Hydrogen technologies will form one part of a range of strategies to decarbonise the aviation industry, making regulation and infrastructure an especially complicated issue for airline and airport operators, according to industry figures speaking at a recent summit hosted by hydrogen and electric aircraft developer ZeroAvia.

Aircraft of varying sizes and on varying routes are likely to use different types of technology to decarbonise, with lighter aircraft using battery and fuel-cell propulsion systems, and heavier aircraft using liquid hydrogen or sustainable aviation fuel (SAF).

Biofuels are currently the only option for SAF— which is the only technology that can work with existing aircraft fleets—but from the late 2020s hydrogen-based SAF could become an option for many aircraft, according to a report from industry alliance the Mission Possible Partnership earlier this year.

“It is not a one-size-fits-all strategy for this industry” Birkett-Rakow, Alaska Air-lines

Airlines will have to execute multiple decarbonisation strategies simultaneously, according to Diana Birkett-Rakow, senior vice-president for sustainability and public affairs at Alaska Airlines.

“It is just not a one-size-fits-all strategy for this industry,” she said. “The question is how do those different technologies sit alongside each other and operate efficiently at an airport?”

The fact that SAF can be used as a drop-in fuel, as well as offering the most efficient long-term decarbonisation pathway for the bulk of the industry, means that many airports are likely to look at that technology first.

“SAF is the best near- and medium-term opportunity, especially with large aircraft,” said Birkett-Rakow.

Compressed hydrogen is not a realistic option for heavy aircraft, leaving liquid hydrogen as the most obvious choice for operators wanting to use pure hydrogen to decarbonise their operations.

The technology is still relatively undeveloped, although big players in the sector such as France’s Air Liquide are looking to build liquid hydrogen supply chains. More than 40% of people surveyed at the ZeroAvia summit felt that liquid hydrogen could be commercialised by 2030.

One often-cited problem is that it takes about a third of the energy content of hydrogen to liquefy it. But this figure can be reduced, according to Jacob Leachman, associate professor at Washington State University.

“We can get down to 4kWh/kg as a theoretical limit—that is 11% of the energy content of the fuel,” he said.

“That is the same amount of energy it takes to process petroleum. And nobody is complaining about the energy used to process petroleum.”

The tyranny of choice

Whether airports look to produce hydrogen on-site or to source it from suppliers depends on a number of factors—including the hydrogen strategy of the country in which they are located.

Some major airports are looking at on-site solutions that would be able to supply liquid hydrogen and on-site SAF manufacture, seeing this an opportunity to generate additional revenues.

Smaller airports that happen to be near hydrogen hubs could opt to be a downstream part of a liquid hydrogen value chain. Others may opt for smaller containerised solutions on-site. But some may choose to bypass pure hydrogen completely and service only battery-electric or SAF flights.

Most airports are looking at these issues, but each one will have a different answer, according to James Peck, chief customer officer at ZeroAvia.

“Hydrogen readiness varies massively,” he said. “Some even have hydrogen ready today—other parts of the world are not quite there yet.”

Many speakers noted that upstream hydrogen generation was a key missing part of the puzzle. Even if supply does emerge in regions such as the US, China and the EU, other parts of the world will take longer to convert.

Another major issue for scaling is certification and regulation, particularly with so many different technologies in play, according to Germain Hurtado, hydrogen technologies and projects director at civil airport developer Vinci Airports.

“In order to scale, there is a necessity to get an industrial consensus on the form of hydrogen required and then get the necessary regulatory approval for how to handle such a form,” he said.

“For liquid hydrogen it will take years to get an answer that is fully validated.”

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Author: Tom Young