The Bartlett


Decarbonising energy and the energy transition

19 April 2021

Wind turbines and solar panels against blue sky with blur

At a glance

  • Burning fossil fuels for energy is the major source of carbon dioxide, which is the most important greenhouse gas (GHG) responsible for warming the climate
  • Decarbonising the energy system to emit almost no GHGs is vital for reducing the extent of global climate change. This process is known ‘the energy transition’.
  • Three key factors contribute to energy-related GHG emissions, each of which needs to be continually tracked and analysed, along with planning for how it can be reduced (where possible): the carbon content of energy; the efficiency of energy use (e.g. the miles per gallon of the cars we use; how much heat our homes leak to the outside); and the quantity of ‘energy services’ we demand (e.g. the number of miles we drive; how hot we keep our homes)
  • Energy transition in the UK could be achieved by 2050, but will require widespread changes to both energy supply and demand, which could have significant implications for everyday life.
  • To deal with uncertainties and reduce risks in the energy transition, we need to improve our understanding of the energy transition process, and aim for a balanced approach that encourages societal participation along with technological innovation.

What is the problem?

Energy transition is a complex problem with many dimensions and uncertainties

Energy transition is the process of reducing GHG emissions to ‘net zero’ (i.e. where remaining emissions are balanced by removals of emissions from the atmosphere). This is also called the ‘decarbonisation’ of the energy system.

The major source of GHG emissions is the burning of fossil fuels for energy. Energy transition requires reducing the use of fossil fuels in both the power sector (that supplies electricity) and in directly powered equipment, such as petrol in vehicles, or gas boilers in homes. Fossil fuels can be replaced with low- or zero-carbon sources of energy such as renewables or nuclear energy. Where fossil fuels cannot be removed completely, capturing the GHG emissions at source will be needed, but this is only practical for large sources of these emissions, such as from power stations or industry.

The energy transition is one of the most complex challenges facing industrialised societies today, requiring widespread social and technological changes over several decades. In the UK, detailed plans for achieving a net-zero emissions economy by 2050 have been developed by several government bodies, including the Climate Change Committee, but there is still much uncertainty about the actual path of decarbonisation that will be followed, arising from two factors:

  • The sheer size of the energy system, which includes the billions of pieces of equipment in use in society, the miles of energy infrastructure networks connecting supply to demand such as the national electricity and gas grids, and the transportation of different types of solid, liquid and gaseous fuels (including imports and exports).
  • The need to transform a system that is essential for everyday life, while simultaneously ensuring that it continues to provide energy reliably and affordably.

What are the key characteristics of the problem?

Three key factors influence GHG emissions

Three key factors determine the quantity of carbon dioxide emissions (CO2) from energy use:

  1. The demand for ‘energy services’ (services that require energy in order to be delivered) per person. Energy services are what people really want out of energy: e.g. a mile of passenger travel, a one-degree increase in home temperature, or a certain weight of washing. Demand for energy services can increase over time through mechanisation (where energy-using machines, like washing machines, substitute for human energy), and through the invention of new energy-using equipment to provide new services (e.g. streaming films).
  2. The ‘energy intensity’ of energy services, which is the ratio between energy use and energy services delivered, and an indicator of the success rate of converting the energy supplied into the services that we want: for example, the amount of petrol that is needed per mile driven, or the amount of heating fuel needed to raise room temperature by one degree. Energy intensity can be equipment that uses energy more efficiently (e.g. vehicle engines that waste less energy as heat, or buildings that leak less heat into the atmosphere). While, in general, the energy efficiency of technologies has been increasing over time, many further improvements are still possible.
  3. The carbon content of energy, known as the ‘carbon intensity’ of energy. It is the ratio between GHG emissions and energy use, i.e. the amount of CO2e (CO2 or equivalent other GHG) that is emitted per unit of fuel used. Carbon intensity is measured separately for electricity drawn from the grid, and for each fuel used directly in equipment.

Emissions are the result of these three factors multiplied together. Therefore each factor is important.

There is considerable potential for reducing each of these factors but outcomes are not certain

To reduce GHG emissions, we need to understand the potential for reducing each of the three contributors to emissions. 

- Can the carbon intensity of energy be reduced to zero? In theory, YES - through three main approaches.

  • “Electricity production from renewables and nuclear”: Generating electricity from natural sources such as wind, flowing water, and directly from the sun. This requires appropriate equipment (such as wind and water turbines, or solar photovoltaic (PV) panels) to ‘harvest’ the energy when it is available, and infrastructure to deliver it to where it is needed. Nuclear electricity also produces no emissions when it is generated. Decarbonised electricity can be used for energy services that currently use fossil fuels, which is mostly vehicles for transport and boilers for building heating. However, end-use equipment would have to be replaced – such as replacing petrol cars with electric cars and gas boilers with heat pumps. 
  • “Decarbonising solid and gaseous fuel supplies”: This option allows decarbonisation by replacing high-carbon fuels with low- or zero-carbon fuels for (e.g. replacing fossil fuels with biofuels) without the need to change the energy-using equipment (e.g. thermal power stations, or internal combustion engine vehicles). There are currently insufficient low GHG fuel supplies to replace all of the oil and natural gas used in this way, but there are new solutions being developed. One option for decarbonising the gas grid would be switching to hydrogen gas made through electrolysis with decarbonised electricity (called ‘green hydrogen’). At present there is not enough decarbonised electricity to do this at scale, and the hydrogen produced is much more expensive than natural gas.
  • “GHG capture”: Capturing GHG emissions at source can be done with several different methods, such as capturing the carbon when it is emitted, and using or storing it in ways that keep it out of the atmosphere (this is called ‘carbon capture use and storage, CCUS). CCUS is being explored for large sources of GHGs, such as large industrial plants and power stations, but no large-scale commercial plant is yet in operation because of its cost. 

Can the energy intensity of energy services reach close to zero? Unlikely, but significant reductions are possible.

There is a limit to the potential for reducing energy intensity, since some energy will always be needed to deliver energy services, and some is always likely to be lost in the process. Energy intensity can be reduced with a combination of: 

  • Increasing the energy efficiency of equipment and buildings; 
  • Reducing energy wastage (e.g. not opening windows with the central heating on, not boiling more water than is required for the desired amount of tea); 
  • Increasing the efficiency of energy production and distribution. 

- Can energy services demand be reduced? Reductions in current levels of energy services in developed societies are possible, but by how much is uncertain, and developing countries are certain to want to increase their demand for energy services.

Reducing the demand for energy services is not straightforward, as they form an essential part of people’s well-being, lifestyles and expectations. Historically, societies have tended to demand more energy services as they have become richer, and this has been the main driver of increased GHG emissions. Moreover, as people get used to more energy services (e.g. warmer homes, foreign holidays), they are resistant to cutting back on them. Eventually, energy services demand does tend to stop increasing (e.g. there is a limit to how much people will want to travel by road each year, and a maximum and minimum desired level of indoor temperature). This is called the ‘saturation’ of demand for these services. The world as a whole is very far from reaching this position. 

UK achievements to date are mixed

The graphs below show trends from 1980 to 2019, in UK carbon intensity and energy use. Energy use is measured in kOE – kilogrammes of oil equivalent, which converts all energy forms to the same unit.

decarbonisation graphs
Data source: UK department for Business, Energy and Industrial Strategy, 2019 Greenhouse gas emissions, and Digest of UK Energy Statistics.

The graph on the left illustrates carbon intensity. Since 1980 the carbon intensity of electricity has fallen by 75%, due to fuel switching from coal to natural gas, and later from both to renewables. The average carbon intensity of all other fuels has remained fairly steady – although biofuels have made a difference. 

The graph on the right illustrates energy consumption per person for different services, which is a combination of energy intensity and energy services demands. 

  • Household (domestic) energy services demand over the last few decades has gradually increased, for example, seen as increasing household appliances and winter indoor temperatures. Since 2010 there has been a decrease in energy use, likely due to a saturation in demand and gains in energy efficiency.
  • Transport consumption has increased steadily since 1980. Surface passenger travel per person increased by over a third, and the number of air passengers rose almost fourfold. There were also improvements in average vehicle efficiency. However, increases in energy efficiency were overtaken by stronger increases in energy services demands, leading to an increase in energy consumption.
  • In non-domestic sectors (e.g. industry, services) energy use per person has more than halved since 1980. This has been in part due to gains in energy efficiency, but also due to reductions in the heavy industries that require high energy use. However, the reduced UK energy use (and associated emissions) from the decline in heavy industries have been offset by increased energy use and emissions relating to the manufacture in other countries of imports to the UK, so globally emissions will have declined much less than the graph of non-domestic energy use suggests. 

What is the solution?

Anticipate and deal with uncertainties, especially social ones, to keep the energy transition on track

Since the energy transition is a complex problem with many dimensions and uncertainties, keeping progress on track will require close monitoring and flexible policy. Each influencing factor for emissions - carbon intensity, energy intensity and energy service demands – is important. Reducing each factor to be close to zero is very difficult, and probably only possible for carbon intensity. Therefore, we need to pay close attention to progress in reducing all three terms throughout the energy transition. For example, if energy intensity is reduced but energy services demand increases, as has happened in UK transport in the last few decades, the net effect will be no progress. 

One particular uncertainty is the expectation of a massive increase in the use of electricity – which is a common feature of all credible decarbonisation pathways from energy models. Electricity is expected to take over from fossil fuels in much of transport (e.g. electric vehicles) and building heating (e.g. heat pumps). This will require at least a doubling of the capacity for electricity generation, provided by renewables and, perhaps, nuclear power.  

Encouraging societal understanding of the need for the energy transition, and participation in it, will facilitate changes in behaviour in respect of energy use, and enable a more balanced overall response, rather than relying on success to come mainly through technology.

What is stopping the solution being implemented?

New methods are needed to deal with the complexity of energy transition, and its social and technical (socio-technical) implications

Today’s energy system is the result of decades of investment in producing and delivering fossil fuels and the equipment to use them. These uses are vital for people’s well-being and have become deeply embedded in people’s habits, lifestyles, expectations and aspirations. Some of the changes in the energy system from decarbonisation (e.g. generating much more electricity from offshore wind, or switching from conventional to electric vehicles) will require huge financial investment but not much change to people’s lifestyles. But some of the changes are both more difficult, and currently more costly, than fossil fuels (e.g. developing adequate alternatives to fossil fuels for aviation, or replacing natural gas with green hydrogen). And some cannot be delivered without considerable (albeit short-term) disruption to our lives (e.g. big increases to the efficiency of our buildings). Understanding how to go forward in this complex situation requires considerable further research and analysis. Yet there is little experience to go on, and new theories, concepts and analytical tools are required. Justifying and building confidence in these takes time, but there is also urgency for strong action.

In addition, encouraging participation from society in management of energy services demand and improving energy efficiency is difficult. Past experience shows that results are highly uncertain. There is a risk that policy makers and businesses will struggle to gain the consent of the public to enact these kinds of changes.

How can these barriers be removed?

Careful and responsive policy making, supported by research, is needed to gain and maintain public support for change

Some people are prepared now to make changes to their lives to reduce emissions. Politicians at all levels have important roles in enacting legislation (e.g. in transport and building planning laws) and bringing forward investments (e.g. in electric vehicle charging points) that will support even more people to make low-carbon choices. To gain and maintain public support, it is essential that the changes made to achieve energy transition do not make life more difficult or expensive for the socially and economically disadvantaged in society.

At UCL our research and modelling tries to provide more understanding of the societal and political factors involved in energy transition. It is clear that society interacts with technologies at many levels, and technologies and energy-using lifestyles evolve together. Our work shows the importance of government first leading on the energy transition on the basis of what can be done now, while preparing the ground for the changes that will be required later, all the time explaining the reasons for their actions and taking people and communities with them – helping those who want to change, and showing that the changes can be achieved in an acceptable and fair way. New approaches could ensure that opportunities for economic and societal improvements exist along with achieving emissions reductions. 

The energy transition will take many decades. 2050 is hardly long enough. There is now no time to waste.

Key references for further information