See Part 1 here: The world’s largest untapped resource: excess heat: Part 1 of 3

In the introduction to this series, we identified some of the sources of excess heat, what it is and why it matters, and also presented the case for exploring how capture and utilization of excess heat can accelerate decarbonization of the industrial sector—the source of over one-third of worldwide energy-related carbon emissions. Below, let’s dig a little deeper into how excess heat can be found in different parts of the industrial sector, in everything from large wastewater treatment facilities to your local neighborhood supermarket, and begin to address the need for approaching this potential new source of energy.


The industrial sector accounts for 39 percent of all global energy-related carbon emissions and is—with its current rate of energy efficiency improvements of 1 percent per annum—not on track to meet the milestones of the Net Zero scenario that would require improvements of 3 percent. The structural challenge for factories all over the world is to meet growing demands for production while curbing emissions. The current energy crisis has placed the industrial sector under a great amount of pressure, since the share of energy costs for production has increased significantly.

Paradoxically, efficiency progress is slowing in the industrial sector. From 2015 to 2020, the rate of improvement in the energy needed to produce one U.S. dollar of industrial value dropped from the almost 2 percent per year achieved over 2010 through 2015 to just under 1 percent. The industrial sector needs to improve its energy efficiency at a rate of 3 percent annually to meet net zero. The overall progress in energy efficiency will continue to be stymied if strong industrial demand for energy persists without a major improvement in industrial energy efficiency.

The good news is that there is a huge, unharnessed potential for the industrial sector, namely utilizing its excess heat. If we look at the European Union, industrial sites constitute the largest source of excess heat. The excess heat from heavy industrial sites in the European Union amounts to over 267 TWh a year. To put that into perspective, this is more than the combined heat generation of Germany, Poland and Sweden in 2021. If we look only at waste heat sources over 203 degrees Fahrenheit (95 degrees Celsius) and within 6 miles of existing district heating infrastructure, there is a potential of 64 TWh already. This corresponds to 12 percent of the energy supplied to European Union district heat infrastructure annually.


The potential is also striking when looking at specific urban areas. Take Essen in the Ruhr district in Germany. There are approximately fifty industrial sites in the urban areas around Essen, and they produce 11.98 TWh of excess heat per year. This is roughly the amount of heat required to heat 1,200,000 households—or close to half of the households in the area.

Three industries—cement, chemicals, and steel—account for almost 60 percent of industrial energy demand worldwide, with emerging and developing economies, in particular China, accountable for 70 to 90 percent of the output of these commodities. These heavy industries offer great potential in terms of efficiency since the excess heat from them is at such high temperatures and therefore easy to reuse.

The industrial sector, which is currently not on track to meet the milestones in the Net Zero Emissions by 2050 Scenario, has the ability to shift the needle on global energy efficiency by reusing excess heat. However, there are multiple ways for the industry to reuse excess heat, for instance, it can be reused to supply a factory with heat and warm water, or it can be exported to neighboring homes and industries through a district energy system.


Historically, excess heat from the likes of steel and power plants has been reused due to the very high temperatures. But as technology has evolved, many more sources that produce excess heat at lower temperatures have become viable to reuse, as we will see in the next chapter. While industrial sites are the largest source of excess heat, large cities without industry also have numerous sources of excess heat that add up to a considerable amount of energy.

Take data centers, for example. Data has become the lifeblood of today’s global digital economy, forming the backbone of the flow of information in cities and powering a range of activities from infrastructure and transport to retail and manufacturing. Data centers are also heavy consumers of electricity. In 2020, data centers in the European Union and United Kingdom consumed 100 TWh of electricity or around 3.5 percent of the region’s final electricity demand. According to the IEA, data centers and data transmission networks account for nearly 1 percent of all energy related greenhouse gas emissions worldwide. Conservative estimates from 2020 counted 1,269 data centers across the European Union and United Kingdom, for a total of 95 TWh of accessible excess heat yearly.

The same goes for supermarkets. Supermarkets are an integral part of communities around the world. They are also big energy consumers. On average, supermarkets consume approximately 3 to 4 percent of the annual electricity production in industrialized countries. In the European Union, there is an excess heat potential from food retail of a total of 44 TWh a year. Although this is significantly lower than the excess heat from industrial sites, this equates to the heat generated by Czech Republic and Belgium in 2021. Adding to this, excess heat from supermarkets can be tapped into very easily and reused in the supermarkets themselves in order to heat the space or to provide warm water. All that’s required is supermarket owners deploying existing, proven technologies. As the supermarket case shows, this can even contribute to significant energy bill savings—even more crucial in the current energy crisis.

Wastewater treatment plants are yet another considerable source of excess heat, with a potential over the whole European Union of 318 TWh of accessible waste heat annually. Even though these sources of excess heat are not as large as the excess heat from industrial sites, together they can cover a considerable amount of energy consumption in urban areas.

For example, let’s look at Greater London. The area has 648 eligible excess heat sources including data centers, subway stations, supermarkets, wastewater treatment plants, and food production facilities. The excess heat from these sources adds up to 9.5 TWh per year, roughly the amount of heat required to heat 790,000 households. The top three sites alone could provide 4.8 TWh of heat yearly.


Keeping food fresh in cooling displays and freezers accounts for most of a supermarket’s energy consumption. It might sound counterintuitive, but cooling displays, freezers and fridges produce a significant amount of heat. Anyone who has ever felt the warmth behind their fridge can confirm that. These cooling systems generate significant amounts of excess heat, which is often released directly into the atmosphere and wasted.

In a small town in Southern Denmark, the local supermarket SuperBrugsen has saved a considerable amount of energy by reusing and selling excess heat from the cooling systems.

Since 2019, 78 percent of SuperBrugsen’s heat consumption has been covered by reused heat from cooling processes. And the supermarket has sold 133.7 MWh to other local buildings through the district heating grid.

Three interlinked initiatives have driven the results:

  • First, the supermarket has converted from chemical refrigerants to a natural refrigerant, namely carbon dioxide, which has very good heat recovery properties.
  • Second, a heat recovery unit is installed at SuperBrugsen, and it is designed to recover the waste heat from carbon dioxide refrigeration systems. The recovered heat is reused to heat up the store and produce domestic hot water.
  • Third, SuperBrugsen runs energy efficiency programs to ensure long-term efficiency. Cooling systems are monitored, technical parameters are adjusted and regular service has improved energy efficiency and lowered energy consumption even more.


Data has become the lifeblood of today’s global digital economy, forming the backbone of the flow of information and powering a range of activities from infrastructure and transport to retail and manufacturing. According to IEA, in 2021 data centers consumed 220-320 TWh of electricity or around 0.9 to 1.3 percent of global final electricity demand—this is more than the electricity consumption of some countries. 

Data centers are also significant producers of excess heat. The servers within a data center generate heat equivalent to their electricity use, and the necessary cooling of these machines also produces a great deal of excess heat. Compared with other sources of excess heat, the flow of excess heat from data centers is uninterruptible and therefore constitutes a very reliant source of clean energy. There are multiple examples that the excess heat from data centers can be reused to heat nearby buildings through a microgrid or it can be exported to the district energy network and used for multiple purposes. 

In the city of Frankfurt am Main, there are several projects in the pipeline working towards assisting the city in taking excess heat from data centers and using it towards its entire heat demand of private households and offices. Mathematically, it has been estimated that the waste heat from the data centers in Frankfurt could, by the year 2030, cover the city’s entire heat demand stemming from private households and office buildings. 

In Dublin, Amazon Web Services has built Ireland’s first, custom-built sustainable solution to provide low-carbon heat to a growing Dublin suburb. The recently completed data center will provide heat for initially 505,000 square feet of public sector buildings. It will also provide heat for 32,000 square feet of commercial space and 135 affordable rental apartments. 

In Norway, a data center has been co-located with the world’s first land-based lobster farm. The co-location company uses a fjord cooling solution to cool its data center, with seawater entering the facility at 46 degrees Fahrenheit (8 degrees Celsius) and then being released back into the fjord at 68 degrees Fahrenheit (20 degrees Celsius). This so happens to be the right temperature for the optimal growth of a lobster. So, moving forward, a new production facility will be built in close proximity to the data center, allowing it to use the heated seawater for the breeding of lobsters.


According to the IEA, the global water sector uses roughly 120 million tons of oil equivalent per year, nearly equivalent to Australia’s total energy use. Without action, global water-related energy consumption will increase by 50 percent by 2030. There is significant potential for energy savings in the water sector if all economically available energy efficiency potentials are exploited—not least when it comes to utilizing excess energy. 

Wastewater contains significant amounts of embedded energy. Sludge can be extracted from wastewater and pumped into digesters. These produce biogas—mostly methane—that can then be burned to make heat and electricity. Consequently, wastewater treatment plants have the potential to be turned from energy consumers to energy producers. 

In Aarhus, Denmark, the Marselisborg Wastewater Treatment Plant (WWTP) produces far more energy than it needs for treating wastewater for the 200,000 people it services. In fact, Marselisborg WWTP produces so much energy that it can cover the energy needed for the demand for drinking water as well. Marselisborg WWTP offers a pathway to an energy-neutral water sector and shows how to decouple energy from water. The Marselisborg WWTP produces enough energy to cover the entire water cycle of a city area of 200,000 people—all with an estimated return on investment of 4.8 years. Furthermore, excess heat from wastewater treatment plants can heat buildings and industries through district energy systems.


Recycling heat is not only an overlooked measure in the current energy crisis, but also the next frontier of the green transition. In the final installment of this series, we’ll present policy recommendations for capturing excess heat that bridge into that exciting frontier. 


Danfoss engineers solutions that increase machine productivity, reduce emissions, lower energy consumption, and enable electrification. Our solutions are used in such areas as refrigeration, air conditioning, heating, power conversion, motor control, industrial machinery, automotive, marine, and off- and on-highway equipment. We also provide solutions for renewable energy, such as solar and wind power, as well as district-energy infrastructure for cities. Our innovative engineering dates back to 1933. Danfoss is family-owned, employing more than 42,000 people, serving customers in more than 100 countries through a global footprint of ninety-five factories. For more information, visit

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