The Future of Sustainable Aviation is Hydrogen

Before the COVID-19 pandemic, aviation accounted for 2.5% of global CO2 emissions according to Our World in Data. This might seem like a small figure, but if you add in the long-term decrease in ozone (O3), decrease in methane (CH4), emissions of water vapor, soot, sulfur aerosols, and water contrails, the warming effect is much stronger. Combining these with CO2 emissions, aviation industry accounts for 3.5% of global warming. Although it is still a relatively small piece of the emissions pie, the difficulty in decarbonizing the industry remains a key challenge. Other larger emitting sectors such as road transport and power generation have had solutions in the form of renewable and nuclear energy, as well as the development of electric cars to counter emissions. The aviation industry has not seen a proven and scalable solution, but things have begun to progress.

In the summer of 2020, a California-based start-up called ZeroAvia successfully conducted a maiden flight in the UK on a six-seater Piper M-Class plane that runs solely on hydrogen. This flight was supported by the UK Government, whose Jet Zero Council is fully committed to the production and operation of sustainable aviation fuels and zero-emission aircrafts. With support from the UK Government, several private investors, and commercial partners, ZeroAvia is working to deliver a hydrogen-electric (fuel cell) powered aircraft capable of carrying up to 20 passengers for about 350 nautical miles (648 km). The company aims to offer commercial flights using the plane by 2023 and looks to expand the range of the aircraft to 500 nautical miles (926 km) with a capacity of 80 seats by 2026. Airbus, the world’s largest aircraft manufacturer, also has its sights on sustainable aviation with its zero-emissions commercial aircraft, ZEROe, looking to enter service by 2035. Airbus has announced three concept planes — a turbopro, a turbofan, and a futuristic-looking blended-wing design — capable of carrying upwards of 100 passengers and flying more than 1,000 nautical miles.

Hydrogen is seen as a good solution for flying without causing harm to the climate. This is because a hydrogen propulsion powered aircraft emits zero CO2 emissions, and creates a 30-50% reduction in impacts from contrail and cirrus formation, compared to traditional fuel aircraft, according to a study by the Clean Sky 2 and Fuel Cells & Hydrogen 2 Joint Undertakings. The study also estimates that hydrogen combustion could reduce climate impact in flight by 50-75%, and with fuel-cell technology by 75-90%. On the energy front, specific to the case of flying, hydrogen packs larger amounts of energy per unit of mass, amounting to three times that of conventional jet fuel and more than a hundred times that of lithium-ion batteries. Fully electric planes have had some successes in smaller planes but lack the feasibility when it comes to larger planes on longer commutes. This is main due to its low energy density and battery efficiency still lagging far behind the traditional fossil fuel systems. Hydrogen-powered planes look to be the most feasible, sustainable solution at its current stage. However, there are questions surrounding its scalability at a competitive price while not incurring a large carbon footprint.

For one, hydrogen gas needs to be compressed or converted to liquid through extreme cooling for it to be stored in large quantities. Another disadvantage is that the energy density of liquid hydrogen is a quarter that of jet fuel, and therefore, for the same amount of energy, it would require a storage tank four times the size. Planes would need to be built bigger or accommodate larger storage tanks, leading to fewer passengers. The process of producing hydrogen from water involves the process of electrolysis, which is both expensive and requires large amounts of energy. With that comes questions on whether the production of hydrogen can be scaled to achieve a competitive price while maintaining a low carbon footprint.

According to Britain’s Royal Society, liquid hydrogen is likely to remain twice as expensive as fossil fuels for the next few decades. As such, the transition to hydrogen requires a consorted effort from the entire aviation ecosystem together with support from government bodies and industrial partners. To tackle the challenges of hydrogen usage, governments must first increase funding for research and technology in order to promote the use of more sustainable fuels while also allowing for modernization of aircraft fleets to new, more environmentally friendly planes. Furthermore, it is important for collaboration and innovation to allow for sustainable and effective scaling of hydrogen production with the ultimate goal of lowering prices closer to that of traditional jet fuel.