Cooking oil won’t be enough to make aviation sustainable

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Making jet fuel from used cooking oil or crops is more sustainable than burning kerosene, but the industry warns it doesn’t represent a long-term solution to decarbonizing aviation.

Reducing its carbon footprint is a growing issue for a sector that generates about 2.5 percent of global CO2 emissions, and is under pressure to slash its impact on the climate.

The fastest way to cut emissions is to shift away from kerosene — a fossil fuel — to sustainable aviation fuels (SAFs) — an alternative made from non-petroleum feedstocks that don’t require a technological revolution in airframes and engines. But worries are growing that the world can’t produce enough green aviation fuel to meet demand.

“It’s very unlikely that the U.K. will be able to produce all of the SAF that it needs,” said Antony Henderson, head of low-carbon fuel international and trade policy at the U.K. Department for Transport, speaking at a POLITICO event at last week’s Farnborough International Airshow.

The EU and the U.K. have mandates requiring that a rising percentage of SAF be blended with conventional fossil jet fuel starting in 2025. The U.S. hasn’t done the same, but has massively subsidized SAF production through its Inflation Reduction Act.

That has created a strong demand for SAFs, but production is far from what is needed to fuel the world’s air fleets. Not to mention that green fuels cost up to six times more than kerosene.

An unsustainable rush for used Chinese cooking oil has already begun, while it is feared that the push to expand SAFs will see vast areas of land set aside to grow crops for feedstocks. The best long-term solution appears to be using renewable energy and CO2 captured from the atmosphere to make “eSAF,” but that’s an extremely costly process, and has tech and efficiency implications.

Growing crops to produce SAF “is probably the most cost-effective thing to do, the problem is that there’s not much land and you don’t want to affect food [production],” Steven Barrett, professor of engineering at the University of Cambridge, said at the POLITICO event.

“[SAF producers] can also use agricultural waste or municipal solid waste, but that’s limited too,” he added. That category includes used cooking oil, but China is already exporting over half its potential product, even before airlines triple demand in the coming years as expected, according to a recent study by green NGO Transport & Environment.

“Provided we all want a growing and sustainable aviation industry, at some point there won’t be enough biomass and you’ll have to go to eSAF,” Barrett said.

That’s also a concern for Henderson, who mentioned “issues around biodiversity loss, deforestation [and] land-use change that can come from crops” that are used to produce SAF. “On the used cooking oil side,” he added, “there’s a greater and greater risk of fraud in the system, as there’s greater and greater demand.”

That’s why the U.K. is already focusing on “second- and third-generation technologies” such as eSAF.

On the other side of the ocean there’s little interest in exploring alternatives to waste and crops to produce SAF, in part due to worries that eSAF production isn’t a sensible use of renewable energy.

Anna Oldani, chief scientific and technical adviser with the U.S. Federal Aviation Administration, noted that “displacing the renewable electricity to make a low-carbon liquid fuel, versus just using that renewable electricity to decarbonize the grid,” will exact a “severe penalty” in terms of sustainability.

“You’re going to have three times the carbon reduction benefit if you actually just decarbonize the grid, and use [renewable energy] as electricity, rather than diverting it to create a liquid fuel that then gets burned,” she said at Farnborough.

Oldani did add, however, that SAF produced from renewables could be a solution in countries that have an excess of renewable electricity.

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