The most important factor determining the planning of Mellach district heating power plant was the phasing out of nuclear power following the referendum on Zwentendorf power plant in November 1978. A decision was taken to construct a new district heating power plant to cover the demand for electrical energy in the winter months and produce district heating.
Steirische Wasserkraft- und Elektrizitäts-AG (STEWEAG) commenced planning early in 1979. Several points favoured a location south of Graz. The close proximity to the Mur allowed once-through cooling with fresh water. In addition, Graz district heating power plant, which is located nearby, could be used as a distribution point for the district heating, road and rail connections could be established and the electrical energy could be dissipated in a cost-effective manner.
When the original plan to construct the power plant in Kalsdorf failed due to the height of the stack and a further location in Werndorf was not approved due to nature protection issues, a decision was taken to construct the power plant in Mellach. Although the district heating pipeline to Graz already extended over a route of 17 km, the proximity to the thermal power plant Neudorf-Werndorf and the planned Mellach power plant on the Mur brought infrastructural advantages.
Following the evaluation of an interdisciplinary opinion, the construction decision was taken in November 1980 and the submissions to the authorities were made in 1981. A decision in accordance with the Steam Boiler Emissions Law [Dampfkesselemissionsgesetz (DKEG)] was rendered in April and May 1982 and approval was gained to use the lands. The construction permit was issued in 1983. Numerous appeals were filed against the positive decision and the approval process therefore went to the authority in the second instance. The decisions issued in January, April and June 1983, which were subject to extensive requirements relating, in particular, to the flue-gas desulphurisation, were also positive.
Complaints against the decision in accordance with the Steam Boiler Emissions Law were, however, filed and, as a result, the second instance decision issued by the Administrative Tribunal was overturned. The appeal hearing in July 1984 stipulated adherence to much stricter limits, also relating to flue gas denitrification, thus necessitating the subsequent integration of a denitrification system. In summer 1986, the supreme court overturned the existing decision in accordance with the Steam Boiler Emissions Law on the grounds that Steirische Wasserkraft- und Elektrizitäts-AG (STEWEAG) had not obtained an approval for the plant under industrial law. The requirements for the outstanding approval now orientated on the draft of the third implementation directive of the Steam Boiler Emissions Law.
Parallel to the approval process, Steirische Wasserkraft- und Elektrizitäts-AG (STEWEAG) proceeded to the greatest possible extent with the planning work for the power plant. Following the organisation of a design contest, the architect Walther Kordon was commissioned to handle the architectural design. The official turning of the first sod took place in July 1983. The work was carried out by Allgemeine Österreichische Baugesellschaft - A. Porr AG. While constructing the power plant a bridge was built over the Mur. This bridge accommodated some of the traffic to and from the construction site and also accommodates the railway tracks for the coal wagons.
Extensive sealing work was necessary to prevent groundwater from soaking in. On completion of the substructure for the machine hall, the stair tower – also known as the "traffic tower" was erected next to the boiler house. The assembly of the steel lattice formwork of the boiler house commenced in April 1984. The stack was erected by the company Mayreder in 1984. On average, the stack was raised 4.88 m per day. A height of 172 m was reached after 35 days.
Work on the construction of the district heating pipeline to Graz commenced in August 1984. Following the construction of the bunker system and the gantry platform for the coal spreaders, the first train carrying Polish hard coal arrived at the power plant on 10 June 1985. The condensing turbine was delivered from Switzerland at the end of July 1985. The assembly of the environmental protection facilities commenced in autumn of the same year. Trial operation of the power plant finally got underway in December 1986.
In 1986, Porzellanfabrik Frauenthal GmbH in West Styria was awarded the Environmental Oscar for the catalytic converters used in Mellach power plant. In spring 1992, cracks occurred in the turbine housing. In the course of the repair work during the summer months, which involved the clamping of the cracks, measuring equipment was attached to the machines. New turbine housing was constructed in 1993 and additional construction improvement measures were implemented. In March 1995, the first eco audit was carried out in accordance with the EU standard EMAS. In 1996, Mellach district heating power plant was awarded the Eco Audit for being the cleanest power plant in Europe:
Work on the construction of a sludge incineration plant commenced in Mellach district heating power plant in March 2003 and trial operation started in November of the same year. Following negotiations with the authorities in 2004 and the issuing of a positive decision in January 2005, the plant was commissioned in October 2005 after a six-month construction period. Within the framework of the "Fast Forward Awards", VERBUND-Austrian Thermal Power GmbH & Co KG (ATP) and the Saubermacher Dienstleistungs AG were awarded the special "Ecotechnik" prize in June 2005.
VERBUND-Austrian Thermal Power GmbH & Co KG (ATP) plans to construct a gas and steam turbine combination power plant near the eastern coal stock. The Environmental Impact Declaration for this project was prepared in 2003 and in 2005 official negotiations took place in accordance with the Environmental Impact Analysis Law.