Over the past decades, significant technological developments have taken place in most areas of the aviation sector, except for the fossil-based fuel used by aircraft, which has remained relatively unchanged. Although alternative clean propulsion technologies are under development - such as electric-powered aircraft or cryogenic hydrogen fuel - these options are unlikely to be commercially ready before 2030. The last decade has seen considerable progress in developing Sustainable Aviation Fuels (SAFs) produced from bio-based feedstocks that have a lower carbon intensity, and which consequently could play an important role in mitigating the environmental impact of aviation.
Bio-based aviation fuels are obtained from sources other than petroleum, such as woody biomass, hydrogenated fats and oils, recycled waste or other renewable sources. In order for these fuels to be used in aircraft operations, they must have ‘drop-in’ characteristics, which means they have to meet strict fuel specifications and have comparable behaviour to fossil fuel during the combustion process. As such, the emissions reductions are achieved in their production process. These biobased aviation fuels can be mixed with conventional fossil-based aviation fuel at a blending ratio that is dependent on how the fuel is produced.
There is not a single internationally agreed definition of SAF. The definitions used can cover a wide set of criteria including not only a reduction in greenhouse gas (GHG) emissions, but also other environmental and social aspects such as biodiversity, land use (forests, wetlands, peatlands), water, labour standards applied in production processes and support to the social and economic development of communities involved in fuel production. For the purposes of this chapter, SAFs are defined as bio-based aviation fuels that reduce GHG emissions relative to conventional aviation fuel, while avoiding other adverse sustainability impacts.
Significant interest exists also for non-bio-based feedstocks, in particular the so-called drop-in Power-to-Liquids ‘electrofuels’. This pathway allows the production of a synthetic alternative fuel to fossil kerosene through the use of renewable electricity to produce hydrogen from water by electrolysis and a combination with carbon from CO2 (ideally captured from the air). The Power to-Liquid process can present a favourable greenhouse gas balance relative to conventional and bio-based aviation fuel streams with close to zero emissions . As of today, electrofuels are a technically viable solution to help decarbonise the aviation sector. However, few demonstrator projects are being brought forward due to the fact that electrofuels are 3 to 6 times more expensive than kerosene . According to one study, using electrofuels to meet the expected remaining fuel demand for aviation in 2050 would require 95% of the electricity currently generated using renewables in Europe .
Bio-based aviation fuels
The American Society for Testing and Materials (ASTM) International has developed standards, to approve new biobased aviation fuels, and currently six production pathways have been certified for blending with conventional aviation fuel. These include:
- FT-SPK (Fischer-Tropsch Synthetic Paraffinic Kerosene). Biomass is converted to synthetic gas and then into bio-based aviation fuel. Maximum blending ratio is 50%.
- FT-SPK/A is a variation of FT-SPK, where alkylation of light aromatics creates a hydrocarbon blend that includes aromatic compounds. Maximum blending ratio is 50%.
- HEFA (Hydroprocessed Fatty Acid Esters and Free Fatty Acid). Lipid feedstocks, such as vegetable oils, used cooking oils, tallow, etc. are converted using hydrogen into green diesel, and this can be further separated to obtain bio-based aviation fuel. Maximum blending ratio is 50%.
- HFS-SIP (Hydroprocessing of Fermented Sugars - Synthetic Iso-Paraffinic kerosene). Using modified yeasts, sugars are converted to hydrocarbons. Maximum blending ratio is 10%.
- ATJ-SPK (Alcohol-to-Jet Synthetic Paraffinic Kerosene). Dehydration, oligomerization and hydroprocessing are used to convert alcohols, such as iso-butanol, into hydrocarbon. Maximum blending ratio is 50%.
- Co-processing8. Biocrude up to 5% by volume of lipidic feedstock in petroleum refinery processes.
Additional pathways are currently in the ASTM certification process.
Defining the maturity level of the available bio-based aviation fuel production pathways, either from a technological or from a commercial point of view, is challenging. Despite the dynamism of the sector, only a few of the ASTM certified pathways are supplying fuel on a commercial scale. The technological maturity of each production pathway can be defined through a Technology Readiness Level - TRL, which ranges from 1 for basic ideas, to 9 for an actual system proven in an operational environment. Alongside the technology readiness, the commercial development of a certain fuel could be different due to various other drivers (e.g. certification issues, costs issues). To better clarify the progress of a specific fuel production pathway towards full commercialisation, the US Commercial Aviation Alternative Fuels Initiative has developed the Fuel Readiness Level (FRL) system, which has been endorsed by ICAO . FRL also ranges from 1 for basic ideas to 9 for production capability established, but is tailored for approval of aviation fuel international standards.
Europe is today a key player in the wider biofuel production technology sector, with several commercial-size plants currently in operation. The production capacity of bio-based aviation fuel in the EU relies on a small number of plants, accounting for a maximum potential output of approximately 2.3 million tonnes per year (Max-EU scenario9), which potentially corresponds to about 4% of the total EU conventional fossil aviation fuel demand. It is important to note the distinction between potential bio-based aviation fuel production capacity that is discussed in this section, and the consumption of such fuels discussed in the next section, as several barriers are currently limiting market uptake.
The largest potential share of EU bio-based aviation fuel relies on the processes able to convert various feedstocks and residues into a fuel suitable for commercial flights. The most developed process to date produces Hydroprocessed Fatty Acid Esters and Free Fatty Acid (HEFA). In this process, vegetable oils and/or animal lipid feedstocks can be used to produce a fully certified bio-based alternative to fossil-based aviation fuel. The certified HEFA is a portion of the Hydrotreated Vegetable Oil (HVO) product, which is currently used within the road sector. A pathway that would allow the use of a greater share of the HVO production, thereby increasing the EU production potential, is currently being certified (HEFA expansion or HEFA+).
Refineries producing biomass derived SAF can tune their process in order to increase the output for aviation, if demand increases (Max-EU scenario). However, in view of the relatively low profitability of producing aviation fuel and road fuels, it is reasonable to assume that the actual bio-based aviation portion from the HEFA process would account for a lower share of the processing plant output than the theoretical maximum. A share of 15% has been assumed in defining a moderate bio-based aviation fuel scenario (Mod-J scenario), which results in an estimate of the current EU potential bio-based aviation fuel output equal to 0.355 million tonnes per year ().
The current potential production capacity is substantially based on HEFA plants, but may increase by 2020 with the announcement of new facilities and the scaling-up of existing facilities within the EU. Moreover, the recently certified coprocessing pathway may unlock a larger potential production capacity. However, significant investments into the other ASTM-certified pathways (e.g. ATJ and SIP) do not seem to be a priority at the moment for major industrial players in Europe, even if new actors are expected to become active in the market after 2020 and contribute to the growth in the moderate bio-based aviation fuel scenario.
Price and consumption
The price of bio-based aviation fuel relative to fossil-based kerosene is one of the major barriers to its greater market penetration. Today the feedstock price represents the major component of the final bio-based aviation fuel price, and its price volatility on the EU market can also create supply problems for fuel producers. While a typical price for fossil-based aviation fuel would be €600/tonne, the price of bio-based aviation fuel produced from used cooking oil can be in the range of €950-€1,015/tonne. In addition, feedstocks that comply with sustainability requirements, such as used cooking oil and tallow used in the HEFA process, are in demand by the road fuel sector for biodiesel and green diesel production. It is expected that this competition between road and aviation will further increase in the coming years.
There are various on-going initiatives at the European level aimed at increasing the market penetration of bio-based aviation fuels. However, despite the presence of these initiatives, the current consumption in Europe is very low when compared to the potential production capacity. Only Germany reported the use of bio-based aviation fuels as part of the official 2016 figures under the framework of the Emissions Trading Directive.
9 The information provided in this section is based on the European Commission Directorate General Joint Research Centre (DG JRC) database on the European biofuels production plants [Prussi et al., 2019 – In press].
Sustainable Aviation Fuel Overview
What is a Sustainable Aviation Fuel?
In order for a bio-based aviation fuel to be considered a SAF, it has to meet sustainability criteria. At present, there is currently not a single definition of SAFs agreed at the international level. In the European regulatory framework, sustainability is defined in the Renewable Energy Directive (RED) EC/2009/28. The Council and European Parliament have recently agreed on a revision of the RED, which sets new ambitious targets and includes revised sustainability criteria.
provides an overview of the sustainability criteria agreed for the revised RED. At international level, discussions are ongoing to agree on criteria to assess the sustainability of aviation fuels, which would be eligible for the purposes of ICAO’s CORSIA scheme (see Market-Based Measures chapter).
Reduction in greenhouse gas emissions
Bio-based aviation fuels may have lower GHG emissions in comparison with traditional fossil fuels. Indeed, the emissions from biofuel combustion are often considered as being zero, given that the fuels are produced from biomass. These are referred to as ‘biogenic emissions’, and they are assumed to be zero on the basis that the growth of the biomass absorbs the same amount of CO2 released during combustion. Conversely, ‘non-biogenic emissions’ are used to refer to production emissions from bio-based aviation fuels, resulting from the cultivation, harvesting and transport of the biomass, as well as from its conversion into fuel. These ‘non-biogenic emissions’ are not offset, and consequently constitute a direct impact of the bio-based aviation fuels. The difference between the ‘non-biogenic emissions’ of the bio-based aviation fuel, and the emissions from using a standard fossil derived fuel, constitutes the potential bio-based aviation fuel GHG saving.
There is ongoing discussion about the most appropriate methodology to assess the emissions reduction performance of the different pathways through a Life-Cycle Assessment. This is particularly relevant for those pathways that are currently entering the market. In many processes more than one product is produced, and it is necessary to divide the GHG impacts between these products. There is also much debate about how to account for indirect emissions such as cultivation emissions closely related to the farming practices and soil types (i.e. forest dynamic). Depending on these indirect effects, the emissions of a bio-based aviation fuel as compared to the emissions from the production and combustion of conventional aviation fuel can be lower, comparable or even higher.
The European Commission’s Joint Research Centre is actively contributing to on-going discussion on the quantification of GHG emissions reduction potential from bio-based aviation fuels. While the GHG emissions from the production of HEFA based on feedstocks such as sunflower and soybean oils can be estimated at around 40 gCO2eq/MJ, the same HEFA process fed by rapeseed oil is estimated to result in higher GHG emissions, of around 51 gCO2eq/MJ due to differences in production chains. In order to calculate the potential GHG reductions from bio-based aviation fuel, it is worth noting that ICAO have defined a reference level of GHG emissions from a fossil-based aviation fuel as 89 gCO2eq/MJ.provides an overview of direct emissions savings for a variety of bio-based aviation fuel pathways.
The EU sees an important role for SAF in contributing to reduce the environmental impact of aviation. This is why it is taking action in a number of areas to support a greater uptake of SAF within the European market, including research within the ‘Horizon 2020’ programme that supports the development and pre-commercial production of SAF. From 2013 to 2020, a total budget of €464 million is available to study advanced biofuels and other renewable sources, of which €25 million has been specifically allocated to SAF.
The Renewable Energy Directive (RED), which was adopted in 2009, established an overall policy framework for the production and promotion of energy from renewable sources in the EU. The RED requires all EU countries to ensure that at least 10% of their transport energy comes from renewable sources by 2020. The RED also includes multipliers which count the contribution of biofuels by a factor greater than 1 in order to encourage the use of advanced biofuels and meet future targets, while capping the contribution of bio-based fuels derived from food/feed-competing crops. The RED targets do not apply to aviation fuel. However, in 2015, the RED was amended 10 and the UK.to recognise the possibility of a so-called ‘voluntary aviation opt-in’ to implement in national legislation, which was taken up by the Netherlands
An agreement has recently been reached on an update to the RED that now requires fuel suppliers to ensure that at least 14% of energy used in the EU transport sector comes from renewable sources by 2030. Under this revision, SAF can contribute to the achievement of the RED targets in all Member States, on condition that they comply with the associated sustainability criteria. In addition, a specific multiplier of 1.2 is to be applied to the quantity of SAF supplied, in calculating its contribution towards the renewable energy targets. The contribution of bio-based fuels from food or feed crops to the targets in each Member State will be capped at around its level in 2020. The contribution of any high-indirect land use change risk food or feed crop-based biofuels, produced from food or feed crops for which a significant expansion of the production area into land with high carbon stock is observed, towards the targets in each Member State will be capped at the 2019 level of consumption of such fuels until 2023, after which their contribution will gradually be reduced to 0% by 2030 at the latest. Biofuels certified as low indirect land use change risk will be excluded from this limit.
The EU Emissions Trading System (EU ETS) provides an incentive to aircraft operators to use SAF that comply with the sustainability criteria defined in the RED by attributing them zero emissions under the scheme. The use of SAF thereby reduces an aircraft operator’s reported emissions, and the number of ETS allowances it has to purchase. This provides a financial incentive for aircraft operators to use SAF instead of conventional aviation fuels.
The European Advanced Biofuels Flightpath was launched in 2011 as a partnership between the European Commission and major European stakeholders, with the aim to accelerate the speed at which SAF are brought to market. It is clear that the goal previously set by the group for 2 million tonnes of SAF to be produced annually by 2020 will not be met. The European Advanced Biofuels Flightpath is working on an updated roadmap towards 2030.
The UN International Civil Aviation Organization (ICAO) recognises SAF as an important element in reducing GHG emissions from aviation. Following ICAO’s 39th Assembly in 2016, Resolution A39-2 requested Member States to put in place coordinated policy actions to accelerate the development, deployment and use of SAF. The second ICAO Conference on Aviation and Alternative Fuels in 2017 subsequently adopted a 2050 Vision for SAFs that called on States and all stakeholders to ensure that a significant proportion of fossil-based aviation fuels be substituted with SAF by 2050. Quantified targets are to be agreed at the next conference due to take place by 2025.
ICAO’s Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) will be implemented as of 2021, and will allow aircraft operators to reduce their offsetting obligations by using SAFs and fossil based ‘lower carbon aviation fuels’. These fuels must comply with sustainability criteria, which as noted in section 3.3 are still the subject of ongoing discussions. The extent to which SAF eligible under CORSIA will make a positive contribution to mitigating the environmental impacts of international aviation will depend on the sustainability criteria for their eligibility. ICAO has not yet adopted these. The reduction in offsetting requirements that can be claimed is equal to the emissions reductions calculated for the specific fuel used. This is based on the difference between the baseline life cycle emissions of 89 gCO2eq/ MJ and the calculated life cycle emissions of the specific bio-based fuel. Work is still on-going to quantify induced land use change reference values that will be used to calculate the total life cycle emissions of the fuels.
Looking to the future
There is broad agreement that SAFs have a potentially important role to play in reducing the environmental impact of European aviation, and in reducing the sector’s exposure to crude oil price volatility.
The current consumption of SAF remains very low in Europe. However, recent developments, including policy actions at the EU and global level, are intended to create incentives to increase the uptake of SAF in Europe. Nevertheless, the uptake of SAF is likely to remain limited to below 1% of total EU aviation fuel consumption in the near future, and its evolution in the mid/long term within the European market is still difficult to predict.
1. Airport initiatives on SAF
During 2016 and 2017 Avinor’s Oslo and Bergen airports became the first in the world to offer SAF to all airlines on a commercial basis, and a total of 1.325 million litres of SAF was uplifted. The bio-based SAF consumption at Swedavia airports in 2016 was 450 tonnes, and currently new SAF initiatives are planned from 2018 onward. Other initiatives include the French ‘Green Deal’, and the ‘Fly Green Fund‘ that is offering travellers the opportunity to contribute to the extra-cost associated with using SAF. The Fly Green Fund has a supply contract with SkyNRG, which in turn sources SAF from AltAir in the USA.
2. IAG Sustainable Aviation Fuels - Turning waste into fuel
IAG is part of a project with UK renewable fuels specialist Velocys to produce aviation fuel from household waste which will then be supplied to British Airways. Production should start in 2022, making it one of the first plants in the world dedicated to producing bio-based aviation fuel on a commercial scale. Ultimately, IAG hopes biofuels could provide up to 25% of its fuel by 2050. The fuel emits 60% less greenhouse gases and 90% fewer particulates than fossil fuels, and the planned plant will produce around 30,000 tonnes a year – delivering CO2 savings of some 60,000 tonnes annually.
Recent changes to the UK Renewable Transport Fuel Obligation, which sets targets for sustainable fuel use in transport, means the new fuel will qualify for government incentives to help develop the technology. The incentives will make it more price competitive with conventional fuels, helping make the business case for its adoption. The government has shown further support for the project by awarding Velocys a grant on the grounds of sustainable fuel’s potential to help meet the UK’s low-carbon vision.
3. Delivery of new Airbus aircraft
Since May 2016, Airbus has offered customers the option of taking delivery of new aircraft using a blend of SAF. More than 25 aircraft have been delivered to date with 3 different airlines. Airbus, along with its partners are currently investigating how to scale-up sustainable fuel deployment across its sites and operations.