When will hydrogen aircraft be ready for take off?

December 11, 2023 Energy

Hydrogen has the potential to revolutionize air transport, promising a pathway to cleaner skies and a reduced carbon footprint. Backed by the Energy & Climate Center and the PIPAA project for sustainable aviation, TSE’s Estelle Malavolti and her coauthors Shangrong Chen, Sai Bravo and Romain Mongeau use evolutionary game theory to assess the prospects for successful adoption of hydrogen technologies by airlines and airports.

Why fly with hydrogen?

Hydrogen is not only the most common chemical element on our planet, it can also be produced by electrolysis using carbon-free electricity. Our paper considers only green hydrogen, which is sustainably produced. Although more expensive than conventional jet fuels, hydrogen offers a much higher energy content per kilogram. When burned, it produces zero carbon emissions. Alternatively, it can be converted into electrical power via fuel cells. 
The implementation of these technologies is not yet economically viable without further government incentives. However, some researchers consider that an uptake of hydrogen for regular commercial aircraft could be possible at the 2035-2050 horizon.

How can economists contribute to cleaner skies?

The high R&D costs involved in developing hydrogen propulsion call for a comprehensive market study to assess the available options and how to reach emissions targets. Should the industry invest in intermediate or hybrid solutions, or focus on the most complex ones? Economic research can help policymakers and firms to answer such questions. Our paper provides a useful reference time at which different technologies could be adopted by airports and airlines without any government support. We also discuss different policies which could reduce this timeline.

How do you study the diffusion of hydrogen technologies?

Successful hydrogen innovations would need simultaneous adoption by airlines and airports that interact in complex networks. For instance, a hydrogen-powered aircraft can only operate if at least one of the airports on the flight path deploys the necessary fuel infrastructure. As aircraft travel across airports, other airports might also have incentives to deploy hydrogen infrastructure, with network effects influencing the spread of the technology. 
Our paper aims to assess the conditions under which hydrogen will generate enough efficiency gains to outweigh its costs. We use evolutionary game theory to consider a large network of airports and airlines which can gradually and dynamically adopt a technology through imitation and learning. In a natural selection process, the market pushes firms to choose the technology with the best fitness. This approach allows us to study the changing trend of group behaviors and accurately predict individual strategy choices. We extend our model to account for the growth of the “flight shame” movement, uncertainty, and different government interventions. 
Using empirical data on French airports and technology costs at the 2030 horizon, we calibrate simulations for different levels of innovation. The tipping point for adoption is determined by the technology’s benefits, extra costs, and ground handling fees. The first scenario considers the easiest step: an external unit used to supply hydrogen power to the aircraft while it is parked. The second considers that the aircraft also uses hydrogen for taxiing after landing and before takeoff. The third considers a fully hydrogen-powered aircraft, both on the ground and in the air.

What are your key findings?

Our results suggest that hydrogen will only be adopted when consumption passes a threshold beyond which its high energy content outweighs its high cost. The percentage of initial hydrogen adopters needs to be sufficiently high among both airports and airlines for the market to push everyone to adopt the technology. Government interventions and environmentally conscious consumers can accelerate arrival of this tipping point. 
Without any government intervention, only fully hydrogen-powered aircraft using direct combustion can reach the goal of carbon neutrality by 2050. However, this result is only possible if the technology is available on the market by 2030. Other intermediate technologies explored in our analysis are not profitable enough to meet net-zero targets. In-aircraft fuel-cell systems will only be adopted if their weight or energy losses can be reduced.

What cards do policymakers have to play?

Our paper confirms the results of existing studies that show a positive effect of both subsidies and taxes on the adoption of low-carbon technologies. Subsidies for hydrogen adopters and taxes for staying with kerosene have the same effect in our model. However, we do not take into account the fact that the public funds used to finance subsidies are raised through taxes on the rest of the economy. 
The advantage of the tax compared to the subsidy is its ability to collect public funds. As taxes raise costs for airports and airlines, passengers might be exposed to higher prices, reducing demand. But if taxes make firms and consumers internalize the external costs of flying, reduced demand could be less costly to society than subsidizing costly technologies. 
Policymakers could also reform the Chicago Convention to allow airports to use discriminatory charges. Hydrogen technology could then be promoted through discounts for greener airlines or by making ground-handling fees less dependent on weight. In recent research with Sai Bravo, we show that modulation of airport charges allows positive discrimination and might help airlines attract green “conscious” consumers, increasing the total number of air passengers.


Adopting and diffusing hydrogen technology in air transport’ and other publications by Estelle are available to view on her TSE web page.

Article published in TSE Reflect, December 2023