Solar District Heating in Crailsheim with Seasonal Borehole Storage

In the German town of Crailsheim, 7,300 m2 of solar thermal flat plate collectors provide 50 % of the heat for a housing area with 260 units. Parts of the collectors are mounted on a noise barrier (see photo). Heat is stored in two water tanks (100 m3 and 480 m3) and in a seasonal borehole storage with 37,500 m3. The current size was originally planned as 1st phase of the solar installation. The second phase is planned to provide heat for additional houses one day, but there is no time frame for that extension. For the second phase, a collector area of 9,700 m2 (6.8 MWth) and a borehole storage of 75,800 m3 were foreseen. Nonetheless, Crailsheim is Germany´s largest solar thermal plant. The system was designed and is scientifically monitored by the Institute of Thermodynamics and Thermal Engineering (ITW) of the University of Stuttgart and the research company Solites, also based in Stuttgart, Germany. A 489 kWth high temperature heat pump transfers heat from the larger buffer storage to the smaller one when necessary, so there is always hot water at 70 °C available. The 370 kWh/m2a specific solar field yield result in 280 kWh/m2*a (2,050 MWh/year) net solar gain that are fed to the district heating network.

Photo: Solites


Name of Project / installation site

Solar District Heating Crailsheim Hirtenwiesen, town of Crailsheim, 150 km south-east of Frankfurt



Start of operations

Autumn 2005 (first part of first phase operative), May 2012 (finalising the first phase)


Solar district heating

Gross collector field size

7,300 m2 flat plate /5.1 MWth

Storage size

100 + 480 m3 buffer storage and 37,500 m3 seasonal borehole thermal energy storage

Supplied process / network

District heating network provides heating and domestic hot water for 260 housing units; supply temperature at 65 °C, return temperature at 35 °C

Specific solar yield per year

370 kWh/m²a

Predicted solar share in process


Customer / operator

Stadtwerke Crailsheim (public utility), Germany

Planning / construction

  • Project development: Stadtwerke Crailsheim , Solites, both Germany
  • System planning:  HGC GmbH Hamburg. Germany
  • BTES storage planning: Kohlsch /EWS GmbH, Germany (insolvency during planning), Stadtwerke Crailsheim, Solites
  • Buffer storage planning: engineering office Lichtenfels, Germany

Collector manufacturer

Three German collector manufacturers: Wagner, Schüco, and Aquasol and the Austrian collector manufacturer Ökotech (today Asgard)


Sebastian Kurz,

More information


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