In last week’s episode, we saw that while hydrogen may be the most plausible solution for proponents of ‘low-carbon’ aviation, this energy is a long way off being produced in a sustainable way. Certainly not at large scale, and not for a very long time. Because despite there being real political interest in the topic in several countries, as well as plenty of state funding, things are still very much in the development stage.
But let’s have a bit of perspective – you know we like a bit of that here at Midnight Trains – and imagine that, despite all the obstacles, we manage to produce enough green hydrogen (that is, hydrogen produced through electrolysis of water and renewable energy) to power our fleets. In this scenario, one key question emerges: can planes really be flown using hydrogen? And if they can, how and in what conditions?
If you were to believe the various announcements made by the press, the answer is a big yes. In fact, reading them, you’d think the future of hydrogen planes looks very bright indeed. At the end of January 2023, France Info informed us of a successful initial test flight for a hydrogen plane above the English countryside. But if you look at the details, only one of its two motors were fuelled by hydrogen, it only stayed in the air for six minutes and it could only carry 19 people. So it was very far removed from, say, a zero-emissions transatlantic flight. But let’s not be uptight, there have been several other promising announcements.
Also in January 2023, French financial newspaper Les Echos told us that despite the doubts of Boeing and Safran, Airbus has, since 2020, been planning to launch a hydrogen plane by 2035. This time, it’s serious talk. And several other industry giants are in on the act too, apparently: Air Liquide, VINCI Airports and ArianeGroup. And on top of all that, a Swiss business named Destinus aims to have a supersonic hydrogen plane linking Paris and New York in just an hour by 2030.
For this to become a reality, there are quite a few technological obstacles when it comes to motorisation. There are three principal ways you could fly planes using hydrogen. The first is to use a hydrogen fuel cell to produce electricity and power electric motors. “If you start from the premise that electric propulsion technology is already there, you would think that the principal problem with fuel cells is safety. Hydrogen is extremely flammable… This issue of safety around hydrogen systems is completely manageable if you install tools to ensure their performance remains consistent regardless of the payload”, explains Emmanuel Bensadoun, of Expertise/Etudes de France Hydrogène, an association bringing together more than 460 actors in the sector.
He continues: “Then, there’s the question of transport, because it’s possible to transport three to five times more hydrogen if cryogenised rather than if it’s still in its gaseous state (under high pressure). To do that, you’d have to liquify it by taking it down to 20 degrees kelvin, that is around –250C. At the moment, the technology is limited to advantage industries like space launch vehicles because thermal insulation and distributing hydrogen at the temperature, pressure and flow required are two functions that are technologically complex, especially in a ‘plane’ environment. To use them at large scale, you’d need to industrialise this technology, lower the costs, train engineers and hand airports all the equipment necessary for cold chain management, etc.”
As Bensadoun explains, the problems with cryogenisation of hydrogen also apply to the second feasible technology, those of propellers burning hydrogen rather than kerosene. But that’s not the only issue that still needs to be resolved. “Modifications to the aircraft would be less significant, but there would be big technological changes required for motors, especially when it comes to injecting the hydrogen in a way that’s reliable, precise and well-regulated. The development of this technology is being looked at by engine manufacturers. It’s their knowhow that will make the difference”, adds Bensadoun.
Finally, there’s a third path, which we touched on last week, which involves making synthetic kerosene using green hydrogen. And don’t be deceived: this is really kerosene we’re talking about. It burns and releases greenhouse gases into the atmosphere. This fuel could, however, also be produced by capturing CO2 emitted by another polluting industry, like the production of cement or similar. The solution isn’t ideal, but is to this day considered central in all scenarios considering the decarbonisation of aviation using hydrogen. Why? Because the two developing technologies are, as most experts agree, incompatible with long-haul flights. In other words, the side of the industry that needs it most…