CLIMATEWIRE | BRUSSELS — The best way to cut greenhouse gas emissions from flying is to fly less — but that’s a nonstarter for the industry and millions of passengers.
Instead, the sector is hunting for a tech fix that would allow airplanes to keep flying while polluting less — and one idea is to use hydrogen. But there are big questions over whether this is a workable solution.
Here are five challenges facing hydrogen-powered aviation.
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1. Sourcing clean hydrogen won’t be easy
Hydrogen can be very clean or very dirty — it all depends on how it’s produced.
Most hydrogen on the market today is so-called gray hydrogen, made by splitting natural gas — which emits a lot of CO2. Blue hydrogen captures those greenhouse gases, but it costs more and there are worries about where to store CO2. The rarest, and most expensive, is green hydrogen, made by using renewable power to split water.
“Hydrogen planes will only be as sustainable as the energy that powers them,” said Carlos López de la Osa, aviation manager with green group Transport & Environment (T&E).
“Most hydrogen for transportation is not zero emission today. It’s not green hydrogen,” said Val Miftakhov, CEO of ZeroAvia, a British-American manufacturer that aims to deliver its first hydrogen-electric aircraft with 40 to 80 seats by 2027.
2. Hydrogen could cut aircraft range
Hydrogen is the lightest element, but it has a much lower energy density than kerosene, meaning aircraft powered by it instead of fossil fuels would actually weigh more.
It can be burned with oxygen to create water, powering a jet, but it has to be stored in liquid form, which means installing high-pressure tanks that keep the highly flammable substance at temperatures below minus 253 Celsius. All that adds weight, cutting into range, cargo and passenger capacity.
Hydrogen can also be used to power a fuel cell, generating electricity to turn a propeller.
According to a 2022 McKinsey study, “with current aircraft designs, hydrogen aircraft could be range limited to up to 2,500 kilometers,” which is the distance between London and Istanbul. Only “redesigning airframes and storage technology might unlock longer ranges without reducing the number of available seats.”
Destination 2050 — the European aviation alliance for creating net-zero air transport by midcentury, which brings together airlines, airports, manufacturers and navigation service providers — predicts that hydrogen-powered aircraft will be available by 2035, but only “suitable for short-range intra-European routes.”
That means they can’t be used for long-haul flights which Eurocontrol, the European air traffic management body, says are responsible for more than 50 percent of aviation’s CO2 emissions.
3. It’s going to be expensive
Today’s airports have been set up to refuel airplanes with fossil fuels; they’d have to be revamped to supply hydrogen instead.
“There’s no hydrogen at the airports today,” said Miftakhov. He’s convinced the solution will be to “make hydrogen on site, at the airports,” which will reduce transport costs.
In January, the California Energy Commission, the state’s energy policy agency, awarded close to $3.3 million to ZeroAvia to develop a mobile liquid-hydrogen refueling truck that will refuel planes alongside kerosene at the Livermore Municipal Airport.
However, the scale of the challenge is daunting.
“We don’t know the full potential of hydrogen in aviation yet, and there are still significant challenges on the road to make it not only technically but also economically feasible,” said Francisco José Lucas, head of sustainable aviation at the Spanish energy multinational Repsol, referring to the difficulties of getting hydrogen to airports. “Nonetheless, we are sure that it is a technology with great potential in the medium and long term.”
4. Red tape will be a problem
Aviation arguably has the toughest safety standards of any industry on the planet. That means switching to hydrogen will face very high regulatory hurdles.
“For aircraft with less than 20 passengers, the rules are performance based, and therefore would not require any adaptation” to hydrogen propulsion, said Janet Northcote, spokesperson for the EU Aviation Safety Agency (EASA).
But, “for larger transport aircraft, the regulations are more prescriptive and these would not be appropriate for all aspects in their current form,” she said.
The agency does have something called a Special Condition, which allows for novel technologies and has been used for the Airbus A321XLR — an extra-long range airplane still awaiting certification.
But in the case of the XLR, that Special Condition applies to a new design for a central fuel tank, not for a novel way of powering flight.
Northcote said EASA is in touch with hydrogen plane developers through the agency’s pre-application services.
“The pre-application process helps them de-risk their projects and allows us to identify where current regulations may need to evolve,” she said.
5. Non-CO2 impact
After all the effort to convert airplanes from kerosene to hydrogen, even such green machines could still have a negative climate impact.
Recent studies show that about 50 percent to 75 percent of aviation’s climate impact is caused by non-CO2 effects — such as nitrogen oxide emissions or water vapor — that contribute to the formation of contrails. These white clouds left in the sky by aircraft may add to climate change if they persist long enough.
“There are still doubts about the climate impact of hydrogen aviation,” said Matteo Mirolo, a sustainable aviation expert at Breakthrough Energy, an organization founded by Bill Gates that is also investing in developing hydrogen aircraft.
“We still don’t know exactly the non-CO2 impact of hydrogen,” said Mirolo, adding that hydrogen-powered aircraft would, however, have “a positive impact, reducing pollution levels compared to fossil kerosene-powered aircraft, including particulate matter.”
T&E’s López de la Osa argues that cleaner-burning hydrogen engines mean contrails are likely to be short-lived. “Hydrogen combustion emits fewer particles where water vapor can attach,” he said.
To test that, Airbus is running a head-to-head comparison in Nevada by flying similar hydrogen and kerosene airplanes.
The aim is to “generate data to understand the differences, via flight testing in environments where contrails would form,” said Glenn Llewellyn, vice president of Airbus’ zero-emissions aircraft program. Results are expected by the end of 2024.
Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2024. E&E News provides essential news for energy and environment professionals.