How will we heat from tomorrow?
The council resolution has been passed: Bonn is to become climate-neutral by 2035. This means that in a few years, Bonn will no longer burn fossil fuels such as gas or oil in heating systems for space heating and hot water ("decarbonization"). This is important for climate protection. But it also makes sense for building residents, as natural gas and heating oil will become significantly more expensive in the future.
How can Bonn be supplied with climate-friendly heat in the future - without fossil natural gas or heating oil? This is what the municipal heating plan (opens in a new tab) aims to find out by May 2025. In October 2024, a map was published showing which types of heat supply are best suited where in Bonn - rather a central district heating orlocal heating network (opens in a new tab), a local heating network in the district or rather a decentralized, individual solution via a heat pump.
An additional hydrogen distribution network or hydrogen supply areas are not planned for the City of Bonn. The reasons for this are the large energy losses in hydrogen production, the expected high costs and the unclear availability of hydrogen.
From January 9 to February 7, 2025, the public is invited to submit comments on the draft target scenarios for the years 2045 and 2035, t local (opens in a new tab) heating network (opens in a new tab), a local heating network in the district or rather a decentralized, individual solution via a heat pump.
An additional hydrogen distribution network (opens in a new tab) or hydrogen supply areas are not planned for the City of Bonn. The reasons for this are the large energy losses in hydrogen production, the expected high costs and the unclear availability of hydrogen.
From January 9 to February 7, 2025, the public is invited to submit comments on the draft target scenarios for the years 2045 and 2035, the heat supply map and the list of measures in the implementation strategy as part of the public consultation (opens in a new tab).
The best start: Reduce heating requirements
It is much easier to provide 100 percent renewable heat if the heat demand is significantly reduced beforehand.
The energy modernization of the building envelope is a key component in reducing the heat demand (more "efficiency"). This includes insulating the building or replacing windows and doors so that the heat stays inside the house better and significantly less "unused" heat escapes outside. This makes your building "more efficient" - with less energy input, it is just as warm as before. An individual renovation roadmap (iSFP), which is also subsidized by the federal government, provides you with a good overview. Most buildings in Bonn are unrenovated or only partially renovated (88 percent). Particularly in buildings that were built before the first Thermal Insulation Ordinance in 1977 and have hardly been refurbished since then, the heat requirement can be more than halved. Almost a third of Bonn's heat consumption is attributable to buildings with the worst energy efficiency class H - buildings with an annual heat consumption of more than 250 kilowatt hours per square meter. The potential for energy-efficient refurbishment of buildings is therefore huge.
- Take advantage of the company-independent and free advice from the Bonn Energy Agency (opens in a new tab). They will tell you what measures you can take to reduce your heating requirements and what subsidies you can receive from the Federal Subsidy for Efficient Buildings (BEG) (opens in a new tab).
- Explanatory film by Stadtwerke Bonn " Optimizing and renewing heating (opens in a new tab)".
Experts call the second building block for reducing heating requirements "sufficiency". Everyone can help here - building owners and tenants alike. For example, by lowering the temperature of the heating and hot water, keeping bedrooms or basements cooler and turning down the heating at night or during vacation periods. The term "housing sufficiency" goes one step further: switching from single-person households to multi-person households or dividing single-family homes into several residential units can help to ensure that less space needs to be heated per resident. Ideas for a "space-saving housing initiative" include, for example, an apartment exchange platform, a right to exchange apartments and a bonus for moving to a smaller apartment. The housing sufficiency strategy can help to ensure that everyone has as much living space available as is suitable for their current stage of life. In addition to reducing heating requirements, space-saving living also has the advantage of counteracting the housing shortage. The basic idea is also transferable to many non-residential buildings: office buildings can be better utilized through desk sharing, so that less heated office space is required overall.
Focus on the goal: 100 percent renewable heat by 2035
The energy still required for space heating, hot water and process heat after the heat demand has been reduced should gradually be covered from various sources of renewable energy. There is no "one solution", but many building blocks:
- For decentralized individual solutions, heat pumps are the best choice for many buildings. Air-source heat pumps are widely used - although geothermal probes and water-source heat pumps are even more efficient. Contrary to common fears, heat pumps can also be used sensibly and efficiently in most old buildings. To assess the efficiency of the heat pump, the heat requirement, flow temperature and heating surfaces should be evaluated before installation. Solar thermal systems on the roof can also generate hot water all year round and support the heating system in spring and fall. Heating with wood pellets, wood chips or logs is only recommended in exceptional cases and infrared heating is only recommended for buildings with a low heat requirement.
- The existing district heating network (opens in a new tab) of the municipal distribution network operator Bonn-Netz GmbH is to be roughly doubled and the number of connections multiplied for the central supply via heating networks. In addition, local heating networks are to be created. Stadtwerke Bonn is also driving forward a sustainable heat supply on its path to CO2 neutrality (opens in a new tab). The generation of district heating is gradually being converted to renewable energies, thereby decarbonizing the transported heat. For example, large heat pumps can be built for this purpose that use heat from the Rhine water or wastewater from sewage treatment plants. Geothermal heat can also be used via deep geothermal probes. Ground-mounted solar thermal systems could also supply heat, especially if they are combined with seasonal storage, so that the summer heat is "stored" for winter heating. In addition, heat suppliers should examine the extent to which waste heat generated as an unavoidable by-product in industry and commerce - for example in data centers - can be fed into heating networks. In addition, Bonn's connection to the hydrogen core network is being examined in order to use green hydrogen in Bonn's combined heat and power plants in the future.
The municipal heating plan
In order to make a significant contribution to saving fossil fuels and protecting the climate, making the heat supply more resilient and reducing existing dependencies, the German government passed an updated Building Energy Act (GEG) (opens in a new tab) on January 1, 2024 and closely interlinked it with the newly introduced Heat Planning Act (WPG) (opens in a new tab). According to the legal requirements, cities with more than 100,000 inhabitants must submit their heating plan by June 30, 2026 at the latest - Bonn intends to submit it to the council for approval as early as May 2025.
Municipal heat planning must provide answers to the following questions:
- How little heat energy can we get by with?
- How can we supply ourselves with heat without emitting CO₂?
- What needs to change in our city to achieve this? And who needs to take care of it?
Following an EU-wide tender, the City of Bonn commissioned the municipal distribution network operator Bonn-Netz GmbH (opens in a new tab) and its partners to carry out municipal heating planning for the entire city area in February 2024.
Numerous stakeholders were informed about and involved in the heat planning in several workshops in summer 2024: Large consumers, potential waste heat suppliers, grid operators, citizen energy cooperatives, the housing and real estate industry, energy consultants, trade guilds, the Chamber of Industry and Commerce, architects' associations, banks, neighboring municipalities, the Rhein-Sieg district, social and youth associations and civil society groups.
Inventory and potential analysis
The basis for any planning is data on the existing situation: What is the current heat consumption in different parts of Bonn? Where are particularly high heat densities - i.e. a particularly high heat demand per hectare? Where are high heat line densities - i.e. the heat demand along a kilometer of road? What is the final energy demand (gas, electricity, heat at the building entrance) and how high are the associated greenhouse gas emissions? How old are the buildings in Bonn, how much have they been renovated and what energy efficiency classes do they currently have? What heating technologies are used and in what proportions? Where are heating networks already in place and where are renewable energies already being used? All of these questions are answered by the inventory analysis - for data protection reasons, not on a building-by-building basis, but only averaged over several buildings.
In the potential analysis, a rough estimate was made of which renewable energies could be used for Bonn's heat supply in the future and how much commercial waste heat exists that could potentially feed heating networks. The potential for reduced heat demand through refurbishment was also examined.
Suitable heat supply types
Citizens are particularly interested in whether a connection to district heating or local heating is possible for their building - and if so, when and at what cost. Unfortunately, these very understandable concrete questions are not yet answered on the basis of the heating plan. This is because the heating plan is a "legally non-binding, strategic technical plan". It enables network operators and heating suppliers to prioritize areas based on the degree of suitability for a heating network area and to check whether an expansion or new construction should be targeted in the next one to two decades. The "suitability" for a heating network cannot be equated with infrastructure planning.
In this respect, the proposed heating network supply areas do not lead to a promise that a heating network will be built there, even after the heating plan has been adopted, nor do they lead to an obligation for building owners to connect their own building to a heating network.
The heating plan cannot replace an individual energy consultation - available free of charge from the Bonn Energy Agency and the consumer advice center. However, it gives building owners an initial orientation for their exit from oil and gas:
- Areas that are likely or very likely to be suitable for a decentralized heat supply.
These heat supply areas are shown in green on the map. There is a great deal of clarity here: building owners should promptly look for an independent heating solution that complies with the Building Energy Act (GEG), particularly in the form of heat pump technologies. - Areas that are very likely to be suitable for a local or district heating network.
In these sub-areas shown in dark orange, the regional distribution network operator, Bonn-Netz GmbH, will carry out concrete expansion planning for district heating following municipal heating planning. Before a heating network can be built, feasibility and profitability studies must be carried out, planning and approval processes must be completed and coordination with other road construction measures must be ensured. On this basis, binding and timely commitments can be made for the expansion of a heating network. The first results can be expected as early as 2025. In principle, the construction of new heating networks is not only possible by Bonn-Netz GmbH, but also by citizen energy cooperatives, for example. - Areas that will probably be suitable for a local or district heating network or, in the case of dual suitability
Areas that are only "probably suitable" for heating networks are shown in light orange on the map. Areas with dual suitability are striped green-orange. In all of these areas, infrastructure expansion can only be expected in part and will tend to occur further in the future. From today's perspective, it seems more than questionable whether it will be possible to multiply the length of the heating network and house connections to the necessary extent due to capacities in planning and approval processes and in civil engineering, for example.
If a heating system needs to be replaced in the near future, it is therefore recommended that the various options for heat pump technologies are considered in good time, even in these areas. The independent decision in favor of a heat pump is permissible in any case and recommended insofar as it is accompanied by a direct reduction in emissions in terms of climate protection.
Here too, the construction of new heating networks by other suppliers, such as citizen energy cooperatives, is possible and desirable - especially in the area of local heating solutions for neighborhoods.
Target scenarios for 2045 and 2035
Germany wants to become climate-neutral by 2045 - Bonn already by 2035. Scenarios have therefore been developed for both target years to show how heat demand, final energy demand and CO2 emissions will have to change. In the 2035 target scenario, heat demand is 28 percent lower than today, with two thirds of Bonn's buildings using heat pumps and one third drawing heat from a local or district heating network. As oil or gas heating systems are no longer in use, CO2 emissions are reduced by 98 percent (see diagram opposite).
Very low residual emissions remain in the 2035 model, as it was assumed that the electric heat pumps are operated using the German electricity mix. This is not yet 100 % renewable by 2035. If you use your own PV electricity and grid electricity from a green electricity provider to operate the heat pump, you can even reduce CO2 emissions to zero.
Recommendation: Do not install any more new gas and oil heating systems
Heat planning makes it clear that for many reasons it no longer makes sense to install new gas or oil heating systems when changing heating systems:
Fossil-fuel heating systems can no longer be operated from 2045 at the latest, as Germany wants to be climate-neutral by then. Building owners would therefore have to replace their heating again by then.
According to the GEG, the installation of new gas heating systems will only be permitted from July 1, 2026 at the latest if they are operated with 65 percent green gas. One variant of green gas is biomethane. However, it is not foreseeable that biomethane will be available in sufficient quantities and at favorable prices instead of natural gas.
Another variant of green gas is hydrogen (H2). However, according to the distribution network operator, a new hydrogen distribution network will not be built in Bonn at present, nor will hydrogen be added to the existing gas network. As a result, building owners will not be able to meet the requirements of the GEG even with H2-ready gas heating systems.
In particular, the 2035 target scenario would not be achievable in Bonn if gas or oil heating systems were to continue to be installed in the coming years, as these generally have a life expectancy of at least 20 years. Based on these results, the administration recommends that no more new gas or oil heating systems be installed today.
The package of measures in the implementation strategy
In January 2025, the city published a draft implementation strategy with around 80 measures that need to be implemented in the short, medium or long term to make Bonn climate-neutral in the heating sector by 2035. The package of measures is divided into the following four fields of action (A-D):
- Heat planning as a process
This field of action includes designating areas for the construction and expansion of heating networks, identifying areas with a particular need for renovation, activating urban open spaces for renewable energy systems and storage facilities, as well as updating the heating plan every five years. - Expansion of renewable energies, waste heat utilization and storage
For example, feasibility studies for the construction of solar thermal and geothermal plants and heat pumps for sewage treatment plants are to be carried out, usable commercial waste heat sources are to be identified in more detail and the construction of electricity storage facilities and seasonal heat storage systems is to be examined more closely. - Heating networks and network infrastructure
The district heating network is to be comprehensively expanded and operator models for small-scale local heating networks at district level are to be found. The electricity grid is also to be expanded and digitalized in order to be able to transport the additional electricity required by heat pumps. Connecting commercial customers with an unavoidable need for hydrogen to the nationwide hydrogen core network is also part of this field of action. - Energy efficiency, energy-efficient refurbishment and heating technologies
This package of measures bundles measures to convert heating systems in buildings, municipal properties and neighborhoods. This also includes the planned municipal funding program for the socially responsible energy-efficient refurbishment of existing buildings and for changing heating technology, as well as advice on reducing heating requirements, using living space and changing heating systems. - Accompanying processes
This field of action includes, for example, measures to simplify coordination and cooperation, build up expertise or speed up planning and approval processes.
Participation of the citizens
From January 9 to February 7, 2025, citizens and public bodies were able to view all draft documents of the municipal heating plan via the online participation platform Bonn-macht-mit (opens in a new tab) and submit comments on the heating supply map, the target scenarios and the implementation strategy as part of the statutory 30-day public participation period (Section 13 (4) WPG). 93 comments with wishes, suggestions and criticism were examined and weighed up and, where appropriate, taken into account in the heating plan. The heating plan is to be submitted to the Bonn City Council for approval in May 2025.
Questions and answers on the heat transition and municipal heat planning can be found here
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