From Energie Steiermarks central District heating plant in Graz, the major part of the City’s District Heating  with a peak load of 550 MW and an annual demand of app. 1200 GWh supplied to the town and some villages around. At the time of construction, winter time supply was mainly from CHP and summer time DH supply mainly from gas heating plants. Therefore it was aimed to learn about the potential of integration of solar thermal and to reduce CO2-emissions by use of solar thermal.

In 2007, 3.5 MW (5000 m²) of solar thermal were built next to the heating plant on the roofs of the municipal recycling center. Later, areas at the heating plant became available and a collector field for all DH feed-in, testing and comparison was installed. Collectors of 7 different manufacturers and of different technologies were installed. Those collectors were tested and evaluated in R&D projects.

The project is owned by the solar energy service company solar.nahwärme and the heat is sold to Energie Steiermark. The project is an important part of the efforts of the city and of the utility to make the district heating supply greener and more sustainable. It is planned to further increase the solar share in Graz district heating in the future.