French hydropower plant aims to increase efficiency and flexibility

The Grand'Maison hydropower plant in the French Alps is testing how Hydraulic Short Circuit (HSC) technology can enable the simultaneous use of very high head pumps and Pelton turbines, using smart digital controls.

HSC allows the tandem operation of the pumps and turbines. It is expected that this technology will enhance the efficiency of the plant and the flexibility services it can deliver to the electricity grid.

Grand'Maison is Europe’s largest pumped storage hydropower plant, at 1,800 MW capacity. The plant has multiple production units including four Pelton turbines and eight reversible pump-turbines. It is one of two EDF hydropower plants involved in the European Union (EU)-funded XFLEX HYDRO initiative.

The initiative is demonstrating how smart hydropower technologies can deliver a low-carbon, reliable and resilient power system. There are 19 organisations participating in demonstrations across France, Portugal and Switzerland.

During the project, one of the four Pelton turbines at Grand'Maison will be operated using HSC mode to offer a new option of frequency control in pumping mode. For this purpose, new turbine runners – as well as smart digital controls developed for the XFLEX HYDRO project, the Smart Power Plant Supervisor (SPPS) – have been implemented for efficiency and flexibility improvements.

“The demonstration phase will provide in-situ data to assess the actual impact of running this mode on the plant, in terms of water cycling, pressure effects and much more,” says Marvyn Mariette, Deputy Plant Manager at EDF.

Jean-Louis Drommi, Electrical Expert at EDF, who is leading the project, says the initial phase of the demonstration focused on modelling and computer science performed by project partners: “The plant controls and the master optimisation algorithm had to be updated in order to allow for the simultaneous operation of the pumps and turbines, which is the core of the HSC.”

Two test campaigns were performed in May 2021, followed by a successful trial of the demonstration for two weeks in June. The official demonstration started in September.

The EDF Grand'Maison hydropower plant in France is taking part in the EU-funded XFLEX HYDRO initiative. Credit: EDF and XFLEX HYDRO project / EU Horizon 2020 grant No 857832 / Photographer: Mathias Magg.

The demonstration’s objectives are to:

  • Maximise plant performance and increase flexibility using HSC and smart digital controls (the SPPS) to extend the plant operating range and regulate the power in pumping mode.
  • Improve maintenance intervals and minimum outage times via the SPPS.

Swiss company Power Vision Engineering (PVE) contributed to the modelling and computer simulation and is a supplier of the HydroClone innovative Real-Time Simulation Monitoring (RTSM) system being used in the demonstration.

Dr. Christophe Nicolet, Managing Director at PVE, says: “A 1-D simulation model of the whole plant was established and validated with the measurements […] to ensure that the extreme pressure and the water level in the surge tank remains always within the allowable limits, to guarantee a safe and reliable operation with increased flexibility.”

Another Swiss project partner, university HES-SO Valais-Wallis, oversees the modelling, numerical analysis and prototype measurements on the demonstration. Commenting on the results of 3-D flow simulations performed to predict energy losses as well as turbulent flow instabilities, Professor Dr. Cecile Munch-Alligne, Professor in Hydraulic Energy, says: “The numerical results have shown relatively low energy losses, representing less than 0.5 percent of the head. Turbulent flow and instability have been predicted, but at this stage we don’t expect that they will negatively affect the machine or the pipes.”

Guillaume Rudelle, Hydro Senior Product Manager at GE Renewable Energy in France, is leading on the development of solutions to extend flexibility services on the demonstration. “GE performed two test campaigns on-site at Grand'Maison. Key mechanical components on the rotating units as well as waterway flows were investigated on the trials. The turbine and pump behavior were excellent. No adverse effects or issues were detected,” he says.

“All results give us confidence that HSC at the Grand'Maison scheme can become an industrial operating mode.

Swiss research institute and university EPFL is also involved in the demonstration.

A new video about the Grand'Maison demonstration has recently been released.

XFLEX HYDRO is a four-year project running until 2023 and has been funded by the EU’s Horizon 2020 research and innovation programme.

For more information about the project and to sign-up for progress updates, visit