The range of battery-electric cars has risen substantially over the past decade, making them increasingly appealing for drivers. Petrol panic-buying in September only served to increase consumer interest.
Chasing the same goal, it might seem that batteries are an obvious choice for aviation’s own ‘net zero’ efforts. Some projects, such as retrofits powered by MagniX electric propulsion systems, have shown great promise.
Batteries have a big problem, however – even the best have only a fraction of the energy density of conventional fossil fuels, limiting the size and range of electric flight.
Hydrogen has emerged as a serious competitor, thanks to its superior energy density, maturing technology and green credentials. Airbus, for example, has announced three hydrogen-powered commercial aircraft concepts, and hopes one could enter service by 2035.
“We don’t need to change the laws of physics to go with hydrogen,” said chief executive Guillaume Faury. “Hydrogen has an energy density three times that of kerosene – it is made for aviation.”
Starting small
While Airbus is the biggest company to pin its flag to hydrogen, initial success is coming from much smaller sources. In September last year, British-American start-up ZeroAvia demonstrated the world’s first hydrogen-electric flight of a passenger plane over Cranfield, Bedfordshire, as part of the government-funded HyFlyer project.
The converted six-seater Piper M-class used hydrogen fuel-cell stacks from Swedish firm PowerCell, which were primarily developed for automotive applications. ZeroAvia optimised the stacks following testing, updating software to handle stronger ramp-ups and ensuring they could be used for aviation.
Since the test flight, ZeroAvia has converted the small plane to a purely hydrogen configuration, removing batteries that were previously used for take-off.
“We achieved that by doing a couple of things,” says Sergey Kiselev, European vice-president at ZeroAvia. “We optimised the operational parameters of the fuel cells, so that it had better thermal cooling parameters and was able to deliver us a higher power output to the prop... and we installed different tanks, and bigger tanks.”
The company has purchased a much larger 19-seat aircraft for conversion, with plans for hydrogen-powered flight by the end of the year. It is also planning for an island-hopping hydrogen-powered flight in the Orkneys by April-May 2022, as part of the Sustainable Aviation Test Environment project.
A large focus of the scheme is infrastructure for zero-carbon flight, says Kiselev, “making sure that we are creating the infrastructure which is in line with the requirements of operators”.
Scaling up
ZeroAvia is confident that hydrogen is the right technology to back. “If you talk to any of the OEMs which produce sizeable aircraft, batteries are not the answer,” says Kiselev. “With the current energy density of the batteries, there is no solution for anything beyond, let’s say, a couple of dozen passengers for a few hundred nautical miles.”
He adds: “Hydrogen, on the other hand, is scaleable. We have a solution for large turboprops, and regional jets up to 100 passenger seats, and that can be done without significant changes to the airframe. For the larger aircraft, of course, we need to make significant airframe corrections.”
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