Vianden is a picturesque town nestling in the Our valley and overlooked by a magnificent medieval chateau. Less well know is that hidden in the mountain behind the chateau is one of the largest pump storage systems in Europe. Plans are afoot to enlarge the system and this was the catalyst for the ICE Luxembourg Local Association on Friday 11th June 2010.
The system was conceived as a joint Luxembourg German initiative with mixed ownership (Luxembourg State and RWE Power AG of Essen) and operated under a concession. Its objective is to supply peak power to the German grid consisting of coal and nuclear base load stations. The Luxembourg demand is small by comparison but the system is integrated. A new development is the increase in wind power requiring energy storage and this has encouraged the need to expand the station.
The system comprises an upper reservoir perched on the top of the mountain (and providing almost the highest point in Luxembourg) with a volume of 7 million M3 and a lower reservoir provided by a 30 m high dam, 300 m below. The powerhouse currently comprises 10 units with total turbine capacity of 1100 MW. Nine of the units are horizontal with the turbine connected to a motor-generator and coupled (or disconnected) to a separate pump. The 10th unit is larger (200 MW) and with recent technology has allowed a simpler vertical axis with the turbine and pump combined in one unit. The new 11th unit will be similar and requires a separate water tunnels and access, and so significant civil works and costs will be needed. The main turbine-pump hall is a cavern of 330 m long, 30 m high and 17 m wide, luckily in very sound rock. Normal daily operation is seven hours pumping and four hours generating with an overall efficiency of 75%.
The expansion project is to provide further equipment capacity (200 MW) as mentioned and requires an increase in the upper storage by heightening the surrounding dykes to give a final volume of 11 million M3. In this way the increasing needs of electrical energy storage in the interconnected European grid will be partially met. This is becoming more important with the increased use of wind energy with its variable supply.
Members had an excellent guide from the operating company SEO to show us around and to explain the complexity of the operation and its optimisation. Work on the new project has started on the upper reservoir but not yet below ground. We hope to make another visit in about 18 months time to see the underground construction site in action.
Peter Bond, ICE representative for Luxembourg