How Green Is Hydrogen Fuel?

First, how likely are hydrogen-powered airliners in the near future? 

Leaders at Boeing have said they’re not interested, for now. They say developing hydrogen-fueled transport aircraft won’t be feasible until at least 2050. However, both Embraer and Airbus are planning to develop hydrogen fuel demonstrator aircraft. Airbus is going further, already collaborating with hydrogen producers and expressing confidence about the fuel’s viability.

“2035 is our targeted entry into service date,” said Glenn Llewellyn, Airbus vice president of zero emission aircraft, during October’s Hydrogen Aviation Summit hosted by ZeroAvia. “Working backwards, it means we’re going to be flight testing propulsion systems around the 2025 timeframe.”

Llewellyn acknowledged that flight testing a hydrogen propulsion system within four years will be a huge challenge. 

“We have a lot of work to converge on the aircraft configurations, which will be done in parallel to technology maturation and the flight demonstration, and also the ecosystem establishment.”

Testing plans at Airbus may already be under way. The OEM didn’t deny reports that it’s planning to test fly an existing CFM International engine converted for hydrogen propulsion. 

“Airbus is in constant talks with all engine manufacturers in order to assess and identify the propulsion technologies that would support its decarbonisation roadmap and enable the company to be ready to launch its first zero-emission airliner in 2025,” an Airbus spokesperson told FLYING. “These talks we keep confidential.”

Although civil aviation only contributes about 2 percent of all worldwide carbon emissions, the industry is increasingly pushing toward reaching net-zero. Many of the world’s largest carriers have already committed to net-zero emissions by 2050, if not sooner, including Air France, American Airlines, British Airways, Delta Air Lines, Lufthansa, Southwest, and others.

In fact, United Airlines and Alaska Air Group have already invested significantly toward research and development of hydrogen-powered aircraft.

Developing the ecosystem and surrounding infrastructure to support wide-scale use of liquid hydrogen as an aviation fuel is a gigantic hurdle that experts point to as key to success. Production, storage, and delivery would all have to be scaled up. To transform the entire hydrogen fuel ecosystem to fully “green” would make this goal even more challenging. 

In 2020, Airbus unveiled three ZEROe concept airliner designs: a turbofan, a turboprop, and a blended-wing body. 

“It’s much more likely that we would have a turbofan or turboprop—a more classical tube and weight configuration in terms of aircraft concept—nonetheless with a disruptively different propulsion system,” Llewellyn said. “That propulsion system will be running on liquid hydrogen stored on board.”

Engineers are looking at multiple ways to use hydrogen fuel, including gas turbines that burn hydrogen, hydrogen fuel cells, and various hybrid combinations, Llewellyn said. 

Hydrogen fuel cells produce electricity without combustion or emissions, similar to conventional batteries. However, unlike car batteries, they don’t run down or need to be recharged as long as they’re fed hydrogen and oxygen. 

On a hydrogen-fuel-cell aircraft, electricity created by fuel cells drives thrust-producing engines. Compare that to hydrogen gas turbines, which power engines with internal combustion, similar to traditional combustion engines that burn jet-A. Unlike traditional combustion engines, hydrogen burns clean. 

Both types of systems would require huge fuel tanks to carry the amount of liquid hydrogen needed for standard short- and medium-haul routes. 

The reason is rooted in the nature of hydrogen itself. It packs more energy by weight than jet fuel, but it has lower energy by density. That’s because at room temperature hydrogen is a gas, making it difficult to store in large quantities unless it’s compressed by turning it into a liquid. To do that, you have to cool hydrogen to extremely low temperatures. 

That means aircraft hydrogen fuel tanks are going to be more complex and heavier than comparable jet-A tanks—and more weight on an aircraft is a disadvantage. 

However, the industry has tried creating a hydrogen-fueled airliner before. In the late 1980s, Soviet engineers developed the experimental Tupolev Tu-155, which completed about 100 test flights before the program was canceled during the collapse of the Soviet Union. 

Transporting hydrogen fuel from production facilities to airports would be critical to widespread adoption. 

“If we don’t have hydrogen at the aircraft, then there’s no point in providing a hydrogen aircraft,” Llewellyn said. “We believe that hydrogen can be used at airports already in the 2020s to start decarbonizing ground based activities.”

Airbus has already launched significant collaborations with Air Liquide, Vinci Airports, Groupe ADP, and Plug Power in the U.S. 

This is when green hydrogen comes in. The fuel industry has created a color-coded system for hydrogen based on how environmentally friendly it is. Green hydrogen is the cleanest. 

Remember, the goal of moving to hydrogen as an aviation fuel is to reduce carbon emissions. But currently, most hydrogen is manufactured by a process called steam-methane reforming. Basically hot steam is mixed with a methane source, like natural gas, which is a fossil fuel. The process releases carbon dioxide (CO2), which is why hydrogen from steam-methane reforming is not considered green. (In fact, the industry has designated hydrogen made this way as “blue” hydrogen.)

But, there is a way to make hydrogen from renewable sources without producing CO2: It’s a process called electrolysis.

As you may have learned in chemistry class, electrolysis uses massive amounts of electricity to separate water into its chemical elements, ripping the H (hydrogen) from H2O (water). 

Hydrogen produced by electrolysis can only be designated “green” if the electricity used in the process comes from a zero-emission source, like wind turbines or solar energy farms or hydro-electric power plants. Currently, only about one percent of the world’s hydrogen is produced this way. But that number likely will increase as several companies are already working to build this production infrastructure. 

For example, Plug Power is on track to produce green hydrogen in New York, Tennessee, Georgia, and California, where the company says it plans to build the “largest green hydrogen production facility on the U.S. West Coast.” 

Near Cologne, Germany, the largest electrolysis plant of its kind in Europe began producing green hydrogen earlier this year, thanks to funding from the European Union. This Shell facility is on track to pump out 1,300 tons of green hydrogen per year. 

According to a 2020 European Union study, producing enough liquid hydrogen to fuel the entire aviation industry worldwide could require between 500 and 1,500 gigawatts of renewable energy capacity, depending on the scenario. That works out to between 20 and 60 percent of total renewable energy capacity available today. 

Currently, the world produces nearly 90 million metric tons of hydrogen per year. That number is expected to more than double to 200 million metric tons in 2030. According to the International Energy Agency, by 2050, global hydrogen production could reach 528 million metric tons per year—more than three-quarters of it green.

The global aviation demand for liquid hydrogen could total more than 9 million metric tons per year by 2040, which would be just 5 percent of total demand, according to the EU study.

If larger hub airports decided to switch just 5 percent of their fuel infrastructure to hydrogen, the EU study estimated it would require about 40,000 tons of liquid hydrogen per year, or about 100 tons per day. 

Regional airports wishing to convert 10 percent of their fuel infrastructure would need about 5,000 tons of liquid hydrogen per year, equal to around 10 tons each day.

The study suggests that hydrogen production facilities—including solar or wind power plants—could be built near airports. For delivering fuel the final mile to airport ramps, hydrogen could be pumped to nearby airports via pipelines. Existing natural gas pipelines could be utilized for this purpose, experts say. 

Producing liquid hydrogen is one thing. Paying for it is another. Skeptics have expressed concern that the cost of producing clean, renewable electricity for green hydrogen will force hydrogen prices to skyrocket.

Currently, green hydrogen costs about $5 per kilogram, according to the U.S. Department of Energy. Keeping in mind that hydrogen contains three times more energy than jet-A—green hydrogen now costs more than twice as much as jet fuel.

But hydrogen companies say their fuel will be at cost parity with jet-A starting in 2025, with costs decreasing exponentially. That idea is getting support from the U.S. government. In June, the Department of Energy launched an initiative aimed at slashing green hydrogen prices by 80 percent to $1 per kilogram in the next decade. 

Airbus has launched a program to help airports transition to hydrogen. It’s promoting the idea of creating hydrogen fuel hubs: turning airports into hydrogen distribution centers not only for aircraft, but for hydrogen powered ground vehicles and other uses. 

The company has also partnered with carriers such as SAS Airlines and easyJet to assess what kind of infrastructure would be necessary to fuel hydrogen and hydrogen-hybrid aircraft. 

“For hydrogen to meet its full potential, the entire airport ecosystem—airport authorities, energy suppliers, regulatory authorities—needs to come together to collaborate,” Airbus said in a statement. 

Experts say all the pieces to make the transition are there, but the challenge is in how to encourage effective and efficient collaboration among industry players. 

The biggest hurdles will include creating affordable large-scale production of green hydrogen and adopting new technology for aviation, specifically along the development and certification tracks, says David Maniaci, an aerospace engineer at Sandia National Laboratories in Albuquerque, New Mexico. 

Currently focusing on wind energy aerodynamics, Maniaci conducted his master’s research at Pennsylvania State University on the feasibility and performance of hydrogen-fueled commercial aircraft. 

“I think technically it’s very feasible,” Maniaci said. “It’s a question of anything we put our focus on and come together on is possible. But there are a lot of changes and investments that would be needed.”

Historically, military and government investments have driven many of aviation’s big technological leaps forward, Maniaci said, paving the way for private industry to follow. “There’s probably something similar needed to really get things going in a large way.”

Much of the real-world hydrogen development going on now in aviation surrounds the retrofitting of existing platforms. 

ZeroAvia, based in the U.S. and U.K., has teamed up with Mitsubishi Heavy Industries Regional Jet Aviation to develop and retrofit regional jets for hydrogen-electric propulsion. Currently they’re working to convert a 19-seat Dornier 220 turboprop. The plan is to certify the conversion and enter service by 2024. 

Alaska Air Group is also working with ZeroAvia to convert a 76-seat de Havilland Canada Dash-8 to hydrogen-electric, aiming for a range of 500 nm. 

And just this week, United Airlines announced a significant investment in ZeroAvia, including an agreement to purchase as many as 100 hydrogen-powered engines that could be retrofitted on existing United Express regional jets as soon as 2028. United singled out Mitsubishi’s 50-seat CRJ-550 as a potential platform for ZeroAvia’s hydrogen engines. The deal makes United the “largest airline to commit to hydrogen-electric aviation,” the carrier said. 

California-based Universal Hydrogen wants to build a green hydrogen supply business for the aviation industry. Universal has developed kits to convert existing Dash-8s and ATR 72s for powertrains driven by hydrogen fuel cells. The kits are expected to be certified and enter service by 2025. The company also has developed a refueling system based on a proprietary, modular, hydrogen fuel capsule designed to easily be loaded onto aircraft.

What about the emerging electric vertical takeoff and landing (eVTOL) industry? As this sector begins to take shape, most prototypes are powered by lithium-ion batteries. However, California-based HyPoint has developed a hydrogen fuel cell targeting the eVTOL market. It has announced deals with eVTOL developers Urban Aeronautics and Piasecki Aircraft Corporation.

A truly green ecosystem supporting hydrogen aviation fuel would likely be expensive and logistically challenging. Making it work would require successful collaboration between airports, airlines, and manufacturers in the coming decades. 

“If hydrogen-powered aircraft are deployed in segments where they are the most cost-efficient means of decarbonization, they could account for 40 percent of all aircraft by 2050,” the EU study said. 

As an expert watching it all from the sidelines, Maniaci is optimistic that the shift can happen, albeit slowly. 

“It’ll be incremental but there will probably be some big leaps,” he says. “Some of those leaps will be through technology and some will be through groups making big investments and pushing technology forward.”