Planes, Trains & Automobiles - Comparing Emissions Intensity in the Coming Era of Cleaner Aviation - ZeroAvia

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    July 17, 2023

    Planes, Trains & Automobiles – Comparing Emissions Intensity in the Coming Era of Cleaner Aviation

    by Dominic Weeks

    At ZeroAvia, buoyed by six months of breakthrough flight testing of a world-first prototype, zero-emission engine for up to 20 seat aircraft, we can hopefully be forgiven an optimistic outlook for truly clean flight in the years ahead. At Paris Airshow we learned that the enthusiasm can be infectious, with many members of the public and of industry heartily offering their support for hydrogen-electric aviation. But we have to also acknowledge that there are many influential voices who are more circumspect.


    There is a fundamental assumption among a good portion of people that green flight is a long way in the future. This is an assumption shared by many in industry who see Sustainable Aviation Fuel as the only route to carbon emission reduction, but also by the industry’s perhaps natural adversaries in environmental NGOs, who call vociferously for strong demand curbs such as frequent flyer taxes. The shared mantra is that zero-emission technology is donkeys years away. The latter groups will argue also that aviation will necessarily be a less environmentally-friendly way to travel than other transport modes.


    We disagree. ZeroAvia is developing zero-emission engine technology that will see up to 80 seat aircraft flying as early as 2027. We plan to have an engine for up to 20 seat aircraft certified even earlier, by 2025. Hydrogen-electric engines use fuel cells to generate electricity which then power electric motors to turn propellers. The only emission is water vapor, and in sub-100 seat regional turboprops even this exhaust will have zero climate impact due to lower altitude of these flights in cruise.


    Zero-emission in flight does not mean zero-emission in the full lifecycle. However, some recent analysis we conducted shows that some of these early applications – which could well be flying UK passengers from Glasgow to London or Birmingham to Belfast, for example – could be not just green, but greener than any form of existing common mode of transport. 


    We compared how hydrogen-electric flights would fare against some existing data on the  emissions per passenger of other typical transport modes (thanks to Georgina Rannard at the BBC for drawing this out for existing transport modes from UK Government data – and painting a stark picture of the disproportionate aviation impact!). 


    Assuming a ramp up of adoption from 40%-90% from 2026-33 to account for the roll-out of corresponding hydrogen infrastructure to support (which is eminently possible by the way), we can see emissions per passenger plummet. Faster adoption would only reduce these figures further.


    If powered by UK wind generated green hydrogen, domestic hydrogen-electric flights would have lower lifecycle carbon emissions per passenger than any other mode of transport, and be roughly the same in terms of the overall CO2e impact as the Eurostar – the notoriously green way to reach the continent. UK solar powered hydrogen production to power flights would lead to emissions per passenger of nearly half that of taking a long coach trip. 


    Even using hydrogen produced using electrolysis powered by the UK grid at the projected carbon intensity for 2050 would mean a total climate impact significantly lower than by travelling by a full car or on a UK rail line. 


    You can read a summary of the key assumptions we made in producing this additional data for comparison below, but these conservative assessments show that if we can deliver the clean flight technologies that are coming to market at pace, then we can make flying the quickest, safest and greenest way to travel. Importantly, it can also be even cheaper due the reduced operating costs that hydrogen-electric aviation offers.  


    This is not a distant pipe dream. We do not need drastic curbs on flight to make 2050 net zero goals. We have flight tested a prototype of our first engine and are targeting to be flying passengers on clean flights within three years. We are working on larger engine systems with a roadmap right through to the single-aisle aircraft like the A320 or 737, the airframes of choice for low-cost carriers ferrying us to sunnier climes and weekend getaways. The technology to tackle the majority of aviation emissions will arrive this generation.


    We need to look ahead and think positively about how we can develop zero-emission flight technologies, and build the renewable power generation to deliver clean, green hydrogen fuel. We’ll all be better off for it.

    Key assumptions


    • 5% H2 leakage in supply chain assumed with a climate impact of 5kg of CO2e per kg of hydrogen
    • Water vapour assumed to have a climate impact of ~0.5kg CO2e per kg of hydrogen
    • Average load factor of 80% assumed on all flights (15 pax on a 19 seater, 64 pax on an 80 seater)
    • UK aviation demand based on total miles flown in 2022
    • Future grid composition taken from the UK’s 6th Carbon Budget from the Climate Change Committee published in 2020
    • 1MW electrolyser capacity is assumed to produce ~145 tonnes of hydrogen per year