Increasingly, it seems to be a matter of when, not if, a hydrogen-powered passenger aircraft will enter service.
Universal Hydrogen and ZeroAvia are both – to a greater or lesser extent – proving the technical feasibility of fuel cell powertrains, having already put their modified aircraft into flight test.
A slew of other manufacturers and suppliers, Airbus among them, are also pushing hard to adapt the technology for aerospace.
It is worth emphasising that it is a case of adaptation not full-scale development; fuel cells are already deployed in other industries, albeit those without aviation’s particular combination of weight, size and safety constraints.
Those factors, and the thorny issue of obtaining certification, still pose significant hurdles to any commercial roll-out.
Yes, they are likely to be overcome, but as yet it is unclear at what cost this will be to vital operational and commercial parameters such as payload and range. As such, how many fuel cell-powered aircraft will enter service, and how soon, remain open questions.
But if technical constraints are less likely to be the factors limiting hydrogen’s adoption, then the availability of the fuel itself will.
Or rather, access to so-called green hydrogen will be key if aviation is truly to achieve the goal of emissions-free flight.
That is both from an infrastructural perspective – is there a distribution network? Do airports have sufficient refuelling capabilities and capacity? – and a production standpoint. Who, exactly, will produce the fuel? And where?
As a recent report, Net zero aviation fuels: resource requirements and environmental impacts, from London-based scientific body the Royal Society points out, producing sufficient green hydrogen to meet the UK’s net-zero ambitions alone would require up to 3.4 times the country’s 2020 renewable energy generation capacity.
Consider too that aviation will be in competition with other industries for green hydrogen and the scale of the problem becomes clear.
The industry’s other great green hope – sustainable aviation fuel (SAF) – faces a similar problem if it is to scale up capacity sufficiently.
The same Royal Society study calculates that if energy crops were used to produce SAF, then more than 50% of the UK’s agricultural land would need to be turned over to their cultivation.
On the other hand, if synthetic SAF becomes the goal, then the UK must grow its renewable generation capacity by five to eight times.
And given that green hydrogen is a vital component of synthetic SAF, the demand for resources only increases.
Now, extrapolate those figures globally and the scale of the problem becomes clear.
What is also evident is that aviation alone cannot resolve these issues. Political commitments to decarbonisation are a vital push towards a greener future; but without concomitant financial support to achieve those goals, the new dash for gas could prove little more than hot air.
