Nant de Drance pumped storage power plant – Energy storage to prevent energy shortages

Abstract

AbstractThe Nant de Drance hydropower plant in the canton of Valais is one of the Swiss energy industry's largest construction projects of recent years. The core component is the underground pumped storage power plant. This pumps water from the existing Emosson reservoir at 1930 m asl to the upper Vieux Emossen reservoir at 2225 m asl, where the surplus energy is stored. When demand exceeds supply, water is released to generate electricity. The head ranges from 290 to 395 m, depending on the water levels. The new power plant, which took 14 years to build, has a pump and turbine capacity of 900 MW.The most important elements of the project were the access tunnel, pressure tunnels, vertical pressure shafts and underground machine and transformer halls, as well as the various access and service galleries, the intake and discharge structures with cofferdam, and the raising of the Vieux Emosson dam by 20 m. The ecologically sensitive use of resources is essential to ensure the success of a complex, high‐altitude construction project of this nature involving enormous quantities of material. Excavated rock, for example, has been processed on site to produce aggregate for concrete. In this case a high‐capacity aggregate production plant was installed on site to process the excavated material required for on‐site concrete production. This created a closed‐loop materials cycle which enabled the construction site to be self‐sufficient in terms of concrete production.The challenges of using excavated tunnel material as a resource are enormous.