January 27, 2023, ©. Leeham News: Last week, we learned the main pathways to Sustainable Aviation Fuel and their production volumes for the next years.
Now we look at the feedstocks, what output we get from these, and how to safeguard the pathway is ethical and sustainable. Finally, we look at the cost of SAF until 2050.
To understand SAF, we use Clean Skies for Tomorrow’s report: Sustainable Aviation Fuels as a Pathway to Net-Zero Aviation. It explains the main pathways (Figure 1) to SAF:
HEFA: Hydroprocessed Esters and Fatty Acids. It’s the classical oils and fats SAF. It’s over 95% of today’s SAF and will stay above 80% by 2030, according to experts.
The Alcohol-to-jet pathway can convert biomass to ethanol into aviation fuel. It widens the biomass types we can use.
Gasification+Fisher Tropsch is the biomass but, more importantly, the waste-based pathway. It has little importance until 2030 but has high long-term potential.
Power to Liquid or e-fuel is a long-term source, but we must have cheap energy that can’t easily be routed to consumers to motivate this pathway.
It’s important to understand these pathways produce SAF at different conversion rates (yields), and the output has different slates (fractions) that can be used for SAF, Figure 2. Other outputs are road fuels like biodiesel and chemical products like naphtha, called “Light ends” in the figure.
You can tune the processes to produce more or less SAF, but it can affect the yield of the process. Note the low yields (amount of feedstock to output) for all pathways except HEFA.
It’s important that the pathway used in producing SAF and biodiesel is a sustainable pathway end to end. It means, for instance, that the feedstock shall not threaten the food supply and not cause indirect land-use changes.
Figure 3 shows different feedstock types and how these contribute to GreenHouseGas (GHG) savings and if they are sensitive to non-ethical use.
We see that the most efficient pathway, HEFA, also has the most potential for non-ethical use of the feedstock. There is scrutiny from several organizations that we are not jumping from Jet fuel to another unsustainable energy supply. ICAO, the Environmental Defence Fund, and other organizations are watching the road to SAF to ensure that it follows high-integrity pathways.
The current production of hydrocarbon fuels has a pathway where we pay nothing for the production of the raw hydrocarbon (the crude). We pump it from reservoirs where it has matured over the last million years and combust it to release its energy content (some is also used for non-combustion use).
The process of releasing carbon now, when it was captured millions of years ago, causes an imbalanced energy system and, thus, our GHG problems.
It’s logical that if we now create circular and sustainable pathways, it carries a higher cost. For the present Jet fuel use, we only pay for the final part of the pathway.
Figure 4 shows the expected development of the production cost of the SAF circular pathways compared with our “dig-up and use” Jet fuel production.
We see the HEFA pathway will be the lowest cost among the SAFs until 2050, when e-fuel should catch up. SAF will be costlier to produce than Jef fuel throughout the period. As discussed, this is logical; we pay the full cost of SAF, not Jet fuel.
In the next Corner, we discuss the non-Carbon effects of SAF.