What is a Sustainable Aviation Fuel?
In order for a bio-based aviation fuel to be considered a SAF, it has to meet sustainability criteria. At present, there is currently not a single definition of SAFs agreed at the international level. In the European regulatory framework, sustainability is defined in the Renewable Energy Directive (RED) EC/2009/28. The Council and European Parliament have recently agreed on a revision of the RED, which sets new ambitious targets and includes revised sustainability criteria.
provides an overview of the sustainability criteria agreed for the revised RED. At international level, discussions are ongoing to agree on criteria to assess the sustainability of aviation fuels, which would be eligible for the purposes of ICAO’s CORSIA scheme (see Market-Based Measures chapter).
Reduction in greenhouse gas emissions
Bio-based aviation fuels may have lower GHG emissions in comparison with traditional fossil fuels. Indeed, the emissions from biofuel combustion are often considered as being zero, given that the fuels are produced from biomass. These are referred to as ‘biogenic emissions’, and they are assumed to be zero on the basis that the growth of the biomass absorbs the same amount of CO2 released during combustion. Conversely, ‘non-biogenic emissions’ are used to refer to production emissions from bio-based aviation fuels, resulting from the cultivation, harvesting and transport of the biomass, as well as from its conversion into fuel. These ‘non-biogenic emissions’ are not offset, and consequently constitute a direct impact of the bio-based aviation fuels. The difference between the ‘non-biogenic emissions’ of the bio-based aviation fuel, and the emissions from using a standard fossil derived fuel, constitutes the potential bio-based aviation fuel GHG saving.
There is ongoing discussion about the most appropriate methodology to assess the emissions reduction performance of the different pathways through a Life-Cycle Assessment. This is particularly relevant for those pathways that are currently entering the market. In many processes more than one product is produced, and it is necessary to divide the GHG impacts between these products. There is also much debate about how to account for indirect emissions such as cultivation emissions closely related to the farming practices and soil types (i.e. forest dynamic). Depending on these indirect effects, the emissions of a bio-based aviation fuel as compared to the emissions from the production and combustion of conventional aviation fuel can be lower, comparable or even higher.
The European Commission’s Joint Research Centre is actively contributing to on-going discussion on the quantification of GHG emissions reduction potential from bio-based aviation fuels. While the GHG emissions from the production of HEFA based on feedstocks such as sunflower and soybean oils can be estimated at around 40 gCO2eq/MJ, the same HEFA process fed by rapeseed oil is estimated to result in higher GHG emissions, of around 51 gCO2eq/MJ due to differences in production chains. In order to calculate the potential GHG reductions from bio-based aviation fuel, it is worth noting that ICAO have defined a reference level of GHG emissions from a fossil-based aviation fuel as 89 gCO2eq/MJ.provides an overview of direct emissions savings for a variety of bio-based aviation fuel pathways.