Sustainable aviation fuel explained

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Wednesday 24 June 2020 13:00 PM

Sustainable aviation fuel explained

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 fuel, and why it’s one of the ways the aviation industry is working to decarbonise flight.

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What is a sustainable aviation fuel (SAF)?

Sustainable aviation fuel (SAF) is made from sustainable and renewable sources that produce significant CO₂ reductions compared with fossil jet fuels.

SAF is not derived from fossil-based oil or gas, and therefore has a lower carbon impact across its lifecycle. Instead, it is made by refining organic or waste substances, or created synthetically, which means it is made from captured carbon dioxide and renewable or zero carbon electricity.

SAF can still emit carbon when burned during flight, but because it’s produced from carbon that has already been captured from the air – either mechanically or by plants, or by other industrial processes that produce waste – it’s an important step towards achieving net zero carbon emissions.

Currently regulations state that SAF 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 SAF, and we think it 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 aviation fuel?

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 SAF needs to satisfy three criteria to be viable:

Suitable: it meets the specifications of an aviation fuel.

Sustainable: it doesn’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 it at scale, with the right infrastructure in place.

Options include:

Cooking oils: Along with animal fats, used cooking oils are the most common materials used to create SAF. 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.

Photosynthesis

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.

SAF is made at special plants, where the raw materials are processed and refined.

Sustainable fuels are made at special plants, where the raw materials are processed and refined.

So there are lots of options, what’s the catch?

Firstly, SAF is more expensive than conventional jet fuels; this is partially because it is relatively new, and partially because of the processes involved in making it.

Some estimates say that fuels are twice as expensive when made with waste-based sources (enviro.aero).

Secondly, SAF is 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, SAF makes 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.

What is Rolls-Royce doing?

“We expect to see a lot of innovation and energy directed at creating sustainable fuel over the next 10-20 years and we are here to support this growth in any way we can. Despite the challenges of affordability and scalability, we believe that Sustainable Aviation Fuels are the only solution to decarbonise long-haul aviation,” Dave Smith, Director, Central Technology, Rolls-Royce.

We strongly believe that no single country or company can solve this challenge, we must work globally and together. Naturally, our airline customers have the same desire and we are working closely with them, as well as our competitors, peers and the oil and gas industry. Governments and regulators also have an important role to play.

Most of our aircraft engines, such as the Trent XWB and the Trent 7000, can already operate using blended SAF. We believe that all of our newer engines would probably be able to operate on 100% SAF and we’re in the process of verifying that so potentially the regulatory cap of 50% blend can be lifted.

We’re involved in a research project at the Brandenburg University of Technology Cottbus-Senftenberg, which includes building a demonstration plant to produce sustainable fuels using electric power. The plant will test the use of sustainable fuel for mobility on land, water and the air. It will look at the generation of heat and power, and what the carbon footprint of the process looks like.

SAF blends can already be used in our engines, including the Trent 7000.

We are working with oil and gas companies to develop more SAF processes and increase the volumes available, as well as exploring whether a small modular nuclear reactor could be used to power a synthetic fuel plant producing fuels that meet the specifications of an aviation fuel (something we call a ‘drop-in’ fuel) to decarbonise flight.

We also have a role to play in driving investment in this technology and making it commercially viable. This will involve working with the public sector and collaborating with the oil and gas industry to drive wider availability of sustainable fuels. We can also ensure our engines are technically underwritten to use higher blends of SAF in the future.

Sustainable aviation fuel is just one of the ways we’re decarbonising aviation. Find out more about how pioneering a net zero carbon future is at the heart of our innovation and growth.