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Sustainable aviation fuel is unlikely to meet the UK government’s claims that flying can be decarbonized within the next few decades, a report by academics at the Royal Society concluded on Tuesday, February 28.
The report from the UK’s oldest scientific academy concluded that supplies of wastes, such as household rubbish or unrecyclable plastics, and green hydrogen, such as e-fuels, are likely to be insufficient to yield the volumes of biofuels required to meet net-zero targets.
Because of this, the UK will be heavily reliant on imports from countries that will likely have biojet mandates in place and similar challenges in securing sufficient supplies of affordable or genuinely sustainable feedstocks.
“Despite best endeavors at developing and rolling out alternative fuels, a scenario may arise where the reliance is predominantly on hydrocarbon fuels if the alternatives can’t be manufactured and safely deployed at the scale needed,” said the report, which has been published at a crucial juncture for the UK’s renewable fuels sector.
Within the next few months, the government is expected to provide responses on a biojet mandate and clearer rules on some waste-based feedstocks.
The government, in the past few years, has said that the UK’s aviation sector can achieve “net-zero” carbon by 2050 through the development of domestic SAF plants using a range of technologies that can deliver “guilt-free” flying and put the country at the vanguard of technologies to produce alternatives to fossil-based kerosene.
That viewpoint – and broad policy considerations that biofuels and aircraft powered by batteries and hydrogen fuel cells can solve the UK’s aviation emissions conundrum – has prompted considerable skepticism already. Many green groups and some transport analysts have pointed out that only a drastic reduction in air travel volume can help the UK meet its carbon targets.
In its analysis on individual feedstocks, the Royal Society report said that the UK’s domestic supply of used cooking oil – the main feedstock for available supplies of SAF – would yield 50 to 100 million liters of biojet fuel, which is equivalent to 0.3-0.6% of the total jet fuel used every year in the UK.
However, this conclusion does not fully acknowledge the current dynamics of waste feedstock markets for road-based biodiesel, where Britain already sources the vast majority of its UCO from countries such as China and Malaysia.
Meanwhile, the UK’s lack of forested areas means that wood-based advanced biofuels for use in SAF would require large volumes of imports of biomass or finished biojet fuel – and at high cost, the report pointed out.
In terms of municipal solid waste, a feedstock that is key to some of the SAF projects that are on the drawing board for the UK, the report concluded that 12 million tonnes per year is potentially available for domestic output but that just 1.2 million metric tonnes per year will be available for SAF, which is 10% of the total amount of fuel required.
In terms of other technologies that have been trumpeted as solutions by the UK government, the report highlighted the large volumes of renewable electricity that would be required to produce hydrogen (207-290 TerraWatt (TWh) hours, ammonia (217-332 TWh), or e-fuels (468-660 TWh) in the quantities required to replace current jet fuel use in the UK.
The report also highlighted the huge cost multiples that would be a major obstacle to mass production of SAF in the UK.
View our data analysis on US feedstock price trends
“The cost of energy of these alternative fuels is much higher (£34.4-£41.3/Gigajoule [GJ] for hydrogen, £32-£62.2/GJ for ammonia and £72.7- 94.5£/GJ for e-fuels) than that of conventional jet fuel (£11-£27/GJ),” the report said.
Lobby groups were not immediately available to respond to the Royal Society’s conclusions, which were widely reported by UK print and broadcast media on Tuesday.
Proponents of SAF in the UK have underlined that, as a new sector, biojet requires the delivery of several major conditions before it can reach mass production, such as stronger financial incentives, greater urgency on legislation required for a dedicated SAF mandate by 2025, and swift progress in getting several projects off the drawing board and into the construction phase.
The availability of many types of feedstocks will likely rise sharply once mandates and stronger price signals are in place, biojet’s backers say, but a UK SAF mandate is needed very soon in view of the EU’s own binding targets – also earmarked for 2025 – and the fiscal incentives offered by the recently enacted Inflation Reduction Act in the US.
The Royal Society’s report also made reference to crop-based feedstocks, which it said would require half of the UK’s farmland to be given over to the production of oilseeds and other commodities required to meet a net-zero target.
But UK policy – and that of the EU, where the majority of flights taking off in Britain end up – has for the last few years proposed that crop-based biofuels be excluded from future mandates, a key consideration that does not appear to have informed the Royal Society’s report.