January 25, 2023 | Updated: April 21, 2023
Transportation is going electric. Trains, buses and passenger cars are moving away from fuels that contribute to global warming – a process often referred to as decarbonization.
But what about air travel?
While there are a number of research pilots involving electrified planes, the lithium batteries used by passenger vehicles are considered by many to be too heavy to be viable for commercial aviation.
Enter hydrogen. Governments, academics, and private companies are investing significant resources into hydrogen powered flight. A recent issue of IEEE Electrification Magazine covers the latest.
“Because hydrogen can be produced from renewable energy sources without emitting any carbon dioxide, and because water is one of its main by-product,” said IEEE Senior Member Manpreet Singh Manna, “it has been highlighted as one of the most promising options for powering a zero-emission airplane.”
Air Travel’s Contribution to Greenhouse Gas Emissions
Air travel has traditionally contributed approximately 2 to 3% of global CO2 emissions – a surprisingly low number given air travel’s outsize impact on the global economy. But passenger miles increase approximately 3 to 5% each year, meaning that the total number of miles flown doubles every 10 to 15 years.
And there are other factors about the air travel industry and its contribution to greenhouse gasses that aren’t clearly understood. For one thing, C02 isn’t the only heat trapping gas that aircraft emit. And aircraft themselves tend to burn fuel at very high elevations, which may mean that emissions from aircraft may have different effects on the atmosphere.
Weight vs volume
One factor that makes hydrogen so attractive is that it is extremely light. Pound for pound (or kilogram for kilogram) hydrogen has roughly 2.8 times the energy of an equivalent mass of kerosene, which is commonly used as aircraft fuel.
But one kilogram of liquid hydrogen needs more space compared to one kilogram of aviation fuel.
“One liter of hydrogen provides approximately eight megajoules of energy, compared to 32 megajoules per liter of gasoline,” Manna said.
The Trouble with Tanks
One challenging area of design is the fuel tanks that will hold the hydrogen. Because liquid hydrogen must be kept at very high pressures, the fuel tanks may need to be made of very thick metal. That adds significant weight to the design of the plane.
Hydrogen-powered Planes Have Design Challenges
In most airplanes, fuel is stored at or near the wings. If this were the case for hydrogen-powered planes, the wings would be massive, and require more power to get off the ground. So most concepts call for more fuel to be stored in the made body of the aircraft.
Will Require a New Airport Infrastructure
Just as the transition to electric cars requires a new charging infrastructure, the rise of hydrogen-powered airplanes would require changes at airports to accommodate a new source of fuel. Experts note that because hydrogen is handled differently, safely refueling the aircraft may require new procedures as well.
What’s the Timeline?
While hydrogen-powered flight is possible, most designs are still in the early stages. We’ll likely see smaller, short-range aircraft before larger long-range ones.
“In general, the state of art related to this technology can be characterized by research and pilot projects, but there is no economy of scale in this field,” said Leonardo Willer de Olveira, IEEE Senior Member.
Learn More: A recent edition of IEEE Electrification Magazine goes in-depth on recent advances in hydrogen-powered aircraft. If you’d like a comprehensive look at this groundbreaking technology, check out this article.