In 2022, 91,000 solar thermal systems with 710,000 m² gross area were installed the Germany. This amounts to an increase of the solar thermal power by 460 MW. The total collector area installed in 2022 amounts to 22.1 million m² in approx. 2.6 million solar thermal systems with a thermal capacity of 14.4 GW (Bundesverband Solarwirtschaft e. V. (March 2023) https://www.solarwirtschaft.de/presse/marktdaten/).

After the record high in 2008, the newly installed solar thermal capacity has been decreasing each year. In 2019, it was down to 360 MW. Since then, it started to slightly increase again, reaching its latest highpoint in 2022, with a 12% increase compared to 2021.

The share of renewable energy sources in final energy consumption for heating and cooling in Germany increased more in 2022 than in previous years, reaching 17.4 percent in 2022, compared to 15.8 percent in 2021. Between 2000 and 2022, the share of solar thermal energy grew from 2 to 5 percent of the total renewable heat in Germany (https://www.umweltbundesamt.de/themen/klima-energie/erneuerbare-energien/erneuerbare-energien-in-zahlen?sprungmarke=waerme%23waerme).

The majority of the solar thermal market still consists of collector arrays on single or two-family houses. Solar thermal is not only integrated in existing gas heating systems but a combination of solar thermal and heat pump systems or pellet heating systems is chosen to achieve a full coverage of renewable energies. There is also a growing market for solar district heating grids and a high potential for solar process heat systems. The demand from public utilities and municipalities is growing, especially with respect to megawatt-scale solar cogeneration plants for feeding into local and district heating networks. Low prices of down to 4 Ct/kWh are one of the driving factors. In 2022, energy providers added eight new heating plants with a total collector capacity of about 30 MW. This corresponds to around 6 % of the solar thermal additions.

Solar District Heating

The solar district heating market has been growing for several years and is picking up speed. Today, there are 49 large-scale solar thermal plants with a total of 146,206 m² in Germany (https://www.solare-waermenetze.de/2023/03/28/solare-waermenetze-in-betrieb-2023/). 33,879 m² of new solar collector areas have been built last year, leading to an increase of the total collector area by 30 percent compared to the previous year's level. The calculated thermal output of district heating solar thermal systems in Germany has thus reached the three-digit megawatt range for the first time, as up to 102 megawatts of solar thermal energy can be fed into district heating.

The strong growth in 2022 is mainly due to the commissioning of the largest solar thermal system in Germany in Greifswald (M-V) with 18,732 m² of collector area alone. This plant has overtaken the former largest plant of Ludwigsburg-Kornwestheim utilities with 14,800 m2. In addition, the third largest system in Lemgo went into operation in 2022 (9,118 m², NRW).

Experts estimate that 15% of district heating in 2050 could be solar (according to 30 million m²). Broad marketing measures were done within the context of the project “SOLNet4.0” and follow up project “SOLNetplus”. Integration of solar thermal systems into heating network systems is expected to expand but remains still ambitious, as nearly all heating networks operate at temperatures from 80° to 130°C requiring highly efficient collectors.

In the past, so called solar assisted bioenergy villages - smaller communities in rural areas- switched from de-central heating oil boilers in every single house to small district heating networks, using renewable energy sources. Solar thermal plants provide the entire heating demand in summer, often combined with large biomass boilers for the winter periods. In 2013, the first solar district heating plant of this type went into operation in the village of Büsingen in the southwestern part of Germany. Another eight plants followed, five of them in the year 2018: Mengsberg (2,950 m²), Randegg (2,400 m²), Liggeringen (1,068 m²), Ellern (1,245 m²), Hallerndorf (1,304 m²), Moosach (1,067 m²), Schluchsee in 2019 (3,364 m²).

Industry

The market for solar process heat in Germany currently totals around 450 systems (2022). In 2022, only 5 new installations went into operation. Solar thermal energy thus remains a niche application in the industrial environment despite good funding conditions. Smaller plants are mainly built in the commercial sector. The largest system currently under construction is the 2,145 m² system for the gas pressure control system for among others the EUGAL natural gas pipeline. Plants with concentrating collectors have a promising range of applications in this field, but there is no plant on the market so far. Guidelines in addition with fact sheets are available on the webpage http://www.solare-prozesswärme.info.

The most typical applications in Germany are still small systems for domestic hot water and space heating for single and two-family houses. Growing markets with great potential are in the field of solar process heat for industrial applications and solar district heating systems as well as smart solar thermal grids. In the last years several large solar thermal systems were installed as demonstration projects.

Solar district heating systems:

• Germans largest solar thermal system in Greifswald, has a gross area of 18,700 m², followed by Ludwigsburg-Kornwestheim with 14,500 m² and Senftenberg with 8,300 m².
• In Crailsheim, 7,500m² of flat plat collectors for district heating and a 39,000 m³ seasonal borehole thermal energy storage were installed. This is still the largest plant with seasonal storage.
• The 2,312 m² system in Dettenhausen (B-W) also deserves a special mention, as it is the largest solar thermal system on a roof. This is in contrast to the other solar heating networks, which mostly rely on more cost-effective ground-mounted systems.
• Büsingen (near Konstanz and close to Switzerland) is Germany´s first solar assisted bioenergy village. More than 1,000 m² CPC vacuum tube collectors are integrated in a newly installed heating network combined with biomass heating. Heat energy price is less than 40 €/MWh.
• Other smaller projects include Bernburg (8,603m²), Potsdam (5157m²), Halle (5091m²) and Ettenheim (1750 m²).

Solar process heat systems:

• In Grafenhausen, with 1,000 m² vacuum tube collectors one of the biggest process heat systems for the brewery Rothaus went into operation in 2018.
• A large plant of the company ONTRAS Gastransport GmbH with a total collector area of 2,145 m² for preheating the gas in the gas pressure regulator station is currently still under construction.

The growing demand for solar thermal in recent years is driven mainly by the high energy prices. Moreover, feed-in-tariffs for PV are much less profitable today than they were years ago. However, there are political funding programs contributing to the market growth.

In Germany, 58% of the final energy consumption is attributable to heat applications (BDEW_2022), with 35% of the final energy consumption being used in applications below 100°C for space heating, domestic hot water, and process heating and heating network, which amounts to 60% of the overall heating demand.

With the amendment to the Climate Change Act, Germany intends to achieve greenhouse gas neutrality by 2045. These goals can only be achieved by reducing the total energy consumption by 50% in 2045 and by the decarbonisation of various sectors, which requires the increase of renewable energies to 60% of the primary energy consumption (FhG ISE). By 2030, a greenhouse gas reduction by 65% is aimed for. Last year, Germany's greenhouse gas emissions fell only slightly compared to the previous year: by 1.9 percent or 15 million tonnes. Around 746 million tonnes of CO₂ equivalents were still released in 2022. The annual target for greenhouse gas emissions was hence met overall in 2022. However, the results for the individual sectors differ significantly: while the targets were met by far in the agriculture and waste sectors, the buildings sector however, missed its target by 4.6 million tonnes of CO₂ equivalents.

One major aspect of the energy transition is the heat transition, which has increasingly come into focus. The heat transition requires insulated buildings and a switch to renewable heat in individual heating systems and in heat grids. According to the plans of the Ministry of Economics, heat pumps play a key role in the heat transition, both in individual buildings, for supplying heat grids and for providing process heat in industry and commerce. All output ranges up to large heat pumps are to be considered and existing heat sources are to be tapped, e.g. waste heat, geothermal energy and solar thermal energy.

The goal is to install 500,000 new heat pumps per year from 2024 onwards, so that 6 million heat pumps will be installed in 2030. In the first quarter of 2023, more than 90,000 heat pumps have already been installed.

Various cornerstones have entered into force or are being drafted in this regard.

• The Federal funding for efficient buildings (Bundesförderung für effiziente Gebäude, BEG) is an attractive national program for funding energy efficient buildings that financially supports house owners with certain renovations, e.g. the improvement of the insulation, the optimization or exchange of heating systems, etc. A 25-35% funding of the acquisition and installation costs is granted, if a solar thermal system is installed instead of an old heating system. The Federal Office of Economics and Export Control reported that there has been a 75% increase of grant applications in 2022 in comparison to 2021 for solar thermal heating systems.
• The Building Energy Act (GEG) came into force in November 2020. The GEG contains requirements for the energy quality of buildings, the preparation and use of energy performance certificates and the use of renewable energies in buildings. The applicable European requirements for the energy performance of buildings were fully implemented with the GEG 2020 and the regulation of the lowest energy building was integrated into the energy conservation law. The Federal Cabinet adopted the amendment to the Building Energy Act in April 2023. The parliamentary procedure in the Bundestag and Bundesrat now follows. The amendment to the GEG requires, that starting from January 2024, every new heating system both in new buildings and in existing buildings must meet a minimum share of 65% renewable energies. This applies to both residential and non-residential buildings. Therefore, there will be no more natural gas-only heating systems.
• Another measure adopted in the government's coalition agreement is the solar roof obligation for all commercial buildings and, as a rule, in new private construction. The obligation stipulates that the entire suitable roof area should be used as far as possible. Both PV and solar thermal energy can be used. However, there are major differences in the requirements between the individual federal states. In addition, a photovoltaics strategie has been presented in Mai 2023 (BMWK, 2023) and documents the necessary measures in the various fields of action. It covered aspects such as the required extension of ground-mounted systems, grid connections, shortage of skilled workers and corresponding tax laws.
• In addition, the federal subsidy for efficient heating networks (Bundesförderung für effiziente Wärmenetze, BEW) was recently launched - a central measure for the new construction, expansion and conversion of heating networks. Solar thermal projects are supported with both investment cost subsidies and operating cost subsidies.
• New pricing of CO₂ emmissions: The Climate Action Programme 2030 has been adopted in November 2019. An important element of the Climate Action Programme 2030 is the new national carbon pricing system, which now includes the transport and building sectors in addition to industry and the energy sector. The national emissions trading system has been launched in 2021 with a fixed price system. A price per tonne CO₂ will be set at political level, starting at 25 euros per tonne CO₂ in 2021, and gradually increasing to 55 euros per tonne by 2025. A price corridor of at least 55 and at most 65 euros is to apply for the year 2026.

In Germany, sales of solar collectors declined sharply between 2009 and 2019. The number of manufacturers of stationary collectors, i.e. flat-plate, vacuum tube and air collectors, has almost halved. Of the 38 German companies that were listed in the World Map of the Solar Thermal Industry of Solrico in 2015, only 23 are still producing in 2022. Four companies have switched to OEM collectors, six have stopped collector production and four companies no longer exist (https://solarthermalworld.org/news/strongly-downsized-but-crisis-ridden-solar-collector-industry-in-germany/).

The market leaders for large scale systems for solar heating network integration and process heat integration are the companies Ritter XL Solar GmbH and Viessmann.

German manufacturers are also trying to enter the market for applications in heat grids and process heat with concentrating solar thermal. However, CST is still quite unknown and due to a lack of examples in Germany there is also a lot of hesitation. Therefore, no commercial plants with parabolic trough or Fresnel collectors have been built in Germany yet.

The German solar thermal industry employed around 20,000 people in 2016, including installers and distributers (database 2016).

The costs for solar thermal energy in Germany range between 10-15 Cent/kWh for hot water and space heating in single and multi-family houses and 5-10 Cent/kWh for large scale systems.

The specific system cost are in the range of 250 to 400 €/m² for flat-plate collectors and 500 to 600 €/m² for evacuated tube collectors, not including installation costs or thermal storage. Costs differ between small and large scale solar systems as well as between systems for domestic hot water and space heating or large systems with and without seasonal storage. For large solar process heating systems and solar assisted heating grids costs from 4-7 Cent/kWh have been realized, 5-3 Cent/kWh could be reached.

The goal of the German solar heating roadmap is to reduce the costs of a solar heating system by a total of 50% by the year 2030. Cost reduction of solar thermal systems is one of the main targets of R&D.

Other key topics are:

• Pre-configured and standardized and simplified quick assembly of the components to reduce installation costs and installation errors
• Advanced building integration and system integration of solar heat and solar power (PV, PVT)
• Solar active houses with higher (up to 100%) solar fraction for heat and power for single and multi-family houses

In Germany, all types of solar technologies for buildings and industry are subject to research, demonstration and market activities. Continuity in national funding schemes for R&D is guaranteed by the 7^th Energy research programme of the German government. The buildings and neighbourhoods sector as well as the trade commerce services and industry sector comprises a broad range of R&D topics.

In the course of sector coupling, buildings and neighbourhoods will in future have to interact more with the power and also transport system, because linking the building infrastructure with energy supply in the transport sector, using vehicles as storage units for locally produced renewable energies, for example, can contribute to improving the climate footprint and energy efficiency.

So called “passive houses” are popular, over 10,000 units were built in Germany according to the “passive house standard” (ig-passivhaus.de), 10% of these certified by the passive house institute (data base 2016).

By the end of 2016, more than 2,200 solar active houses, so-called “Sonnenhäuser” (so called “sunhouses”) were built in Germany.

Additionally efficiency house plus initiative is worth mentioning: grid connected PV provides electricity for a heat pump based heating system and power for appliances. The main problem is the higher primary energy demand as this concept needs electricity from the grid in wintertime.

Again, attractive feed-in-tariffs for PV are today less profitable than there were years ago. In combination with the German BEG – an attractive programme for funding energy efficient buildings (see above) - this framework helped the market growth.

More and more federal states and cities implement “solar obligations”, in many cases PV obligations with strong impact for solar thermal technology.

In addition, the new pricing of CO₂ emmissions in the scope of the Climate Action Programme 2030 drives this development (see above).

There is no information available at this time.

For the last years there has been a new subject of focus, “economic viability”, within the accompanying research model projects (construction costs, building usage costs and lifecycle costs, as well as the associated optimization potential in regards to minimized CO₂ emissions).

German energy research is a strategic element of German energy policy and is indispensable for the long-term success of the energy transition.

Since 2014, the funding is concentrated in the new Federal Ministry for Economic Affairs and Climate Action. R&D for solar thermal and for solar buildings is part of the Energy research Programme of the German Federal Government (www.bmwi.bund.de).

In April 2016, the Federal Ministry for Economic Affairs and Climate Action together with the Federal Ministry of Education and Research started the R&D-Programme for "Solar buildings and energy efficient cities/ areas"  with a budget of 150 million € for 3 years. 6 milestone projects have been started in city districts.

The 7th Energy Research Programme defines the current principles and priorities for Federal Government for an environmentally-friendly, reliable and affordable energy supply funding for innovative energy technology. In September 2018, the Federal Cabinet adopted the 7th Energy Research Programme entitled “Innovations for the Energy Transition”. It contains the guidelines for energy research funding in the coming years. In addition to specific technologies, funding is made available for overarching, cross-sector issues such as energy efficiency, reduction of consumption, sector coupling and digitisation. This contributes to ensuring a holistic funding approach.

The Federal Government is currently developing a new energy research programme. By introducing missions, the 8th Energy Research Programme will be more closely aligned with the Federal Government's energy policy goals.

Thanks to the innovative funding format of ‘living labs’, the energy system of the future can already be tested today. The results and experience serve as a blueprint for the actual practical implementation. At the same time, more funding is planned to be made available to start-ups, which are essential to provide fresh impetus to the energy transition. It is essential that research is closely linked at European and international level. For this reason, cooperation with international organisations will be expanded and scientific exchange will be promoted. Furthermore, the improvement of the capacity to export and of the competitiveness plays an important role.

Since the launch of the 1st Energy Research Programme in 1977, the Federal Government has invested around 12 billion € to fund over 17,300 non-nuclear energy research projects (as of 2018), with the funding increasing every year. In the three years from 2019 to 2021 alone, subsidies amounting to 3.675 billion € have been invested.

Active solar thermal systems for different solar thermal applications such as water and space heating and cooling, solar district heating and storages are included in the sub-program “Energy optimized buildings and areas”, solar process heat is includes in the sub-program “commerce, trade, services sector and industry”.

In 2019 we looked back on 25 years R&D in solar energy. R&D started with the support programmes “Solarthermie 2000” and “2000plus” with pilot and demo systems. In recent years, it has delivered impressive results.

Market: Solar water and space heating, large solar systems > 100 m² collector area, low energy buildings, solar active houses with solar fraction > 50%, solar process heating systems for different industries

Demonstration: Solar process heating, large scale solar thermal systems with seasonal and multifunctional storages, solar district heating systems, smart solar thermal grids, solar thermal absorption and adsorption cooling for small and medium outputs, combined solar/CHP-systems.

Concentrating collector systems for process heating and cooling (PTC, Fresnel), solar facades, intelligent control systems for solar buildings.

Research:

• New collector and storage materials; Cost reduction for solar thermal systems through standardization and plug&play- installations
• System integration for solar process heat,
• advanced building integrated photovoltaics and solar thermal power
• Advanced thermal storages with higher storage capacity (PCM/PCS, TCM); PVT-systems with optimized heat and power output

“Energiewende” means a drastic transition of the energy system. The goal of reducing CO₂ emissions down to zero by the year 2045 can only be reached with strict shifting to renewable energy sources in the heating sector combined with a significant reduction of the energy demand. When the amendment of the new Buildings Energy Law (GEG) comes into force, a minimum renewable ratio of 65% of energy supply is mandatory. Of course, this is typically impossible with Solar thermal alone. However, a hybrid solution consisting of solar thermal combined with for example a heat pump, is a good possibility with quite low lifetime prices.

Due to the rising energy prices, caused by the war in the Ukraine, there is an additional need for a fast transition from fossile to renewable heat.

After having made major progress in many areas, the energy transition is now entering a new phase. While the initial main concern was with expanding renewable energies and energy-efficient technologies, greater focus will be placed now on systemic issues. In addition, the heat transition and thus also heat research are increasingly coming into focus.

The Federal Ministry for Economics and Climate Action (BMWK) coordinates the federal energy research.

Project Management Jülich (PtJ) supports its clients in the German Federal Government and the federal states as well as the European Commission in implementing their research policy goals with a focus on project funding. This includes SHC on advanced new concepts and technologies to improve the energy efficiency and lower the specific primary energy demand of buildings in R&D projects for energy efficient and solar buildings and active solar thermal systems and thermal energy storages.

The Federal Government has amalgamated the funding of research, development and demonstration measures for energy-efficient buildings and neighbourhoods in the research initiative ENERGIEWENDEBAUEN (Energy transition construction). Within the research network, there is a working group focusing on solar thermal energy, in which experts can network and exchange ideas. In addition to ongoing calls for proposals and specialist portals, this also includes its own research network (https://www.forschungsnetzwerke-energie.de/energy-transition-construction).

A new attractive incenting scheme was implemented at the end of 2019. Since the beginning of 2019 funding for solar process heat systems is reorganised within the framework of Federal funding for energy and resource efficiency in industry - Module 2: Measures to provide process heat from renewable energies.

Feasibility studies and realization for new generation of district heating systems are subsidized within the frame of Federal funding for efficient heat grids (BEW) (2022). By 2026, around 3 billion euros will be available for renewable heat generation, for example from geothermal energy, solar thermal energy and the use of large-scale heat pumps, as well as further heat grid infrastructure. BEW supports the construction of new heating grids with at least 75 percent renewable energies and waste heat and the decarbonisation of existing grids.

The solar industry is represented in different associations:

• German Renewable Energy Association (BEE)
• German Solar Industry Association (BSW)
• German Industry Association of Heating Technologies (BDH)
• German Heat and Power Association (AGFW)
• German Association for Concentrated Solar Power (DSCP)

For research, important actors are:

• the Renewable Energy Research Association (FVEE) (www.fvee.de)
• Working Group on  Solar Thermal Technology (in the past German Solar Thermal Technology Platform; DSTTP)

• German Sustainable Building Council (DGNB – Deutsche Gesellschaft für Nachhaltiges Bauen e.V.)
  Founded in 2007 by 16 initiators from various subject areas within the construction and real estate sectors. Their goal is to promote sustainable and economically efficient buildings even more strongly in the future
• Passive House Institute (PHI) 
  Independent research institute that has played an especially crucial role in the development of the Passive House concept - the only internationally recognized, performance-based energy standard in construction
• German Energy Agency
  Focuses on energy efficiency, renewable energy sources and intelligent energy systems at the interface between politics and business
• Deutsche Bundesstiftung Umwelt DBU (German Federal Environmental Foundation)
  One of Europe's largest foundations promotes innovative and exemplary environmental projects

Federal Report on Energy Research: transparency for the Federal Government’s funding policy: The report is published every year and serves to give an extensive overview over the Federal Government's research promotion policy in the field of energy. Progress made and current trends in the field of research promotion are presented in the report in a transparent manner. The figures on project funding contained in the Federal Report on Energy Research are also made transparent by EnArgus, the central information system on energy research of the Federal Ministry for Economic Affairs and Climate Action.

The most important source for information and dissemination of research projects in solar thermal and solar buildings:

• Overview of research in the field of buildings and neighbourhoods www.energiewendebauen.de
• German website on solar process heat: www.solare-prozesswärme.info
• Website for saisonal storage (https://www.saisonalspeicher.de/).
• German website on solar heat networks: (https://www.solare-waermenetze.de/)