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Is Hydrogen the Future of Aviation? Possibly, but in the Far Future

03.01.22 | Blog | By:

A bit more than a century ago, Icarus’ dream came true, man finally could fly, not just float and drift in the lower atmosphere in hot air balloons, really fly, from A to B. Original designs were flimsy, out of wood and paper, but, soon, aeronautics engineers got serious about flying, the familiar shape of tube-and-wings emerged and allowed the massive development of air transport since the 1950s. Liquid fuels, co-developed by the aviation and fuels industry, for propellers, then for turbines, ended up smartly stored in various parts of the airframe, in the wings and in the tube, by the way also helping with additional in-air services, like heating and cooling or hydraulic fluid.

Energy efficiency, as measured in fuel consumption per passenger per kilometer, has dramatically improved, divided by 5 across the second half of the 20th century, but further progress seems now limited, less than 1 % per year, in line with the theory of diminishing returns for mature technologies. The tube-and-wings + turbines design seems to be reaching its asymptotic limit, just under 2 liters of aviation fuel (a.k.a. kerosene, jet-fuel, produced from fossil crude oil) per passenger per 100 kilometers, close to what you get in a modern car running on an internal combustion engine.

If air transport keeps on growing, doubling in the next 20 years according to some projections, mostly driven by the emergence of vast middle classes in Asia, greenhouse gas (GHG) emissions could become a serious societal issue for the sustainability, thus the acceptability, of aviation, in a world aiming for net zero emissions in 2050. In short, air transport would move from a minor actor, with 3% of man-made GHG emissions today, to a major villain, causing 20% of GHG emissions in 2050 in a business-as-usual scenario. This is well documented.

We have had the solution to this ominous equation, for more than 10 years: Sustainable Aviation Fuels (SAF). SAF, as energy dense as fossil jet-fuel, can be produced as biofuels from biomass. These fuels use diverse and mature technologies like lipids hydrogenation. They can also be produced synthetically from less mature technologies using renewable electricity and CO2, with GHG emissions reductions typically around 80%, more if using wastes and residues. SAF is fully fungible with existing equipment, be it logistics or airplanes. And it is potentially available in sufficient volumes to make aviation acceptable in 2050, less vulnerable to “flight shame” initiatives.

But this brilliant solution has been designed by the industry, which makes it suspect in the eyes of a part of the civil society, vociferous self-appointed preachers of the Do’s and Don’ts in our era threatened by climate change. What about the grab of arable land, what about deforestation, what about other usages for biomass or renewable electricity? And why don’t we just fly less (flying is a privilege, for just 11% of the world population)? Well, the latter may actually happen anyway, on a smaller scale though, as SAF is, and will very likely remain, much more expensive than fossil-based aviation fuel. The passenger is eventually to pay for this premium, which could increase the ticket price by up to 20%.

Another approach, in the spirit of Professor Robert Proctor (Stanford University)’s agnotology, is to just shove SAF in a “well of disinterest” by pushing to the front hydrogen as the magical solution for flying.  Although no sooner than the second half of this century when considering commercial scale, once specific airplanes and supply chains are available, electrolyzing technology has been scaled-up and renewable electricity is confirmed as plentiful available and durably affordable, all of the above not granted. But we are talking here of a blurry future, way beyond the human horizon, which seems today around twenty years ahead.

Hydrogen is clearly the flavor of the day, no doubt, and Europe is pushing hard, in the hope it could bring back some technological leadership and energy independence. And, as said above, the beauty of hydrogen is that it will not materialize on a big scale any time soon, which makes it a wonderful solution for politicians addicted to short-term measures, presentism in sociologic terminology, who will not bear the responsibility of the cost impact on their electors.

Because hydrogen is not cheap to produce, even though prospects look promising in the long-term, 30 years from now. According to recent research, projecting an average of 2$/kg in 2050. With fossil jet-fuel in the 0.5 to 1 $/kg range, depending on crude oil price, energy parity seems feasible, as hydrogen is three times more energy dense compared to hydrocarbons.

But total cost of operation, a key metrics for transport, does not stop at the fuel component level. If renewable hydrogen replaces gray or black, fossil-based, hydrogen in the industry, to produce fertilizers or base chemicals, it does, but not in transport, where a whole new architecture is to be installed, as hydrogen is ten times less dense at ambient temperature than jet-fuel or needs a temperature of – 250 °C to be in liquid, dense enough, form.

According to Airbus, which targets the first flight of an hydrogen-powered plane in 2035, airframe designs must evolve from the classical tube-and-wings to a flying wing.

And dedicated hydrogen logistics in airport fuel tank farms and distribution networks would have to be built, at a significant cost, combining cryogenics and increased safety measures as hydrogen can be quite fugitive. Could SAF and hydrogen co-exist in all airports, or would hydrogen only be considered for major platforms, as replacing the whole commercial aviation fleet, more than 20 000 aircrafts, will take time anyway, and not be cheap for airlines … and passengers?

Cost parity may then be more elusive.

The far future, way beyond 2050, can be considered for hydrogen to possibly take over from traditional liquid aviation fuels in air transport. In the meantime, the carbon footprint of aviation has to be drastically reduced and the only readily available solution is SAF, so let us not accept hydrogen to become the smoke screen to downplay SAF. Hydrogen in air transport may be a good idea, but it should be confined in the domain of R&D for the time being, not to lure the public to believe it is replacing conventional jet-fuel any time soon.

And should this not prevent having a proper debate about the pertinence of hydrogen in transport in the first place? Such a debate should take into account the following headwinds:

  • Electrification is the heavy trend for road transport, at a cost (90 B$/year for infrastructure until 2030, to build 40 million recharging points, and 1.6 T$ on top of that to 2050), so why invest in another infrastructure, likely much more expensive (high pressure or low temperature)?
  • Conclusion? Dedicate hydrogen to deeper-to-abate transport modes: marine and aviation, but:
  • Marine fuels have cheaper green alternatives for trans-continental voyages, where the majority of GHG emissions occur: methanol, ammonia, which are liquid, natural gas with biogas, as a cheaper and readily available transition.
  • As for aviation, not so easy, as SAF is squarely in place.
  • Hydrogen requires new airframes, thus capex for airlines, not the case for SAF.
  • Opex: SAF, biofuels and e-fuels, will likely be operable at 100% (full replacement).
  • SAF is liquid: no need to change logistics, airport storage and distribution.
  • SAF is readily available, at least advanced biofuels, from waste and residue (circular economy) (see study by Imperial College for Concawe, volumes are significant for 2030 and 2050).
  • No safety issue with storage, contrary to hydrogen (Hindenburg syndrome).
  • SAF cost will likely remain competitive v. hydrogen.

 

Philippe Marchand is a Bioenergy Steering Committee Member of the European Technology and Innovation Platform (ETIP).

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