The main power station in Mayrhofen has produced around 670 million kWh of electric energy annually since 1970. It consists mainly of the Stillup Reservoir and a working water conduit that supplies water to the power plant in Mayrhofen. The dam at the Stillup Reservoir lies at an altitude of 1,120 metres above sea level. This reservoir is located at the rear of the Stillup Valley, one of the subsidiary valleys that begins behind Mayrhofen. 6.6 million m³ of water is stored in the reservoir. The dam was built over a length of 480 metres with a central core of asphalt concrete The dam and its base are constantly monitored for impermeability using a complex measuring system. The Stillup Reservoir is the key point of the Zemm-Ziller power plant group. It has a double function as reservoir for the Mayrhofen Power Plant as well as water supply from where the Rosshag and Häusling sub-power plants can pump water back into the Schelgeis and Zillergründl Reservoirs.
Six machine units with a combined power output of 345,000 kW are housed in the Power Plant, at the end of the Tuxer Strasse. One machine unit consists of a generator and double Pelton turbine. TECHNICAL DATA Power plant type: annual storage power plant In operation since: 1969/1970 Annual power output: approx. 670 million kwh Conduit drop height: 469.7m The Zemm-Ziller Power Plant Group consists essentially of two upper stages; the pump storage plants at Rosshag and Häusling with the Schelegies and Zillergründl Reservoirs, which are each located in one of the four subsidiary valleys behind Mayrhofen, as well as the main plant in Mayrhofen with its feeder reservoir, the Stillup. Together with the Gunggl, Bösdornau and Tuxbach plants, the Zemm-Ziller power plant group has a combined output of 965.700 kW, plus 600.000 kW from the Rosshag and Häusling plants. This results in a power output range of over 1.5 million kW, making it the most powerful storage plant group in Austria. Annual production is around 1.7 billion kWh