Green hydrogen will have an important role to play in aviation’s transition away from fossil fuels. This factsheet explains how this is the case, and why a focus on green hydrogen for aviation will drive UK innovation.

Background

• Aviation is a high-emitting sector, which currently accounts for 3% of global emissions (with additional non-CO2 impacts that could double its impact).  

• Lowering emissions through improvements to fuel efficiency, among other factors, will be crucial. But ultimately, we need alternatives to the fossil jet fuel used today.

• But not all alternatives are made equally. Decisions must be taken now to ensure investment is targeted towards the alternatives with the greatest potential to lower emissions and drive UK growth. 

The options available

• Broadly speaking, the main alternatives to fossil jet fuel available to the aviation industry are 1) direct electrification, 2) use of gaseous or liquid hydrogen propulsion aircraft or 3) producing jet fuel from renewable sources, through a range of fuels commonly referred to as ‘sustainable aviation fuels’ (SAFs).

• Green hydrogen will play a role in all pathways to producing alternative fuels for the aviation industry (other than for direct electrification).

But do all the alternatives offer the potential to provide a secure supply of low-emission fuel for the sector? Let’s look at the options…

Direct electrification

• Without the need to use renewable electricity to produce alternative fuels, direct electrification offers the most efficient alternative available to the aviation industry.

• When considering the non-CO2 effects of aviation, electric aircraft would not produce exhaust products and therefore no contrail effect (a key driver of non-CO2 climate impacts). To ensure the lowest possible lifecycle emissions, it is important that renewable electricity is used to charge the batteries powering electric aircraft.

• Strides are being taken towards developing electric aircraft. However, a significant amount of research and development is still required to develop batteries that are capable of storing enough energy to power an aeroplane.

Green hydrogen Propulsion

• Green hydrogen has great potential to be used as a fuel itself, whether that be via combustion or using fuel cell technology.

• Crucially, when green hydrogen is combusted it does not release CO2 emissions (further research is needed to fully understand the non-CO2 impacts of hydrogen aircraft). To maximise emission reductions, it’s important that green hydrogen – made using renewable electricity – is used to produce any hydrogen used in the aviation sector.

• The vast majority of hydrogen used today is produced using fossil fuels, and scaling Ggreen hydrogen production is not challenge-free, being energy- and water-intensive.  Big changes will also be needed to both the aircraft and airports to facilitate this transition: new storage and transportation infrastructure will be required, and hydrogen-powered aircraft will need alternative engines and fuel storage.

• It is likely that, at least initially, hydrogen-powered aircraft will be best suited to commuter to medium-range flights, with market leaders suggesting hydrogen propulsion aircraft could be operating this decade.

• Despite these infrastructural challenges, the UK is the world leader in hydrogen propulsion aviation innovation and has huge potential to export worldwide. SASHA members Cranfield Aerospace Solutions and ZeroAvia are world leaders in this space.

‘Sustainable aviation fuels’ (SAFs)

• The term SAF is a catch-all phrase, and in many cases a misnomer due to the limited emission reductions from some production pathways.

• Simply put, there are two main types of SAF: biofuels, produced using biomass, and e-fuels, made from a source of hydrogen and a source of carbon.

• Unlike hydrogen aircraft, which do not emit carbon, SAFs emit the same amount of carbon as traditional jet fuel, so their ability to lower emissions is entirely based on the full lifecycle emissions of the fuel and the feedstock used to produce it. They will, however, require far fewer modifications to aircraft and airports than using hydrogen directly due to their chemical similarity to jet fuel.

• For biofuels, first generation crop-based biofuels (produced using crops grown specifically to be used as a fuel) and used cooking oils and animal fats will be available in such limited quantities that they don’t present a long-term, viable route to producing alternative fuels for the aviation sector. Crop-based fuels also come with additional land use impacts, while used oils and fats have competing, existing uses.

• E-fuels, on the other hand, can be produced using green hydrogen and carbon captured via direct air capture (DAC). As long as a renewable source of electricity is used, this makes them close to carbon neutral.

• Like green hydrogen propulsion, producing e-fuels in the quantities needed will require significant amounts of renewable electricity. Work to scale supply from across the supply chain therefore needs to start now if e-fuels are to be scaled at the pace required.    

• E-fuels therefore present the best option to sustainably produce aviation fuel in the long-term.

  Willis Lease Financial Corporation (WLFC) have laid out plans to construct a plant to produce aviation fuel using green hydrogen in Teesside. The project is part of a wider plan to create a National Hydrogen Hub in the Tees Valley and promote the area as a decarbonisation leader in the UK, in turn bringing highly skilled jobs and investment to the area.]

What is the current policy landscape?

• The UK SAF mandate will come into effect from 2025 onwards, with a headline target of at least 10% of jet fuel to be made from sustainable sources by 2030 – rising to 22% of jet fuel in 2040

• Underneath this overarching target are both a sub-mandate for green hydrogen-derived fuels and a cap on ‘HEFA’ fuels. The power-to-liquid (green hydrogen-derived) fuel mandate will begin in 2028 with an obligation for 0.2% of fuel to be this type, rising to 3.5% in 2040. Meanwhile, HEFA fuels will be capped at 71% of fuels in 2030, going down to 35% by 2040.

What we need from policymakers

Underpinning aviation’s decarbonisation trajectory is a huge demand for green hydrogen. For aviation to have access to the fuels it needs and at the pace needed, supply needs to start being scaled up now. Regulations will be key to sending the demand signal that producers need to start scaling supply.

Here are our policy recommendations:

• We need cross-departmental coordination on aviation decarbonisation – ensuring that transport stakeholders are involved in decision making on future uses of green hydrogen (and DAC).

• A cross-departmental approach to align industrial strategies with decarbonisation policy, making the transition away from fossil fuels boost rather than hinder economic growth across the whole of the UK.

• Hydrogen strategies must also recognise that the hydrogen used in decarbonising aviation, along with other hard-to-electrify sectors, must be green.

• The SAF mandate does not go far enough in regulating for the use of green hydrogen fuels over others that do not have the same potential to lower emissions. Unless the ambition of the power-to-liquid submandate is raised, there is a risk that UK investment will continue to go towards what will ultimately be stranded assets.

• The same approach to incentivising the lowest emission fuels must also be taken when putting in place other mechanisms to drive the supply of alternative fuels for the sector (for example, any revenue certainty mechanism for SAF production).

• UK policy should recognise the leading edge the UK has in hydrogen aircraft (through Cranfield Aerospace Solutions and ZeroAvia) to support the export of these technologies worldwide.  

Want to know more? Read our Green Hydrogen Gap report here.*

* This factsheet draws on information and statistics included in the Green Hydrogen Gap report and supporting research conducted by Arup.