First, what is sustainable aviation fuel, exactly? Sustainable aviation fuel is still jet fuel - the same kerosene that has been burning in airplane engines for decades. The difference is that sustainable aviation fuel is created from renewable sources, in contrast to conventional petroleum-based fuels. SAF can be derived from renewable crops, as well as from waste products such as vegetable oil and recyclable cooking oil, even algae and captured carbon dioxide. It ends up being the same hydrocarbon mixture called kerosene that we know as jet fuel, however. Recent months have seen important progress in the use of SAF:
Airlines have actually been tinkering with SAF for many years - KLM operated the first commercial flight that used a blend of biofuels and regular jet fuel in 2011. Even before that, in 2008, test flights were flown by Virgin Atlantic and Air New Zealand.
Beyond creating SAF from cooking oils, there is another type of SAF in development that uses renewable energy to extract hydrogen from water and then mix it with carbon dioxide taken directly from the air, such as through direct air capture. The result is a synthetic liquid fuel with a potentially endless supply.
So what’s the holdup? Why isn’t SAF more widely used? The reason is that SAF is still two to six times more expensive than traditional jet fuel. To solve this the world needs more production facilities for low-cost biofuels, and more support the development of the synthetics, which require renewable energy sources.
There’s a movement afoot to help address this at scale, though too: Breakthrough Energy Catalyst is a program within the larger Breakthrough Energy network founded by Bill Gates that is investing in clean technology projects to help to bring down their price and make them more widely available. In addition to direct air capture, green hydrogen and long-duration energy storage, SAF is a focus area.