Andrew Stevens looks at the ability of sustainable aviation fuels to help reduce the industry’s emissions.

US university researchers are looking at whether waste products from craft brewing can power low emissions flight. Scientists have just published research on carbon negative aviation fuel, and Shell is investing in LanzaJet to scale up production of sustainable aviation fuel (SAF).

All three announcements came within days of each other, adding to the steady drumbeat of news about SAF. Since the start of the year rarely a week passes without new reports of research into low emission fuels or deals to boost production.

SAF is breaking out of the trade and special interest publications to become a mainstream topic as the aviation industry builds pathways to its climate target of cutting emissions to 50% of 2005 levels by 2050.

It is the most important weapon in the industry’s quest to meet its target. Although hydrogen-powered electric flight and battery-powered flight potentially delivers zero emissions, scaling up these technologies could still take decades.


Ramping up production

SAF has been around since 2008. More than 300,000 flights have used it blended with regular aviation—without the need for any modification of engines or aircraft—and production continues to grow.

The amount of SAF used by commercial aircraft rose 65% between 2019 and 2020, despite the devastating financial impact of COVID-19 on airlines. In 2021, it is expected to jump another 70%, according to Robert Boyd, IATA Assistant Director of Aviation Environment and Head of SAF.

Although the uptake rate looks impressive it is still a drop in the ocean. SAF accounts for less than 0.1% of total jet fuel.

“Production has increased steadily in recent years despite it being two to four times more expensive than jet fuel,” says Boyd. “We still have a long way to go but the momentum is moving in the right direction to reach critical production mass, and when that happens it will be a game-changing moment for airlines.”

Boyd estimates that on the current trajectory, SAF production could hit 2% of the total fuel demand by 2025. At that level, the price gap between SAF and regular kerosene would be starting to close.

“There is no substitute to liquid fuel on long haul flights on the horizon yet so SAF will be critical in the industry reaching its emissions targets,” notes Boyd.


Three scenarios

The point is backed up by the comprehensive cross-industry Air Transport Action Group (ATAG) report, Waypoint 2050, published in 2020, which establishes how the industry can reach its climate targets.

Researchers developed three scenarios. The first pushed technology and improvements in aircraft operations and infrastructure. It found that SAF would still be responsible for reducing emissions by 61%.

A second scenario looking at the aggressive deployment of SAF found it would be responsible for a 75% reduction of emissions. The third focused on “aspirational and aggressive” development of technology, including hydrogen and electric powered flight. SAF was still expected to account for 50% of emissions reduction.

Whichever way you measure it, SAF remains the industry’s main hope to meet its emissions pledge.

But the clock is ticking.

“The next 10 years are going to be critical for SAF,” says Michael Gill, Director of Aviation Environment at IATA. “We need to get the right policy support from governments to achieve scale. There has never been a better time. Governments around the world are looking to build back better from COVID with a strong focus on sustainability. We must encourage the breaks that other clean energy industries were given at their nascent stages.”


Carbon negative

The argument for SAF is compelling. It reduces lifecycle CO2 emissions some 80%, a figure which is expected to rise significantly in the coming years. According to research by the US-based National Renewable Energy Laboratory, it may be possible to produce carbon negative SAF.

In a paper published by the Proceedings of the National Academy of Sciences, it was reported that targeting food waste, which generates a huge greenhouse gas footprint, could reduce emissions 165%.

Food waste produces methane, a gas 20 times more potent than carbon dioxide. But interrupting the methane generation with fermenters can transform the energy from food waste into volatile fatty acids, which can be upgraded to jet fuel.

SAF can, in fact, be produced from a host of organic material. Waste cooking oil, non-food crops, agriculture waste, landfill, industrial off-gasses, and potentially even from the air itself. The latter is known as power-to-liquid and converts CO2 to SAF using electricity. The catch is that the process is energy intensive and would need sustainably generated electricity to create true zero lifecycle emissions.

There is also a widespread misconception that there is not enough feedstock, or that to create enough would mean competing against food crops, precious water resources, or potentially causing deforestation.

“None of that is true,” says IATA’s Gill. “Research has shown there is enough feedstock available even under the very strict sustainability criteria of what can be used as feedstock.”

There are several compliance schemes to certify SAF as well as Certificates of Sustainability issued by accredited organizations that verify the fuel is from a specific origin and produced using a specific processing pathway.

According to a McKinsey report for the World Economic Forum’s Clean Skies for Tomorrow initiative, by 2030, there will be enough feedstock to power the entire global airline fleet, sustainably. And that is before power-to-liquid SAF is taken into account.

From craft brewing waste, to the oil used to cook your food, to landfills to creating fuel literally out of thin air, the prospects for SAF production are potentially huge. And more and more, that potential is being turned into reality.


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