Decarbonising heat: The hot topic we can’t ignore

Heat. It may often be too hot to handle, but it’s not impossible to decarbonise. And because it accounts for around half of global energy consumption, we need to get on with it. Christian Hüttl and Norbert Wenn from Siemens Energy outline the tools for decarbonising heat at home, in buildings and in industry.

It marries the past with the future. This spring, in the German town of Mannheim on the river Rhine, construction began on a massive heat pump, 18 metres long, five metres tall, directly on the site of a coal-fired power station.

The heat pump will take heat from the river at temperatures as low as 5°C in the winter and up to 25°C (77°F) in the summer and deliver around 20MW of heat.

It is one of five large-scale field trials – called ‘Reallabore’ in German – for large-scale heat pumps in Germany that are using various sources of heat, such as industrial waste heat, geothermal or solar energy, river water, the sea, ambient air, and others.

The heat pump in Mannheim was provided by Siemens Energy and once operational in 2023 it will supply heat to 3500 households in the region – and in return, allow Mannheim to reduce its CO2 emissions by around 10,000 tonnes a year.

Improving efficiencies

The decarbonisation of heat has been largely ignored in public debate. The focus has been mainly on exchanging old oil-systems and adding insulation in buildings, which has only a marginal effect on the carbon intensity of the heat sector.

This is despite the fact that, according to 2020 figures, heat accounts for around half of final energy consumption, contributing 40% of global CO2 emissions. Of that, only 11% are delivered via renewable energy. Today, we cannot ignore heat any longer.

Decarbonisation of heat is not only urgent in order to reach net-zero emissions by the middle of the century, it is also imperative to achieve security of energy supply in geopolitical uncertain times.

To achieve the goal, every lever needs to be pulled. An obvious one is reducing heat demand and improving efficiencies, be it in buildings or industrial processes. But after that, what we you do?

Decarbonisation of heat is not only urgent in order to reach net-zero emissions by the middle of the century, it is also imperative to achieve security of energy supply in geopolitical uncertain times.

Making heat renewable

Heat is mainly used for space heating or industrial processes and most of it is generated with oil, natural gas, or coal.

In order to change this, there are various options, including solar water heating, heat pumps, and the reuse of industrial waste heat. There are also electric heaters or boilers running on green electricity, and burning clean fuels such as biomass or green hydrogen for high temperatures.

This way, heat becomes renewable and the fossil fuels that still dominate today should become a thing of the past.

Most of these solutions use electricity directly or indirectly to replace the fossil-fuelled generation of heat – and electricity is arguably overall the most effective, if not the only means at our disposal to replace fossil fuels.

One solution using electricity is heat pumps. They are indispensable when it comes to the decarbonisation of heat. Why? Because they operate on a relatively simple working principle: with a certain amount of additional energy, in most cases electricity, they lift temperature from a low-temperature heat source to a usable level at the heat sink or consumer.

Therefore, they provide more heat than a direct conversion of electric power to heat. And if the electricity used is green, all the heat produced is also carbon-free.

Space heating for heat pumps

Heat pumps are expected to be deployed worldwide at a large scale in the coming years, paving the way for electrifying the heat sector. Their main application: buildings. That’s not surprising, given that globally 47% of heat was consumed for space and water heating in 2020 according to the International Energy Agency.

For example, heat pumps in Europe are currently mainly used in smaller units for heating buildings. They’re mostly limited to a temperature range below 90° C and their number is growing: in Germany, the Federal Ministry for Economic Affairs and Energy expects around 5.5 million heat pumps installed mostly for individual buildings to deliver around 33 TWh annually by 2030.

Larger industrial size heat pumps, using state of the art low global warming potential (GWP) refrigerants on top of it, can be used for district heating.

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Waste heat from data centres

Another example is the world’s first 8MW-high-temperature-heat pump that is currently being completed in Berlin at Potsdamer Platz, using waste heat from a cooling plant. It upgrades and feeds into the city’s district heating network flexibly at temperatures between 85°C and 120°C.

This concept is easily transferable to data centres for district heating. For servers and IT systems not to overheat, data centres need to be cooled. That in turn generates waste heat.

Also, as every millisecond of data traffic counts, they need to be close to internet exchange points, usually situated in urban areas – and that’s where you find district heating networks.

So, with the help of heat pumps, you can feed district heating systems waste heat of data centres.

For example, at Nokia’s Vlab data centre in Tempere, Finland, six heat pumps take in waste heat and boost it to a temperature of 95°C. That heat is then being fed into Tampere’s district heating system.

Half of the heat consumed in 2020 was used in industrial processes.

Decarbonising industrial process heat

But heat not only gets used for buildings, also for industrial processes. Half of the heat consumed in 2020 was used in industrial processes. There are many heat-intensive processes, be it in steel or chemical industries, glass, pulp and paper, cement factories, textiles manufacturing or mining.

Industrial heat-based processes are numerous: there’s hot air for drying, preheating boiler feedwater, steam production, direct heating, and chemical reactions that need heat ranging from ambient temperatures to thousand degrees of Celsius… and that’s listing just a few applications.

To date, most of this heat demand is being met by fossil fuels. But if we manage to decarbonize industrial heat, it’s estimated we could reduce global CO2 emissions by around 20%.

Read more about decarbonisation on Enlit World

Electric heater advantages

Here, heat pumps have also a role to play as well. In recent developments, industrial heat pumps are being proposed for applications with temperatures of up to 150° C. These high-temperature heat pumps help industries capture waste heat and reuse it to provide hot water or steam for process heating. In steam production, this temperature limit can be pushed even further, for example by applying steam compression.

Electric heaters are another option, using different basic heating principles such as resistive, inductive, or radiative heating.

They have various advantages: they deliver consistent temperatures over time; they are comparatively compact as they don’t need a smokestack; and, if fired with green electricity, they also run carbon-free.

Which method to use depends on the application, be it a crude oil furnace, a cracker in the petrochemical industry, or a molten salt heater.

Firing boilers with clean fuels

All these power-to-heat solutions are suited for the use of renewable energy, either to be fed directly to heaters or via storage solutions. And there is room to grow: so far, renewable electricity makes up only around 1% of industrial heat usage, such as for steel recycling.

Another application is boilers fired with clean fuels, such as biofuels, biogas, or green hydrogen. That’s especially the case in industries that do produce biomass waste, such as pulp and paper, or that make use of incinerating municipal waste.

Biofuels also show that electrification of heat is not the whole story for decarbonisation of heat.

Improving CHP plants

Finally, while combined heat and power (CHP) plants are rather efficient, they can be improved upon. Switching from a coal district heating plant to a gas-fired CHP reduces greenhouse gas emissions considerably.

And by transferring to low-carbon or zero-emissions fuel, such as hydrogen or biomass, maximum fuel efficiency can be achieved. So CHP plants are another relevant factor for decarbonising heat.

Still, it’s clear when it comes to decarbonising heat, there is no one size fits all. First of all, it depends on heat demand. And as heat cannot be transported efficiently over long distances, it should be produced in local proximity to where it’s needed: which in turn requires finding regional carbon-free solutions that can meet this demand.

Challenges to overcome in decarbonising heat

For heat pumps, this means the necessity to find an adequate heat source, be it waste heat, ambient air, geothermal, or any other local heat source.

Also, for producing heat at higher temperatures, it depends on the availability of electricity or of clean fuels, which can be limited by the lack of a distribution network or storage options.

And some challenges still need to be addressed, not least the long-term issue that electrification of heat overall means electricity demand will go up.

As a consequence, we need even more renewable energy, and a mix of energy storage solutions as well as power plants fired with clean fuels to safeguard baseload, as solar and wind fluctuate. And we need grid stability services to be in place.

More immediately, we need positive business cases for decarbonising heat. Today’s rising fossil fuel prices, as well as carbon pricing, support the switch to renewable heat.

While the cost of electrified heating using heat pumps today is already competitive, using electrified heat directly is still more expensive than fossil-based heat. Here regulators can help enabling new business models.

For high temperatures to be achieved with clean fuels, especially green hydrogen, the case for cost-efficient production has still to be made.

Yet, while the need for the business case is clear, we also face the necessity to wean ourselves off fossil fuels. Not just because of climate change, but also to ensure security of energy supply.

Keeping these challenges in mind, it’s important to see that we have most of the technologies in our toolbox to make the decarbonisation of heat a reality.

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