ($2.18bn).

The construction works on the project were started in September 2008, while the first two units were synchronised and connected to the grid in August and September 2020.

The facility is expected to generate up to 2.5 billion kWh of electricity annually at full capacity with the commissioning of the remaining four units expected by the end of 2021.

Location and site details

The Nant de Drance pumped storage hydroelectric project is located in the Valais municipality, between the towns of Martigny and Chamonix, in Finhaut, near the French border, in the canton of Valais, Switzerland.

Nant de Drance pumped-storage facility make-up

The Nant de Drance pumped-storage hydroelectric power station comprises six sets of Francis type reversible pump-turbine units of 150MW capacity each, placed in an underground powerhouse cavern measuring 52m-high, 32m-wide, and 190m-long.

The power generation facility is situated in between the lower-level Emosson and the high-site Vieux Emosson reservoirs connected by a system of water galleries. The vertical difference between the two reservoirs is more than 350m.

The Vieux Emosson reservoir features a double arch dam with 76.5m maximum height and a crest length of 205m and has a storage capacity of approximately 23.5 million cubic metres (mcm).

The project also involves two 425m-high vertical penstocks with a diameter of 7m, a 5.6km-long access tunnel, two 1.5km surge tunnels, a transformer cavern, approximately 4.5km of access and service galleries, the intake and discharge structures of the Vieux Emosson reservoir, and eight electrical substations.

Power evacuation

The electricity generated by the Nant de Drance hydroelectric power station will be evacuated through two 6.5km-long, 380kV power transmission lines connected to the 380/220kV Châtelard substation.

Contractors involved

GMI Groupment Marti Implenia, a consortium of Marti tunnel and Implenia Bau was contracted for the main civil construction works of the project in August 2008.

General Electric (GE) supplied the pump-turbines, motor generators, and inverters along with the piping.

Afry Consultant (formerly AF Colenco) was contracted for the project management services along with the tendering, design, site supervision, and commissioning services.

Swiss transmission system operator (TSO) Swissgrid is responsible for connecting the power station to the extra high voltage grid.

Tucon was subcontracted by GMI Groupment Marti Implenia for the underground construction of the caverns, while Herrenknecht supplied the Gripper tunnel boring machine (TBM).

ABB supplied six generator circuit-breakers and six 175MVA power transformers, while Hager Group supplied four Unimes H main distributors and 16 Unimes H sub-distributors electrical equipment.

Doka delivered a custom formwork solution to support the construction works of the underground powerhouse in 2014.

PINI Group provided the services related to the concrete work of the machine and transformer caverns, as well as auxiliary construction management services.

Sika Solutions supplied superplasticizers, air void entrainer, and retarder to support the project-specific special concrete production, while Kummler and Matter EVT AG was awarded a contract worth approximately £45.66m ($70m) for the installation of in-house power supplies and facility services, along with related painting and plumbing works for the project in October 2015.

Solutec was engaged by Alpiq for the project management and commissioning supervision services, while Rialex Crane Systems was contracted for the delivery and installation of cranes, and BG Consulting Engineers for the supply and installation of the ventilation system.

Nant de Drance power project background

The Nant de Drance pumped storage hydroelectric project was initiated by Aare-Tessin for Electricity (Atel) (now Alpiq), along with the partner SBB in February 2006.

While FMV joined the consortium in June 2009, IWB acquired a 15% share in the hydroelectric pumped storage project in December 2012.

The capacity of the pumped storage power project was revised from 600MW to 900MW  with a height-raise in the dam wall by 20m in July 2011.