Electric flight seems to be all the rage, but its place in the aviation market has yet to be worked out. We talked to Ralph Müller, CEO of H2Fly, to discuss the state of play of electric aircraft, hybrid hydrogen fuel, and the future of the industry.
H2Fly is no newcomer to aviation. Founded in 2015 by five aerospace engineers from the German Aerospace Center (DLR) and the University of Ulm, the company operates as a wholly owned subsidiary of California-based advanced air mobility firm Joby Aviation, Inc., which acquired H2Fly in April 2021.
Based in Stuttgart, Germany, the company not only has a track record of developing hydrogen-fueled electric aircraft, but is also notable for its technical consultancy for aircraft manufacturers for whom they provide simulations, modeling and design work, as well as supporting airports in creating infrastructure specifications for next-generation aircraft.
Recently, we sat down with Müller to discuss what H2Fly is up to and what he predicts electric aviation will be like in 2040.
You've been dealing with the question of hydrogen-powered flight for some time, but what was the impetus behind getting into this?
Basically, it's not so much about hydrogen, actually. It's more about the electrification of aviation. That is the biggest motivation. When we looked at electric vehicles on the streets, we realized that the technology is there. It's reliable, it's affordable, and it's attractive for consumers. Pretty much the same technology used in electric vehicles is available for aircraft of all kinds. This is a massive motivation because electrified aircraft could encompass drones of all sizes – which we have seen flying for a couple of years now – eVTOLs, or conventional aircraft starting from small regional sizes up to 100 seats and even more.
That's possible because electric engines have been available for a long time, and now they have decreased in weight and become more durable. All the power electronics and computers you need to run them just got lighter, smaller, and less expensive. This is driving new aircraft concepts, which also allow for new business models. Take cargo drones as an example, where you can haul cargo of all kinds across short or long distances.
However, to drive electric engines, you need a battery, and batteries are heavy when you compare their energy density – the energy-to-weight ratio. When you want to fly a battery-electric aircraft, there is a limit to the weight you can carry. Right now, this limits range to about 100 miles to 120 miles (160 km to 193 km). Whenever you want to fly longer ranges or pull higher payloads, liquid hydrogen fuel cells make the most sense.
Hydrogen has its own problems. It's very bulky for one thing, and cryogenic fuel is very difficult to handle. How do you offset those problems when you're dealing with electric propulsion?
There are two points to that. First, when it comes to cryogenic hydrogen, we believe that if you put in the engineering hours and keep innovating, you will find ways to handle it. That involves insulation to keep liquid hydrogen cryogenic as long as possible to keep boil-off down, as well as addressing the durability aspects of liquid hydrogen storage. We believe there are ways to keep it safe and make it viable.
Regarding the volume that comes with it: if you look at conventional aircraft as we know them today, they are designed to store the main portion of their fuel in the wings. Conventional fuel is three times heavier than liquid hydrogen. Therefore, the aircraft we see today are specifically tailored for conventional fuel-powered engines. Electrified engines and hydrogen-electric aircraft will be designed differently. They will be designed to accommodate the fuel cells and the liquid hydrogen, whilst addressing safety aspects. We are speaking about a new kind of aviation, utilizing aircraft that will look completely different from those of today.
Are you going for the smaller aircraft, or are you aiming for the bigger ones? Where do you see yourselves entering the competition?
What we have learned and what we believe is that the amount of capital required to develop and certify a smaller aircraft is lower than for a larger aircraft. That is why we believe there will be more players in the smaller aircraft segments initially. Furthermore, the technology scales very nicely. With pretty much the same technology, you can scale liquid hydrogen storage systems and fuel cells to address smaller, mid-sized, and larger aircraft with the same fundamental technology, scaled and adjusted for specific applications.
We believe smaller aircraft will lead the way, starting perhaps with cargo drones. We will also see eVTOLs and up to 9-seater CS-23 types of aircraft being the first. I believe they will look a bit different to accommodate the tanks and the fuel cells, and they will feature far more efficient wings. This will drive the overall efficiency not only of the powertrain, but of the aircraft itself.
Are you looking at building a specific aircraft, or are you focusing on the fundamental engineering of electric propulsion, hydrogen fuel systems, and that sort of thing?
It's the latter. We are developing the liquid hydrogen fuel cell systems, storage systems, and the integration. We are also looking into the whole powertrain. This comes naturally when you have an engineering team capable of developing hydrogen-electric systems and the entire powertrain. There is a lot of synergy and an advantage in reducing integration complexity, which reduces overall weight and cost. Throughout the development and certification process, there will be higher synergies than if you were bringing several distinct aspects together from different suppliers. You can achieve a far more optimized overall system when you cover everything.
Let me also add that we believe the fuel cell system should be tailored to the aircraft. This is different from today, where you have base engines integrated into various airframes – take a turboprop engine like the PT6, which is available in various power settings and models. You can do that with a fuel cell system as well, but you achieve far greater improvements and optimization when you tailor-make the tank, the liquid hydrogen storage, the fuel cell system, and the powertrain to the specific aircraft and its mission.
That brings up an interesting point. You've basically got three parts to the setup: the electric motor, the fuel cell system, and the hydrogen storage. Which do you find to be the greatest challenge in developing these systems? Where are you concentrating most of your efforts?
I would say it's both the fuel cell and the liquid hydrogen storage.
When dealing with smaller systems, you often hit an inverse problem of scale. How do you make a fuel cell system that will work efficiently with a small cargo drone? That must be a tremendous challenge.
Absolutely. Right now, we are covering fuel cells on hand ranging from 30 kilowatts gross up to 600 kilowatts, and we have higher power ratings in development. You can very nicely combine and scale the available technology. The question is just when does it make sense to keep commonality high by using the same stack and balance-of-plant components. There is an area where it makes sense to use identical subsystems and just scale or combine them. Conversely, there are applications where it doesn't make sense. For us, we decided not to go into air-cooled fuel cells. Below 30 kilowatts, there is hardly an application that makes sense for us to address. We use liquid-cooled systems, and that is what we can scale.
So what is H2Fly working on at the moment? Do you have any big projects on the horizon that you'd like to discuss?
We have several projects. Most of them belong to aircraft manufacturers and are confidential, but we are also supporting projects funded by the German federal government and the European Union. One of the European initiatives is the Goliath project, where we propose to conduct liquid hydrogen refueling tests at three airports across Europe next year. We will be using our own refueling unit and our well-known test airplane, the HY4. The aircraft will be rebuilt with our own equipment, our own liquid hydrogen fuel tank, and the technology will be fully H2Fly. Additionally, for the German BALIS 2 project, we will be demonstrating a 300-kilowatt to 350-kilowatt serial-connected, two-module system that could be used for eVTOLs or as a redundant system for CS-23 aircraft.
What sort of challenges do you see with this refueling project? It can't simply be a matter of managing cold fuel.
We have developed a different perspective on this after dealing with the topic in great detail for many years. We see distinct difficulties when it comes to large aircraft and major airports with a massive demand for liquid hydrogen. However, those large aircraft won't be available in significant numbers before roughly 2045, meaning we have about 20 years to solve that.
In the meantime, due to the efficiency and low specific weight of liquid hydrogen, you can actually produce it directly at the airport. The positive aspect is that you just need power. With the global increase in available green power, we see more airports and smaller connected airfields gaining access to green hydrogen. You can produce gaseous hydrogen on-site during periods of low-cost energy – when the sun is shining and the wind is blowing, leaving an excess of green power. Then, you can liquefy the hydrogen according to your flight schedule. This optimizes the supply chain, reduces losses, and ensures you produce hydrogen when power is cheapest.
That raises one more question. Taking a big-picture look at things, you mentioned 2045 as part of the timeframe. Where do you see the aviation industry by the middle of the century?
I think by 2045, we will see an increasing number of large, 100-plus seater aircraft that are fully electric, most of them driven by liquid hydrogen fuel cells. We will see increased production capacity for liquid hydrogen on-site at airports, as well as external supply chains. Roughly ten years prior to that, we will see widespread electrification and battery-electric aircraft handling shorter-range, medium-duty missions. We will see a growing number of liquid hydrogen-powered aircraft, with the hydrogen being liquefied right at the airports.
Where the gaseous hydrogen comes from will mainly depend on the country. In Germany, we have a high and growing number of large electrolysers starting operations. You can buy gaseous hydrogen near the airports, have it delivered, and then liquefy it on-site using green power tailored to your flight schedules. This is where I see aviation heading.
As I mentioned, we will see a lot of new aircraft types. We have already caught a glimpse of this with air taxis, electrified conventional aircraft, unmanned air systems, cargo drones, and dual-use applications. All of this technology will be scaled up and deployed. Crucially, the regulations and certification programs will be established, and several manufacturers will be well into the certification process or receiving operational approval.
That sounds like a remarkable vision, and very different from what we have today. Thank you so very much for taking the time for this.
Thank you so much.
