Sustainable Aviation Fuel and the E-Kerosene Solution

The Thanksgiving travel season broke records in the U.S., and millions around the world plan to travel for the winter holidays. The bustling airports and long baggage lines bring renewed attention to the massive scale of global air travel. When it comes to how flying impacts the fight against climate change, the aviation sector is largely banking on sustainable aviation fuel to reach net zero by 2050. One advocacy group is painting a gloomy picture in terms of uptake and lifecycle emissions for conventional sustainable aviation fuels, but the emerging e-fuels industry could help push airlines in the right direction.

Not enough sustainable aviation fuel, and not the right kind

Traditional jet fuel is made from refined kerosene, a petroleum product that creates carbon emissions when burned while planes are idling on the runway or flying from place to place. Sustainable aviation fuel, also known as SAF, is a type of biofuel made from non-petroleum inputs like agricultural waste or plant-based oils that significantly lower emissions while performing up to industry standards. 

The Brussels-based organization Transport & Environment tracks the uptake of sustainable fuels at 77 of the world's largest airlines — and it spotted a serious problem with the pace. Those airlines consumed only 2.6 million barrels of sustainable aviation fuel last year, accounting for less than 0.15 percent of their total jet fuel consumption, according to the research. 

The organization determined only 10 out of the 77 airlines are making substantial efforts to find sustainable alternatives. “The remaining 67 are either buying too little SAF, the wrong kind of SAF, or are not considering SAFs at all in their decarbonization plans,” Transport & Environment concluded in its research.

By the "wrong kind" of sustainable aviation fuel, T&E researchers mean fuel made from food or feed crops like corn, which they describe as “not sustainable at all.” The organization calculates that corn, soy oil, and other crops account for more than 30 percent of airlines’ sustainable fuel agreements.

Considering T&E’s position on crop-based fuel, perhaps it’s just as well that uptake is so slow. Bio-based sustainable aviation fuels can cut tailpipe emissions, but that can be outweighed by supply chain impacts.

“Many scientists and international regulatory bodies have concluded that growing crops to make aviation fuel does not reduce emissions on a full lifecycle basis,” World Resources Institute researchers Dan Lashof and Audrey Denvir observed earlier this year. They warned that if left unchecked, energy crops will replace food crops in a rising market for SAF, or energy crops will expand into forests and grasslands, releasing stored carbon from those lands and inhibiting their ability to store carbon in the future. 

The e-kerosene solution

Other sources of SAF are potentially more sustainable. That includes municipal waste, used cooking oils and fats, and animal waste products. All else being equal, though, the complexity of the waste supply chain can involve additional expenses and interruptions.

A more predictable, streamlined source is emerging in the new field of e-fuels. Also called solar fuels, e-fuels leverage electricity from renewable resources to jolt green hydrogen loose from water. The hydrogen can be combined with captured carbon to produce e-kerosene and other synthetic fuels. As underscored by research from the University of California, Davis, e-kerosene is chemically identical to conventional jet fuel.

The primary obstacle to widespread deployment is the cost of green hydrogen, which remains stubbornly high compared to conventional hydrogen sourced from natural gas. However, technology improvements and further cuts in the cost of renewable energy are making green hydrogen more competitive. A recent study from the University of Texas at Austin indicates the cost of green hydrogen could reach parity with fossil-sourced hydrogen by 2030, providing hydrogen and e-fuel stakeholders in Texas with new opportunities to compete for overseas markets.

Many paths to sustainable flight

While T&E advocates strongly for a sharp pivot into e-kerosense, other pathways to sustainable flight are still in motion.

Another UC-Davis research team, for example, has discovered a more cost-effective system for producing bio-based aviation fuel from lignin, the tough cell walls of plants. That would help SAF producers to avoid energy crops and use agricultural or forestry waste instead.

The Joe Biden and Kamala Harris administration also supports multiple avenues to accelerate uptake. In August, the Federal Aviation Administration (FAA) announced a new round of $244.5 million from the Inflation Reduction Act to support 22 sustainable aviation fuel projects, including supply chain analyses, fuel production and aircraft fuel efficiency. For example, the California startup JetZero received $8 million to support its work on an ultra-efficient aircraft design in collaboration with the FAA, NASA and the U.S. Department of Defense.

The electric solution for sustainable flight, eventually

The FAA funding also supports new electric aircraft technology that does away with liquid fuel entirely, in favor of batteries, fuel cells or a combination of both. In this group, the University of Illinois Urbana-Champaign received $2.7 million to upgrade its existing POETS electric aircraft test facility. The new facility will accommodate safety tests for electrical systems designed to power small regional jets. 

As the POETS award suggests, full-sized, long-distance electric flight is still far off in the future. But short-hop electric flight is nearing commercial deployment. One example is the hydrogen fuel cell aviation startup ZeroAvia, which received $4.2 million from the FAA to validate its 2- to 5-megawatt powertrain for planes with 40 to 80 seats.

Between e-kerosene, electric flight and sustainability improvements in the SAF supply chain, there is much cause for optimism. Still, the airline industry is years away from making a substantial dent in its thirst for fossil energy. In the meantime, U.S. businesses that are serious about cutting aviation-related carbon emissions can make a difference by keeping a sharp eye on their use of air travel, and by advocating for improvements in rail systems and other low-carbon alternatives.