The IEA TCP SHC has set the goal that by 2050, solar energy technologies will cover more than 50% of the heating and cooling demand for buildings, thereby making a significant contribution to reducing global CO₂ emissions.

In this context, IEA SHC Task 55 was carried out, focusing on the technical and economic parameters and requirements of very large solar thermal plants (>0.5 MW up to the GW scale). The work on solar district heating systems was continued, deepened, and expanded with new questions and developments in Task 68 – Efficient Solar District Heating Systems.

Task 68 pursued four main objectives:

1. Efficient provision of heat at the desired temperature level for district heating systems
2. Increasing the degree of digitalization of solar thermal systems
3. Reducing the costs of solar district heating systems and identifying new business models
4. Raising awareness and disseminating results on solar district heating systems in a well-founded manner

Task 68 provided a platform for industry and research to jointly address the opportunities, challenges, and benefits associated with these main objectives at an international level – under Austrian leadership. For this purpose, Task 68 was structured into four Subtasks, as shown in the following figure.

In addition to leading the overall Task, Austria was also responsible for coordinating Subtask B. Moreover, leading Austrian experts from industry and research were actively involved in the national consortium. A logo board illustrating international cooperation is shown in the figure below.

Key findings from the project

• Technology: Modern collector types can reliably deliver heat even above 100 °C. Solar fractions of up to 20 % can be achieved in district heating systems; significantly higher shares are possible when combined with seasonal storage.
• Digitalization: Standardized data acquisition, AI-based fault detection, and predictive control strategies enable more reliable operation, faster fault correction, and efficiency gains of up to 15 %.
• Economics: According to expert assessments, investment costs can be reduced by approximately 11 %, operating costs by around 9 %, and life-cycle costs by about 22 % through standardization, industrial prefabrication, larger systems, and optimised planning.
• Policy & Market: Long-term stable heat prices and high security of supply are achievable but require attractive financing models, adapted support schemes, and improved data availability.

Conclusion

Solar district heating is technologically mature, economically competitive, and a key solution for decarbonizing urban heating networks – provided that the potential of digitalization is harnessed and suitable framework conditions are established.

Concrete results from the project, to which the Austrian consortium made substantial contributions, include an AI-based fault detection algorithm, a rule-based predictive control algorithm for the operation of solar thermal plants with storage, a comprehensive overview of open data in the solar thermal sector, and a guide to ISO 24194:2022 for performance assessment. These results will continue to inform future work on standard development and implementation, including through open-source software.

Project management

Klaus Lichtenegger
BEST – Bioenergy and Sustainable Technologies GmbH
Inffeldgasse 21b, 8010Graz
E-Mail: klaus.lichtenegger@best-research.eu
Web: best-research.eu

Project partners

Christoph Rohringer
AEE - Institut für Nachhaltige Technologien
Feldgasse 19, 8200 Gleisdorf
E-Mail: c.rohringer@aee.at

Thomas Natiesta
AIT Austrian Institute of Technology GmbH
Giefinggasse 4, 1210 Wien
E-Mail: thomas.natiesta@ait.ac.at

Maria Moser
SOLID Solar Energy Systems GmbH
Am Pfangberg 117, 8045 Graz-Andritz
E-Mail: m.moser@solid.at

Fabian Ochs
Universität Innsbruck – Institut für Konstruktion und Materialwissenschaften
Technikerstraße 13, 6020 Innsbruck
E-Mail: fabian.ochs@uibk.ac.at

Austria (Operating Agent), China, Denmark, Finland*, France, Germany, Israel, Italy, Netherlands, Poland, Spain, Sweden, Switzerland, United Kingdom

* via cooperation with TCP District Heating and Cooling (DHC)