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The challenges for sustainable aviation fuel (SAF)

© Shutterstock / ScharfsinnAirplane run by Sustainable Aviation Fuel (SAF).

Sustainable aviation fuel (SAF) is expected to play a substantial role in the decarbonisation of air travel, but challenges around its source, use, technology, lifecycle emissions reduction potential and impact on food security must be addressed if it is to fulfil its potential.

Today SAF is blended with jet fuel – as the airline industry grows, is this sufficient decarbonisation or just masking a problem?

Corporate travel accounts for around one third of all aviation emissions, making it a key battleground for corporate emissions management.

Despite there being unresolved challenges to the deployment of SAF, the number of deals being announced is rapidly increasing.

The airline industry is estimated to account for around 2.5% of global greenhouse gas emissions, highlighting the urgency of addressing its significant environmental impact.

Global air travel is expected to increase, however, with its fuel consumption projected to rise from 100 billion gallons per year to around 230 billion gallons by 2025. SAF is therefore likely to play a crucial role in reducing aviation emissions.

According to the US Department of Energy, forestry and agricultural residues alone could provide enough biomass energy to generate enough SAF jet fuel to displace 75% of US aviation fuel consumption – but it’s only going to work if it’s done right.

So, what is sustainable aviation fuel?

There is a variety of solutions and technologies purporting to create a more sustainable fuel for aviation. Current options typically use biomass or waste biomass to create new types of jet fuel to replace fossil fuel-based kerosene, or convert captured carbon into synthetic fuels.

Pathways for the production of SAF must be approved by international standards organisation ASTM, with seven processes currently accepted.

Sustainable aviation fuel (SAF) cost

According to Dr Jamie Hollaway, transportation sector manager for the Pacific Northwest National Laboratory (PNNL), “their use is limited. Airlines really want to use SAF but it needs to be cost-competitive with petroleum-based fuels since fuel makes up about 30% of the operating cost of an airline”.

The costs involved in feedstock supply chains, including the infrastructure needed for storage and delivery, pose a significant challenge to the scaling and commercialisation of SAF technologies.

Even the most commercially viable SAFs remain substantially more expensive than conventional kerosene, and covering the difference is a struggle for airlines that already compete based on thin profit margins and incur 22% of their direct costs from fuel.

According to a 2021 report from the International Energy Agency, current policy measures are not adequately supporting the commercialisation and widespread deployment of SAF.

Sustainable aviation fuel is considered by many to have a significant environmental advantage over traditional jet fuel, with up to a 100% reduction in greenhouse gas (GHG) emissions on a lifecycle basis when using low carbon energy and feedstocks along with carbon sequestration. The storage part of the equation, however, is rarely articulated clearly.

Environmental, technical and social implications of SAF production

As well as economic factors, the environmental, technical and social implications of each SAF production pathway must be carefully considered, which makes stakeholder decisions on policy and investment extremely complex.

For example, quantifying the carbon impact of different production pathways can be difficult given the diverse range of feedstocks, infrastructure and technologies they involve. SAFs vary significantly in their decarbonisation potential, with certain biological feedstocks causing particular concern over emissions generated by the land use change required for their growth. Greenpeace has argued that no fuel based on a food crop can be considered sustainable.

This also poses socio-economic issues, as crops that could otherwise be used as food, energy or road transport fuels might be diverted for use in air travel – arguably the lowest priority.

Dedicated energy crops, which can be grown on non-arable land, provide an alternative option, but typically come at an even greater cost.

Technological challenges must also be considered, with different processes varying both in potential yield and in their ability to replicate the characteristics of traditional jet fuel.

Although recent years have seen a number of test flights operated on 100% SAF, each ASTM-approved production pathway is subject to a limitation on the concentration that can be used in standard flights. Even those with the highest limit are capped at a 50% blend of SAF with conventional kerosene, while some have a maximum blending allowance of just 10%.

Many airlines have already begun blending SAF into their fuel supply for commercial flights but, as the aviation industry continues to grow, it is still a far cry from sustainable.

SAF continues to attract significant investment

Despite concerns about the long-term role of SAF in achieving net zero targets, large-scale investment continues. The US Department of Energy (DoE) has just licenced its own technology to Tallgrass and Green Plains, while renewable fuels company Aemetis closed a long-term supply chain for $7 billion of sustainable aviation fuel and renewable diesel in September 2022.

In the same month, Aemetis also confirmed that it has made contracts with 10 different airlines, including a deal with Cathay Pacific, for a total of 916 million gallons of blended SAF. The combined value of the 10 airline contracts, including policy incentives, is approximately $3.8 billion.

The agreements will see Aemetis delivering SAF over a seven-to-ten year time period, to customers including Delta Air Lines, Jet Blue Airlines and oneworld Alliance members American Airlines, Alaska Airlines, British Airways, Cathay Pacific, Finnair, Iberia, Japan Airlines and Qantas.

The fuel being supplied by Aemetis comprises 40% “neat” SAF and 60% petroleum jet fuel, bringing it in line with standardised international blending requirements.

Additional plans to capitalise on SAF come from Boeing (NYSE: B.A.) and Alder Fuels, which aim to expand SAF production globally under a recently announced partnership.

Using Boeing airplanes, the companies will test and qualify Alder’s SAF, advance policies to expedite the transition to renewable energy in aviation, and improve the availability of SAF for the global aerospace market.

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