The Malta Main Stage pumped storage power plant in Rottau is the core element of the Malta-Reisseck power plant group. The three-stage power plant group was constructed from 1971 to 1979.
The Malta Main Stage power plant, along with the Rottau power station, is located in the Mölltal Valley. Four machine units with a vertical shaft and a nominal capacity of altogether 730 MW have been installed. Two machine units are each made up of a 6-nozzle Pelton turbine and one generator. Both of the other machine units are additionally equipped with a 4-level storage pump, a hydraulic converter and a motor generator instead of a generator.
Galgenbichl pre-storage basin
The pre-storage basin of Galgenbichl serves as an intermediate storage basin for water from the stream diversion and as an equalizing basin for turbine operation in the Galgenbichl power station. From here, the water can be pumped into and stored in the roughly 200 m high annual storage reservoir in Kölnbrein or diverted to the Rottau power station via the waterway and processed into peak current. The dam of the Galgenbichl pre-storage basin is made up of two dam constructions, a 50 m high gravel fill dam with asphalt concrete dam watertight blanket and a 15 m high concrete gravity dam.
Gösskar compensation reservoir
Along with the Göss streams, the Gösskar compensation storage reservoir has the task of minimising the loss of the flow rate. The dam constructions for the Gösskar compensation reservoir makes up the Gösskar dam, a 55 m high gravel fill dam with asphalt concrete dam watertight blanket.
The reservoir is connected to the Malta Main Stage power plant head race tunnel via a 180 m long tunnel with a diameter of 4 m. The maximum operating level of both reservoirs is 1,704 m, the cubic capacity is altogether around 6.2 million m3.
Rottau compensation reservoir
The Möll River is dammed up in the Rottau Valley floor in the weir system and thus makes up an almost 2 km long equalizing basin, which due to its design gives the impression of being a naturally formed lake. It serves as an equalizer for turbine operation at the Rottau power plant as well as an extraction basin for the storage pumps.