2.3 Sustainable Mobility & its Implications for Aviation
The aviation industry recognises the contribution it makes to global carbon emissions. Although the percentage of emissions from aviation is lower than in other industries they are predicted to rise proportionately as demand for air travel continues to grow, particularly in developing economies. The industry is responding to this in various ways.
Sustainable Aviation Fuel (SAF)
SAF is already in use with some major airlines. The attraction with SAF is that it can be used on existing aircraft with minimal or no alterations. It can simply be blended with jet fuel as it has similar chemical properties. It is not used at scale yet but there are an increasing number of manufacturers. SAF is manufactured from renewable waste and residue raw materials, including used cooking oil and animal fat waste.
The following statistics from ICAO demonstrate the current market for SAF:
- 54 airports distributing SAF
- 24 policies adopted or under development
- 4 billion litres of SAF under offtake agreements
- 9 conversion processes certified for aviation
- Over 360k commercial flights have used SAF
Electric Aircraft
Electric aircraft technology is advancing rapidly, particularly in the general aviation and the vertical take-off and landing (VTOL) markets. Electric powered aircraft are already on the market but they are typically small aircraft with relatively short range. Technology is developing to increase the energy density of batteries to increase the size and range of electric aircraft.
One of the issues with electric aircraft is the weight of the aircraft. Aircraft powered by jet fuel will reduce their weight as the fuel is burned during flight. Maximum landing weights of electric-powered aircraft is higher than those powered by jet fuel. These issues could be resolved with engineering solutions at airports by strengthening runways and redesigning landing gear to withstand higher loads. However, the main issue for scaling up electric aircraft is currently the problems with energy storage.
Hydrogen Aircraft
Hydrogen could be used in the future to power aircraft and there are many projects examining this, with prototypes and test aircraft in development. Hydrogen can be used to power a fuel cell or directly combusted and the only waste from either method is water. The large manufacturers, including Airbus, are developing concepts with plans to introduce commercial aircraft to the market from the 2030’s.
Hydrogen has higher energy by mass than jet fuel, but it has lower energy by volume. This means it requires larger amounts of storage space than jet fuel.
There are different colours of hydrogen, each referring to the methods of production. The main ones are green, blue and brown. Green is the only truly zero carbon hydrogen and is produced from a process called electrolysis. Only a tiny fraction of hydrogen produced today uses this method.
Promoting Alternative Transport
KLM and Lufthansa are two airlines that have started to promote alternative means of travel by combining rail with air. They have both promoted the use of rail for short-haul trips to connect with air services.