11.2023 - 04.2024

Heat pumps along watercourses – analysis of the theoretical potential in Bavaria

Key results

The technology is ready for use

Heat pump technology is mature and suitable for use with river water as a heat source. This is also demonstrated by the projects implemented to date. River waters offer several advantages over other heat sources, such as outside air. However, the use of heat pumps along watercourses as heat source is not yet sufficiently standardized due to their special characteristics.

The cooling of water bodies can generally be seen as positive

The cooling of watercourses with heat pumps can generally be regarded as positive and is less critical than the warming of water. However, there are no uniform regulatory requirements in this regard.

The river landscape in Bavaria offers great potential in many regions

The results show that even partial exploitation of the existing potential could make a significant contribution to meeting the heat demand and thus also to decarbonizing the energy system.

Actual potential depends on many different regional factors

A wide variety of framework conditions and location factors must be considered when developing the potential and planning specific plants. In addition to the selection of suitable sites and the development of new sites, including existing (hydro) power plants or industrial sites, and ensuring economic viability, the regulatory guidelines and existing permit requirements are particularly crucial.


In view of the political goals in the heating sector, great efforts must be made to increase the integration of renewable heat sources. Heat pumps, especially large-scale industrial heat pumps, will play a significant role in these efforts. Their use in district heating networks has been researched in Germany, for example, in real-world laboratory projects since 2021. In other countries, such as Sweden, Denmark, and Switzerland, they have already been in use for some time.

Rivers can offer several advantages over other heat sources. Corresponding plants that use river water for heating purposes are already in operation in Germany and more are currently being planned.

In this context, the Bavarian Energy and Water Management Association (VBEW), the Bavarian regional group of the German Association of Local Public Utilities (VKU), the Union of Hydropower Plants in Bavaria (VWB) and the Bavarian Hydropower Plants Association (LVBW) have commissioned a study to determine the theoretical potential of Bavarian rivers.

Project Objectives

The following points were to be investigated as part of the study:

  • Quantification of the total theoretical potential of Bavarian watercourses, considering a variety of possible temperature spreads
  • Regionalization of the theoretical total potential at municipal level
  • Consideration of the potential in relation to heat demand and taking into account seasonal effects
  • Preparation and presentation of example projects in the form of project profiles
  • Investigation of the framework conditions for the use of heat pumps on watercourses with the help of expert interviews

Objectives which weren’t part of the study:

  • Detailed analyses for individual regions
  • Quantification of the potential, while assuming possible locations and planning of individual technical systems


As part of the study, the thermal energy, which can be extracted from river waters, was calculated, and described as theoretical potential. Electric energy, needed for the heat pump compressor, which is dependent on the respective efficiency, was only considered qualitatively.

The temperature reduction and the flow volume are decisive for determining the theoretical potential. Values of 0.5 °C to 3 °C were used as the basis for the temperature reduction in the study (in figures, the temperature difference is given in Kelvin [K]). The flow volume of water bodies of the I. and II. order with corresponding measuring points was considered and averaged for the period between 1990 and 2022. Measured data from the Bavarian Hydrological Service (GKD) was used as the data basis. From this, the potentials per watercourse and month were calculated and then aggregated into an overall potential for Bavaria. A temperature reduction of 1.5 °C was assumed for the regionalized consideration of the potentials at municipal level. The resulting total potential per watercourse was distributed to the neighbouring municipalities based on the length of watercourses per municipality.

To better classify this theoretical potential, the resulting values were considered in the context of heat demand in Bavaria. For this purpose, the final energy consumption in the building sector (sectors “private households” and “trade, commerce and services”) for space heating and hot water applications in Bavaria from the “Bayernplan Energie 2040” study for 2019 is used in the amount of 142.5 TWh [1].

Further information and comments on the methodology of the potential analysis and the resulting limitations can be found in Chapter 2 of the study.

For the consideration of river water heat pump technology, a literature review was first carried out. The results of this research were prepared in the form of profiles for two projects already implemented in Germany. Finally, four expert interviews were conducted with various interest groups (system operators, manufacturers, and planners) to investigate the framework conditions for the use of heat pumps on rivers. These followed a standardized guideline, which covered the following topics:

  1. technology status quo
  2. boundary conditions, restrictions, and obstacles
  3. choice of location and legal framework
  4. opportunities, risks, and outlook


Total potential

The sum of the annual theoretical potential in Bavaria for different temperature spreads is shown in Figure 1. The linear relationship between the theoretical potential and the assumed temperature spread can be clearly seen. The more the water is cooled, the greater the amount of heat which can be provided.

Figure 1: Theoretical potential for Bavaria in relation to the temperature spread

The theoretical potential is of a similar order of magnitude to the heat demand in Bavaria for space heating and hot water (142.5 TWh, see above). Under certain assumptions (regarding the temperature spread) the total theoretical potential is higher than the total yearly heating demand. However, due to seasonal effects and regional differences, this is only true for the sum totals of potential and demand. The heating demand cannot be met at all times and at all locations when these dimensions are considered (e.g. for a temperature spread of 1.5 °C).


Figure 2 shows the energy consumption for space heating and hot water as well as the theoretical potential for Bavaria depending on different temperature spreads.

Potential, heat, temperature reduction
Figure 2: Theoretical potential for Bavaria in relation to the temperature spread

First, it is clear to see that heat demand over the course of the year doesn’t correlate with the theoretical potential. In the months between October and March in particular (depending on the temperature spread), demand is greater than the theoretical potential. With a temperature reduction of 2 °C, seasonal effects play a subordinate role. Although demand here is greater than the theoretical potential between November and February inclusive, this still results in a coverage ratio of 95 % over the entire year. A reduced temperature spread of 1.5 °C leads to a coverage ratio of 87 %. At 1 °C, in addition to a longer period of coverage deficit (October to April inclusive), this results in a coverage ratio of around 75 %. These seasonal effects must be considered when planning specific systems.

Regionalized considerations

With the approach chosen in the study, 52 % of the Bavarian municipalities have access to a theoretical potential. The remaining 48 % of municipalities do not overlap with any of the watercourses considered, which is why no potential is shown for them in the study. This shows that at least half of all Bavarian municipalities should include heat generation using river water heat pumps in their municipal heat planning. If smaller watercourses, which could not be analysed in this study, are included, this value increases further.

Figure 3 and Figure 4 show the coverage ratio at municipal level for the months of January and June respectively. High degrees of coverage are found along the Danube and the catchment areas of its tributaries Isar, Inn and Salzach in the south and Naab and Wörnitz in the north. In the catchment area of the Main, there are high degrees of coverage in the Rodach, Itz and Fränkische Saale.

Bavaria, representation of coverage, winter
Figure 3: Coverage ratio per municipality for January
Bavaria, representation of coverage, summer
Figure 4: Coverage ratio per municipality for June

Due to the low demand for heat and the high potential in summer (see Figure 4), around 80 % of the municipalities that are assigned a potential have a coverage ratio of at least 100 % (= local heat demand can be fully covered by river water heat pumps) in June. In January, however, this applies to only 41 % of these municipalities, as the relationship between heat demand and theoretical potential is generally reversed in the winter months.

For over a third (37 %) of the municipalities that are assigned a potential, the theoretical potential shown is sufficient to fully cover the heating demand described above all year round under the assumptions described. This corresponds to just under a fifth of all municipalities in Bavaria (19 %). Assuming a temperature drop of 1.5 °C, these municipalities could therefore be supplied exclusively by river water heat pumps all year round. Assuming a river water cooling of 2 °C, the value increases to around a quarter of all Bavarian municipalities (24 %).

Extract from the chapter on framework conditions for the use of river heat pumps (results of the expert interviews)

Regarding the status quo, it was determined that the technology is mature and the development of water bodies potential through existing cooling water utilization has already been tested. For large capacity classes, open systems with direct water extraction are preferable. Although additional intermediate circuits reduce efficiency, they offer advantages in terms of water protection. Current challenges exist in the selection of suitable refrigerants, the prevention of refrigerant leaks and the protection of the heat exchanger against damage.

Regarding the determining boundary conditions, it was stated that there are no generally applicable regulations and rules for the permitted cooling of the entire water body and that the permissible temperature spread therefore is highly dependent on the individual case. The cooling of the extracted water flow is usually variable over the course of the year. This is particularly relevant in winter, when the water temperature and the (minimum) return temperature to be maintained can restrict operation for frost protection reasons. The partial extraction of water from the overall water body is also dependent on the individual case and approval. It can also be varied over the course of the season to compensate for fluctuations in temperature.

Locations in the immediate vicinity of water bodies with existing extraction infrastructure and interventions in the ecosystem are particularly suitable for the installation of river water heat pumps. These include, for example, hydropower plants, industrial and power plant sites, mills, or canals. When selecting a specific location, the heat sink must be considered in addition to the heat source, as this has a significant influence on the efficiency of the heat pump. In addition to conventional heating networks, 5th generation heating networks, which provide low-temperature heat, should also be considered. Ideally, existing permits and water rights should be used for the development of new heat pump sites.

When watercourses are used for heating purposes, they are cooled down. Regarding the advantages and disadvantages or rather opportunities and risks, it was made clear that this cooling of watercourses in times of global warming is (to a certain extent) not critical and tends to be ecologically beneficial. In addition, river water heat pumps offer a great opportunity for local value creation during municipal heat planning and for developing the existing environmental heat sources, particularly in urban areas, where there are sometimes no alternatives. The existing disadvantages and risks mentioned were the lack of standardization in some cases, the need for redundancies to ensure security of supply and the current dependence on subsidies for economic viability.

Finally, recommendations for political decision-makers and future users were requested. It was stated that it would make sense to specify and standardize the relevant regulatory framework conditions (water protection, cooling specifications, refrigerants) in the future. A stable economic framework should also be created to enable the further distribution of river water heat pumps. Potential users are urged to have the courage to implement “quick wins”, particularly where existing permits and the corresponding infrastructure are available. Coupled with targeted stakeholder involvement and transparent reporting, this can ensure the further development of acceptance of this technology.

More information


[1] Guminski, Andrej: Bayernplan Energie 2040 – Wege zur Treibhausgasneutralität – Zusammenfassung. München: FfE, 2023.