Increasing power production from the Emosson reservoirs in the Swiss Alps using one of the most powerful pumped storage plants in Europe with a storage capacity of 25 million m³.
The Nant de Drance pumped storage facility was designed to exploit part of the enormous hydroelectric potential of the Swiss Alps for stabilizing the European grid and securing Switzerland's power supply.
AFRY was commissioned by the client in 2002 to develop this project and to bring it to implementation maturity via the feasibility study, the preliminary, construction and conditional project as well as via the tenders.
Construction work began in autumn 2008, with AFRY as overall planner until autumn 2012. From autumn 2012, AFRY took on various key roles in the project. Among other things, AFRY was in charge of the technical coordination of the overall project, execution planning, project controlling, setting up a data management system, construction planning and management, hydraulic steel structures, electro-mechanics and electrical engineering, as well as increased monitoring of dams and valley deformations.
The plant was commissioned in autumn 2022.
AFRY's role in Nant de Drance as hydropower consultants
The 900 MW Nant de Drance pumped storage power plant was developed incorporating the two existing reservoirs Vieux Emosson (upper reservoir) and Emosson (lower reservoir) in the Valaisian Alps along the Swiss and French border. The available head between these two reservoirs is up to 395 m. The capacity of the upper reservoir was doubled by increasing the height of the existing dam wall by 20 m.
The headrace system is designed in two independent parts. Each part consists of approx. 2350 m of pressure tunnels and a 425 m deep vertical shaft. 13 km of tunnels provide year-round access to the facilities.
The underground power plant complex consists of the power plant cavern (194x52x32 m), the transformer cavern (132x18x18 m) and three access tunnels. The longest tunnel is the main access tunnel to the machine cavern. It is 5.6 km long, driven by a hard rock TBM with a diameter of 9.45 m and a maximum gradient of 12% (winter access).
The six vertical reversible Francis pump-turbine units of maximum 157 MW each and the vertical asynchronous motor-generator units of 170 MVA as well as other central plant elements constitute the core equipment of the Nant de Drance pumped storage power plant.
Nant de Drance as a project of the century
With costs of just over 2 billion Swiss francs, the project will be an important component of the Swiss and European energy strategy. Thanks to the installed capacity of 900 MW, the power plant will be able to produce large amounts of electricity or store energy within a very short time. The high flexibility will be one of the main strengths of this plant, as the volatile amount of electricity generated from the new, renewable energy sources can be optimally stored in this way.
Find more information on our project page:
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