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“No clear winner now” says the Royal Society,
but horses are only just out of the gates
Dominic Weeks
March 14, 2023

It was a very positive development to see the Royal Society calling for further R&D into non-CO2 impacts and also efficient production, storage and use of green hydrogen in aviation in its recently published policy briefing on sustainable aviation fuel options. Having convened leading academics, the report brought forward the scale of the challenge and highlighted the need for a mix of solutions in the short term.

The policy briefing from the prestigious society is correct to identify that there is currently no single answer to all of the sector’s emissions. Some responses have taken this to mean that clean flight is not achievable soon. As we are proving at ZeroAvia, that’s not the case. ZeroAvia has just flight tested a prototype zero-emission engine in a 19 seat aircraft, and plans to have a certified version of this in service carrying passengers and cargo by 2025. We are looking at scaling the technology for up to 80 seat aircraft by 2027, and then for single-aisle aircraft by the mid 2030s. By 2040 propulsion technologies capable of tackling the majority of the industry’s emissions will be in service.

While many of the points made relating to biofuel and synthetic SAF should raise concerns, the doubling of renewable energy capacity to support hydrogen production all flights that take-off from UK airports should be treated with optimism when seen against the timeline. The hydrogen technology will develop progressively (as our roadmap above outlines) and initial demand profile grows steadily, so there is time to invest in renewable capacity to support airport hydrogen production and liquefaction.

Again, the report is correct to raise the need to explore hydrogen’s contrail reduction benefits in more detail, but should make more differentiation between combustion and fuel cell engines. The authors suggest that both combustion and fuel cell engines will have similar contrail impacts, which are thought to represent less radiative forcing than those formed by jet kerosene combustion. However, with hydrogen fuel cell exhaust, emissions will be at much lower temperatures and speeds, so contrail impacts are far easier to mitigate than their hydrogen combustion equivalents.

Further, the report does not make clear recognition of fuel cells’ potential to eliminate 90% plus of greenhouse gas emissions (per CleanSky/McKinsey). Nor does it reference efficiency of fuel usage, likely trajectory of hydrogen costs compared with other fuels and the lower maintenance costs that hydrogen-electric propulsion can offer. It would be fair to expect the most economically attractive alternatives to existing propulsion to have a long-term advantage.

There may be no clear winner yet, but the horses are only just out of the gate. There’s enough of a form guide to suggest where you might want to place your bets.

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