Sector coupling

Linking different sectors for a sustainable energy supply


When you hear the word "sector coupling", the first question you probably ask yourself is: What is it? This is precisely the question we want to explore here. What is sector coupling? Which sectors are involved? Why are these sectors being coupled? What does this have to do with the energy transition? This rather complex topic has gained a lot of importance in recent years due to the increasing decentralised generation of energy and the intended decarbonisation in the areas of energy generation, transport and industry. In addition to decentralised generation, the increasing demand for electricity and the distribution of electricity are also becoming the focus of sector coupling. In the following, we explain step by step what the topic is all about and what potential it brings for the energy transition.

What is meant by sector coupling?

The term sector coupling refers to the connection of different sectors in the context of the energy transition in order to drive decarbonisation through the generation of renewable energies in several sectors. Through the sustainable generation of electricity, avoided emissions can thereby be transferred to other sectors. These are the electricity, heat, buildings, transport and industry sectors. Through various technologies, the energy distribution across these sectors is to be optimised together in order to advance decarbonisation in all sectors.

In the following, the individual sectors are briefly explained and described how renewable energies can improve decarbonisation there.

Image: Schematic representation of the coupling of the heat, gas and electricity sectors through fuel cells and electrolysers. (Source: own representation)

Maik Heuer

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Dr.-Eng. Maik Heuer

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Philipp Kuehne

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Philipp Kühne

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The electricity sector

In the electricity sector, the decarbonisation path is clear. The use of fossil raw materials for electricity generation will be reduced. Germany has decided to phase out coal by 2038 at the latest. There are already voices calling for an earlier phase-out in order to be able to achieve the set climate targets at all. The reduction of energy production from fossil fuels increases the demand for renewable energies considerably.

This demand is to be met predominantly by a strong addition of wind power and photovoltaic plants. By converting naturally occurring energy, such as solar energy and wind energy, into electrical energy, no emissions are caused during generation. However, hydroelectric power plants, which convert the kinetic energy of water into electrical energy, or tidal power plants are also among the renewable energy sources that do not produce any emissions during generation.

The heat sector

Along with the electricity sector, the heating sector is one of the largest CO2 emitters. Thus, it is important to strive for strong decarbonisation through new technologies and sensible and efficient coupling with other sectors. The heat sectors include heating for residential and commercial properties as well as process heat for commercial or industrial production processes. A big step that has been taken in the past is combined heat and power generation. Currently, however, the majority of CHP plants run on a combustion engine, which produces a lot of CO2 and other emissions.

On the one hand, it is important to improve CHP technology through innovations, such as the fuel cell, and to make it fit for the future. Here, for example, one can convert renewable electricity into renewable heat. This is done by efficient heat pumps that use (in the future mainly renewable) electrical energy and geothermal heat, water or ambient air to heat the properties sustainably. The heating sector offers very many opportunities for sector coupling to save large amounts of emissions in the long term.

The building sector

The building sector has a high demand for energy. This can come in different forms, e.g. electrical energy, heating energy but also cooling energy. The type of supply to buildings also plays a role in the energy demand. The status of refurbishment of the properties also has a significant influence. This interaction results in energy-efficient and less energy-efficient buildings with different energy requirements of all kinds.

Buildings have a very large potential for sector coupling. This is where the building sector meets the electricity, heat and transport sectors. Under certain circumstances, also the industrial sector. In the future, buildings that are optimally coupled with other sectors could look like this: An apartment building has a PV system on the roof and a fuel cell CHP in the basement. A high heat demand in winter is covered by an air heat pump, which is operated with electricity from a battery storage (the electricity in the battery storage comes from the CHP or from the PV system). The fuel cell CHP, which runs on hydrogen from the gas pipeline, supplies the base load of the house with electricity and heat. There are charging points for electric cars in front of the building, which tenants can use to charge their cars.

In this example, the building combines all the sectors mentioned here except the industrial sector and is largely self-sufficient through a decentralised energy supply.

The industrial sector

The industrial sector is the largest emitter of CO2 emissions. Industrial production causes a very high level of various pollutants, e.g. in chemical processes or steel production. Accordingly, the potential for savings through the efficient use of resources and the coupling of sectors is greatest here.

The greatest savings potentials in industry lie in the linking of the electricity and heating sectors. Depending on the sector and production process, new technologies can lead to significant savings in emissions. Especially the Power-to-X technologies can be well applied here. This can be used to generate heat or chemicals for production processes in a CO2-neutral way.

The transport sector

The decarbonisation of the transport sector is one of the major projects of the EU and the German government. Major automobile manufacturers have already announced that they will soon no longer build combustion engines. Thus, renewable electricity is to be used for transport. For the passenger car sector with battery-electric vehicles this will certainly work.

However, battery solutions will not deliver the desired effect in the heavy load sector or air and sea transport. Here, other technologies such as hydrogen technologies or fuel cells must provide the propulsion of the future. Renewable energy should also be used for the production of so-called green hydrogen in order to decarbonise these transport sectors.

Which technological solutions are used for the coupling of the different sectors?

In order to enable the coupling of the different sectors, various new technologies are being used. In the following, we will briefly present three essential technologies for this purpose.

Storage systems

To prevent energy from being lost, it makes sense to store it. Unfortunately, however, this is not always so simple. It also depends on the form of the energy. Electric energy is stored in batteries today. These are becoming more efficient and also cheaper every year. Surplus renewable electricity can thus be stored.

Another option for storing electricity is hydrogen. This can be produced and stored from water and electricity with the help of electrolysers. Through fuel cells, the energy in the hydrogen can be converted back into electrical energy. Unfortunately, there are high energy losses in this conversion process compared to storage in a battery. Thermal energy can also be stored. For example, hot water storage, which can be found in almost every house, ice storage for storing cold or latent heat storage such as insulation materials in buildings.

Power-to-X technologies

Power-to-X refers to technologies that convert electrical energy (power) into another form of energy (X). There are several options here:

  • Power-to-Heat converts electricity into heat, e.g. in heat pumps.
  • Power-to-Gas converts electricity into gas. Various gases are possible here, such as hydrogen or methane.
  • Power-to-Liquids converts electricity into liquid fuels or produces chemicals to create fuels.
  • Power-to-Chemicals converts electricity into basic chemicals for production processes in industry.

With these technologies, it is important for sustainability that either renewable or surplus electricity is used. Thus, this is also a form of storage technologies.

Combined heat and power generation (CHP)

CHP technology harnesses the thermal energy generated during electricity production. In the process for generating electricity, heat is released through the conversion or combustion process (depending on the technology). This is not released into the environment, but made usable. Depending on the technology, electrical efficiencies well above 40% can be achieved. Added to this is the thermal efficiency due to the residual waste product heat.

This means that CHP plants can achieve overall efficiencies of over 90%. CHP technologies are considered particularly efficient. In the context of the energy transition, they can make their contribution to decentralised energy supply through micro or mini CHP plants. This is because the decentralised generation of electricity through efficient CHP plants can reduce transmission losses and generate electricity and heat from a single energy source, thus saving emissions.

Image: Combined heat and power for your boiler room: The fuel cell CHP unit inhouse5000+.

What are the advantages of coupling the sectors?

  • Less CO2 emissions
  • Sustainable and efficient energy supply
  • Conservation of resources
  • Lower electricity prices (electricity from PV and wind energy is becoming cheaper and cheaper in the long term and energy from fossil fuels is becoming more and more expensive)
  • Securing security of supply in the long term
  • More flexibility for consumers (decentralisation of energy supply)

What role does sector coupling play in the energy transition?

Sector coupling plays a decisive and very central role in the energy transition. By connecting the different sectors, new highly efficient technologies can be used. As a result, scarce resources can either be better utilised or energies can be generated in a renewable way and used sensibly. This will significantly drive the reduction of emissions.

What role do hydrogen and hydrogen technologies play in the context of sector coupling?

Hydrogen plays a central and supporting role in sector coupling. Hydrogen offers the possibility of storing excess electricity. This is done by generating it from water via electrolysis. Electricity that cannot be used at the time of generation is thus made usable. Hydrogen can be stored and transported, just like other fuels.

The hydrogen can then be converted back into electricity in a fuel cell. This can be used to power cars, trucks, trains or ships in the transport sector. Furthermore, the hydrogen can be converted into heat and electricity in a hydrogen heating system or in a fuel cell CHP unit through combined heat and power. In this way, the hydrogen can be reintroduced into the heat, electricity and building sectors. Generated hydrogen can also be used in the industrial sector. This is where there is currently still the greatest demand for hydrogen, e.g. for chemical processes or for steel production.

What potential does sector coupling have for the future?

The sector coupling, using the right technologies, can lead the desired energy transition to success. Many of the technologies mentioned here are still at the beginning of their commercial development and there is still much potential to be exploited. Technologies that remove and bind CO2 from the environment also have a lot of potential. So-called carbon capture and storage (CCS) technologies. This would theoretically make a CO2-negative energy supply possible.

In addition, sector coupling offers many other potentials in terms of using already existing infrastructures, such as the gas grids. Here, the question must be answered in the future whether the gas grids are also possible for the transport of the very volatile gas hydrogen or also other renewable gases. The fact is that sector coupling is a very exciting topic, very important for the energy transition and thus also for managing the upcoming future task: achieving the set climate targets while maintaining security of supply.

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