The 450MW (3 x 150MW) underground plant is located near the Ill river in Montafon Valley in west Austria, in the province of Vorarlberg.
The facility is operating with separate pumps and Pelton turbines instead of reversible pump turbines. The design enables both turbines and pumps to be operated at the same time in “short hydraulic circuits”.
There is a head difference of just over 800m between the Kops upper reservoir and the Rifa lower, balancing reservoir. The pressure tunnel to the plant is 5.5km long and is of 4.9m diameter, there is a two-chamber surge tank and an almost 1.2km long, 3.8m wide steel penstock.
Voith Hydro and Andritz Hydro supplied the pumps and turbines, respectively, plus other equipment.
Construction of the plant started in late 2004 and underground excavation was undertaken for the powerhouse and transformer caverns and associated tunnels to late 2005. The powerhouse cavern is 88m long, 30.5m wide and 60.5m high.
It was originally planned to have all units commissioned by the first half of 2008.
