37% of UK carbon emissions come from heating – domestic, public and commercial, and industrial. About 85% of the heating comes from gas. In its Net Zero report, the Committee on Climate Change argues that we must reduce carbon emissions from heating to zero.

There are two routes to cut carbon emissions from heating, reducing the demand and decarbonising the supply.

In a previous blog, I argued that we should drive the demand for domestic space and hot water heating to the absolute minimum and decarbonise the rest. So what is happening in the world of heat supply? What are the approaches, and what progress are we making?

Decarbonising heat supply

At a recent conference on the Future of Heat, the main focus was on decarbonising heat supply. There are benefits to this approach. It works at the level of national infrastructure and tries to keep the complex transition away from the eyes of the consumer. Instead of having to deal with 29 million households, asking them to make long payback investments in an uncertain world, a smaller number of national utility companies, used to handling complex engineering projects over many years, tackle the problem.

One approach is to keep the gas network but to switch from fossil methane to alternative renewable gases. The main options are:

  • biomethane – from anaerobic digestion of organic waste
  • synthetic natural gas (SNG) – from pyrolysis of organic waste
  • hydrogen – using excess renewable energy

We can use biomethane and SNG in our existing infrastructure with no changes in consumer equipment. By injecting them directly into our storage and transport networks, we can transition from fossil methane to ‘green’ methane as production increases.

However, no matter where the methane comes from, burning it still releases CO2 and methane is a powerful greenhouse gas if it escapes. Unless combined with some form of carbon capture, it can never reach net-zero emissions.

Creating a hydrogen energy system

Hydrogen is more interesting gas. Emissions at point of use are zero, although it means changing heating equipment to use it. The challenge with hydrogen is in production, storage and transport.

The current production method for hydrogen is steam methane reformation, reacting water and methane to produce hydrogen and CO2. This consumes a lot of energy and releases CO2, so is not a route to decarbonise heating. We can also generate hydrogen by electrolysis using excess renewable electricity. Hydrogen becomes both a clean energy source and a useful form of storage for spare renewable electricity.

Clean hydrogen is an active area of research. Companies like ITM Power have demonstrated ‘power-to-gas’ systems where hydrogen is injected into the gas network and burned alongside the methane. At the other end of the scale, the Hydrogen 100 project is looking at the challenge of creating a pure hydrogen demonstration network at three demonstration sites. The goal is to tackle the commercial and safety challenges and to provide ‘social proof’ of the viability of hydrogen networks. By 2100 we could transition to 100% ‘green’ hydrogen.

There are many alternative technologies and pathways to decarbonising heat supply through alternative gases; analysed in a report from Imperial College, London. The key takeaway is that there is no unique solution. We will see a slow transition to a decarbonised gas grid using different options based on geography, key resources and end-user demand. Whichever technologies are in use, the UK’s gas grid will be a useful storage battery for renewable energy. A recent report shows that by varying the pressure in the pipeline network, we should be able to provide short-term storage for over 370 GWh.

Heat networks make decarbonisation easier

An alternative route to decarbonisation is heat networks. Supplying heat from a central station through a network of pipes is far more common in European countries than in the UK. Denmark has 31,000 km of heating pipes, reaching 63% of the population. In Copenhagen, 98% of homes use a heat network. They cut carbon emissions by 40% compared to gas boilers and consumer costs by about the same amount.

With a central generation point to inject heat into the network, it is easier to switch to a low carbon heat source. Heat companies in Denmark plan to be using 100% renewable energy by 2030.

Unlike other utilities, heat networks in the UK are not regulated. This is a barrier to wider deployment as there are fewer protections for consumers and less confidence from investors in return on capital. As a speaker from the Association for Decentralised Energy said: “this leads to a Catch 22 – anyone who wants to connect to a heat network likely won’t connect unless the heat network is already built, and anyone who wants to build a heat network will find it hard to build without connections”.

“Catch 22 – anyone who wants to connect to a heat network likely won’t connect unless the heat network is already built, and anyone who wants to build a heat network will find it hard to build without connections”

Hybrid heat pumps

Heat pumps are another distributed approach to low carbon heating, but they place stress on the electricity network during winter, especially if homes are not properly insulated. The Freedom Project has experimented with hybrid systems that use both heat pumps and gas boilers. Using smart control systems, you can minimise emissions by switching between gas heating and heat pumps depending on demand and the minute by minute electricity generation mix.

Hybrid heat pumps deliver savings on energy bills, are easy to retrofit to homes both on and off the gas grid and offer lower carbon heat than using a heat pump alone.

As a transition technology bridging between our current systems and net zero carbon heating, hybrid heat pumps could be part of the overall solution.

There is no single solution but a mixed economy

“all pathways for decarbonisation of heat are of similar cost, so what matters is what can be delivered in the real world… we need to get on with it”

David Joffe of the Committee on Climate Change pointed out what was, for me, one of the key messages from the conference – “all pathways for decarbonisation of heat are of similar cost, so what matters is what can be delivered in the real world… we need to get on with it”.

There is no single solution to the decarbonisation of heat. We will need a mixed economy where multiple technologies contribute to the goal. Energy efficient homes and decarbonised heat sources are not alternatives. It is not a choice of one or the other, we must focus on both.

Zero-Carbon Heat – Pathways to the Future
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