Fuelling sustainable aviation
24th June 2020
Can you really turn rubbish into jet fuel? Can potato skins power a plane? Can you capture carbon from the air and create fuel out of it? Here’s everything you need to know about Sustainable Aviation Fuels, and why they’re one of the ways the aviation industry is working to decarbonise flight.
What is a Sustainable Aviation Fuel?
A Sustainable Aviation Fuel is made from sustainable and renewable sources that produce significant CO2 reductions compared with fossil jet fuels.
Sustainable Aviation Fuels are not derived from fossil-based oil or gas, and therefore have a lower carbon impact across their lifecycle. Instead, they are made by refining organic or waste substances, or created synthetically, which means they are made from captured carbon dioxide and renewable or zero carbon electricity.
These fuels still emit carbon when they are burned during flight, but because they are produced from carbon that has already been captured from the air – either mechanically or by plants, or by other industrial processes that produce waste – they are an important step towards achieving net zero carbon emissions.
Currently regulations state that sustainable fuels can be used when they are blended with traditional jet fuel (kerosene), up to a maximum of 50%.
Hundreds of thousands of flights have already taken off fuelled by Sustainable Aviation Fuels, and we think they could cut carbon emissions by around 80%, compared to conventional fossil-based jet fuels. Alternative fuels will play an important role in ensuring we can keep enjoying the benefits of aviation, while achieving a net zero carbon future.
What can be used to make sustainable fuels?
There are many options, from cooking oil, to household waste and algae. They can also be produced synthetically (more on that later). Because there are so many possible sources, different materials can be used in different locations, depending on the local resources available. It also means that plants can supply the airports nearest to them, rather than needing to ship fuel around the world.
We believe that Sustainable Aviation Fuels need to satisfy three criteria to be viable:
Suitable: they meet the specifications of an aviation fuel.
Sustainable: they don’t compete with land use for food or habitation, or place significant demand on other natural resources such as fresh water.
Scalable: there’s potential to produce them at scale, with the right infrastructure in place.
Cooking oils: Along with animal fats, used cooking oils are the most common materials used to create Sustainable Aviation Fuels. Waste oil from vegetable oil production plants can be used, as well as inedible oils which are created as a by-product of ethanol. Waste cooking oil can even be collected from restaurants and other businesses, sent to refineries and used to fuel flights.
Synthetic fuels: These are produced by capturing CO2, such as directly from the air or from industrial processes, and creating the fuel using electricity. They are in the early stages of testing, but if they can be commercialised and made using zero carbon electricity, such as from a small modular nuclear reactor, they are a promising source of energy for the aviation industry.
Waste: Fuels can be made from municipal or household waste that would otherwise end up in landfill. Using rubbish has added benefits; firstly landfill waste can be a source of methane emissions which have a warming effect far greater than CO2, so by not burying rubbish, we avoid extra emissions. Secondly, any plastics in the waste, once broken down into their constituent components, represent a valuable energy source in the finished fuel.
Crops: Plant or animal materials such as wood, wheat or algae can be used. As these materials grow, carbon is removed from the atmosphere through photosynthesis, converted into fuel and released via combustion. When using crops, broader sustainability impacts must be taken into account, such as not competing with the food supply, limiting the use of fresh water, and avoiding deforestation. For that reason we believe fuels created from waste feedstocks or synthetically using low carbon energy are the most attractive for aviation.
If school science classes seem like a long time ago, photosynthesis is a chemical reaction that takes place inside a plant, producing food for the plant to survive. The plant takes in carbon dioxide from the air, water from the ground, and light from the sun. The sun provides the energy for photosynthesis to take place. The carbon dioxide and water are converted back in to oxygen, which goes back in to the atmosphere, and glucose, which the plant uses for energy.
So there are lots of options, what’s the catch?
Firstly, Sustainable Aviation Fuels are more expensive than conventional jet fuels; this is partially because they are relatively new, and partially because of the processes involved in making them.
Some estimates say that fuels are twice as expensive when made with waste-based sources (enviro.aero).
Secondly, Sustainable Aviation Fuels are currently relatively scarce. However, there are many new production facilities being built and planned around the world, and airlines have placed ‘forward purchase’ agreements – essentially commitments to energy suppliers that they will purchase the fuel when it is available. There are currently £6 billion of forward purchase agreements, which helps energy suppliers finance new plants.
Currently, Sustainable Aviation Fuels make up just 0.01% of global jet fuel use. But with the right policy support, this could reach a tipping point for the aviation industry, and in future make a real impact in decarbonising aviation.