Understanding the Sustainable Aviation Fuels (SAF) for the Greener Aviation
Introduction
In Nov. 2023, the 1st trans – Atlantic flight using 100% SAF departed from London to New York operated by Virgin Atlantic with regulatory approval from Britain's Civil Aviation Authority. Previously, other commercial airlines that have powered on to the SAF had been on shorter journeys and in up to 50% blends with aviation turbine fuel (ATF, the conventional fuel) as per regulatory limit.
The first commercial test flight powered with SAF (20% blend of biofuel, made from coconut and babassu) flew was from London to Amsterdam by the Virgin Atlantic in Feb. 2008.
If the aviation sector has to align itself with the goals enshrined in the Paris Agreement of 2015 and curb the global warming, the industry needs to transit completely from fossil fuels in long – term. One of the ways, the sector is seeking to replace ATF is by scaling – up the adoption of SAF.
The aviation sector been amongst one of the carbon – intensive sector, contributes 2% of all carbon emissions produced annually and 12% of all CO2 emissions produced by transportation sector as a whole. According to studies from International Council on Clean Transportation, on average, the global passenger aircraft emitted 90 g CO2 per RPK (revenue passenger km) in 2019.
In general, SAF aids to reduce the climate impact of the aviation sector. Compared with other sectors, aviation is relatively a small contributor to the global GHG emissions. However, it is recognized as one of the fastest – growing and the number of flights is expected to grow at an alarming rate over the next decades.
Challenges to decarbonization in the aviation sector
Airlines and startups in SAF space are still in nascent stages of testing breakthrough technologies including multiple approaches towards green hydrogen. It is due to the unique challenge and inherent to the aviation sector as compared to other modes of transport. Differently from the roadways and railways, which have mostly made significant progress towards electrification of the power shaft, whereas in the aviation sector, 80% of emissions are long – haul flights that cover a distance over 1,600 km and for which there are no commercially – viable alternative to the ATFs.
Compared with automobile and power generation sector, where significant progress has been made towards decarbonization, the aviation sector is still in the experimental days of commercializing the new fuel technology. It is worth to note that, the electric batteries at best have a role to play on shorter, regional routes and urban travel and airlines are making these investments.
Whereas, the critics are of the opinion that the aviation industry has been too slow and late – mover to decarbonize and seek climate solutions, but concede that it is a tough task to formulate net – zero strategies for the aviation sector, because of its unique safety and regulatory requirements.
On the positive side, the airlines have completed the test – flights with SAF and deals with SAF producers have started to accumulate.
In 2022, American Airlines — one of the largest airlines globally, finalized the deal with biofuel company Gevo to procure 500 million gallons of SAF over 5 years as a part of its net – zero carbon directive. Thus, the American Airlines became the first airline globally to receive validation from Science Based Targets initiative (SBTi) for its intermediate GHG emissions reduction targets.
Sustainable Aviation Fuel (SAF)
SAF is an umbrella term for energy sources (which are non – fossil derived/ biofuel fuels) and/or replacement fuel made from raw materials to decarbonize the aviation industry.
Alternatively, they may be called as ‘aviation biofuel’, ‘bio – jet fuel’ or ‘bio – aviation fuel (BAF)’.
It is a chemically indistinguishable from ATFs, but the production process is significantly different and greener than traditional fuels.
Depending on the feedstock and technologies (solid biomass using pyrolysis processed with Fischer – Tropsch process (FT-SPK), alcohol – to – jet (ATJ) process from waste fermentation, synthetic biology through a solar reactor, etc.) used to produce the SAF, it still produces fewer emissions, but overall the reduction of “lifecycle GHG emissions” is drastically as compared to the conventional jet fuel.
However, some emerging SAF pathways even have a net – negative carbon footprint such as the integration of carbon capture, utilization and storage (CCUS) to achieve net – negative lifecycle emissions.
Hence, the ability of SAFs to reduce the carbon intensity makes it an important instrument towards aviation sector’s net – zero goals.
Sources/Feedstock of SAF
The most common feedstock for the production of SAF are derived from plants and/or animal materials, municipal waste and agricultural residues. The feedstock for the production of the SAF include:
Generally, the SAF is produced through used cooking oil and agricultural waste, which is widely viewed as the aviation industry best option for cutting – down the GHG emissions.
The SAF undergoes the strict testing at U.S. Federal Aviation Administration Clearinghouse to meet the standards required for ASTM (American Society for Testing and Materials) D4054 certification from ASTM International.
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They are certified as being sustainable by a third-party organisation such as Roundtable on Sustainable Biomaterials (RSB) “ICAO CORSIA”.
Significance of SAF
According to the International Air Transport Association (IATA), the SAF could contribute around 65% of the emission reduction needed by the aviation sector to reach net – zero by 2050. This will require a massive scale – up the production in order to meet demand. It has the potential to decarbonize medium – and long – haul flights which generates the most emission and could extend the life of older aircraft types by lowering their carbon footprint.
In addition, there are various combinations available to decarbonize the aviation sector such as elimination of emissions at the source, offsetting and carbon capture technologies, etc.
The largest acceleration is expected in the 2030s as policy support becomes global, SAF becomes competitive with fossil kerosene, and credible offsets become scarcer.
According to the International Energy Agency (IEA) forecast, the SAF production should expand from 18 to 75 billion litres between 2025 and 2040, representing an increased share of SAF from 5% to 19% in the aviation sector. However, according to the technical review conducted by the U.S. Department of Energy, the SAF are is more expensive than fossil jet kerosene taking taxation and subsidies into account as of 2020.
Advantages
Following are some the direct and additional (indirect) benefits from the adoption of SAF across the aviation sector:
However, despite the significant direct and indirect advantages aiding the adoption of SAF, the critical challenge still remains to figure – out the “sustainable” pathways to increase the supply of SAF while lowering the cost.
Disadvantages/Criticism of SAF
Following are major concerns related to upscaling of the SAF:
Due to these challenges, airlines looking to cut their GHG emissions further faces two hurdles:
Policy initiatives for adoption of SAF
Significant Industry – led initiatives to boost SAF adoption
Conclusion
The decarbonization of the aviation sector is a crucial pathway to move ahead towards low carbon economic model and sustainable and climate – resilient future.
Thus, the initial pivot to SAF would likely rely mainly on bio – based aviation fuels, but that they would eventually be replaced more sophisticated power - to - liquid fuels or e – fuels.
Probably in the long – run, there would be a sustainable and optimized way of sustainable energy, but in the transition, the fastest way is to scale – up adoption of the SAF.
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