Hydrogen to save aviation’s fuel hurdles

But aviation companies working to make cleaner aircraft are exploring the use of hydrogen, the world’s most abundant element, to power both electric and combustion engines — and to make air travel more eco-friendly. 

Hydrogen-powered planes are already aloft, although mostly as small, experimental aircraft. Yet those planes are helping to pave the way for net-zero carbon aviation by 2050, the goal set by many government and environmental groups. 

But hydrogen isn’t without controversy: For now, it’s expensive, not always green, and some say dangerous.

“There are three ways of using hydrogen as fuel onboard an aircraft,” said Amanda Simpson, who leads green initiatives for the aircraft manufacturer Airbus. Hydrogen can be a source of power for battery-like fuel cells, in hybrid aircraft, or as combustible fuel. 

Alternative-fuel technologies are well established in the automotive world, of course. Cars that burn alternative fuels — remember diesels converted to burn used French-fry oil? — have been around since the earliest days of horseless carriages. And hybrid gas and electric cars, such as the Toyota Prius, have been available since 1997.

But only a few models, including the Toyota Mirai and the Hyundai Nexo, use hydrogen fuel cells. When Val Miftakhov founded ZeroAvia to develop electric aircraft, he first considered battery power. A Siberian émigré and physicist, his earlier start-up converted gasoline cars to electric, then incorporated an improved charging system. 

But batteries can sustain only the shortest excursions, like training flights. “Where a mission is an hour, batteries might work,” he said. Battery-powered trainers also exist, such as the Pipistrel Alfa Electro which claims a one-hour flight time.

ZeroAvia instead chose fuel cells, which are essentially a chemical battery that substitutes lighter-than-air hydrogen for the weighty lithium ion. Hydrogen is notable for its energy density — the amount of energy per kilogram — which is about three times that of jet fuel. 

The byproduct of burning hydrogen is water. Hydrogen can be made from water and renewable energy, although most is now made from natural gas, which is not particularly green.

Miftakhov acknowledged that hydrogen storage containers, which were generally designed for ground transportation, were not practical for aircraft. 

“We need to focus on reducing the weight,” he said, “We have some fairly low-hanging fruit.” Unlike electric batteries, hydrogen fuel cells can be recharged in minutes, but there is a lack of fuelling stations, and building them would be a huge undertaking. That problem is less critical for hybrid aircraft, which use a combination of electric and combustion power, said Pat Anderson, a professor of Aerospace Engineering at Embry-Riddle Aeronautical University. “It can pull up to a fuel pump that exists today and fill up,” he said. 

Anderson’s students used a hybrid system in a 2011 eco-flight competition. They didn’t win, but it sold Anderson on the merits of hybrid power engines, which he now builds at VerdeGo Aero, a Florida company that counts Erik Lindbergh, an X-Prize Foundation board member and Charles Lindbergh’s grandson, as executive chairman. 

Modern hybrid systems can use a variable mix of electric and combustion power, and can even use the combustion motor as an electric generator in flight. It may give planes more range than battery or fuel cells alone, Anderson said.