September 2023
Alternative non-fossil fuels such as hydrogen and bioenergy are emerging areas of scientific research, each with their benefits and drawbacks. The true sustainability and emission reducing effect of these fuels is unclear and dependent on many factors.
Bioenergy
Bioenergy is the heat or electricity produced from the burning of biomass. When burned it will emit GHGs (equivalent to the amount consumed by the biological material while it was growing) back into the atmosphere, resulting in a net neutral CO2 energy source (note that burning biomass releases small quantities of methane and nitrous oxides that are not absorbed during the growing process and are reported out of scopes in carbon accounting). The type of emissions is highly varied and depends on the type of biomass. Bioenergy is not a zero direct emission heating technology. The sustainability of bioenergy is reliant on the continued growth of biomass to replace that consumed as fuel.
In 2020, 6.4% of Scotland’s non-electrical heat demand was met by renewable technologies; falling short of the 11% target (Renewable Heat in Scotland Report). 70% of this heat came from biomass with the next largest contribution coming from biomethane at 14%.
Reducing the carbon intensity of the GB gas network by blending natural gas with an alternative “decarbonised” gas - sustainably sourced biomethane or low carbon hydrogen – is one approach to reduce heating associated emissions. Subject to the safety and commercial case being established gas blending of GB gas network could become a reality. In autumn 2021 The UK government launched the Green Gas Support Scheme (replacing the Non-domestic Renewable Heat Incentive), which is trialling injecting biomethane into the grid. This scheme will run for four years.
The Scottish government sees a limited role for bioenergy in the decarbonisation of heat (discussed in the Heat in Buildings Strategy) however it will be required in a limited number of hard-to-treat off gas-grid homes where other technologies are inappropriate or, for some small-scale biomass use in local CHP and district heat schemes.
Hydrogen
When burned hydrogen does not produce CO2, making it an attractive alternative energy source to fossil fuels. However, global hydrogen production is dominated by the process of Steam Methane Reforming which emits significant GHG emissions. Hydrogen produced this way is labelled “grey”. Low-carbon or “blue” hydrogen is made by this same process but utilises carbon capture and storage (CCS) technologies. Hydrogen can be made a process called electrolysis powered by renewable energy which it emits no direct GHG emissions, this is then deemed “green”. Currently only 0.04% of global hydrogen production is made in this way (Hydrogen Science Coalition).
Hydrogen could play a useful role in delivering large-scale long-term energy storage in an integrated energy system but its use for heating is, in general, economically, technically, and logistically infeasible. Heating by hydrogen boilers would require approximately 6 times more electricity than with heat pumps to produce the same amount of heat, due to losses in energy along the production chain before use (Hydrogen Science Coalition). The role of hydrogen will depend upon decisions made by the UK Government over the coming years. The Scottish government does not consider that hydrogen will play a central role in the overall decarbonisation of domestic heat, as stated in the draft Energy and Just Transition plan. The most effective uses of hydrogen are expressed as a hierarchy in the Hydrogen Action (p24-26) and Energy and Just Transition Plan (p77-79). In the future (late 2020s), subject to review of the benefits, cost-effectiveness and safety of case trials, there is a possibility that hydrogen will be blended into the gas network up to 20%, greater percentages than this would require pipeline replacement. The required scale and speed of the heat transition means that decarbonisation progress for areas currently on the gas grid is required before the potential for hydrogen is known. At this point, direct use of hydrogen for heating is energy intensive, energy inefficient and unlikely to be a cheap and easy option. It should therefore, in general, be discounted for any retrofits taking place in the short and medium term.
