Sustainable Aviation Fuel Overview

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 [47].

Table 3.3 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) [48]. 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.

Induced indirect effects of Sustainable Aviation Fuel production and use

The environmental benefit of using bio-based aviation fuel can be significantly reduced by induced indirect effects related to their production. The best known indirect effect relates to the impact on land use. Biomass production typically takes place on cropland that was previously used for other agriculture such as growing food or feed. Since this agricultural production is still necessary, it may be, at least partly, displaced to previously non-cropland such as grasslands and forests. This process is known as indirect land use change.

Another widely accepted indirect effect relates to the competition with food and feed production, when agricultural feedstocks are used. An example is the use of rapeseed oil as feedstock for producing bio-based aviation fuel, which by increasing the demand for rapeseed oil can contribute to increasing its price on the food and feed markets.

One option to limit these induced indirect effects is to use waste materials as feedstock. Recycled household waste (Municipal Solid Wastes) is a good example, as today the non-recycled part is mainly sent to landfill or is incinerated. However, it is not always easy to define a production stream as ‘waste’, as other industrial sectors may already be using this by-product for other purposes. This is the case with sugar molasses, which are processed and reused for the production of animal feed. If residual molasses are used to produce bio-based aviation fuel, and the feed industry increases its demand for low cost sugar sources, this would generate again a land use change effect.

 

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. Table 3.4 provides an overview of direct emissions savings for a variety of bio-based aviation fuel pathways.