ICAO. International aviation accounts for roughly half of all the fuel used for aviation globally. According to ICAO analysis, about half of the required emissions reductions can be achieved through enhanced efficiency. These include reduced fuel requirements per distance traveled, as a result of lighter and more fuel-efficient aircraft. These also include reduced fuel requirements from improved logistics, reducing the distance traveled for a given route and reducing loss of fuel from aircraft delays. Roughly speaking, efficiency has improved by an average of 1.5% per annum, and this should continue. But the other half of required emissions reductions, will have to come from the introduction of renewable aviation fuel. Biofuels can sharply reduce carbon emissions if they are produced from sustainable feedstocks on existing farm land or existing managed forest, so that no increase in greenhouse gas emissions arises from land-use change. The associated resource potential is very large – from sources like greater use of agricultural residues, restoration of degraded lands with wood crops, and freeing up land for energy crops by raising food crop yields, raising livestock on less pastureland, and reducing waste and losses in the food chain. While fossil kerosene emits 3 or 4 kg of CO2 per litre, biojet emits just 1 or 2 or even less. Ultimately, if emissions from aviation are to approach zero, renewable biojet must become universal. RECENT PROGRESS IS ENCOURAGING, BUT MUCH MORE IS NEEDED Since the first test flight performed by Virgin Atlantic in 2008, more than 150,000 commercial flights 38 Be
have been performed using biojet fuel by the end of 2018, according to the IATA. These flights used a variety of feedstocks and conversion pathways including blends of up to 50% biojet fuel from feedstocks like used cooking oil, jatropha, camelina, algae and sugarcane. Several airlines have concluded long-term offtake agreements with biofuel suppliers, most of which are reported as commercially competitive. A number of airports have agreed to supply SAF through their hydrant system. But the volumes of biojet in use today are still very small, accounting for less than 1% of the total jet fuel demand globally (IATA). Only few airports and airlines include permanent use of biojet in their operations. While market penetration of such fuel has so far been very limited and is expected to remain so for another decade, there will be plenty of potential for cost-effective renewable jet fuel to supply all the required amounts by 2050. Fortunately, there is a wide variety of abundant feedstocks from which biojet can be manufactured. Oleochemical pathways can be used to produce biojet from oil-based crops such as oilseed trees in South Asia, Salicornia grown with sea water in desert regions, rapeseed grown widely in temperate regions, and even oil palm if certified as grown sustainably on existing farmland in the tropics. Thermochemical processes can be used to make biojet with wood residues from temporal and boreal forest industries. Biochemical processes can be applied to make ethanol from carbohydrate crops like corn and sugarcane, with conventional processes for fermentation of the carbohydrate portion and advanced processes for digestion of the lignocellulosic portion, followed by upgrade of the ethanol to kerosene.
There is a very large potential to produce biofuels cost effectively on existing farmland and grassland, without encroaching upon rainforests, and in surplus to growing food requirements. Pockets of potential that do not involve carbon-releasing land use change – either direct or indirect – include energy crops grown on land made available by raising food crop yields or reducing food waste, as well as set-aside lands or contaminated lands on which food production is prohibited. Greater use could be made of food crop residues and forestry residues, while maintaining enough residues to enrich the soil and preserve biodiversity. IRENA analysis shows that the sustainable biomass supply that could be available in 2050 far exceeds the demand for primary biomass required in the energy transition. If only agricultural residues and wood residues are taken into account, the potential supply of primary biomass in 2050 would reach well over 130 EJ per year. When cultivation of energy crops in land made available from intensification of agriculture and reduction of food waste is considered, an additional potential of over 150 EJ per year would be added. COSTS WILL DECLINE, BUT ECONOMIC COMPETITION WILL BE TOUGH In economic terms, biojet has to compete with petroleum-based jet fuel. Provided we get from firstof-a-kind plants to Nth-of-a-kind plants at scale, with continued technology progress and supply chains that ensure reliable access to sustainable biomass, biojet fuel costs can be expected to come down over time. In that scenario, it should be possible for biojet from any of the feedstock-types to compete with fossil-based jet fuel if oil prices roughly double. In recent years, crude oil prices have fluctuated widely, but mostly between $50 and