Can Rivers Replace Gas in Urban Heating Networks?

A former lorry park beside the Rhine in northern Cologne is set to become one of Europe’s most important urban heating sites. From 2028, Rheinenergie plans to use a 150-megawatt river-water heat pump to supply enough energy for approximately 50,000 households. The plant is expected to provide as much as 40 percent of the low-carbon heat required by the city-centre district-heating network.

The scale is exceptional, but the idea behind it is not exclusive to Cologne. Many European cities have rivers running close to residential districts, industrial land and municipal energy infrastructure. Large heat pumps can extract thermal energy from that water, raise it to a usable temperature with electricity and feed it into a district-heating network.

For cities trying to reduce their dependence on gas, Cologne offers something more useful than another ambitious climate target. It provides a working model of the assets, decisions and compromises required to turn a river into part of an urban energy system.

The lesson is not that every river city should order a 150-megawatt heat pump. It is that municipalities should begin looking at rivers, former power stations, district-heating networks and electricity connections as parts of the same infrastructure map.

Begin With the Infrastructure the City Already Has

Cologne did not select an undeveloped site and then attempt to build an entirely new energy system around it. The heat pump is planned for the Niehl energy site, which has served the city for decades and already lies between the Rhine and a harbour basin.

That location brings together several assets that would be expensive and time-consuming to create from scratch. Water is directly accessible, the site is suitable for large industrial equipment, an established district-heating network is nearby and the existing energy complex has a powerful electricity connection.

This pattern is not unique to Cologne. Across Europe, conventional power stations, combined heat and power plants and other industrial energy sites were frequently built beside rivers. The water was used for cooling, while the sites were connected to strong electricity networks and, in some cases, municipal heating systems.

As fossil-fuel generation is reduced, these locations do not necessarily lose their value. They can be repurposed as clean-energy hubs, using infrastructure that was originally built for a different energy economy.

A city considering river heat should therefore begin by examining its existing energy and industrial sites. A former power station beside a river may be more valuable than a seemingly ideal undeveloped plot because it already provides the difficult connections between water, electricity and heat demand.

Cologne’s example suggests that urban energy transitions may depend as much on intelligent reuse as on new construction.

Map Heat Demand Before Choosing the Technology

A river contains a vast quantity of thermal energy, but that energy is useful only when it can reach enough buildings at a reasonable cost.

Cologne already has a district-heating network serving parts of the inner city. Although district heating currently accounts for a relatively modest share of the city’s total heating demand, the network provides an immediate destination for the heat generated at Niehl. Rheinenergie intends to expand its role further over the coming years.

Other cities need to begin with the same basic question: where is heat demand sufficiently concentrated to support a network?

Large apartment blocks, hospitals, schools, offices, universities, hotels and public buildings can create a stable base of demand. Dense neighbourhoods are generally more suitable than areas dominated by detached houses because each kilometre of pipe can serve more buildings.

The location of those neighbourhoods matters. A river heat pump positioned many kilometres from the nearest network may be technically possible but financially unattractive. New pipelines require roadworks, complex planning and substantial capital. They can also generate years of disruption in already congested city centres.

Municipal heat mapping can identify where demand is concentrated, which buildings already use district heating and where planned development could support future expansion. The river can then be assessed in relation to this map rather than treated as an isolated source of renewable energy.

Cologne’s project works because the heat pump is being integrated into a wider heating strategy. Cities that reverse the sequence—selecting an impressive technology before establishing where its output will go—risk creating an expensive plant without an adequate market.

Look for a Strong Electricity Connection

River-water heat pumps do not burn fuel, but they require substantial quantities of electricity. The compressor raises low-temperature energy extracted from the river to the level needed by the district-heating network.

For a large installation, grid access can determine whether a project is viable. A useful planning rule cited by the Cologne project team is that the electricity connection may need to provide roughly half the thermal capacity of the heat pump. A 150-megawatt installation could therefore require a connection of at least 75 megawatts.

Securing that capacity at a new site can be difficult. Grid operators are already processing connection requests from data centres, battery-storage projects, renewable-energy installations, industrial electrification and electric-vehicle infrastructure. A new high-capacity connection may take years to plan and build.

Former power-station sites again offer an advantage. They were designed to export large quantities of electricity into the grid. A heat-pump project can adapt part of that infrastructure to draw electricity in the opposite direction.

Cities should include electricity capacity in their earliest screening of possible sites. Access to a river is visible; access to the necessary grid connection is less obvious and potentially more decisive.

The calculation should also consider where the electricity will come from and how its price will affect the cost of heat. A heat pump powered by low-carbon electricity can reduce emissions significantly, but its economics remain exposed to the relationship between electricity and gas prices.

Long-term renewable-power contracts, municipal generation and thermal storage can help. A city may also design the plant to operate more intensively when renewable electricity is abundant and store heat for later distribution.

This turns river heat into part of a more flexible urban energy system rather than a single-purpose replacement for a gas boiler.

Bring Environmental Authorities Into the Project Early

Cologne also offers a warning. The project has moved more slowly than originally expected because the permitting process raised questions about its possible effects on fish and other aquatic organisms.

Using river water for heating requires more than permission to construct an industrial building. The operator needs approval to extract water, pass it through the system and return it to the river at a lower temperature.

Cooling river water may appear environmentally benign, particularly as European rivers increasingly experience high summer temperatures. The local effects still have to be assessed. Intake systems can affect fish and smaller organisms, while altered water temperatures may influence habitats near the discharge point.

Flow levels, seasonal temperature changes, flooding and drought also affect how much heat can be extracted safely. A plant must remain within ecological limits throughout its operating life, including under conditions that may differ from historic averages.

The Cologne experience shows why environmental approval should not be treated as the final administrative stage of a technically completed project. Regulators, water authorities and ecological specialists should participate while intake structures, operating limits and discharge systems are still being designed.

Mannheim, where another large river heat project is planned, has emphasised the value of involving authorities early. That approach cannot remove every complication, but it can reveal concerns before they become expensive delays.

For other cities, the practical lesson is straightforward: permitting strategy belongs inside project design, not after it.

Use the River as One Source Among Several

Cologne’s heat pump is not expected to heat the entire city. Even after the planned expansion of district heating, many households will continue to require individual or neighbourhood-level solutions.

This makes the project more replicable, not less. A city does not need to replace every gas boiler with river heat before the investment becomes worthwhile. It can use the river to decarbonise the parts of the urban heating system where centralised supply works best.

Dense inner-city districts may be connected to a river-fed heat network, while less densely built areas use individual heat pumps, geothermal systems or local energy networks. Industrial waste heat, sewage heat, solar thermal installations and data-centre heat can complement the river source.

A diversified system can also manage seasonal demand more effectively. River heat may provide a large share of the base load, while other plants cover the coldest days, maintenance periods or times when environmental restrictions limit water extraction.

Cologne’s project is being developed at an existing energy site where different technologies can operate together. Other cities should consider the same portfolio approach. The objective is not to identify one perfect source but to combine locally available resources into a reliable system.

Connect the Project to Urban Development

A river heat pump should not be planned solely by the municipal utility. Its value depends on decisions made by planning departments, housing authorities, property developers and transport agencies.

New residential districts can be designed around low-temperature district heating from the beginning. Public buildings can provide dependable demand, while renovation programmes can prepare older properties for lower network temperatures. Streets scheduled for transport or utility works can be used to install heating pipes at the same time, reducing disruption and cost.

Cities can also reserve suitable riverfront and industrial sites before competing developments make them unavailable. A former energy site may appear unattractive for housing or public space, but it can carry strategic value because of its grid connection and proximity to water.

Cologne’s choice of a former lorry park within an established energy complex illustrates the importance of land-use coordination. The project uses space that is compatible with industrial infrastructure without displacing a dense residential neighbourhood.

Other cities should include potential river heat sites in master plans and municipal heat strategies even when construction is years away. Grid capacity, land ownership and network corridors become much harder to secure once development has progressed.

Decide Who Will Pay for the Network

The heat pump itself may be the most visible part of the project, but the network can determine its reach and financial performance.

Cologne has an existing district-heating system, yet expanding it to additional neighbourhoods will require new pipes and building connections. The city aims to increase the proportion of heating supplied by district networks, but technical and economic limits mean that universal coverage is unlikely.

Cities with little district-heating infrastructure face a larger challenge. Building a new network involves high upfront costs and a long period before the investment is recovered. Utilities need confidence that enough buildings will connect and remain connected.

This creates a coordination problem. Property owners may hesitate to commit before the network exists, while utilities may hesitate to build before enough clients have committed.

Municipal governments can reduce the uncertainty by defining future heating zones, connecting public buildings, coordinating roadworks and establishing clear consumer protections. Funding models may combine utility investment, public support, development contributions and long-term heat contracts.

The tariff structure deserves particular attention. Residents will judge the project through their heating bills, not its installed megawatts. A technically successful plant will still lose public support if the cost is unpredictable or if households feel trapped in an expensive monopoly.

Cologne’s scale may not be transferable to every city, but the financing question is universal: who pays for the plant, who pays for the pipes and who carries the risk if fewer buildings connect than expected?

Build a Replicable City Model, Not a Showcase

Large infrastructure projects are often described through superlatives. Cologne is planning Europe’s largest river-water heat pump; Mannheim hopes to go larger, while Hamburg has announced a 200-megawatt installation for the end of the decade.

The competition attracts attention, but capacity alone is not the most useful measure of progress. A smaller plant connected efficiently to a dense district may deliver a better local result than a record-breaking facility whose network expansion is delayed.

Cologne’s real significance lies in the relationships around the heat pump. The city has a major river, an existing energy site, a strong electricity connection, an operating district-heating system and sufficient concentrated demand. It also has a municipal utility capable of coordinating a project across multiple decades.

Other cities can use these conditions as a screening framework:

Does the city have a suitable water source with sufficient year-round flow? Is there an existing energy or industrial site beside it? Can the electricity grid support a large heat pump? Is a district-heating network already available, or can one be expanded economically? Are there dense neighbourhoods and large buildings that can provide stable demand? Can environmental authorities be involved before the final design is fixed?

A city that can answer most of these questions positively may have a credible river heat opportunity. One that cannot may be better served by another source or a smaller local system.

The Rhine project should therefore be understood as an adaptable model rather than a blueprint to copy at the same scale. Cologne shows how cities can identify an overlooked local resource, connect it to infrastructure built for the fossil-fuel era and use it to support a lower-carbon heating system.

The river is only the beginning. What makes the model transferable is the planning around it.