| Nant de Drance | |
| Coordinates: | 46.0636°N 6.91°W |
| Country: | Switzerland |
| Location: | Finhaut, Saint-Maurice, Valais |
| Status: | O |
| Construction Began: | September 2008 |
| Opening: | July 2022 |
| Cost: | US$2.1 billion (CHF 1.9 billion, €1.5 billion) |
| Owner: | Nant de Drance SA |
| Res Name: | Lac du Vieux Emosson |
| Lower Res Name: | Lac d'Emosson |
| Plant Pumpgenerators: | 6 x 150 MW reversible Francis-type |
| Plant Capacity: | 900 MW |
| Plant Annual Gen: | 2,500 GWh (est.) |
| Extra: | 20 GWh energy storage |
The Nant de Drance Hydropower Plant is a pumped-storage power station in the canton of Valais in Switzerland. It is within the municipality of Finhaut, district of Saint-Maurice and about southwest of Martigny. Construction on the power plant began in 2008 and it began operations in 2022.[1] [2] It is owned by Nant de Drance SA, a consortium of Alpiq (39%), SBB (36%), (15%) and (FMV) (10%). The US$1.9 billion plant has an installed capacity of 900 MW[3] [4] and an energy storage capacity of 20 GWh.
On 25 August 2008, the Swiss Federal Department of Environment, Transport, Energy and Communications granted a building permit to Nant de Drance SA for the construction of the plant with a 600 MW design. Preliminary construction began in September 2008 but a concession was granted in April 2011 which allowed for a larger 900 MW plant. Excavation of the tunnels began in 2009 and the caverns commenced in 2010.[5] Raising of the upper Vieux Emosson Dam began in Spring 2013. The underground power house excavation was completed in April 2014.[6] The first generators were tested in 2017.[5]
In December 2014, at the International Tunnelling & Underground Space Awards, the project was awarded the Major Tunnelling Project of the Year award in the category of projects over US$500 million.[7]
The power plant uses two existing reservoirs to operate. The lower reservoir, Lac d'Emosson, is formed by the tall, long Émosson Dam, an arch dam which was completed in 1974. It withholds a reservoir with a storage capacity of and surface area of . The lower reservoir is long and when full, lies above sea level.
The upper reservoir for the plant, Lac du Vieux Emosson, is formed by a tall and long arch dam originally completed in 1955. The dam is tall. Lac du Vieux Emosson's storage capacity is and has a surface area of . When full, the upper reservoir lies above sea level.[8]
The power plant is between both reservoirs and uses the pumped-storage hydroelectric method. To accomplish this, when energy demand is high, water is released from the upper reservoir, down a series of penstocks to the six 150 MW reversible Francis turbine-generators in the power plant.[8] The large underground power house measures long, high and wide.[6] After generating power, water from the power plant is discharged to the lower reservoir, releasing up to 20 GWh of energy.[9] When power demand is low, such as at night, the turbines reverse and water can be pumped back up to the upper reservoir for use during high demand periods. As such, it serves as a peaking power plant[8] with 80% efficiency.[10]
Under the guidance of AF-Consult Switzerland Ltd as general planner, the civil engineering works were carried out by GMI (a joint venture of Marti and Implenia) and the electro-mechanical works were done by GE Hydro.[11]