Embracing biofuels to reduce reliance on fossil fuels, sustainable aviation fuel has the potential to reduce air travel’s carbon footprint – but perhaps at the expense of other industries in need of sustainable energy.
As the global airline industry recovers from the impact of travel restrictions during the COVID-19 pandemic, there is renewed focus of reducing air travel’s significant carbon emissions to help meet net zero targets.
Aviation accounted for 2% of global energy-related CO2 emissions in 2022, having grown faster in recent decades than rail, road or shipping, according to the International Energy Agency. While this is a relatively small share of global emissions, it is one of the most challenging sectors to decarbonise.
Aviation accounts for around 15% of global oil demand growth up to 2030, according to the International Energy Agency’s New Policies Scenario, a similar amount to the growth from passenger vehicles. Such a rise means that aviation will account for 3.5% of global energy related CO2 emissions by 2030, despite ongoing improvements in aviation efficiency.
In 2021, the International Air Transport Association released a plan for airlines to achieve net-zero carbon by 2050. Individual airlines have made similar commitments, including American Airlines, Qantas and Air New Zealand.
There are efforts to improve aircraft fuel efficiency, along with a push to curb unnecessary air travel, such as France’s ban on short-haul domestic flights. Meanwhile, the industry is also gradually reducing its reliance on fossil fuels with the introduction of biofuels.
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What is sustainable aviation fuel?
Sustainable aviation fuel (SAF) is a hydrocarbon fuel which is derived from biomass, such as plant material or animal waste, rather than relying on fossil fuels. Biofuels are produced over a short period of time, with the input of external energy, using a biomass of living or recently-deceased organisms. This differs from fossil fuels, which are created over millions of years from decomposing plants and animals under geological heat and pressure.
It should also be said that while organic biofuel is being discussed here and made now, the better, longer-term choice is synthetic biofuel, however at this point that technology is new, and not ready for widespread use.
Aircraft makers have successfully trialled running engines solely on SAF, known as “pure SAF”. Yet for now, rather than SAF completely replacing traditional jet fuel, the two are typically blended together.
Currently in the United States, SAFs are approved when blended with jet fuel up to a 50% mix, after which quality tests are completed as per a traditional jet fuel. The blend is then re-certified as Jet A or Jet A-1 fuel.
How is sustainable aviation fuel made?
There are many types of biofuels made from a wide variety of biomass. Likewise, a variety of biofuels can be used as SAF.
First-generation biofuels, which are the most common, rely on high-energy crops such as sugar, starch, and vegetable oil. They have the potential to reduce CO2 emissions compared to conventional jet fuel by 50 to 80% over the lifecycle of the product. That said, first-generation biofuels are the least environmentally friendly biofuels, plus they compete with food crops for precious farming land, which could place pressure on global food supplies. On this topic, land use issues would place some strain on those somewhat optimistic numbers regarding reduction of CO2 emissions.
As such, the EU has committed to start phasing out first-generation biofuels in 2030 and the current ReFuelEU Aviation plan excludes crop-based SAFs due to sustainability concerns.
Second-generation biofuels, which are on the verge of commercialisation, can come from a much broader range of plant materials. They can also come from biomass which has already served a purpose, such as industrial waste, manure, and used cooking oil. These have the potential to reduce greenhouse gas emissions over their life cycle compared to traditional fossil-based jet fuel.
Currently, airlines use a combination of first and second-generation, with the industry working towards using more second-generation biofuels. The potential to scale up biojet kerosene supply based on animal fat and waste oil feedstocks is (very) limited by their supply, according to the International Energy Agency.
Many long-term aviation decarbonisation plans also incorporate synthetic e-kerosene, which is produced by combining hydrogen and carbon dioxide. To ensure zero emissions, the hydrogen must be produced using renewable electricity and the carbon dioxide must be recaptured.
What are the benefits of sustainable aviation fuel?
Sustainable aviation fuel packs a lot of energy for its weight, offering a similar energy density to traditional jet fuel. This makes it a more practical option for aviation, particularly long-haul flights, than alternatives like relying on batteries or liquid hydrogen.
With a similar chemical structure to traditional jet fuel, SAF can be handled in the same way, meaning no changes are required for aircraft or fuelling infrastructure. This allows for a smooth transition with minimal disruptions.
Because SAF is chemically similar to jet fuel, it produces similar CO2 emissions when burned. The reductions come from the overall lifecycle of the product.
This said, many SAFs contain fewer aromatic components, which enables them to burn cleaner. This means lower local emissions of harmful compounds around airports. Aromatic components are also precursors to contrails, which can exacerbate the impacts of climate change. However, the science is not conclusive at this point and claims that SAF does produce fewer non-CO2 impacts need to be treated with caution.
Reducing Australia’s reliance on fossil fuels for aviation would also improve the nation’s energy security. Much of Australia’s jet fuel is imported, leaving the country vulnerable to shortages. Factors threatening supply include international market fluctuations and shortages due to war, sanctions, and environmental disasters.
What is the take-up of sustainable aviation fuel?
Currently, demand for aviation fuel is dominated by jet kerosene, with sustainable aviation fuel accounting for less than 0.1%of all aviation fuels consumed, according to the International Energy Agency.
According to a commitment by the International Air Transport Association (IATA), the aviation industry will reduce carbon emissions by 50% from their 2005 level by 2050. Blending SAF with traditional jet fuel will be essential to meeting this goal. This is reflected in the IEA’s Sustainable Development Scenario (SDS), which anticipates biofuels reaching around 10% of aviation fuel demand by 2030, and close to 20% by 2040. While this sounds significant, it falls short of the numbers committed to in other transport sectors.
One challenge is that planned production capacities will provide only 1 to 2% of jet fuel demand by 2027. This is exacerbated by the push to phase out first-generation biofuels and increasing demand for second-generation biofuels from a wide range of industries.
Finland-based Neste, the world’s largest SAF producer, says it is expanding its facilities in Europe and elsewhere, but points to challenges including sourcing raw materials. Even with investment, new plants take years to build, leaving little time to make the volumes needed to meet the European targets.
Increasing SAF use in aviation to 10% by 2030, in line with net zero targets, will require a significant ramp-up of investment in production capacity, along with supportive policies such as fuel taxes and low-carbon fuels standards.
What are the challenges of sustainable aviation fuel?
One of the biggest challenges of sustainable aviation fuel is cost, currently sitting at around four times that of conventional jet fuel.
The economies of scale required to bring down that cost will be difficult to reach, considering the phasing out of first-generation biofuels and subsequent strong demand for the raw materials to make second-generation biofuels.
Even if the aviation industry could make the shift to SAF, researchers say that the various roadmaps for decarbonising the global aviation industry largely omit a number of fundamental problems.
There is not enough land or renewable energy potential on Earth to produce all the sustainable fuels airlines need. On average across the roadmaps developed by different aviation and non-aviation organisations, producing SAF would require about 9% of global renewable electricity and 30% of available biomass in 2050 – meaning demand for SAF risks displacing other industries. Even then, according to the roadmaps about 30% of fuel used by airlines in 2050 would still be fossil-derived.
The process of converting raw materials into SAFs also leads to a major loss of energy, in the form of heat. In the case of e-kerosene, only about 15% of the primary renewable electricity remains to power the aircraft. Not only is this inefficient, it leaves less clean energy for other industries wanting to decarbonise.
What is the future of sustainable aviation fuel?
Despite questions around supply, governments around the world are introducing Sustainable Aviation Fuel targets.
The EU’s ReFuelEU Aviation Plan requires airlines to use a minimum proportion of SAFs: 2% by 2025, ramping up to 70% by 2050.
In the US, the Sustainable Aviation Fuel Grand Challenge is a government-wide approach to work with industry to reduce cost, enhance sustainability and expand production to achieve 2 billion gallons (rather than the planned 3 billion) per year of domestic SAF production. It aims to achieve a minimum of a 50% reduction in life cycle greenhouse gas emissions compared to conventional fuel by 2030, and 100% of projected aviation jet fuel use, or 35 billion gallons of annual production, by 2050.
Australia announced a Jet Zero Council in June 2023, aimed at reducing carbon emissions and exploring and encouraging a local SAF industry. The Queensland Government and Qantas have formed a partnership to leverage sugarcane and agricultural by-products for SAF biofuel production. Qantas and Airbus announced support for Jet Zero Australia to commence a feasibility study for a new biorefinery in Queensland, which could produce up to 100 million litres of SAF a year.
In the longer term, synthetic fuels like e-kerosene can provide an alternative to biofuels. The need to produce hydrogen from renewable electricity, combined with extracting CO2 from biogenic, concentrated waste streams or atmospheric sources, means that commercialisation “may be challenging” according to the International Energy Agency.
iMOVE Australia’s Developing a low/zero emission transport strategy for Australia project was timely, and important, and the comprehensive final report, FACTS: Framework for an Australian Clean Transport Strategy, is now available for download.
Currently, Australia’s transport system is responsible for approximately 19% of Australia’s total greenhouse gas emissions. And growing! If Australia is to meet its overall obligations to Net Zero 2050, it is patently obvious that transport must shift, and must shift quickly, to decarbonise. In order to do so absolutely requires sustained government and industry action.
The product of the iMOVE project is an important, broad sweep of a document, FACTS: Framework for an Australian Clean Transport Strategy. It is the result of an assembly of a large group of Australian scientific experts, providing evidence-based guidance to local, state/territory and federal governments on how they can support transport decarbonisation in a timeframe congruent with global climate targets
The report is downloadable from FACTS: A Framework for an Australian Clean Transport Strategy.
Emma Whittlesea: Flying toward Net Zero
Sustainable aviation fuel resources
Here’s a selection of articles and documents on the topic of sustainable aviation fuel.
Sustainable aviation fuel: Facts and figures
- Since 2017, activity in Australia’s international aviation sector has decreased significantly due to impacts of COVID-19 on air travel demand. Border restrictions on international passenger movement saw scheduled international passenger numbers decrease from 3.421 million passengers in November 2019 to 155,796 in November 2021.
- Over the same period, demand for international scheduled freight fluctuated, with 103,442 tonnes in November 2019, 81,467 tonnes in November 2020 and 89,909 tonnes in November 2021. The reduction in international air services has had various effects, including reducing fuel efficiency as load factors reduced.
- Australia has a new ambitious 2030 target to reduce greenhouse gas emissions by 43%t below 2005 levels, putting us on track to achieve our net zero emissions by 2050 target. On 16 June 2022, the Australian Government lodged the new 2030 target and reaffirmed the 2050 target as an updated Nationally Determined Contribution under the Paris Agreement.
- The transport sector contributed around 19% of the nation’s emissions in 2020. Within the transport sector, domestic aviation accounted for 7%, compared with cars which accounted for 44% and railways contributing 4%.
Source: Australia’s State Action Plan – International Civil Aviation Organization (ICAO) Assembly Resolution A37-19 on Climate Change
- The challenge for aviation is to abate carbon dioxide (CO2) emissions of over 1 billion tonnes (Gt) in 2019 (the pre-COVID-19 base year), whilst at the same time aiming to grow the sector.
- The total climate impact of air travel is larger than CO2 alone due to other emissions, in particular nitrogen oxides (NOx, where NOx = NO2 + NO), water vapor and soot.
Source: Implications of preferential access to land and clean energy for Sustainable Aviation Fuels
- Unless global aviation changes tack, its greenhouse gas emissions are projected to cause about 0.1℃ of total global warming by 2050.
- The use of batteries and liquid hydrogen to power air travel face significant challenges. Neither are suitable for long-haul flights, and this is why the industry is turning to sustainable aviation fuels.
- Sustainable aviation fuels effectively perform in the same way as their fossil fuel-derived counterparts. They are suitable for long flights and can be used in existing planes so airlines wouldn’t have to replace whole fleets.
- However, at the moment, very little sustainable aviation fuel is being produced – and it’s much more expensive than fossil jet fuel.
Source: There’s a buzz about ‘sustainable’ fuels – but they cannot solve aviation’s colossal climate woes
Australian aviation statistics: 2000—2021
The graphs below show both the impact of COVID-19 on international and domestic air travel, and an illustration of the reduction of fuel efficiency as load factors reduced (along with increased patronage as COVID had less of an influence on people’s travel habits).
