The FMHL+ pumped-storage project

The pumped storage power station belonging to Forces Motrices Hongrin-Léman SA (FMHL) was built between 1968 and 1971. In view of the growing demand for capacity and the extension of the 380 kV network, the owners evaluated various options for expanding the power station.

This led to the construction of a new cavern (FMHL+), which began in 2011 and is scheduled to be commissioned in 2016.

Use of the four elements

The disadvantage of certain natural resources, such as the sun and the wind, is the uncertainty associated with energy production forecasts. This factor complicates the management of electricity networks and compromises their stability. Faced with the depletion of oil and gas deposits, the development of the use of natural energy sources is, however, unavoidable. The FMHL+ project helps stabilise electricity production by storing surplus energy from solar and wind installations in the form of hydraulic energy in the reservoir lake. Thanks to the pumped-storage turbines, water from Lake Geneva can be stored in the reservoir, converted back into electricity and fed into the grid.

Hydraulic energy stabilises the electricity grid

With a power output increased from 240 to 420 MW and a power reserve of 60 MW, the expanded pumped storage power station at Veytaux is perfectly suited to the growing demands of today's electricity market.

The total output of the new facility will reach approximately 1000 MWh.

In addition to the increase in power, the extension offers greater flexibility for energy production as well as a high level of security of supply, the ultimate objective being to stabilise the electricity networks in Switzerland and Europe. To this end, surplus energy from solar and wind power installations is stored with a view to balancing electricity supply and demand in real time.

Special requirements

Such a project naturally involves its share of challenges, such as carrying out the work without interrupting the operation of the existing power plant or connecting the new structure to the existing reach.

The pumped-storage power station, which must meet strict requirements in terms of production flexibility, is characterised by complex operation and fast switching times. Using physical modelling tests and numerical calculations, the various parts of the installation have been verified and optimised in relation to dynamic operating models. The small- and large-scale flow modelling was carried out using the scale models of the Laboratory of Hydraulic Constructions (LCH) of the EPF Lausanne and the hydraulic, hydrological and glaciological test station of the EPF Zurich, in order to optimise the design of the installation.

Another challenge is that the project is completely underground and must be carried out from a single portal. However, this has the significant advantage that the project has no impact on the environment.

Lake Geneva as an energy plant

The existing pumped-storage power station at Veytaux (dating from 1971) consists of Lac de l'Hongrin, located at an altitude of 1250 metres and with a volume of 52 million m³ as the upper reservoir, and Lake Geneva, located at an altitude of 375 metres as the lower reservoir, an 8 km penstock (4 m in diameter), a 160 m high water tower, a 1.2 km long lined shaft and the power station cavern. The project includes the construction of a new autonomous power station cavern 57 m high, 25 m wide and 128 m long. The power station is equipped with two ternary groups with a respective turbine power of 120 MW, comprising a Pelton turbine, a motor-generator and a five-stage pump. The latter is located approximately 25 m below Lake Geneva. The existing reach, as well as the penstock, the shaft and the tailrace are largely retained as part of the project.

When the turbines are in operation, i.e. when there is a demand for energy, the water from the Hongrin reservoir flows through the turbines towards Lake Geneva. During periods of low electricity demand or excess energy, water from Lake Geneva is pumped to the upper basin to be stored until it is needed to power the turbines when electricity demand is higher again.

Efficiency and profitability

The total cost of the project is around CHF 331 million. Because it operates in pump-turbine mode, the power station consumes around 20% more electricity than the water that passes through the turbines downstream produces. However, the profitability of the installation is calculated by taking the difference between the reduced rate for electricity in pump mode and the higher rate for electricity in turbine mode.

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