Esbjerg Deploys Large-Scale Seawater Heat Pumps for District Heating
Denmark utilizes North Sea thermal energy to replace retired coal-fired power infrastructure.
1Innovative Thermal Extraction
Esbjerg, Denmark, is actively utilizing large-scale electric heat pumps to extract thermal energy from the North Sea. This system supports the city's district-heating network, effectively replacing a retired coal-fired power plant. During recent winter testing, the facility successfully converted cold seawater into high-temperature heat for the municipal grid infrastructure.
2Operational Performance Metrics
A two-hour winter test recorded seawater entering at 3.3°C and exiting at 1.2°C. The system consumed 19.9 MW of electricity to supply 55.2 MW of heat at 90°C. This resulted in a coefficient of performance of 2.8, meaning 2.8 units of heat were delivered for every unit of electricity consumed.
3Technical System Design
The installation features a nominal heating capacity of 70 MW and utilizes carbon dioxide as a refrigerant in a high-pressure cycle. By transferring thermal energy from a colder source to a warmer destination, the plant avoids the inefficiencies of traditional resistance heating, which would require significantly more electricity for identical output.
4Integration and Challenges
The city's broader heating supply also incorporates wood-chip boilers and waste-incineration heat alongside these pumps. Engineers must manage complex variables, including corrosion, biological fouling, and freezing protection as seawater temperatures fluctuate. Full guarantee testing remains pending, and emissions reductions cannot be attributed solely to the new heat pump installation.
5Economic and Temperature Factors
Electricity prices and network temperatures directly dictate operational costs. With electricity at €100/MWh, compressor power costs roughly €36 per MWh of heat. Older networks requiring 90°C water face higher operational hurdles than modern, lower-temperature systems, as the compressor must perform a larger temperature increase to meet the required heat delivery standards.
6Historical Context and Precedents
Esbjerg builds upon decades of global experience with seawater heating. Monaco pioneered this technology in 1963, while Stockholm has operated large-scale seawater-sourced systems since the 1980s. Other projects, such as Vancouver's Horseshoe Bay, utilize closed-loop submerged heat exchangers, demonstrating that diverse marine arrangements exist to suit specific local load requirements.
7Environmental and Site Considerations
Environmental assessments must account for local marine ecosystems and the discharge of colder water back into the sea. While seawater heat pumps offer a viable path, they are not universal solutions. In some locations, wastewater, industrial waste heat, or ground-source systems may provide more cost-effective alternatives for local heat demand.
8Strategic Value of Flexibility
Hot-water storage adds critical value by allowing utilities to produce heat when electricity prices are low. Esbjerg’s test provides empirical evidence that cold seawater can reliably support high-temperature district heating. Coastal utilities can now use these results to evaluate network investments and the long-term feasibility of replacing combustion-based heating systems.