Progress in Solar Thermal Energy in District Heating: Only minor growth made in 2024

Setting the scene in Germany last year, 2024, we saw the launch of three large-scale solar thermal power stations. These included solar thermal energy systems for district heating in Ammerbuch-Breitenholz in Baden-Württemberg, which laid claim to a 1.4 MW capacity generated by 2,045 m2 vacuum tube collectors. On top of this, Sondershausen in Thuringia saw a system with a 4.3 MW capacity backed by 6,086 m2 high-temperature flat panel collectors. Lastly, Häusern in Baden-Württemberg boasted a system with a 1.2 MW capacity powered by 1,733 m2 vacuum tube collectors.

A summarized update from March 2025 indicates that Germany is home to 61 solar heating networks. These pack a combined 173,275 m2 gross collector area, which translates to 121 MW of solar capacity. At the moment, orders for 16 additional large-scale solar thermal plants have been granted. Some of these are already in the construction phase, including a car park roof in Regensburg and a solar thermal village facility in Bracht, Hessen. Stralsund is building one of the biggest solar heating plants while Leipzig's utility companies are creating Germany's currently largest solar thermal plant. Large solar heating works are also in the planning or construction stages in Bad Rappenau, Steyerberg and Tübingen.

Expectations for 2026: Solar Thermal Energy in District Heating Doubles These solar thermal plants are set to inject an additional 135 MW of solar thermal power after commissioning in 2026, substantially more than doubling the total installed capacity compared to 2024.

However, this expansion of solar district heating is not enough. To facilitate the heat transition, significant acceleration in project planning and approval is necessary. The mentioned solar heating plants have had long administrative lead times, much of which was spent finding suitable land, creating building rights and obtaining approval.

An outlook report, "Future of District Heating", suggests that it would be sensible to provide 4 TWH/year of heat through solar thermal power in the German district heating mix by 2045. This equates to just over 2% of German heat demand for heating networks but would equate to approximately 7 GW of heating capacity. To achieve this, around 500,000 m2 of gross solar thermal collector area should be put into operation annually.

Political Framework Remains Uncertain Hamilton's ability to implement completed heat planning with solar thermal power as a heating network supplier quickly depends largely on the upcoming federal government's political framework and the structuring of necessary investment support. As it stands, federal funding for efficient heating networks (BEW) is only available until September 2028.

Similarly, the implementation of the European Directive REDIII will occur in the upcoming legislative period. To significantly ramp up the expansion of renewable energies, the federal government must integrate so-called "acceleration zones" into German planning law. First drafts show drastic changes in local land use planning, potentially allowing solar energy infrastructures and heat storage to be built in the absence of zoning plans. The new area types "Solar Energy Area" and "Acceleration Area" (new Building Code §§249b and c) could simplify building rights in the land-use planning for municipalities, making it considerably easier to build large solar thermal plants for heating networks, if municipalities use this new planning law tool.

Non-European Trends: Concentrated Solar Thermal (CST) On the international front, there's a growing use of concentrated solar thermal (CST) outside Europe. CST usually employs curved parabolic mirrors that track the solar path. This system allows collectors to be capable of either tuning out of the sun or following it, adjusting the power supply as needed. The heat provided, depending on the collector technology, can vary between 50 and 800 degrees Celsius, making this an ideal heat generator for heating networks or industrial process heat.

For more information on CST technologies and their potential applications, check out the workshop "Future of Concentrated Solar Thermal Systems" taking place on 20 May 2025 at the Symposium Zukunft Wärme in Kloster Banz. This workshop is organized by the research project ProSolNetz, in which Solites is involved.