Large heat pumps to replace coal in heating networks

24.06.2025

Source: E & M powernews

How can large heat pumps at power plant sites tap into natural and industrial heat sources for climate-neutral district heating? Researchers at the Fraunhofer IEG are investigating this.

District heating in Germany should also be greenhouse gas-neutral by 2045. A significant proportion of the grid-based heat supply still comes from coal-fired power plants that generate electricity and heat simultaneously using combined heat and power (CHP). According to the Federal Network Agency, 123 out of 141 power plant units nationwide were cogenerating heat at the start of 2024. Alternatives need to be found for the majority of these so that climate-neutral heat can pass through the grids in future.

One way of replacing fossil CHP plants is to use large heat pumps that utilize environmental heat or industrial waste heat. In the "FernWP" project funded by the German Federal Ministry for Economic Affairs and Energy (BMWE), scientists from the Fraunhofer Institute for Energy Infrastructures and Geothermal Energy (Fraunhofer IEG, based in Bochum) analyzed the technical and economic potential of large heat pumps for district heating supply. Other partners in the research project include

• the Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg
• the energy efficiency association AGFW,
• industrial companies such as Gesmex Exchangers GmbH and Johnson Controls Systems & Service GmbH
• as well as municipal utilities such as Cottbus.

Site analyses for eight power plant sites

The project team examined eight power plant sites as examples of their suitability for the integration of large heat pumps. Natural heat sources such as surface water, air or geothermal energy as well as industrial waste heat sources were taken into account. The decisive factors for the evaluation were the temporal and spatial availability of the heat sources, their temperature levels and the specific requirements of the connected district heating networks.

According to the researchers, low-temperature heat sources in particular, such as rivers or waste heat, can cover a significant proportion of the heat demand. Where the infrastructure is available, existing coal-fired power plants could be partially or completely replaced as heat sources by large heat pumps. According to the project report, the usable potential depends heavily on the respective location - both geographically and in terms of the existing grid infrastructure.

Flexible integration of renewable heat sources

"With large heat pumps, natural heat sources can be used efficiently and heat generation from coal can be gradually replaced," summarizes project manager Anja Hanßke from Fraunhofer IEG. The technology can react flexibly to different temperature levels and thus tap into both environmental heat and industrial waste heat. In combination with a possible reduction in grid supply temperatures, this could further increase the efficiency of the systems.

The project also investigated the economic obstacles to the increased use of large heat pumps and which regulatory conditions would need to be adapted. The transformation of existing power plant sites into heat pump hubs is possible in principle, but requires investment and infrastructural adjustments, according to the recommendations from the project. The BMWE is supporting the project with 4.4 million euros.

Further information on the "FernWP" project is available on the Internet.

Author: Susanne Harmsen