Summary: Sustainable Aviation Fuels or SAF's have the potential to replace some (maybe most) of the fossil fuels used to produce jet kerosene. This could reduce, but not eliminate the industry's Green House Gas (GHG) emissions. But, there are some material obstacles to overcome including cost, and an absence of enough suitable biological feedstocks. The cost aspect looks solvable, but the feedstock challenge could be more material.
Why this is important: Sustainable Aviation Fuel (SAF) is a core element in the aviation industry plans to deliver on their net zero pledges. While electric planes (and maybe one day green hydrogen ones) are possible, its highly likely that we will be relying on traditional jet engines for a long time, maybe a decade or more. This means even if we can find ways of reducing our desire to fly, the industry is going to need SAF at scale.
The big theme: Before the pandemic, in 2019, aviation accounted for about 3.1% of total global carbon dioxide emissions from fossil fuel combustion, and the number of passenger miles traveled each year was rising. If aviation emissions were a country, that would make it the sixth-largest emitter, closely following Japan. While aviation is not the largest GHG emitting sector, demand growth means the problem gets larger as each year goes by.
I expected this to be an easy blog to write. We know that aviation will probably be one of the later major industrial sectors to fully decarbonise. The most financially sensible path for the airline industry is to find a 'drop in' fuel technology, that works in existing jet engines. One that generates lower GHG emissions, making it a good bridging technology for the next decade or maybe a bit more.
And then, as aircraft get replaced, they can gradually transition to electric aircraft for short and medium haul, and maybe hydrogen for long haul (the later part of the plan still needs some thought).
And Sustainable Aviation Fuel (SAF) looks like the perfect answer. It is a type of biofuel that can currently replace 50% of jet fuel, and 100% replacement looks to be deliverable. Properly produced it massively cuts end to end GHG emissions. Yes, its expensive, but not so expensive that we cannot find solutions.
BUT - to produce enough we apparently need to use most of the potential biofuel feedstocks. AND a lot of other industries are already saying 'biofuels are the answer to our decarbonisation challenge' as well. So, while each solution makes sense on its own, if you add them together, we have a raw material shortfall.
And our politicians are fudging. They are not saying 'this solution has priority', but instead they are pretending (greenwashing) that we can deliver on all of the solutions. We face some hard decisions. Let's make them informed decisions. Unless aviation gets political priority, SAF looks like its going to struggle to be a financially viable decarbonisation solution for the aviation industry.
Summary of a study to be published in Nature Sustainability
- The idea of jetliners running solely on fuel made from used cooking oil from restaurants or corn stalks might seem futuristic, but it’s not that far away. Airlines are already experimenting with sustainable aviation fuels, including biofuels made from agriculture residues, trees, corn and used cooking oil, and synthetic fuels made with captured carbon and green hydrogen. Before the pandemic, in 2019, aviation accounted for about 3.1% of total global carbon dioxide emissions from fossil fuel combustion, and the number of passenger miles traveled each year was rising. If aviation emissions were a country, that would make it the sixth-largest emitter, closely following Japan.
- But, a rapid expansion in biofuel sustainable aviation fuels is easier said than done. It could require as much as 1.2 million square miles (300 million hectares) of dedicated land to grow crops to turn into fuel – roughly 19% of global cropland today. Another challenge is cost. The global average price of fossil jet fuel is about about US$3 per gallon ($0.80 per liter), while the cost to produce bio-based jet fuels is often more than twice as much. The cheapest, HEFA, which uses fats, oils and greases, ranges in cost from $2.95 to $8.67 per gallon ($0.78 to $2.29 per liter), but it depends on the availability of waste oil.