Analysis: The transition to sustainable aviation fuels represents both a tremendous opportunity and a complex challenge for the aviation sector
As global awareness and regulatory pressures intensify around reducing carbon emissions, the aviation industry faces a monumental challenge to decarbonise effectively. With few viable options for immediate impact, sustainable aviation fuels have emerged as a leading solution with the potential to dramatically reduce lifecycle emissions compared to traditional jet fuels.
Recognising this potential, international bodies like the European Union are rolling out policies, including the ReFuelEU Aviation regulation, which mandates airlines to incorporate sustainable aviation fuels at increasing rates over the coming decades. Under these regulations, fuel suppliers will need to blend at least 2% sustainable fuels by 2025, increasing to 6% by 2030 and a substantial 70% by 2050. Notably, from 2030, 1.2% of all fuel will need to come from synthetic fuels, a requirement that rises to 35% by 2050.
What are sustainable aviation fuels?
Sustainable aviation fuel encompasses a range of alternative fuels designed to replace conventional fossil-based jet fuels. They can be produced from diverse renewable resources, including waste oils, agricultural residues, algae, and non-food crops. Recent advancements have also introduced synthetic or "electro-fuels" (e-fuels), created through carbon capture and renewable energy. E-fuels operate in a closed carbon loop: they're synthesized by capturing CO2 from the atmosphere or industrial emissions and combining it with hydrogen produced using renewable electricity. The result is a fuel that is chemically identical to conventional jet fuel, making it compatible with existing aircraft engines and infrastructure.
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From RTÉ Radio 1's Today with Claire Byrne, is sustainable aviation fuel a silver bullet for the sector - or a white elephant?
This dual approach to production—both bio-based and synthetic—allows for a versatile and scalable strategy, harnessing renewable feedstocks and carbon-neutral processes. Depending on its production method, sustainable fuel has the potential to reduce aviation’s carbon footprint by up to 80% over its lifecycle. Because it is nearly identical in chemical composition to traditional jet fuel, it’s considered "drop-in fuel," meaning it can be used in existing aircraft without engine modifications. It offers a promising route to significantly reducing aviation’s carbon emissions, potentially cutting lifecycle greenhouse gas emissions by 50 to 80%.
However, not all sustainable aviation fuels are created equal. Different production methods, such as Fischer-Tropsch, Alcohol-to-Jet, and Hydrotreated Esters and Fatty Acids offer varying levels of emissions reduction, energy density and pollutant profiles. For example, sustainable fuels derived from waste oils, agricultural residues, or forest biomass often provide significant emissions savings since these feedstocks are renewable and can sequester carbon during growth.
E-fuels, produced by combining captured CO2 with renewable hydrogen, can achieve near-zero emissions over their lifecycle when powered entirely by renewable sources. This variability in environmental impact makes it essential to consider both feedstock and manufacturing process in any comprehensive sustainability assessment—a complexity not fully addressed in the current ReFuelEU mandate.
From Airbus, how is sustainable aviation fuel created?
Energy density is another critical consideration, as it affects fuel efficiency and operational range. Some bio-based sustainable fuels have slightly lower energy density than conventional jet fuel, which could marginally affect fuel consumption and emissions for longer flights. In contrast, synthetic e-fuels match the energy density of conventional kerosene, making them particularly suitable for high-altitude, long-haul flights.
Beyond CO2, sustainable aviation fuels can also reduce sulfur emissions and particulate matter, which are harmful to both human health and the environment. Conventional jet fuel contains sulfur compounds that degrade air quality near airports, but the low sulfur content in sustainable aviation fuels leads to cleaner emissions and reduces contrail formation. However, some bio-based sustainable fuels may still emit trace particulates, while synthetic fuels can be designed to minimize even these minor pollutants. These benefits vary across sustainable aviation fuel types, highlighting the importance of considering the specific environmental profile of each option.
The issue with aromatics
Then, there is the issue with aromatics - a type of hydrocarbon with ring-shaped molecular structures - which play a crucial role in aviation fuel. They contribute to the fuel's density and impact its ability to swell and seal rubber components in aircraft fuel systems, such as gaskets and seals, which prevent leaks.
Most sustainable aviation fuels contain little to no aromatics, which plays a crucial role in aviation fuel and safety
Conventional jet fuels derived from crude oil naturally contain aromatics, but most sustainable aviation fuels, especially synthetic ones and those produced from biomass, contain little to no aromatics. While low-aromatic sustainable aviation fuel offers a cleaner alternative to fossil jet fuel, adding them meets operational and safety standards without amendments to the existing technology.
Challenges with costs and supply
However promising sustainable aviation fuels may be, scaling it for widespread industry adoption presents serious challenges. Currently, production is costly, with prices around three to five times higher than those of conventional jet fuel. This cost disparity, without supportive economic incentives like the Inflation Reduction Act in the US and blending mandates such as ReFuelEU, could hinder adoption. Demand and supply driven policies for sustainable aviation fuels can create a balanced approach to ensure both their adoption and their affordability
The fuels currently represent less than 0.1% of the aviation fuel market, with insufficient production facilities to meet ReFuelEU’s ambitious targets. Scaling production demands extensive investment in infrastructure, not only in refineries but also in logistics for blending and distributing sustainable aviation fuels at both hubs and regional airports This requirement for a comprehensive infrastructure poses further challenges, particularly for airports and regions with limited resources, potentially leading to disparities in sustainable aviation fuels access across Europe.
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The stocks of used cooking oils, agricultural residues and non-food crops required for the fuels face competing demand from other sectors, notably renewable diesel production. Managing sustainability to avoid unintended environmental impacts such as deforestation, habitat destruction and food security issues is essential. Although promising, these fuels come with high resource requirements, needing substantial renewable electricity and advanced carbon capture technologies that are still under development.
The cost of sustainable aviation fuels could also affect public perception of air travel, as higher airfare prices may result and potentially limit travel accessibility. Additionally, recent sustainable aviation fuels scandals, where airlines and fuel suppliers have been scrutinised for greenwashing claims or inaccuracies in sustainable aviation fuels content labeling, have shown that transparency in sourcing and emissions claims will be crucial to maintain consumer trust and support.
The transition to sustainable aviation fuels represents both a tremendous opportunity and a complex challenge for the aviation industry. As a critical tool in the quest for decarbonisation, the fuels offer significant potential to reduce emissions, improve air quality, and move aviation closer to its net-zero ambitions, but take-off faces technological, economic and logistical challenges. As industry, governments, and environmental groups push for adoption, it’s essential that we approach its development with transparency, balancing sustainability goals with operational realities.
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The views expressed here are those of the author and do not represent or reflect the views of RTÉ
