The airlines contribute roughly 2% to 2.5% of global greenhouse gas emissions, which is small relative to the industrial sector. However, as the jet age matures, that could get worse. Kerosene fuels the planes, although the industry is exploring cleaner alternatives such as hydrogen, electricity, and sustainable aviation fuels.
Hydrogen and electric aircraft represent a significant advancement in aviation, but they are unlikely to replace jet-fueled airliners for the foreseeable future. Instead, these technologies will complement existing ones, gradually reducing emissions.
By the middle of the century, we could see a diverse fleet of aircraft. Electricity or hydrogen could power short trips, while sustainable aviation fuels from biomass will power longer flights. The path forward is challenging, but the potential benefits for the planet and the aviation industry could make it a fruitful journey.
“I would compare today’s aviation sector to the car industry in the early 2000s. At that time, we were convinced that biofuels were the solution, and we invested heavily in them. Then came the ‘Tesla moment,’ when battery electric cars emerged and changed everything,” says Rob Miller, an aviation professor at the University of Cambridge.
Last week, Miller and I spoke at length at a virtual web conference hosted by ZeroAvia, which develops hydrogen-electric engines for planes. Miller is the director of the Whittle Lab at the school. They research all potential options. The goal is to reach a tipping point — where the aviation industry can shoot the moon and change the world. Hydrogen may offer this possibility. If not, and by his admission, “we may need to double down on sustainable fuels.”
The U.S. Energy Department reports that the biofuel industry has produced 17 billion gallons of fuel and has prevented the release of 544 million tons of CO2 into the atmosphere. The primary objective is to use this biofuel to reduce reliance on petroleum. Renewable energy sources such as food, animal waste, and sewage sludge make aviation fuels sustainable. According to the department, the carbon footprint can be up to 165% smaller than traditional petroleum-based jet fuel.
Sustainable aviation fuels will likely remain the preferred solution for international routes for the time being. That source can significantly reduce emissions while leveraging existing aircraft and infrastructure.
Sustainable Aviation Fuels Or Electric Planes
Does producing biofuels creates more greenhouse gases than burning fuel directly? The Journal of Environmental Science and Technology examined the life cycle of algae compared to other biofuels, such as corn and switchgrass. It concluded that using conventional crops to create fuels will result in fewer greenhouse gas emissions and less water consumption than using algae to do the same thing.
However, Professor Miller says that’s not ideal. He notes that the amount of biomass worldwide is limited, and several industries are bargaining for it. Moreover, green hydrogen or green electricity can produce more fuel, which is a solution that he says is more carbon-efficient.
Aircraft makers have submitted a handful of applications to the Energy Department. Take Air Canada, which aims to be net zero by 2050: It has ordered 30 hybrid aircraft from Heart Aerospace — a plane called ES-30. Not only has the airline taken a $5 billion stake, but so has Corp. founder Bill Gates. United Airlines is also an investor in Heart and will buy up to 100 electric aircraft. Those planes have an all-electric range of 124 miles — double that if combined with jet fuel. They fly at an altitude of 20,000 feet. The aircraft will fly to and from regional airports and hold 30 passengers.
Meanwhile, hydrogen can power aircraft through combustion or fuel cells. When used in a fuel cell, hydrogen combines with oxygen to produce electricity, with water as the only byproduct. This makes hydrogen an excellent choice for reducing greenhouse gas emissions. It also boasts high energy density, potentially supporting longer flights than batteries. American Airlines, KLM Royal Dutch Airlines, and ASL Aviation Holdings are collaborating with ZeroAvia.
Weight is a controlling factor in flying: According to Cambridge’s Miller, jet fuel accounts for 45% of the weight on a long-haul flight. “We think there is an advantage of hydrogen over kerosene. Hydrogen is a third of the weight. So you’re at least 15% lower fuel burn than a kerosene aircraft at long range.”
The time frame? Miller says hydrogen fuel cell aircraft will take off within a decade, traveling 1,000 to 1,500 kilometers. Their performance will improve exponentially; by 2035 or 2040, they will fly 4,000 kilometers.
It Won’t Come Easy
The aviation industry faces several challenges. Jet fuel is energy-dense, which allows airliners to achieve the longer range and better fuel efficiency. In contrast, batteries are considerably heavier and provide lower energy density. While hydrogen is more energy-dense than batteries, it requires large, pressurized tanks, complicating aircraft design. Hydrogen production must also scale up, relying on green hydrogen from renewable energy sources, while airports must have hydrogen refueling stations or charging facilities.
Professor Miller and the Whittle Lab are tackling some of these issues. The aviation industry is doing much to upgrade fuel efficiency and reduce fuel burn, although it has a ways to go. According to Miller, significant improvements could reduce fuel burn by 2050. The industry could cut that figure in half.
However, that may not be the winning horse three decades from now. A better bet could be hydrogen aircraft, provided that hydrogen fuel prices decrease. If that becomes economical, producing kerosene for aviation won’t make sense. “These transformative innovations happen once in a generation,” says Miller. “I’m not certain if hydrogen will win, but it’s worth a chance.”
No matter what, “Aviation is easily the safest way of traveling,” which will continue, he concludes.
The aviation sector has come a long way, enabling people to travel across continents. The next step is to become cleaner and more efficient. By the mid-21st century, we could see hydrogen as the primary fuel for intercontinental travel and electric jets for short trips. Together, these technologies will combine to reduce aviation’s carbon footprint.
https://www.forbes.com/sites/kensilverstein/2024/12/09/the-aviation-sectors-trip-may-land-at-hydrogen-fueled-planes/