Is hydrogen the answer for a low-carbon aviation future?

The use of hydrogen as a fuel in the transportation sector is not a new concept. Examples include the automotive industry producing hydrogen powered cars, hydrogen powered buses in use in Europe, North America, Japan and China and hydrogen ferry trials in Orkney. Within the aviation sector airports such as Memphis and Oslo have for some time invested in hydrogen powered ground support equipment. More recently aircraft test flights powered by hydrogen fuel cells have taken place, the latest being this September at Cranfield Airfield where a six-seater aircraft became the largest aircraft to fly using a hydrogen fuel cell.

So why use hydrogen?

Unlike fossil fuels hydrogen doesn't exist naturally in usable quantities. Globally, the majority of hydrogen is produced from natural gas through a method called steam reforming. This is an energy intensive process that uses steam to separate hydrogen molecules from methane (CH₄). An energy efficient and ‘cleaner’ process is to use surplus renewable electricity at times of low demand to separate water into hydrogen and water by electrolysis. This is known as ‘green hydrogen’. ‘Blue hydrogen’ from natural gas is carbon neutral when combined with carbon capture and storage. The benefit of hydrogen fuel is it eliminates CO₂ emissions when used in propulsion. It can also be used in fuel cells to produce electricity for electric powered aircraft, again eliminating CO₂ emissions.

What are the implications for aircraft?

Once produced hydrogen needs to be either compressed or liquefied. A significant amount of research is currently being undertaken within the aviation industry on hydrogen propulsion. Liquid hydrogen is likely to be the preferred format as storage tanks are smaller than compressed gas phase hydrogen, although still at least four times as big when compared to the current kerosene fuel tanks. Technology developments therefore need to continue to address storage requirements and reliable fuel distribution; this could involve adapting existing airframe and aircraft fuselage or new aerodynamic concepts. A likely initial scenario is that hydrogen powered aircraft will be developed for the commuter and short haul market, in addition to using hydrogen fuel cells to power electric aircraft. Hydrogen powered aircraft for the medium and long haul pose  more of a challenge but could come at a later stage of development.

What are the implications for the airport and the infrastructure?

If hydrogen propulsion is initially more suited to the commuter, regional, short range and electrical aviation markets then regional airports, rather than larger international airports, are best placed to take the lead. Airport operators will need to consider:

• Storage – hydrogen can be transported to the airport, but storage requirements will need to consider cryogenic technologies which keeps hydrogen in a liquid state. This would require additional land use, factoring in the required safety distances due to combustion hazard. Monitoring and leak detection and fire safety systems would also be required.
• Hydrogen production – is it cost effective to produce hydrogen using an onsite solar farm to provide ‘green hydrogen’ or will it be delivered to site by road tanker?
• Safety – handling and safety regulations need to be assessed as there are major differences in the properties of hydrogen and kerosene fuel.
• Refuelling – The introduction of hydrogen fuel aircraft will be phased so airport operations will potentially face a long transitional period with both hydrogen and kerosene refuelling. This raises questions – will safety distances allow refuelling with different fuels on adjacent stands? Do airports need ‘hydrogen only’ stands? Liquid hydrogen refuelling trucks will be different to kerosene trucks so training and safety assurance will be required.
• Refuelling methods – refuelling times will be slower due to the very low density of hydrogen which could affect aircraft turnaround times. Maybe the use of more refuelling hoses could mitigate this, but additional training would be required.
• Airfield hydrant systems – not always used at regional airports and couldn’t be used for two types of fuel i.e. kerosene and hydrogen. Due to the likely phased introduction of hydrogen fuel, the use of tankers would be the primary source of fuel delivery to the aircraft stand.
• Airside vehicles – Perhaps the first step should be to use hydrogen powered vehicles i.e. passenger boarding buses, ground support equipment to understand the safety and operational requirements of using hydrogen?

What could be the next steps?

Aircraft manufacturers, fuel companies, airports and airlines need to collaborate to ensure that the aircraft, fuel and infrastructure developments happen concurrently. A road map is required to ensure hydrogen provides a major part in delivering our global carbon targets by 2050 within the aviation sector. The UK Government included the production of low carbon hydrogen in their Ten Point Plan for a Green Industrial Revolution, so this must be the time for the aviation sector to start collaborating, the next question is – who and how?

If you want to join in the conversation or talk to us about how RPS can assist with airport planning or net zero carbon, then please don’t hesitate to get in touch.