Exploring the world’s largest untapped source of energy

A new Danfoss whitepaper takes a deep dive into how excess heat can be harnessed using existing solutions. Stuart Duff listened to a panel of industry experts exploring this topic.

In the UK and EU alone, excess heat amounts to 2,860TWh/yr – roughly equivalent to the EU’s total energy demand for heat and hot water in residential and service sector buildings. This astonishing statistic is highlighted in data the Danfoss whitepaper on how excess heat can be harnessed using existing solutions.

As part of its drive to convey this message, Danfoss assembled a panel of experts at the Danish Embassy in London to share their views on the whys and wherefores of unlocking the potential of excess heat.

Moderated by Climate Group’s Toby Morgan and introduced by René Dinesen, Ambassador of Denmark to the UK, the panel featured:

The whitepaper, The world’s largest untapped energy source: Excess heat, assesses the potential of excess heat as an efficient energy source. According to the International Energy Agency (IEA), a global push for more efficient use of energy can reduce CO2 emissions by an additional 5 gigatons per year by 2030 compared with current policy settings. According to the IEA net zero scenario, a third of the reduction needed in energy-related CO2 emissions this decade must come from improvements in energy efficiency.

In terms of energy security, these energy savings can help to avoid almost 30 million barrels of oil per day and 650 billion cubic meters of natural gas per year (around four times the EU’s import total from Russia in 2021).

Toby Morgan, Senior Manager, Built Environment, Climate Group states: “The global energy crisis is a wake-up call to stop wasting energy, and Danfoss is right to call for governments and corporates to seize the enormous potential of excess heat. Now more than ever, we need to make better use of the energy we already produce; we simply can’t afford to let it literally escape out the window. Energy efficiency improvements, like capturing and recycling excess heat, are absolutely critical to lower fossil fuel demand and lower bills.”

District heating

Heat networks and district heating underpinned much of the discussion. As Jan Rosenow points out, heat accounts for around 40% of final energy demand in the UK but only 2% of heat demand stems from district heating (with 91% of that total currently served by natural gas). This leaves the UK lagging some way behind countries such as Denmark, where district heating makes up around 60% of demand. This presents a two-pronged challenge: to increase the share of district heating, and to facilitate its decarbonisation. Again, northern Europe provides an example of a more successful model, with Norway’s district heating using heat pumps and excess heat for around 20%. In Jan’s words, it’s “still not amazing but it’s a lot better than the UK, where there’s almost nothing”.

BEIS research from 2021 shows the potential share of total heat demand that could be attributed to district heating, with the figure coming in at 20%. This demonstrates the opportunity that exists if that heat can be decarbonised.

One example of how this decarbonisation is achievable comes from Thames Water, which could capture around 10TWh of excess heat from its operations.


As detailed in the Danfoss whitepaper, there is significant potential for energy savings in the water sector if all of the economically available energy efficiency potential is exploited. Wastewater contains significant amounts of embedded energy. Sludge can be extracted and pumped into digesters which produce biogas – predominantly 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, for example, the Marselisborg Wastewater Treatment Plant produces far more energy than it needs to treat wastewater for the people it services. In fact, it can cover the entire water cycle of a city area of 200,000 people – all with an estimated return on investment of under five years.

Large heat pumps and gas phase-out

“The policy towards large heat pumps in this country is almost entirely absent… whether that’s in terms of supply chain or in terms of technical standards… as we move towards the use of wastewater, that will become increasingly problematic.” Caroline Bragg from ADE pulls no punches on this topic, and is similarly forthright on the need for a phase-out date for gas boilers. Parallels have been drawn with the automotive industry, where the roadmap to ban the sale of new petrol and diesel cars and vans – followed by hybrids – is firmly in place. Caroline states that without that strategic decision, “we are looking at yet another cliff edge where there isn’t a broader framework in place to allow low carbon, exceptionally cost-effective provision of decarbonised heating through heat networks to compete fairly”.

Lessons from around the globe

Astrid Mozes, President Emerging, Growth Regions at Danfoss, makes an impassioned call to action: “This is a social responsibility that every company has in the world to decarbonise… technologies exist today, proven technologies, that can make our heating and cooling much safer, much cheaper, and much more efficient.” To build around that statement, Astrid emphasises that this call needs to be made easily understandable by all: “The excess heat is there, we’re just letting it vanish into thin air… It comes down to awareness; learning and teaching.”

Within its whitepaper, Danfoss presents several examples of real successes in the capture of excess heat which, with the right framework in place, are translatable to the UK.

Case study: Supermarket

Keeping food fresh in cooling displays and freezers accounts for most of a supermarket’s energy consumption. These 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 SuperBrugsen supermarket has saved a considerable amount of energy by reusing and selling excess heat from its cooling systems.

Since 2019, 78% 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. Firstly, the supermarket has converted from chemical refrigerants to a natural refrigerant – CO2 – which has very good heat recovery properties. Secondly, a heat recovery unit is in situ, designed to recover the waste heat from CO2 refrigeration systems. The recovered heat is reused to heat up the store and produce domestic hot water. Thirdly, SuperBrugsen runs energy efficiency programs to ensure long-term efficiency. Cooling systems are monitored, technical parameters are adjusted, and regular servicing has improved energy efficiency and lowered energy consumption further.

Case study: Data centres

According to IEA, in 2021 data centres consumed between 220 and 320 TWh of electricity (0.9 to 1.3% of global final electricity demand). They are also significant producers of excess heat. Compared with other sources, the flow of excess heat from data centres is uninterruptible and therefore constitutes a reliable source of clean energy.

Among the many examples from across Europe of this excess heat being reused, Amazon Web Services has created Ireland’s first, custom-built sustainable solution to provide low-carbon heat to a growing Dublin suburb. The recently completed data centre will initially provide heat for 47,000m2 of public sector buildings, as well as 3,000 m2 of commercial space and 135 affordable rental apartments.

More unusually, in Norway a data centre 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 centre, with seawater entering the facility at 8°C and being released back into the fjord at 20°C. This happens to be the right temperature for the optimal growth of a lobster so a new production facility will be built close by, allowing it to use the heated seawater for lobster breeding.

What’s stopping us from exploiting excess heat?

Essentially nothing, but at the same time a number of factors – not least the lack of either carrot or stick. Regulation is considered to be key in terms of levelling the field and driving the reuse of excess heat. Incentives have a vital role to play too, particularly in the differentiation of technologies with regard to carbon intensity. The technological solutions themselves though, shouldn’t present an issue. As Astrid notes: “We’re not talking about technologies that are coming down the road. We’re talking about technologies that are here and available.”

The Danfoss whitepaper, The world’s largest untapped energy source: Excess heat, is available to download here

Danfoss is exhibiting at InstallerSHOW 2023, which runs 27th to 29th June at the NEC. See the full list of exhibitors here: installershow.com/exhibitors.

Free registration is open.