Sustainable aviation fuels

The EU executive has proposed a number of policies aimed at the aviation industry, as part of its goal to significantly curtail transport emissions. [Tobias Rehbein / Pixabay]

To achieve the EU’s aim of a 90% drop in transport emissions by 2050, the European Commission has proposed a range of measures, including scrapping the tax-free status of kerosene, and phasing out free CO2 permits handed out to airlines under the bloc’s carbon market.

But one of the measures which could have the most immediate effect on aircraft emissions are proposals to impose a sustainable aviation fuel (SAF) mandate on all flights landing or departing from Europe.

The proposal was tabled in July as part of wider EU plans to cut emissions by 55% at least before 2030. It would require all planes refuelling at EU airports to uplift a set percentage of green jet fuel blended with kerosene.

This policy brief looks at the various types of SAF available and analyses the role of SAFs in decarbonising aviation.

[Edited by Alice Taylor and Frédéric Simon]

Under the ReFuelEU Aviation proposal, all aircraft that depart from an airport inside the bloc will be required to refuel using a kerosene and SAF blend.

The SAF blending requirement will increase over time, rising from 2% in 2025 to 5% in 2030, reaching 63% In 2050.

A sub-target has been set for e-fuels, which should reach 0.7% of SAFs by 2030, scaling up to 28% in 2050.

The requirement will come in the form of a regulation, meaning it will immediately apply across member states once adopted.

To make the regulation as simple to adhere to as possible, there is no green fuel take-up obligation on airlines individually.

Rather, the regulation obliges EU airports to carry SAFs, meaning all tanking aircraft will use green jet fuel.

All planes will be required to refuel with the SAF available at the airport in question. Parallel restrictions would limit a practice that allows airlines to fly in cheaper fuel from elsewhere for the return trip – a process known as “tankering” – meaning the new SAF quota on suppliers would more easily translate into use by airlines.

“Our proposal supports the most innovative, scalable and sustainable aviation fuels, including dedicated sub targets for e-fuels,” said transport commissioner Adina Vălean. “We are preparing Europe to be a front runner and to lead production of sustainable alternative fuels globally.”

The blending mandate will ensure “a level playing field” for operators working out of European airports, and rapidly boost the production of SAFs, according to the European Commission.


The decision to include all trips – whether travelling inside the EU or outside of the bloc – in the SAF mandate has proven controversial, with budget airlines and legacy carriers split on the subject.

National carriers tended to argue that obliging intercontinental flights to include SAFs in their fuel mix puts EU carriers at a competitive disadvantage and will lead to airlines minimising the amount of refuelling they do while in the EU.

But low-cost carriers argued that long-haul flights are the sector’s biggest polluters, making it imperative that they are included in the regulation.

“Cutting just a fraction of these long-haul emissions would reduce more CO2 than is emitted from all of Europe’s short-haul flights combined,” said Michael O’Leary, the CEO of Ryanair. “There is no logic in excluding long-haul flights from SAF usage obligations as this is their only possible way to decarbonise,” he said in a statement.

The International Air Transport Association (IATA), which represents around 290 airlines globally, also warned in the run up to the legislation that applying the SAF mandate to intercontinental flights too quickly could have unintended consequences.

“If the EU unilaterally apply a SAF mandate on all flights to and from the EU before there is international consensus (ideally agreed at the UN’s International Civil Aviation Organization level) and before the price of SAF has fallen to a competitive level, it will create an unfair competitive advantage for non-EU carriers,” said an IATA spokesperson in an emailed statement to EURACTIV.

Rather, the airline body wanted to see the SAF mandate applied “to intra-EU flights only in the first phase, with a potential to be extended in a second phase” once greater international consensus on SAF uptake has been reached.

EU Commissioner Vălean acknowledged that the new requirements will lead to higher fuel costs for industry but said that any increase in fuel costs “should be modest”.

“The cost for clean fuels must be shared as early as possible, just as the transition to sustainable fuels must be driven and endorsed by the entire aviation community,” said the commissioner.

The ReFuelEU Aviation proposal will now be negotiated by lawmakers in the European Parliament and Council before a final version enters into force, a process which is likely to take around two years.

The European Commission has defined SAFs as liquid advanced biofuels (renewable and waste derived) and electro-fuels (produced using renewable energy). When replacing traditional jet fuel, SAFs can reduce carbon emissions by up to 70%.

They can be blended with kerosene up to 50% without requiring changes to airline engines, making them a popular choice with industry to meet green goals.

Engines capable of running on 100% SAF are expected to be rolled out as standard in the coming years. British jet engine manufacturer Rolls-Royce has partnered with oil company Shell to develop and certify commercial engines capable of running on 100% SAF, with an eye to making all engines produced by the company fully SAF compatible by 2023.

The clean-burning nature of SAFs also means that other harmful pollutants emitted by kerosene, such as particulate emissions and sulphur, are much reduced: a 50% SAF blend with conventional jet fuel could reduce particulate emissions by up to 65% and oxides of sulphur by nearly 40%, according to a study sponsored by the US National Academies of Sciences.

However, the widespread uptake of SAFs faces several hurdles.

At present, SAFs are around three times more expensive than kerosene and available in significantly more limited quantities. They currently account for less than 1% of jet fuel used in the EU.

There are also lingering debates over what constitutes a sustainable aviation fuel – and what doesn’t.

The European Commission has set out its rules on SAF in the proposed regulation “ReFuelEU Aviation”.

This legislative proposal must now be approved by the European Parliament and the Council of the European Union, meaning the version of the legislation that passes into law may ultimately be quite different to the text proposed by the Commission.

The sections below explore the various types of SAF in greater detail.

First-generation biofuels are derived from crops. They include cereals, sugar cane, soy, and rapeseed, which are processed into biodiesel and bioethanol.

Currently, these fuels are primarily used in the road transport sector as a means of lowering emissions by displacing fossil fuels.

ReFuelEU Aviation has excluded feedstocks used to make first-generation biofuels from the approved list for SAFs, much to the dissatisfaction of the crop-based biofuels industry.

The European Commission reasons that such crops can drive indirect land use change – a phenomenon whereby crops intended for food are supplanted by crops intended for fuel.

“For sustainability reasons, first generation biofuels such as feed and food crop-based biofuels, which have limited scalability potential and raise sustainability concerns, should not be supported,” states the ReFuelEU Aviation proposal.

Specifically, crop-based biofuels are excluded “because of their limited environmental benefits, limited greenhouse gas savings potential, and the fact that such biofuels are in direct competition with the food and feed sectors for access to feedstock.”

“Such additional demand increases the pressure on land and can lead to the extension of agricultural land into areas with high-carbon stock, such as forests, wetlands and peatland, causing additional greenhouse gas emissions,” the legislative proposal states.

The Commission also wishes to avoid a scenario in which biofuels are used for aviation at the expense of the road transport sector, where they are seen as a key transitional fuel as road vehicles moves towards electricity and hydrogen-power.

The crop-based biofuels industry has reacted strongly to the Commission’s decision to exclude biofuels, questioning why the EU executive is content to allow the use of biofuels to decarbonise cars but not aircraft.

“The Commission’s differentiated approach for road, aviation, and maritime, with different sustainability regimes and limits on feedstocks for biodiesel, is not logical,” André Paula Santos, public affairs director of the European Biodiesel Board (EBB), told EURACTIV.

“One set of sustainability criteria should apply to all transport modes: what is sustainable on European roads should be sustainable in the sea and sky,” EBB president Kristell Guizouarn said in a statement.

Renewable ethanol association ePURE argued that EU measures to phase out feedstock deemed to contribute to indirect land use change, such as palm oil, have already settled the question of biofuel sustainability.

“We know that deforestation and outdated ‘food vs. fuel’ arguments do not apply to EU renewable ethanol… we should be taking the next logical step and unleashing the potential of good biofuels,” said Emmanuel Desplechin, Secretary-General of ePURE.

Debates are yet to take place among co-legislative branches, however, it is not expected that crop-based biofuels will play a significant role in the manufacture of SAFs within the EU.

Feedstock that are approved for the production of sustainable aviation fuels are set out in Annex IX of the Renewable Energy Directive (also updated as part of the European Commission’s “Fit for 55” climate and energy laws package).

The feedstocks included in this list are considered to have zero life-cycle greenhouse gas emissions.

This annex – well known by those in the energy industry – is separated into parts A and B.

Part A covers advanced biofuels feedstock. The feedstock listed contains biomass that is not used as food, including straw, nut shells, animal manure, and biowaste from private households.

Part B is composed of waste lipids and has two entries: used cooking oil and certain animal fats (also known as tallow).

While waste-based biofuels are considered more sustainable than their first-generation counterparts, they too present a number of challenges.

Higher second-generation biofuels targets have raised questions as to whether there is sufficient availability of sustainable advanced fuels to meet the EU’s goals.

Scalability remains a serious challenge – while crop-based biofuels can be increased by simply dedicating more land and growing more crops, waste-based biofuels are much harder to scale.

Efforts tend to focus on expanding waste recovery, ensuring more waste is captured for the production of advanced biofuels. Waste such as used cooking oil is also shipped into Europe from overseas, particularly from Asia.

Mindful of potential production issues, the European Commission has proposed a staggered increase in the mandated SAF targets.


The Commission’s decision to opt for a mandate has been criticised by some in the industry.

The European Waste-based & Advanced Biofuels Association (EWABA) has warned that the mandate as currently proposed, which relies heavily on waste lipid feedstock, could have unintended negative effects and actually make it more difficult to meet the EU’s wider sustainability targets.

EWABA has expressed concerns that ringfencing these waste feedstocks for the aviation sector would severely deplete supply, inhibiting manufacturers’ ability to provide advanced biofuels for the road and maritime sectors, thereby increasing emissions.

The association also believes that ReFuelEU will hurt SMEs in the advanced biofuels industry in favour of big players.

Waste lipids are processed by most SMEs in the industry into a type of biodiesel capable of powering trucks and ships, but generally unsuitable as an aviation fuel.

Processing these waste lipids into a fuel that can be used in airliners – known as Hydrotreated Vegetable Oil (HVO) and Hydrotreated Esters and Fatty Acids (HEFA) – requires an advanced process that only a handful of mega-refineries in Europe can carry out.

“We are not asking to exclude waste lipids from aviation. We advocate for a fair level-playing field in which waste lipids are not included in a separate blending mandate that will ringfence the market for three to four major refiners with waste HVO/HEFA production capacity,” said Leonidas Kanonis, director for communications and analysis at EWABA.

The association says the legislation as proposed essentially grants industry giants an EU-backed revenue stream, enabling them to buy up waste supplies and leaving SMEs with a lack of feedstock to process.

Such a scenario would be catastrophic and force smaller players in the advanced and waste-based biodiesel industry to close more than 50 plants that indirectly employ over 25,000 people, according to EWABA.

E-fuels, known officially as RFNBOs (renewable fuels of non-biological origin), are produced by converting renewable electricity to liquid hydrocarbons through the electrolysis of water. These hydrocarbons are then synthesised with carbon dioxide molecules captured from the air. When the fuels are burned this carbon is released, theoretically rendering the fuel carbon neutral.

Proponents of e-fuels (also called electro-fuels or synthetic fuels) say they offer a scalable alternative to advanced biofuels. As long as there is enough additional renewable energy to power electrolysers, a theoretically unlimited quantity of e-fuels could be generated.

In order to qualify as a SAF, e-fuels must be generated using renewable energy, such as energy from wind or solar – e-fuels made from fossil energy will not count towards SAF targets.

However, one of the biggest questions that hangs over efuels is where the carbon used in its manufacture should be extracted from.

If the carbon is taken from industrial processes using fossil fuels, then the impact of those fossil fuels is still felt, as the e-fuel will eventually release the carbon. Sourcing carbon for renewable fuels is likely to be a larger discussion as e-fuels become more prominent.

Environmental groups, concerned that taking carbon from industrial sources will give tacit encouragement to continue polluting activities, tend to advocate that carbon be taken from the atmosphere through direct air capture (DAC), or other sources like biomass.

Another issue is the quantity of renewably energy required for electrolysis. The process is very energy intensive – a challenging proposition given the relatively limited renewable energy generation capacity of Europe at present.

If scarce renewable energy is used for the creation of e-fuels, this may leave gaps elsewhere, stimulating the use of fossil fuels to plug the gap. If this was to happen, it would essentially erase the environmental benefit.

Proponents say this challenge will ease as Europe ramps up its renewable energy capabilities, but short-term problems remain.

The issue of price is also a major barrier to the uptake of electro-fuels, with e-fuels at present more than five times the price of kerosene and available in significantly smaller quantities.

ReFuelEU sets out a sub-mandate for e-fuels, which the Commission hopes will boost supply and so drop the price of synthetic fuels.

When plans to tax kerosene are factored in, some estimate that fossil kerosene and e-kerosene could reach price parity within the next decade.

Hydrogen and electricity may well be the aviation fuel sources of the future, but for now they remain niche. Both technologies are not yet mature enough for wide scale roll out in aviation.

There are, however, promising signs. Already Velis Electro, a two-seater, propeller-driven plane made by the Slovenian company Pipistrel, has been certified and authorised to fly by the EU’s Aviation Safety Agency (EASA).

Aerospace manufacturing powerhouse Airbus also aims to have a commercial, hydrogen-powered airline in service by 2035.

Electric aircraft are significantly smaller than commercial jetliners – for example, the largest electric airline test flown in Europe to date had space for six passengers, while commercial kerosene-powered jetliners carry upwards of 200 passengers.

One of the main limiting factors for electric jets is the weight of the onboard batteries. To generate the required propulsion, many batteries – space consuming and heavy – are needed.

This has meant that electric planes have a much shorter range than their fossil fuel counterparts and it is not expected that electric aviation will be ready for commercial roll out until 2030.

Hydrogen is also touted as a promising zero-emission fuel source. It is the most abundant element on Earth and a contains two and a half times the energy of kerosene per kilogramme.

However, hydrogen requires more space than kerosene to achieve the same journey length thanks to its lower volumetric density. It needs roughly four times the space of kerosene, meaning larger fuel tanks are required, leaving less room for passengers and cargo.

To ensure that hydrogen remains as a liquid rather than reverting to a gas, it also needs to be kept extremely cold.

“The problem [with hydrogen as a fuel] is with its density,” said Eric Trappier, chairman and CEO of Dassault Aviation, the French manufacturer of military and business jets.

“If we want to carry enough hydrogen in an aircraft, we have to compress it at very high pressures, or liquefy it at very low temperatures,” Trappier said, adding: “The consensus is that hydrogen use may be limited to short and medium range flights.”

Airbus has echoed these comments, telling European Union officials that the company expects hydrogen to be reserved for short- and medium-range planes.

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