With aviation responsible for close to 3% of global CO2 emissions and other transportation modes gradually making their green and electric transition, there has been increasing pressure on the airline industry to reduce its carbon footprint.
Given that aircrafts can be in service for decades, blending fossil jet fuel with biofuels (or SAF, for Sustainable Aviation Fuels), that can be used in existing aircrafts with few modifications, has been widely regarded as the way to go and the International Energy Agency estimates that the share of biofuels in total jet consumption will reach 78% by 2050 in a net zero environment. Neste appears as a global biofuel leader as it inked numerous supply agreements with airlines and airports.
But, even if biofuels are estimated to reduce greenhouse gases up to 80% compared to traditional fuels, they will not be sufficient to meet the International Air Transport Association (IATA)’s commitment to “Fly Net Zero” by 2050.
Here comes hydrogen, which can be used either in an internal combustion engine or in fuel cells, and which has long been contemplated as a serious clean energy candidate in heavy-duty transport industries as it is totally clean when released in the atmosphere, offers a high energy density, and weighs much less than an electric battery.
If hydrogen adoption in aviation has unsurprisingly faced challenges (on-board storage and safety management, lack of ground infrastructures, still high hydrogen costs…), it seems like significant progress has been made in the last couple of years with several test flights conducted since the beginning of 2023.
Early this year, start-up ZeroAvia (in which Shell is an investor) carried out a test flight of a 19-seat two engines aircraft, one of them being an electric motor coupled to a hydrogen-powered fuel cell. The company plans to start hydrogen-only commercial flights by 2025. Universal Hydrogen and Plug Power also successfully tested a 40-passenger regional airliner just a couple of weeks ago.
Interestingly, both ZeroAvia and Universal Hydrogen are developing technology to convert small aircrafts to hydrogen fuel, with Universal Hydrogen planning to start shipping fuel cell conversion kits for regional aircrafts as soon as 2025 and announcing that it has already received 250 retrofit orders valued at more than $1 billion from 16 customers. Needless to say, retrofitting current aircraft fleets could significantly accelerate hydrogen adoption in aviation, considering that the lifetime of aviation assets in service today can reach several decades and that airlines would benefit from the hydrogen benefits without having to spend billions on a new generation of aircrafts.
Meanwhile, industry giants do not stay idle and are working on large, hydrogen-powered aircrafts capable of carrying hundreds of passengers on long hauls. UK-based aerospace companies notably have made inroads recently with engine maker Rolls-Royce performing with easyJet the ground test of a jet engine running on hydrogen and GKN testing liquid hydrogen for fuel cell systems and having completed the preliminary design of a fuel cell powertrain that it expects to test by 2025 for 19-, 48- and 96-seat models.
As for Airbus, its ambitions are more remote, but the aerospace giant is working on different designs, including fuel cells that it plans to test flight by 2026 and a hydrogen combustion engine for an aircraft that is scheduled to enter into service by 2035.
While all these initiatives are unsurprisingly raising expectations for hydrogen use in aviation, there’s still a lot to be done before rolling out the technology on a large scale. Regarding the infrastructure and hydrogen costs challenges we mentioned earlier, recent government plans including the US’s Inflation Reduction Act or the EU’s Net Zero Industry Act should massively incentivize the production of green hydrogen ($3 per kilogram subsidy for green hydrogen in the US) and the development of an infrastructure.
But other challenges are still a work in progress. Notably, hydrogen needs to be chilled and stored at -253 degrees Celsius to remain in its liquid form that requires 4x more storage space than jet fuel for the same amount of energy. Wing tanks should be sufficient for short flights but for longer flights, storage space will have to be found in the fuselage with obvious consequences in terms of design.
Finally, another type of carbon-neutral fuel involving hydrogen and called electrofuel or e-fuel could also have its chance in the race towards the development of green internal combustion engines. Mainly pushed by Porsche (which set up a pilot e-fuel plant in Chile), it consists in capturing carbon dioxide or carbon monoxide in the air and combining it with green hydrogen produced by electrolysis. Burning e-fuel releases the same amount of carbon captured to produce it, hence the carbon-neutral balance. The whole process is obviously very expensive and is currently at the experimental stage.