The real deal on sustainable aviation fuel and electro fuels

In 2021, the aviation industry accounted for over 2% of global energy-related CO2 emissions, growing faster than road, rail or shipping. Unlike other transport industries, the aviation industry will lag in its transformation to fuels such as hydrogen or to electrified solutions due to the very significant complexities in making changes to what is, necessarily, a highly regulated industry. These complexities will lead to extended timeframes in achieving appropriate technical and commercial readiness and fleet replacement. In addition, air transport is predicted to keep increasing for the foreseeable future.  

To curb growth in net aviation emissions and meet net zero targets, the aviation industry must accelerate its transition to renewable sources of fuel and fuels that can be utilised as “drop-in” alternatives for the existing fossil-based fuels. Australia is well placed to help the world transition to Sustainable Aviation Fuel (SAF) given its vast land mass and emerging renewable energy markets.

Aviation fuel derived from hydrocarbon sources such as crude oil contributes 90% of emissions from the aviation industry. Replacing this with SAF will have the biggest impact on reducing the industry’s carbon footprint.

Sustainable aviation fuel can be derived from biomass or waste materials but also from renewable power and electrolysis of water to produce hydrogen and fuel synthesis using renewable sources of carbon. SAF commonly refers to biomass or waste derived fuels which do not rely heavily on renewable power supplies. e-SAF typically refers to fuels based on renewable electricity and water electrolysis.

For SAF, biomass is harvested, processed to produce an intermediate “bio-liquid” and hydrotreated and separated into various boiling points to produce SAF and other liquid fuels. There are various processing pathways to convert biomass into the intermediate “bio-liquid”, of which seven are currently ASTM-approved for SAF production.

For e-SAF, renewable power drives water electrolysis to produce hydrogen, and the required carbon is typically sourced from a biogenic source, captured from an industrial source or even captured from the air through direct air capture. Hydrogen and carbon are then combined via methanol synthesis o r Fischer-Tropsch and finally hydrotreated and separated to produce e-SAF and other liquid fuels. The e-SAF process is also referred to as “Power-to-Liquid" or PtL.

For both SAF and e-SAF production, water, land and power is required, but in different amounts depending on project specifics. In general, the requirement for water is significantly higher for SAF production and mostly driven by the water required to grow the crops and to process the biomass through to SAF. The water requirement for e-SAF is generally more modest depending on cooling methods selected, but still, by no means insignificant.

Overall land requirements are generally larger for SAF than for e-SAF due to the extensive land requirements for sustainable biomass cropping. Given e-SAF looks preferable from a water and land use perspective, one might expect e-SAF to emerge as the dominant solution. However, the differences in power requirements and cost of production will dominate the early and medium-term solution to decarbonising aviation fuel.

The deployment of renewable power, power storage and transmission play the biggest role in global decarbonisation and all net zero studies indicate that these sectors need to grow at high rates for at least the next decade and likely a lot longer. The entire supply chains for these sectors need to respond to this growth requirement, making deployment of renewable power systems a likely bottleneck to achieving net zero and possibly delaying the reduction in power prices. Furthermore, the decarbonisation impact achieved with renewable power is significantly higher when it is used to decarbonise fossil-based power and to electrify other energy demands than if it is used to generate hydrogen.

The early emergence of a large e-SAF industry would compete with these other requirements for renewable power and will continue to come at a significant cost premium to SAF because of the cost of the power. By contrast the bulk of the energy source for a SAF industry is not reliant on the renewable power sector and avoids that potential bottleneck because it comes from photosynthesis via biomass.

Whilst it is important to initiate demonstration-scale e-SAF projects to commence the development of that industry, it is even more important to initiate the rapid scale-up of the SAF industry to be able to confidently meet the medium-term aviation industry demand and de-risk the industry’s energy transition. Regulatory policy and other government-generated stimulus is urgently needed to get the SAF industry moving.

Australia is now well known internationally for its potential to be a major supplier of renewable energy to the world. This has focused almost exclusively on renewable power and its export via hydrogen derivatives or subsea cable and is due to Australia’s very strong solar and wind resources and land area availability.

Much less is said about Australia’s ability to be a major supplier of biofuel or SAF. The same strengths benefit a biofuels industry, particularly if we consider that drought risk to a biofuels industry could, in many scenarios, be overcome through seawater desalination. Relatively speaking, the power requirement for freshwater production is much less than that required for an electrolysis hydrogen industry.

As well as looking at Australia’s much-spoken-about green hydrogen and e-SAF potential, those exploring ways to source decarbonised fuel for the airline industry should encourage rapid progress in biofuel-based SAF from Australia to de-risk short- and medium-term decarbonisation goals. There are opportunities to work with proponents who are finding ways to mitigate the traditional challenges of a biofuels industry with respect to biomass supplies and conversion technologies. With a burgeoning biofuel industry, Australia would in turn benefit from greater security and diversity of energy supply.

CSIRO is currently working in collaboration with Boeing to assess the SAF feedstock availability and production potential in the Asia-Pacific region. The analysis will help develop a roadmap for the cost-effective production of SAF with regionally appropriate feedstocks and to inform decisions around policy and investment.

GHD is currently supporting a major airline to evaluate investment opportunities in biobased SAF in Australia and looking forward to deploying its technical biofuels and project management skills to support the industry as it takes off.

• Urgent regulatory policy and other government-generated stimulus is needed to rapidly scale up the SAF industry.
• A roadmap for the cost-effective production of SAF will help inform decisions around policy and investment.
• Australian biofuel-based SAF can help meet the medium-term aviation industry demand and de-risk the industry's energy transition.