Long-haul flights will remain the greatest source of CO2 from aviation for “the foreseeable future”, with no alternative to kerosene for long-haul travel likely for decades other than sustainable aviation fuel (SAF).
That is according to a report on The challenge of long-haul flight decarbonisation by European air traffic management body Eurocontrol.
It notes long-haul flights, operating more than 3,000 km (1,864 miles) or roughly the distance between London and Istanbul, accounted for 9% of UK and EU departures in 2019 but 54% of aviation CO2 emissions – and are forecast to account for 60%-plus by 2050.
The study considers potential alternatives to jet fuel or SAF – battery, fuel cell, hydrogen, methane, ammonia and solar energy – and what each would involve in powering a widebody flight from Paris to Singapore.
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It concludes: “We are a long way from being able to use any of these technologies.”
Electric batteries in their current form “would make a long-haul flight too heavy to take off” and require a “massive step-change in battery density”, involving tripling energy density in each of the next three decades.
Liquid hydrogen would require long-haul aircraft be fitted with large ‘cryogenic’ tanks capable of remaining below -253C for 14 hours or more.
Hydrogen fuel would produce “significant contrails and potentially NOx [nitrous oxide] . . . considered the most important non-CO2 contributors to global warming” from aviation.
Liquid hydrogen also presents “inherent risks” due to its flammability, and a liquid hydrogen aircraft would probably require “several stopovers” to complete an entire flight.
Liquid methane would be easier to handle and could be produced from ‘green’ hydrogen using renewable energy or from agricultural, forestry and waste feedstocks.
But it poses technical challenges as well as significant climate risks from any leakage. Methane is at at least 30 times more potent than CO2 as a contributor to global warming over the course of a century and 82 times more potent than CO2 over 20 years.
Liquid ammonia, produced from ‘green’ hydrogen using renewable energy, would also be easier to handle. It’s not explosive or corrosive and produces no CO2.
But ammonia vapour is “highly toxic” and it would require “excessively heavy” aircraft, double the take-off weight of an A380.
Eurocontrol rules out solar energy, noting the solar panels required to power an Airbus A380 would not only cover the entire aircraft but require an additional 7.4 km of panels.
It concludes: “A widebody [aircraft] powered by any of these technologies cannot be expected in the foreseeable future. Significant progress is not expected for decades.”
Energy demand ‘unlikely to be met’
All the potential alternative aviation fuels would require “colossal amounts of electricity” to produce them.
Eurocontrol calculates UK and EU fuel requirements would mean between 10% and a quarter (23%) of all EU and UK electricity generation would be require to power aviation.
And all of these alternative technologies would need to be available at airports across all destination countries, with the elaborate infrastructure to support them.
The extent of decarbonisation would depend on the ‘carbon intensity’ of the electricity used to produce any fuel.
Wind-generated power could reduce aviation CO2 by up to 96% compared with jet fuel. However, coal-sourced electricity would multiply the existing CO2 emissions from aviation by between three and 11 times.
Eurocontrol warns this energy demand is “extremely unlikely to be met given the various political considerations and industries competing for the same sustainable power source”.
It all-but rules out electric-powered long-haul flight, with safety “a major showstopper” of battery-powered aircraft not just because current lithium batteries are “highly flammable”, but because a long-haul version would weigh almost double the weight of a Saturn V space rocket used in the Apollo space programme.
The batteries would also need to last at least six times longer than the present maximum.
Eurocontrol rules solar-powered widebody flight “impossible to envisage under any circumstances”, noting that solar panels covering the entire surface of an A380 would provide just 0.17% of the power needed to take off on a sunny day, or 0.02% if it was cloudy.
It notes almost 90% of aviation CO2 emissions are currently produced by the largest aircraft – the Boeing 777, 747 and 787, and Airbus A380, A330, A340 and A350 – and that the average long-haul aircraft remains in service 23 years, meaning new aircraft delivered today are likely to be operating into the late 2040s.
Photo: franconiaphoto/Shutterstock.com
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