Hydrogen fuel cells could offer significant advantages for eVTOL systems in terms of endurance, range and other benefits. While it is still early days for the power source — and for urban air mobility (UAM) itself — industry experts are turning their focus to a crucial consideration: infrastructure.
Using hydrogen as a power source could significantly expand the possibilities of air taxis beyond the limitations posed by battery-electric powertrains, according to proponents of the fuel. It has a higher energy density than lithium batteries, meaning it can increase operational range and flight time. Additionally, hydrogen systems can be refueled fairly quickly, increasing the utilization rate of those platforms.
While hydrogen can be used as a liquid fuel to power internal combustion engines, most companies in the aviation space are looking to hydrogen fuel cells, effectively a battery that uses the fuel source to produce electricity. But the highly flammable fuel creates significant challenges for use in rooftop-based vertiports, as many envision for future UAM. There are also logistical difficulties and expense associated with transporting the fuel to such environments, said Darrell Swanson, an electric aviation consultant with a focus on infrastructure.
“The challenge for the infrastructure side is the ability to transport hydrogen to the rooftop and perform a refueling in a safe manner that is allowable under the fire regulations,” he said. “Personally, I think it is challenging, and that doesn’t even address the fact that you would need a hydrogen economy in place.”
This means that any future refueling operations are likely to take place at ground-based vertiports or other infrastructure, Swanson said. This would make sense for hydrogen-powered eVTOLs, given their increased range capacity, he added.
Dr. Alex Ivanenko, co-founder and CEO of HyPoint, which designs hydrogen fuel cells for eVTOL and urban air mobility, said the most straightforward approach would likely be to deploy hydrogen refueling at sites that already utilize flammable gases and fuels — airports being particularly well suited, as they handle large quantities of jet fuel. As with natural gas, a network of pipelines would need to be built to support short-distance point-to-point gaseous hydrogen transportation, he added, while liquid hydrogen would be moved by truck.
Ideally, future airports, vertiports or other hubs would include as much hydrogen generation infrastructure as possible on-site, Ivanenko said, such as water electrolysis technology using solar or wind-generated electricity.
“In this way, hydrogen fuel would not need to be delivered by truck or tanker, which is currently a costly method, especially when sites are remote.”
Much of the future of hydrogen-powered eVTOLs remains speculative. While current models assume that hydrogen aviation in general will use pressurized gas, in the short term — perhaps over a five- to 10-year period — there is a widespread belief that liquid hydrogen will then be required, said Chris Jackson, chair of the UK Hydrogen and Fuel Cell Association and CEO of Protium, a provider of hydrogen solutions. Liquid hydrogen is less challenging from a technical perspective and doesn’t require the same volume of demand to be commercially appealing, he said.
From a UK perspective, the key consideration is to understand planning and other regulations, Jackson added. For urban areas it will be harder to store large quantities of hydrogen onsite, which will lead either towards regular deliveries of hydrogen (pressurized or liquid) or to onsite hydrogen production. For rural areas, the scope is much broader and more manageable, he noted. For the UK, as with many other countries, government policy suggests that the most commercially attractive hydrogen will be “green” hydrogen — produced using solar or wind power — “which can add another layer of complexity when optimizing the location.”
For eVTOLs, it’s important to understand that “the amount of hydrogen we’re talking about is quite small,” said John-Paul Clarke, co-founder and chief technology officer (CTO) of Universal Hydrogen, which is working on developing an end-to-end hydrogen logistics business to drive decarbonization of the aviation industry.
It is unlikely that operators will run a hydrogen pipeline to a rooftop vertiport, he said; ground-based vertiports will be easier to support in the medium term. However, Clarke noted that there are challenges involved with transporting any eVTOL fuel source to a rooftop, so he expects such difficulties to be overcome.
The infrastructure requirements are likely to be driven by the manufacturers themselves, said Swanson, most of which are largely focused on platforms powered by lithium batteries.
“Until infrastructure [designers] see somebody that’s getting a hydrogen vehicle through the certification process, they might not necessarily start planning for it,” he said. However, the best economic model will likely win out in the end, he added. Swanson sees potential for a market where lithium batteries are used over shorter ranges, with hydrogen adopted more for longer-haul journeys.
Hydrogen is increasingly in focus for various aspects of national economies, so it may make sense to look at the bigger picture when it comes to infrastructure investments. “People underestimate the multimodal benefits of hydrogen in vertiports, airports, [sea] ports and other natural transport hubs,” said Jackson. Building hydrogen production and supply infrastructure could support users across these facilities and beyond, while generating economies of scale.
Governments and investors must strive to avoid “death by pilot schemes,” Jackson warned. Instead, they should focus on the minimally commercially viable demand for hydrogen on a broader level, rather than looking to a particular sector — like urban air mobility — in isolation.
“The capital investment is higher than other options, but the flexibility and sustainability arguments, I would argue, are stronger,” he said.