Upstream of the Romanche Valley

Published on 31 January 2008 (updated on 1 February 2008)
(EDF Photo library)

The Grand’Maison "high head" dam is located upstream of the Romanche valley. It uses 8 pump turbines to drive water back up to the upper pondage in order to store it for use during periods of high demand.

The most powerful hydro-electric power stations in France are at Grand’Maison at the boundary between the Départements of Savoie and Isère in the French Alps. The dams are located on a bend of a tributary of the Romanche, the Eau D’Olle, between the Belledone and Grandes Rousses ranges.

The power station has a total output of 1820MW (12 turbine sets each producing 150MW). Its annual production of 1,420GWh (Gigawatt hours) accounts for 8% of France’s hydro-electric power. The total amount of power required for pumping is 1,720 (i.e. an overall loss of 300GWh or 30%). The rate of flow is of little importance at this mountain site, what matters is the 950 metre drop.

The Grand’Maison power station is unusual in that used water can be pumped back to the upper pondage by 8 turbine-pumps. The Grand’Maison dam is at an altitude of 1,700m and can store 140 million m3 of water, about 100 of which comes from melted snow. The potential energy drives the turbines during periods of high demand. A pondage downstream of the dam stores some of the water that has already passed through the turbines. This lower pondage (which is at an altidude of 770m at Verney) has a capacity of 15 million m3, i.e. one-tenth that of the upper pond at Grand’Maison. Because of the water reutilization cycle, the total volume of water that can be used every year is five times that of the upper pondage, i.e. 700 million m3.