The 1.8GW Grand Maison hydroelectric power station at Allemont, Isere is the biggest hydropower facility in France, as well as the biggest pumped storage hydroelectric facility in Europe.

Owned and operated by state-run Electricité de France (EDF), the Grand Maison hydroelectric has been in service since 1986.

The pumped storage hydropower project involved the construction of the Grand Maison Dam (Barrage de Grand'Maison) on L'Eau d'Olle, a tributary of the Romanche River.

The Grand Maison Dam that creates the upper reservoir was built during 1978 and 1985, while the power station started commercial operations in 1987.

The pumped storage facility can ramp up within three minutes to feed up to 1.8GW of electricity into the National Electricity Grid of France during peak demand.

The Grand Maison facility has been chosen as one of the demonstration sites for the EU-funded XFLEX HYDRO project to test a set of smart technologies for boosting the grid stabilisation capability of hydroelectric facilities.

Location and site details

The Grand Maison power station is situated in the French Alps within the Romanche valley between the Belledonne and Grandes Rousses massifs, in the southwestern Isere region of France.

Grand Maison power plant make-up

The 160m-tall and 550m-long Grand Maison rock-filled embankment dam is located at an altitude of 1,695m. It creates the facility’s upper reservoir called Lac de Grand Maison which has a storage capacity of 140 million cubic metres. The majority of water in the upper reservoir comes from melted snow.

Lac du Verney, an artificial reservoir spread over 185 acres at an altitude of 770m, forms the lower reservoir with 15 million cubic metres of storage capacity.

The Grand Maison pumped storage power station comprises two powerhouses that include an above-ground powerhouse for conventional hydropower generation and an underground powerhouse for both pumping and electricity generation.

The surface powerhouse is equipped with four multi-jet Pelton turbine generator units of 158.5MW capacity each. The head height for the powerhouse is 922m, while the total discharge capacity is 78m3/s.

The underground powerhouse which is situated 70m below the surface powerhouse measures 161m-long, 16m-wide, and 40m-high.

The underground powerhouse is equipped with eight reversible, four-stage Francis pump-turbine units. The rated capacity of each unit is 152.5MW in turbine mode and 157MW in pump mode. The head height for the underground powerhouse is 955m, while the total discharge capacities in turbine and pump modes are 144m3/s and 138m3/s, respectively.

Water flows from the upper reservoir to the powerhouses through a 7.1km-long head-race tunnel which further splits into three 1.4km-long penstocks.

Grand Maison pumped-storage operations

The Grand Maison facility operates as a peaking power plant by pumping water from the lower reservoir to the upper reservoir for storage during periods of low electricity demand and by releasing the stored water from the upper reservoir for power generation when the electricity demand is high.

The power station annually produces up to 1,420GWh of electricity and consumes up to 1,720GWh of cheap electricity for pumping and storage operations.

Contractors involved

Coyne & Bellier (now Tractebel Engie) provided the design for the Grand Maison Dam, while the other contractors involved in the dam project included Bec Frères, Bouygues Construction, Chantiers Modernes and Groupe Razel.

Andritz Hydro was the original supplier of electro-mechanical equipment for the Grand Maison hydroelectric power station.

It was also contracted to supply static excitation systems to enable back-to-back starts between all Pelton and Francis units of the facility, as part of a recent a rehabilitation programme at the Grand Maison site.

XFLEX HYDRO demonstration at Grand Maison

The Grand Maison hydroelectric facility has been selected to demonstrate the hydraulic short circuit technology for advanced control and efficiency as part of the ongoing Hydropower Extending Power System Flexibility (XFLEX HYDRO) project.

New turbine runners and advanced automation techniques will be used at the Grand Maison surface powerhouse units to test the instantaneous use of pumps and Pelton turbines for enhanced grid flexibility services by the plant.

The participants for the demonstration project at Grand Maison include EDF, Ecole Polytechnique Fédérale de Lausanne (EPFL, GE, the HES-SO University, Switzerland, and Power Vision Engineering.