Hydrogen-powered planes: pie in the sky?


This article is the third in a FT series examining whether hydrogen can help cut emissions across industries from transport to construction

The Apix fertiliser factory outside West Palm Beach, Florida was one of the great deceits of the cold war era. Built in the late 1950s, it was a front for the world’s largest liquefied hydrogen plant and part of a secret project to develop a hydrogen-powered spy plane. 

Two years after Project Suntan started, it shut down. The challenges of delivering a hydrogen-fuelled aircraft of the right size and range were too great.

More than 60 years later, hydrogen is back on the aerospace agenda, even if many of the challenges faced by Project Suntan remain. This time the debate is spurred not by cold war rivalry but by the need to resolve one of commercial aviation’s most urgent challenges: how to radically reduce its role in global warming by 2050, when many countries are committed to net neutrality on carbon emissions under the Paris accord.

“Hydrogen is one of the technologies to take us there,” said Grazia Vittadini chief technology officer at Airbus, which is planning to have a zero-emission, hydrogen-powered aircraft ready for service by 2035. The project is a flagship of the EU’s multibillion-euro Covid-19 stimulus package, aimed at greening the bloc’s economy. 

Yet not everyone shares Airbus’s confidence that the obstacles encountered by Project Suntan can be overcome by 2050. These remain its stability as an aviation fuel, as well as its transportation and storage.

Rival Boeing takes a more cautious view. “Our belief is that it will take a while for all the technology and elements of hydrogen propulsion to be worked out before we can get to . . . commercial use,” said Sean Newsum, director of environmental strategy at Boeing Commercial. “Our belief is that sustainable aviation fuels are a higher near-term priority.”

Aviation remains one of the hardest sectors to decarbonise. Nothing propels a commercial aircraft as efficiently and economically as fossil fuel. 

Before the pandemic grounded the world’s passenger fleet, aviation accounted for about 2.4 per cent of global emissions. Including non-carbon effects such as nitrogen oxide and contrails — icy vapour trails left in an aircraft’s wake — aviation’s environmental impact rises to about 3.5 per cent, according to Manchester Metropolitan University’s Aviation and Climate Research group.

As other sectors move more quickly to cut their carbon impact, aviation’s share will increase. Although CO2 emissions per passenger flight have fallen 54 per cent since 1990 thanks to better engines and improved operations, the total volume has jumped 34 per cent over the past five years because of rising air traffic. 

Aviation emissions are forecast to rise by 220-290 per cent between 2015 and 2050

In that context hydrogen looks attractive. With three times the energy density of kerosene, it promises not just net carbon neutrality, but zero CO2 emissions. Hydrogen can also be used to create sustainable synthetic fuels, by combining with carbon captured from the air. 

Proving the technology is not the problem. A Russian Tupolev-155 flew on liquid hydrogen in 1988. KLM last month completed the first flight using synthetic fuel. 

Yet both forms have limitations that raise questions over their commercial viability. Liquid hydrogen, which is easier to store onboard than gas, has to be kept at -253C or it boils off. The tanks to contain it are not only heavier but four times the size of conventional fuel storage. This imposes constraints on range and capacity that commercial aviation may struggle to accept. Hydrogen fuel cell systems also have weight challenges.

One aero-engine executive estimated that “you would have to remove 25 per cent of the passengers” from a conventional single-aisle aircraft to fit in fuel tanks.

Chart showing an overview of where low- and zero-carbon energy could be deployed in commercial aviation. It demonstrates that hydrogen will not play a major role in reducing aviation emissions before 2050, with most contributions coming from sustainable aviation fuel

Even the keenest advocates admit hydrogen technology will initially be limited to smaller, shorter-range aircraft. “The crossover point is probably around the . . . 100-seat size ,” said Val Miftakhov, founder of ZeroAvia, a California-based start-up developing a hydrogen power-train system for aircraft. “Below that you can get away with existing aircraft design but with some mission constraints.”

For example, an aircraft carrying 20 passengers might fly about 500 nautical miles, against the 1,000nm achieved with fossil fuels, he said. Roughly half of all flights are below 500nm, he adds.

The result is that hydrogen — much like electric batteries — is not likely to serve the dirtiest segment of aviation

in any substantial way before 2050, and not without a radical redesign of aircraft. Flights of more than 1,500km account for roughly 80 per cent of the sector’s carbon emissions, according to the industry’s Air Transport Action Group.

“It is clear the long-range segment will not be able to fly on zero-emission fuel, said Airbus’s Vittadini, although she does not rule out that this could change as technology progresses.

But even for the shorter-range aircraft, hydrogen’s deployment would require billions of dollars of investment in infrastructure, transport and storage. Airlines could also face increased operational complexities and higher costs from mixed fleets.

“Switching to direct hydrogen adds decades into the transition,” said David Joffe, of the UK’s Climate Change Committee, the advisory body to the government.

Aviation fuel consumption

Synthetic fuels are not straightforward either. The creation of so-called power-to-liquid or e-fuels requires huge amounts of green electricity, which makes them very expensive — and massive investment is needed in both renewable energy and fuel production to cut the cost. Synthetic fuels also emit carbon, although only what has been taken from the atmosphere.

“The cost of these e-fuels in the 2030s could be as low as today’s low-cost biofuels,” said Daniel Riefer, aviation partner at consultants McKinsey. “But you cannot scale up right away.”

E-fuels have one big advantage. Like clean biofuel, they can be dropped into the tanks of today’s aircraft and use existing fuel infrastructure.

“The benefit of sustainable aviation fuel is that we don’t have to change very much,” said Russ Dunn, CTO at GKN Aerospace. GKN is working on hydrogen propulsion and sustainable fuel technologies. Dunn said a variety of solutions will be needed to keep the global fleet flying. “There will be conventional aircraft flying for decades. If we can enable those to burn sustainable fuel rather than fossil fuel that has got to be a good thing.”

Roland Gerhards, head of Germany’s ZAL Center of Applied Aeronautical Research, said more work was needed to establish the true costs — both financial and environmental — of sustainable fuels vs hydrogen-powered flight.

Hydrogen propulsion may not emit carbon but it will expel more water vapour than kerosene, perhaps contributing to contrails. Nor does hydrogen completely eliminate nitrogen oxide. 

“We are at the very beginning of understanding these technologies,” said Gerhards. “We are doing the research. We have to be honest and say we don’t have the answers.”

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Paul Stein, CTO at Rolls-Royce, said vested interests are driving the debate about hydrogen versus sustainable fuel. “Many people would like to preserve the status quo and there are others who see a whole new industry in which they can participate,” he said. The answer would not be one or the other, but a mix, he added.

Airlines are watching the debate closely. David Morgan, director of flight operations at easyJet, said the low-cost carrier would be at the front of the queue when hydrogen aircraft finally come to market.

With the majority of European routes coming in at less than 1,500km, hydrogen could be viable. “I would like to think by 2035 easyJet has ordered its first batch of zero-emissions, short-haul aircraft,” Morgan said. “Ultimately the goal should be to strive towards zero environmental emissions.”

But Britain’s CCC is not counting on the technology to make a big difference by 2050. “We are not that bullish on hydrogen in aviation,” Joffe said. “In emissions terms it’s the longer-distance flights that are much more important.”

FT Series: Hydrogen — Fantasy or fuel of the future?

Long heralded as an alternative to fossil fuels, can the gas really help solve the world’s dirtiest energy problems?

In private, aerospace executives agreed. But they also know that with so much government funding for hydrogen, there is a risk outsiders will disrupt the business models that have defined global aerospace for decades. 

“There is a new way of thinking about the propulsion system as a whole,” said one senior French aerospace executive. “Using a cryogenic [ultra-low temperature] fuel onboard an aircraft is somehow a game changer.”

Paul Eremenko, former CTO at Airbus and United Technologies and founder of logistics start-up Universal Hydrogen, wants to be one of those disrupters.

“It is very difficult to get the industry to do this from the inside because there is a mindset of incrementalism,” he said. “This requires a paradigm shift, a disruptive change, and it is easier to do that as an external disrupter than to do it from the inside.”

Nevertheless, even incumbents agreed that in the longer term hydrogen will find its place in commercial aviation. 

“Somewhere there is likely to be a role for hydrogen and we will be ready,” said Michael Winter, senior fellow for advanced technology at US aero-engine group Pratt & Whitney. “But hydrogen will be really hard. Not insurmountable, but really hard.”

The colours of the hydrogen rainbow

© Christopher Furlong/Getty Images

Green hydrogen Made by using clean electricity from renewable energy technologies to electrolyse water (H2O), separating the hydrogen atom within it from its molecular twin oxygen. Currently very expensive.

Blue hydrogen Produced using natural gas but with carbon emissions being captured and stored, or reused. Negligible amounts in production because of a lack of capture projects.

Grey hydrogen This is the most common form of hydrogen production. It comes from natural gas via steam methane reformation but without emissions capture.

Brown hydrogen The cheapest way to make hydrogen but also the most environmentally damaging because of the use of thermal coal in the production process.

Turquoise hydrogen Uses a process called methane pyrolysis to produce hydrogen and solid carbon. Not proven at scale. Concerns around methane leakage.

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