You might be surprised that the first hydrogen-powered vehicle dates all the way back in 1863, Belgian inventor Étienne Lenoir’s “hippomobile.” Of course, it’s only in the last decade that hydrogen has been hailed as the transport fuel of the future, with more than 7,500 fuel-cell cars on the road worldwide today.
And now, airline manufacturers are also plugging into the trend, with the notable September 25 announcement that London and California-based startup ZeroAvia had carried out the first flight of a hydrogen-powered, commercial-grade aircraft in the UK. As the six-seater plane managed a taxi, takeoff, flight circuit, and landing without a hitch, ZeroAvia sees the event as a milestone in its quest to decarbonize commercial aviation.
But while the company claims that hydrogen-powered craft already have the potential to "match the flight distances and payload of the current fossil fuel aircraft," many industry experts still caution that zero-emission commercial flights are a far-off reality. To better understand where we’re at and where we may be headed, here’s a bird’s-eye view of the benefits, the challenges and projects underway in the quest for viable hydrogen aviation:
The Benefits
- ZERO CARBON Today, modern planes use kerosene as fuel which releases harmful carbon dioxide into the atmosphere. Planes using hydrogen emit only water, and tests suggest they can be just as fast as traditional planes. Full-scale implementation would lead to a considerable reduction of global carbon emissions; according to the European Environment Agency, aviation was responsible for 3.6% of EU greenhouse gas emissions in 2019.
- SILENT FLIGHTS A hydrogen engine is also very quiet compared to the combustion roar of a jet engine. In fact, a smaller propeller plane would produce about the same amount of noise as the internal combustion engine of a car. It would of course mean a more pleasant, quieter flight for passengers, but it also opens the door to flying (and even landing) near residential areas.
- ETERNAL SUPPLY: Hydrogen is the most abundant element in the universe, making up roughly 75% of the universe’s mass. It also has a very high energy density — approximately 120 MJ/kg which is almost three times more than diesel or gasoline.
The Challenges
- DESIGN An aircraft’s fuel cell can be powered by either compressed or liquid hydrogen. While the latter is both denser and lighter, it requires a more complex system and is harder to certify for commercial use. ZeroAvia has therefore chosen to use compressed hydrogen for its planes, which may need to be stored in ‘drop’ or wing-tip tanks mounted externally on the airframe. Liquid hydrogen is less voluminous, but would still require cryogenic tanks – adding substantially to an aircraft’s drag while the cooling uses as much as 45% of the stored energy content. Overall, in order to scale up to bigger aircraft and longer distances, aircrafts will need to be redesigned to match the propulsion system.
- INFRASTRUCTURE Another challenge for turning to hydrogen as aviation fuel is the lack of infrastructure for everyday operations. One option for fuel delivery to airports is via existing gas networks which could be converted for the transportation of hydrogen gas. However, it would require significant cross-sector investment.
- EFFICIENCY Current hydrogen production is dominated by "gray" processes, with an estimated 95% of hydrogen produced directly from carbon-emitting processes such as steam methane reforming or coal gasification. The cleaner alternative is through electrolysis, where water is cleaved into hydrogen and oxygen. If the electricity used in the process comes from renewables, then it is carbon-free “green” hydrogen. However, this process is only 75% energy-efficient, so around one-quarter of the electricity is automatically lost. For fuel-cell cars, for example, where further energy is lost during transport and later as hydrogen needs to be converted into electricity, Wood Mackenzie estimated in 2019 that green hydrogen has an end-to-end efficiency of around 30%.
New Developments
- NEXT-GEN. TECH Despite these challenges, Wood Mackenzie estimated in a 2019 report that more than 3.2 gigawatts of green hydrogen electrolyzer capacity will be deployed between now and 2025 — a 1,272% increase on the 253 megawatts installed from 2000 to 2019. This will be driven partly by the dropping prices in renewable energy, and also as next-generation electrolyzers are set to make the process more energy-efficient.
- INFRASTRUCTURE In Europe, there are plans underway to develop the continent’s first commercial plant for hydrogen-based aviation fuel. Spearheaded by Norsk e-Fuel, the joint venture with four other companies aims at having the Norwegian plant operational by 2023, offering a maximum capacity of 10 million liters of hydrogen-based jet fuel with ramped-up production capacity to 100 million liters by 2026. Meanwhile, leading “hydrogen nations” across the world are rolling out new hydrogen infrastructure which can also serve the aviation industry. In Japan — the first country to adopt an official hydrogen strategy in 2017 — a 2019 study by market research company Fuji Keizai, forecasts a 56-fold growth in the hydrogen market by 2030. The number of fueling stations are forecast to rise from 111 (2019) to 1,321 by 2030. Other countries rapidly expanding their hydrogen infrastructure include the U.S., Australia, China, South Korea, UK, France and Germany.
- OTHER PROJECTS While ZeroAvia might have been the first company to pull off a successful test flight, other companies across the world are making rapid advances in hydrogen aviation. Examples include European multinational aerospace corporation Airbus, which recently revealed three different concepts for commercial aircraft that could enter service by 2035; and aerospace company Alaka'i Technologies, based in the U.S. state of Massachusetts, that aims to roll out next year a five-seat, multi-rotor aircraft powered by hydrogen fuel cells that is designed to take off and land vertically.
