How do you decarbonise heat? It’s a quite intractable problem. Some 47% of final energy consumption goes on heat, between residential heat and industrial and commercial space heating, most of which is supplied by means of gas (it makes up over 80% of the fuel for home heating and hot water) and that is not to about to go away soon. Only 7% of heat and hot water is electrified. According to the recently-adopted UK Fifth Carbon Budget, by 2030, 13% of heat in homes and about half of business demand should be coming from low carbon sources if we are to meet emissions targets. Although we are doing well on power targets for 2020, on heat we are failing lamentably; and in danger of falling short of 2020 European low carbon heat targets, let alone getting to grips with the Fifth Carbon Budget.
It can be argued that heat has already had its lower carbon revolution, with the move away from heating by coal to gas – between 1980 and 1990, emissions from heat dropped by 15% as gas replaced coal – but very little has happened since, except for the boost to efficient gas use provided by the switch to condensing boilers in the early 2000s. We cannot then argue that gas in heating, as has been argued for power, is a transition fuel to a low carbon economy. Except for the welcome development of Combined Heat and Power district heating schemes, there are no, or few further emissions reductions in sight for home and commercial heating, and district heating is tenable only in more densely populated areas, and preferably in new developments.
The received wisdom on heat is that, eventually, the problem will be solved by electrifying all heat and hot water. Homes will be heated largely by electrically-driven air and ground source heat pumps. This looks to be quite improbable over the next twenty years or so for two reasons. Firstly, the expansion of electricity generation required to provide the additional capacity needed to cope with far greater swings in demand compared with electricity for power looks almost impossible to achieve. And secondly, the practicality of ripping out everyone’s boilers and gas networks to install hundreds of thousands of heat pumps a year from the present installation of a few thousand per annum looks to be an unlikely proposition over the next few years.
So are we stuck with gas forever? Another route is possible and is now gaining some traction, which is to attack the problem from the other end. Rather than change the plant that provides the heat, why not change the fuel that goes into them? This route envisages the substitution of mineral gas going through the mains with biogas injected into them, arising from a variety of processes, including biodigestion of organic matter, resulting in the production of biomethane, which can safely replace about 10% of natural gas in mains supply. We should be talking here, however, about biogases, rather than biogas, since there are several different possible products, each with its own advantages and disadvantages. Hydrogen can be injected into mains to about 10% of the total without changing the specification of plant, but may cause equipment and leakage problems in higher concentrations and is best used in custom-made systems, as is being proved currently in a pilot in Leeds. BioSNG (Bio Substitute Natural Gas) can be produced from waste, is chemically identical to natural gas, and can be injected in greater amounts.
Biomethane production is a quiet success story and to some extent an unanticipated win for the Renewable Heat Incentive. Starting from one or two plants just a few years ago, there are now over fifty plants processing organic material and injecting green gas into the grid. The total amount injected in 2016 is likely to top 3TWh of power for heat – just over 1% of domestic gas consumption, but continuing to grow.
There isn’t a magic ‘silver bullet’ which can unlock heat decarbonisation, and none of these developments stand up by themselves. They are what I have called ‘10% solutions’: if we can envisage each making its 10% contribution, together with district heating heat pumps in their proper place, and of course effective programmes of household energy efficiency enabling demand to be met through lower consumption, then the challenge of decarbonising heat starts to become a realistic proposition by the 2030s. What a green gas route to decarbonisation does need, though, is the kind of support from Government shown in the past for other renewable sources of energy hitherto confined to electricity generation and the adoption of a proactive green gas strategy. The Parliamentary Labour Party’s Energy and Climate Change Committee has produced a short book gathering together a number of contributions on the development of green gas, and an overview of how it can work towards heat decarbonisation. If you would like to view an electronic click here, or if you would prefer a hardcopy get in touch for more information.