As the world looks for new ways to combat climate change, hydrogen has emerged as a potential saviour for polluting industries like aviation.
It’s the most common element in the world, and packs more energy than conventional aviation jet fuel without the side effect of producing massive emissions of carbon dioxide.
But hydrogen and air travel have a complicated history.
More than 80 years ago the hydrogen-filled Hindenburg airship burst into flames when attempting to moor at Lakehurst in New Jersey.
The extent to which the buoyant hydrogen gas can be blamed for the disaster has been the subject of much debate.
But the image of the airship crashing to the ground is something the aviation industry is hoping to leave behind as it re-embraces hydrogen.
One company is confident it can make it work, and is hoping to take paying passengers on a hydrogen-powered flight within just a few years.
The push for hydrogen flight
From its base at Kemble in England’s scenic Cotswolds, ZeroAvia is developing an aircraft that could make the world’s first commercial hydrogen-electric flight in 2024, between London and Rotterdam in the Netherlands.
The benefit of using hydrogen fuel cells, ZeroAvia argues, is that the only waste product is clean water.
“It’s essentially a zero-emission process,” says Sergey Kiselev, who heads ZeroAvia’s Europe division.
“The only by-product is water vapour.”
The concept has won financial backing from the UK government and from IAG, the parent company of British Airways.
While hydrogen played at least a partial role in the Hindenburg crash, the team at ZeroAvia says modern storage systems make it a reliable fuel.
“Certainly hydrogen is safe,” says John Kells, the company’s head of technical operations.
“Today there are electric vehicles with hydrogen fuel cell systems and it’s not more dangerous than kerosene [which fuels modern-day jets].”
Hydrogen is much lighter than air, so will quickly dissipate when released, unlike regular fuel, ZeroAvia says.
But developing the plane hasn’t been easy.
In September 2020, the team from ZeroAvia reached a major milestone after performing a take-off, circuits and landing in a six-seater Piper Malibu powered by hydrogen fuel cells.
The plane carried out dozens of successful test flights. Then in April this year, it crashed.
The 6-seat hydrogen fuel cell plane was badly damaged during a test flight but nobody was injured.
The plane made a forced landing in a field near Cranfield airport, in Bedfordshire.
While trying to come to a stop on the uneven surface, one of its wings was torn off. Nobody was hurt.
“I think when you test novel technology, things like that happen,” Mr Kiselev tells the ABC.
He says while the incident is still being investigated, the hydrogen itself was not the cause.
“We’ve gone through quite a bit of learning … to avoid that and make sure that doesn’t happen again.”
Stephen Lawes, who was on the plane when it crashed, is still convinced hydrogen is the future.
“The technology we’ve got today works,” he says.
“You don’t have to wait until 2030, 2040, 2050. You can do it now, basically.”
Just outside ZeroAvia’s hangar at the airport in the Cotswolds are dozens of fossil-fuel-guzzling passenger jets.
They were sent there for temporary storage during the COVID-19 pandemic. But the long-term future of some of these jets is in doubt, amid a push for greener flying.
Some young travellers say they plan to reduce their air travel as a result of worries around global warming.(AAP: Paul Miller)
At the same time, there is growing community awareness about air travel’s contribution to climate change.
It currently accounts for about 2.5 per cent of global emissions, but some forecasts predict that figure could reach about 25 per cent by 2050.
A McKinsey survey of 5,300 passengers found that more than 50 per cent were “really worried” about global warming.
Forty per cent of those aged between 18 and 24 said they planned to reduce their air travel as a result.
“We’ve got the social support,” Mr Lawes says.
“There’s this big wave coming, supporting change.”
Instead of building a new plane from scratch, ZeroAvia is installing hydrogen gas tanks inside a 19-seat Dornier 228 regional airliner.
The company is hoping airlines will be more likely to adopt the technology if they can add it to their existing planes.
The hydrogen fuel cells will power electric motors, which will rotate the propellers.
“It sounds easy, but it isn’t,” Mr Lawes cautions.
ZeroAvia make their own fuel on-site, passing an electrical current through water to split it into oxygen and hydrogen.
“The beauty of hydrogen electrolysis is it needs only two inputs. One is water, the second is electricity,” Mr Kiselev says.
However, for the process to be truly carbon zero, the electricity needs to come from renewable sources.
Mr Kiselev says so-called green hydrogen presents big opportunities for countries like Australia.
“Especially in Australia with all the solar resources, there can be quite a bit of renewable power … generated very close to airports,” he says.
Green hydrogen currently accounts for just 1 per cent of global supply. But it’s not the only pathway to a greener future for aviation.
For small planes, electric propulsion is already shaping up as a viable alternative.
But while batteries are becoming increasingly efficient, they still don’t pack the punch required for longer trips.
One of the world’s biggest aircraft manufacturers, Airbus, is also putting its faith in hydrogen. But instead of using the gas to supply a fuel cell, it plans to burn hydrogen in its liquid form.
It’s working on three concept designs for a ‘ZEROe’ aircraft, which it’s hoping to have in service by 2035.
One of them looks unlike any passenger aircraft currently in the sky, requiring a radical new design if it’s to store enough hydrogen to fly long-haul.
Aviation is growing at immense speed, but its expansion comes at the expense of the environment. So what if flight routes were changed to minimise this?
Jo Dardenne, the aviation manager at the European sustainability group Transport and Environment, says the world can’t wait until 2035 to drastically cut long-haul airline emissions.
“You don’t need a new airframe like a hydrogen plane, you can just use today’s technology,” she says.
Ms Dardenne says sustainable aviation fuel (SAFs) like e-kerosene, also known as electrofuel or synthetic kerosene, provide the best short-term solution.
That’s because it can be blended with conventional jet fuel (kerosene) and used in today’s aircraft.
“That’s the beauty of electrofuel. It can be treated as normal kerosene.”
The fuel is made by combining green hydrogen with CO2 captured from the atmosphere, at high temperature. This produces a crude oil which is later refined.
When it’s burned, e-kerosene emits the same amount of carbon as was previously removed from the atmosphere during its production, making it carbon neutral.
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However, the 500 litres produced by oil giant Shell represented just 5 per cent of the total fuel needed for the flight from Amsterdam to Madrid.
Sustainable synthetic kerosene isn’t being produced on a large scale. In October, a new plant opened in Germany, promising to produce just over 300 gallons a day.
That would only fill about 5 per cent of a single Boeing 737-800’s fuel tanks.
Jo Dardenne says that until production is drastically ramped up, electrofuels will struggle to compete with cheaper jet fuel.
“That’s why we need governments to invest in them… and make sure they force airlines to shift towards those kinds of fuels.”
Yet while all these technologies promise to reduce the airline industry’s carbon emissions, one major problem remains.
Carbon is not the only enemy
If you look up at the sky, sometimes you can spot white condensation trails behind a plane when it passes overhead.
These are called contrails, and according to scientists, they can have a significant impact on the environment.
Contrails are largely made of water vapour that comes out of aircraft exhausts.(Wikimedia Commons: NOAA)
“The consensus is… contrails have an effect that is similar in magnitude, if not larger, than the total effect from CO2 emissions,” says Dr Marc Stettler, a senior lecturer in transport and the environment at Imperial College London.
A plane’s hot exhaust produces water vapour which clings to soot particles emitted from the engines.
In the cold sky, these particles freeze, creating clouds of ice crystals.
While the clouds can sometimes reflect the sun’s radiation and cool the planet, Dr Stettler says the overall effect is to trap heat that would otherwise be lost into space.
However, there is a potential solution.
By predicting the atmospheric conditions that are most likely to produce the longest-lasting contrails, airlines and traffic controllers can stop planes flying through them.
After studying Japanese airspace, researchers at Imperial College, led by Dr Stettler, concluded that by altering the altitude of less than 2 per cent of total flights, you could reduce contrail-related climate change by 59 per cent.
“This isn’t something that we need to do for every single flight” he tells the ABC.
“[But] I do think we need to be creative about how we reduce the climate impact of aviation.”
E-kerosene promises to reduce the impact of contrails by burning more cleanly than regular jet fuel.
Alternative jet fuels that create less soot could reduce the global warming effect of contrails, according to new research.
Hydrogen combustion engines like those planned by Airbus will be even cleaner, but may still emit particles that cause contrails to form, Dr Stettler says.
And hydrogen fuel cell aircraft, like Zero Avia’s, will theoretically produce only water vapour.
But Dr Stettler says it’s still unclear how quickly those contrails will disappear.
“In terms of hydrogen [planes], the jury’s out in terms of their effect on contrails.”
He says while technology catches up, passengers may have to think carefully about the impact their flights are having on the environment, and potentially pay more for their pollution.
But he hopes the “privilege” of flight can still be experienced by more than just the most fortunate in society.
“We are a global community and I think we are better for it.
“We really don’t want to be building walls.”