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# 8.2 International aviation

In 2019, globally CO2 emissions from aviation made up about 2.9% of the total. Most of the fuel was consumed in the form of jet kerosene, which is a tightly specified, internationally traded, commodity.

Decarbonising aviation poses an even greater challenge than for shipping. What are the options?

## Battery electric aircraft

A small electric aircraft, the Solar Impulse 2, powered directly by PV panels (plus a small lithium ion battery) has managed a 40,000 km trip in 17 stages right round the world in 2015 and 2016.

However, full size battery electric aircraft remain limited by the energy density of batteries. As described in Section 7.1, the stored energy per unit weight for the best current (2025) lithium ion batteries is only a small fraction of that of petroleum fuel. New battery technologies with higher energy densities are likely to be required before short haul battery electric passenger aircraft become commercially available.

## Hydrogen

Industrial gas turbines as used for power stations are being manufactured that can run on hydrogen, so why not jet engines in aircraft? Or electric aircraft using fuel cells?

The Zeroavia company has been testing a small hydrogen powered aircraft using a 600 kW fuel cell. It aims to develop a short-haul 20-seat plane.

Again, although hydrogen has a weight advantage over kerosene in terms of energy density, the difficulty is the volume of the hydrogen fuel. Currently, long distance aircraft store their kerosene fuel in flexible tanks in the wings. Hydrogen would need to be stored at a very high pressure and the storage tanks will need to be within the body of the aircraft, reducing the number of passengers that can be carried.

## Sustainable aircraft fuel (SAF)

Small quantities of ‘bio-kerosene’ produced from biomass sources have been produced and tested in commercial jet engines. However, the cost is high and the future demand for such a fuel would probably outstrip the available supply. This is thus a ‘technical possibility’ but with severe limits on its future deployment.

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