Poop-powered planes? A green hydrogen revolution? Binliners to jetliners?
All these questions come directly from recent headlines debating the merits of aviation using alternative fuels to decarbonise.
However, behind the headlines, there are many issues that need to be understood in order to support effective policy. All alternative fuels come with their own challenges that would need to be addressed before these fuels could be considered viable solutions.
In January, AEF hosted a series of webinars to publicise the findings from three new reports that we commissioned in 2023 to explore specific issues relating to alternative fuels:
Green hydrogen and so-called ‘Sustainable Aviation Fuels’ currently make up a large part of the alternative fuels debate. But could ammonia also have a role? Despite being commonly used in other applications such as agriculture and plastics (albeit from fossil-derived production methods), little research to date has looked at its potential applications in aviation.
Responding to this gap, AEF asked researchers from the Tyndall Centre for Climate Research to assess the prospects of ammonia as a potential fuel alternative for aviation. The resulting report, ‘The potential role of ammonia as a low-carbon aviation fuel,’ reviews the current state of knowledge in relation to ammonia as an aviation fuel and pinpoints the knowledge gaps that require investigation before ammonia can be considered a viable option in aviation decarbonisation scenarios.
Hydrogen aircraft face many challenges. The aircraft technology is still being developed and tested, early market entrants are likely to operate only short to medium-haul routes, airports would need to be redesigned to provide the right infrastructure for refuelling, and customers would need persuading that the planes would be safe to fly in. That’s before you even start to think about the challenge of providing enough green hydrogen (produced by using renewable energy to split out hydrogen from water) given competing demands from other sectors.
Nevertheless, there’s real hope that hydrogen, whether as a liquid fuel or in a fuel cell, could offer the potential for no in-flight CO2 emissions as green hydrogen can, in theory, be produced without fossil fuels. One important issue to weigh in the balance, though, is the non-CO₂ impacts of hydrogen. As well as the CO₂ emissions that build up in the atmosphere and cause warming, aviation has specific ‘non-CO₂ impacts’ on the climate, including from NOₓ and contrails. These effects are shorter-lived but, overall, have tripled the total warming effect of aviation to date compared to its CO2 emissions alone. This webinar and report from the University of Leeds examine the likely non-CO2 impacts of using hydrogen as a fuel.
The sustainability of so-called ‘Sustainable Aviation Fuels’ is typically based upon life cycle analysis, which is the methodology used to estimate and evaluate the emissions associated with the production and use of each fuel pathway.
Chris Malins’ work for the AEF explores the implications – and limitations – of this approach in detail. Part 1 reviews issues in lifecycle analysis, part 2 reviews issues relating to the use of waste and by-product materials as feedstock, and part 3 looks at the role of alternative fuels in the pathway to decarbonisation of aviation by 2050. The summary report briefly reviews each of these in turn and concludes with some implications for alternative aviation fuel policy.
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