Can We Keep Flying on Sustainable Aviation Fuels?

They do reduce the carbon footprint of aviation, but there will never be enough of them.

Neste Delivering Fuel
Neste Delivering Fuel.

NESTE media release

Sustainable Aviation Fuel, or SAF, is in the news these days; Bill Gates recently wrote that he has been filling his private jet with it since 2020. Treehugger recently covered KLM's use of Neste's fuel which is a "drop-in" alternative that can replace up to 50% of the fossil fuel, although at this time they do not go higher than 35%.

Commenters complained that KLM's fuel was made from palm oil, and the Indonesian government recently announced that they are going to start making SAF – but most western suppliers of SAF recognize the problems with palm oil production. Neste, for example, says their fuel is "based on waste and residue feedstocks that significantly reduce the CO2 footprint and do not have a negative impact on food production or the environment," meaning that it is not competing for corn and palm oil, and says it is "sustainably sourced, 100 percent renewable waste and residue materials, like used cooking oil or animal fats."

This raises a basic question: how much of the stuff is there? There are only so many deep fryers to be emptied. A recent working paper, "Estimating sustainable aviation fuel feedstock availability to meet growing European Union demand" from the International Council on Clean Transportation (ICCT) looked at the question. It is talking Europe only, but it is likely that the same circumstances apply in North America.

Currently, SAF covers only 0.05% of the world's jet fuel, and is almost entirely made from fats, oil, and grease (FOG). But there is limited waste grease and oil out there, and only so much lard and beef tallow available, and there are competing uses for them, including food products, soap manufacture and being turned right back into pet food and animal feed in the United States. So while FOG are the easiest and most efficient alternative to petroleum-based aviation fuel, there are limits on how much of it is available. I have also wondered how happy vegans would be, knowing that they are flying on fat.

Palm oil can also be used, but the study authors discount it because "given the high land use GHG emissions associated with palm oil, use of Palm Fatty Acid Distillates (PFADs) in biofuel production would most likely cause high indirect GHG emissions."

Cellulosic wastes can be used, but this is expensive and difficult to produce; even with serious U.S. government support, nobody has been able to make it work cost-effectively.

Agricultural residues such as stems and leaves and wheat chaff could be converted into fuel, but most of this is left in the ground now to provide nutrients and moisture for the soil. It is also used for animal bedding and other functions now, that would compete with fuel. The same is true of forestry residues.

The study authors also look at municipal waste, cover crops, and high-tech alternatives such as electrofuels and industrial flue gases. All of these are either already being used, or too pie-in-the-sky to be realistic.

Feedstock availability

The working paper looks at the availability of the various feedstocks, and the efficiency of the conversions to fuel, which varies dramatically, from 90% for FOGs down to 20% for agricultural waste. In the end, they find that there just isn't enough of the stuff.

Percentages of total demand
"Taking into account sustainable availability and an optimistic assumption for the deployment rate of novel conversion technologies, we estimate that there is a resource base to meet approximately 5.5% of the European Union’s projected 2030 jet fuel demand using advanced SAFs. However, if the European Union adopts weaker incentives that primarily encourage the use of waste oils and diversion from the road sector, we estimate a maximum advanced SAF deployment of only 1.9% of projected 2030 EU jet fuel demand... The limited resource base for producing advanced SAFs suggests that biogenic SAFs alone cannot decarbonize aviation in the EU and will have only a limited impact through 2030."

Essentially, without a lot of investment, it is not going to make a whole lot of difference to the industry.

"Absent strong policy support and long-term commitments to advanced fuels, it will be difficult to do more than divert waste oils from other sectors. High blending targets in the absence of complementary policies may instead open the door to higher use of food-based biofuels in aviation. Even with strong policies in place, the limited availability of the best-performing feedstocks suggests that SAF production alone cannot achieve the EU aviation sector’s long-term GHG reduction obligations."

Meanwhile, Back in the USA

Corn grown for Ethanol
 Scott Olson/Getty Images

No doubt an American study would look at corn and soybeans as a source; 40% of American corn is already grown for ethanol making 15.8 billion gallons in 2019 that was blended into gasoline, and 30% of soybeans go into making 2.1 billion gallons of biodiesel. Somebody is going to say that since cars and trucks are going electric, then those biofuels can all be diverted to airplanes. The industry is already calling this "farm to fly" and talking about converting sugar, corn, and other feedstocks. This all involves land, deforestation, fertilizers, water and all of the other problems that we now have with large-scale cultivation. Given the inputs that go into making ethanol and biodiesel, it has always been questionable whether they really do have lower greenhouse gas and other impacts than petroleum based fuels; some people say they are worse.

Given that 17 billion gallons of aviation fuel are burned in a normal year in the U.S., and that airplanes are getting more efficient, one could crunch the math and find that you could plant corn and soy fencerow to fencerow from coast to coast and make enough biofuel to keep planes in the air, but at what cost? And would it really reduce greenhouse gas emissions? And who besides Bill Gates actually benefits?

Sustainable Aviation Fuels are like hydrogen: a diversion, a form of predatory delay. Instead of actually investing in more efficient forms of travel, like high-speed rail, or reducing the amount of travel, The industry is promising that hey, in the future we can fix this, probably by 2050 with all the other net-zero promises we are making. But it will never happen; there just aren't enough dead cows and there is not enough land to keep us all up in the air.