One can fairly say that the concept of hydrogen propulsion has become a mainstream concept in commercial aviation. A new research program, project, or alliance to advance the development of hydrogen-powered aircraft and a related hydrogen (H2) ecosystem gets launched almost weekly as national or regional governments increase funding to help decarbonize aviation and their wider economies. For the aviation industry, hydrogen propulsion stands as one of the main avenues toward net zero emissions by 2050.
The UK’s Jet Zero strategy estimates that rapid investment in hydrogen aviation could see the country secure up to 19 percent of the global aerospace industry share, valued at £178 billion ($222 billion) per year in 2050, and 60,000 aerospace jobs on zero-carbon aircraft by the same year. In line with that strategy, the UK is supporting the Aerospace Technology Institute (ATI) program with £685 million in funding from 2022 to 2025 to research the development of zero-carbon and ultra-low emission aircraft technology.
Across the channel, the European Union has adopted a hydrogen strategy to achieve the European Green Deal—targeting climate neutrality by 2050 and a 55 percent reduction of net greenhouse gas (GHG) emissions by 2030 compared to 1990 levels—and a clean energy transition. The multibillion-euro EU Hydrogen Strategy sets the framework to decarbonize hydrogen production and expand its use in sectors where it can replace fossil fuels. For the aviation sector, the long-term policy sees a twofold use of hydrogen: directly on-board aircraft for propulsion through combustion in a turbine and for on-board power generation through fuel cells, or indirectly as a feedstock for synthetic aviation fuel (power-to-liquid). The upcoming EU-wide sustainable aviation fuel (SAF) blending mandate requires that a specific proportion of the fuel mix—1.2 percent in 2030, progressively reaching 35 percent in 2050—must comprise synthetic fuels.
Through the Clean Aviation public-private partnership, budgeted at €4.1 billion ($4.5 billion) over seven years, Europe provides funding for the integration and demonstration of hydrogen-powered aviation technologies and subsequent aircraft architectures. In parallel, the Clean Hydrogen public-private partnership has allocated part of its €2 billion research and investment budget to scale up so-called hydrogen valleys and H2 airports while other EU Horizon research funding supports the demonstration of hydrogen refueling and supply from air transport ground infrastructures to the aircraft and follow-on demonstrations of ground-based aircraft movements (e.g. taxiing).
Almost all large OEMs—including Rolls-Royce, Pratt & Whitney, and CFM International—and their suppliers are working on hydrogen propulsion. With the launch of its ZEROe project involving three hybrid-hydrogen aircraft concepts in 2020 and a recurring pledge that it will bring a novel hydrogen-powered short- to medium-haul commercial aircraft to market by 2035, Airbus has proved the most vocal of all. The European airframer last November added a fourth ZEROe concept aircraft, a high-wing 100-seat regional airliner powered by a megawatt-class fuel-cell engine. Airbus will test such a fuel-cell engine architecture onboard its ZEROe multi-modal flight test platform, A380 MSN001, towards the middle of the decade.
Boeing so far has steered away from committing to developing a hydrogen-powered narrowbody, though since the mid-2000s it has completed six hydrogen technology demonstrations including crewed and un-crewed aircraft using hydrogen fuel cells, a combustion engine, and a 2021 cryogenic storage tank built and tested with NASA.
A study commissioned by Clean Aviation and Clean Hydrogen projects that hydrogen-powered aircraft—mainly commuter and regional and 50 percent of short- to medium-range single-aisle—could account for 40 percent of all in-service aircraft by 2050. On a European level, that means hydrogen-powered aircraft could connect all of the continent’s big cities, according to Clean Hydrogen executive director Bart Biebuyck.
Several start-ups have already started projects to adapt commuter and regional airliners to fly on H2. In January, British-American company ZeroAvia completed a 10-minute test flight of a 19-seat Dornier 228 turboprop powered by a hydrogen-electric powertrain on its left wing and a standard Honeywell TPE331 powerplant on its right. U.S.-based Universal Hydrogen in March conducted a 15-minute flight with a 40-seat De Havilland Canada Dash 8-300 with a hydrogen-powered fuel cell propulsion system— driving the electric motor directly—replacing the turboprop's right-hand Pratt & Whitney PW150A turbine engine.
Lacking Green Hydrogen
“We must go all in on hydrogen,” insisted Universal Hydrogen COO Arnaud Namer, speaking at the Clean Aviation Forum in Brussels earlier this year. “We need to go faster.” If the aviation industry wants to meet the Paris Agreement carbon dioxide emissions target and get to net zero by 2050, adopting commuter and regional aircraft to hydrogen propulsion will need to start this decade. “Airbus has to bring a true zero emissions single-aisle platform in 2035,” he insisted. “We have no other choice.”
Boeing chief sustainability officer Christopher Raymond characterized the notion of replacing the world’s fleets with hydrogen-powered airplanes in time to meet the industry’s 2050 target as “arithmetically impossible.” The U.S. aircraft manufacturer estimates that by the late 2030s more than 40,000 non-hydrogen commercial jets will remain in service. “Each will last decades,” said Raymond. “Given that the most airplanes ever produced around the world in a year so far has been about 1,800, we can’t just switch overnight to hydrogen.”
While flying on hydrogen does not emit carbon, its production often does. “Truly reducing emissions by flying on hydrogen will also require a wholesale transformation of the energy industry to ensure sufficient so-called green hydrogen produced from renewable electricity exists for aviation,” remarked Raymond. Moreover, he said, aviation must compete with other sectors for green hydrogen as it becomes available.
Airbus CEO Guillaume Faury admitted last November to uncertainty over the availability of affordable clean hydrogen in the near future. “The lack of availability of clean hydrogen at the right quantity in the right place at the right price in the second half of the decade is a big concern for me,” he said. Uncertainty over future green hydrogen supply could be a reason to delay the launch of the company’s first ZEROe hydrogen airliner, he conceded.
Kearney, a global management consulting firm, has identified the production of green hydrogen at a sufficient scale as the main challenge to meet the large energy needs of the aviation industry. It also raises a practical problem: producing enough hydrogen to fuel just 30 percent of flights at Paris Orly Airport would require 270 tonnes of liquid hydrogen (LH2) per day, assuming consumption of 1.5 tonnes for a 1,500-kilometer flight of a turboprop. That translates to an energy need equivalent to the production of a typical nuclear plant or 44 square kilometers of solar panels—a footprint representing three times the entire surface area of Orly itself. Covering the entire Orly airport with solar panels would only produce enough hydrogen for two to three aircraft per day.
Meanwhile, a shift to hydrogen will require airports to adapt their infrastructure and logistical systems. Compared with conventional jet fuel, hydrogen requires four times more volume to provide the same amount of energy, resulting in four times the number of fueling trucks adding to the congestion of airside roadways at several airports. Delivery of hydrogen could be done through pipelines, but because hydrogen can't mix with kerosene and liquid hydrogen must be stored below -253 degrees C (-423 degrees F), airports would need to manage two energy supply chains simultaneously until a complete transition to hydrogen happens, Kearney pointed out.
Despite all the challenges and the uncertainty of if or when a hydrogen-powered narrowbody airliner will enter commercial service, agreements between energy suppliers, airports, OEMs, and airlines to identify infrastructure requirements for future hydrogen aircraft continue to emerge across the continent. In France, for instance, industrial gas company Air Liquide and Groupe ADP, operators of some 30 airports across the world including Paris-Charles de Gaulle and Paris-Orly, agreed to establish a 50/50 joint venture to provide airports in France and across the world with the engineering and services they will need for their transition to hydrogen. Vinci Airports has teamed with Airbus and Air Liquide to build a future network of hydrogen-powered airports and make Lyon-Saint Exupéry a hydrogen hub. In the Netherlands, Shell, Rotterdam The Hague Airport, Rotterdam The Hague Innovation Airport, and ZeroAvia signed a collaboration agreement earlier this year to develop a concept of operations for hydrogen in airports and demonstration flights to European destinations by the end of 2024. In Germany, Hamburg Airport, Lufthansa Technik, the German Aerospace Center, and the Center for Applied Aeronautical Research now collaborate on testing the effects of LH2 on maintenance and ground processes.