In the arena of Net zero and life cycle emissions, not all biofuels are created equal. The pathways for sustainable aviation fuel (SAF) are plenty, and their underlying lifecycle emissions vary. According to the International Air Transport Association (IATA), the fuel is expected to serve about 65% of the demand from international aviation by 2050. As the global demand for “sustainable” fuel continues, consumers need to be increasingly aware of its varying and sometimes even troubling carbon intensities.
Some carbon reduction schemes don’t account for the fuel’s entire life cycle emission. Emission trading systems like the EU ETS and the California-Quebec program allow all biogenic fuels to claim ‘zero’ CO2 emissions.
The accounting standards assume that the carbon emissions from burning the fuel are the same as the carbon sequestered by the feedstock (energy plants) during its growth. This standard ignores land use change-related emissions from the allocation of untouched lands towards feedstock cultivation, besides emissions from transportation, fuel refining and distribution. These additional life cycle elements can be a significant addition to the final carbon intensity of the fuel.
One recent initiative corrects for this accounting error. The CORSIA scheme (Carbon Offsetting and Reduction Scheme for International Aviation) adjusts for the land use change equation. This factor can singlehandedly reshape our outlook on feedstocks.
The graph below illustrates the disparity of average carbon intensities from popular feedstocks in the HEFA production pathway (Hydroprocessed Esters and Fatty Acids). Disturbingly, SAF, derived from palm oil feedstock grown in Malaysia & Indonesia, can have higher carbon intensities than conventional jet fuel.
Acknowledging this land use change factor creates a fresh potential for feedstocks like ‘Brassica Carinata’. This oil seed crop can be grown in winter as a rotational crop, bringing in additional income for farmers. So, it doesn’t require new land allocated towards SAF.
Moreover, the cover crop protects the topsoil from erosion since only the grains are harvested, and around half of the plant’s mass remains in the field, making it highly efficient at storing carbon in the soil. The carbon cycle for this feedstock is a negative emissions equation, which makes the land use change factor negative. Therefore, the derived SAF has a much lower carbon intensity (13 gCO2e/MJ) than its peers.
So, under CORSIA, an airline operator can claim more significant emission reductions with feedstocks like ‘Brassica Carinata’. This is also the case with used cooking oil and tallow, which are by-products or waste and therefore don’t require new allocation of agricultural land. What works in favour of energy plants is that feedstocks like used cooking oil and tallow face the perpetual challenge of feedstock collection.
The combustion of sustainable aviation fuel still releases carbon into the atmosphere. But the emissions are considerably lower than that of burning conventional Jet fuel. Assuming the end-use carbon intensity of SAF as 22.5g CO2e/MJ (Tallow) and that of standard Jet fuel as 89g CO2e/MJ, the combustion of 1,000 gals of neat SAF would amount to 2.5 tons CO2e. Which is a clear reduction in emissions of 75% compared to 9 tones of emissions from traditional jet fuel emissions.
How does this impact the future supply of better-quality SAF?
Well, the CORSIA program covers about 77% of all international aviation activity Many commercial airlines have already secured offtake agreements for the future supply of SAF. In the case of the fuel producer, the pathways for producing SAF are scaling up with substantial investments, which means focusing on the right feedstocks from the start will ensure that we don’t create a secondary problem in our attempts to decarbonize aviation.
More awareness of land use change can subsequently discourage the use of troubling feedstocks like Palm oil, Industrial Rapeseed oil and Soybean oil. Additional carbon reductions from better feedstocks call for a premium in price, but if we aim to make SAF commercially available and abundant, we should start with our best foot forward. The team at Azzera aims to provide ratings for sustainable aviation fuel that then enables aviation customers to make the right choices in their fuel use.
How much emission reductions can you claim from choosing the right feedstock?
The ICAOs’ (International Civil Aviation Organization) Volume IV Annex 16 details that equation (below). The Emission Reduction Factor (ERF), “(1 – LSf / LC)”, is essentially the percentage reduction in emissions relative to conventional Jet fuel. The net reduction in the aircraft’s emissions depends on how much of SAF is blended within the jet fuel.
The graph below presents this Emissions Reduction Factor from using different feedstocks for SAF.
The future availability of a feedstock depends entirely on its perceived value today. The CORSIA methodology, which accounts for land use change, brings out just that.
