When it comes to ‘decarbonising’ aviation, one source of energy is often praised to the skies by those who want to defend maintaining air traffic at its current levels: hydrogen. “It’s a well-known element that’s already used in our energy system, and represents 2 to 3 percent of greenhouse-gas emissions nationally and globally. But you don’t really see it, as it’s largely used in industry, refineries, the production of ammonia for chemical fertilisers, in other words more as a reactive chemical than an energy vector”, explains Ines Bouacida, climate and energy researcher at France’s Institut du Développement Durable et des Relations Internationales.
However, hydrogen could produce energy across a range of sectors, including aviation. Rather than fill planes with the traditional kerosene – a product derived from petrol – we would use hydrogen. This could be used to run combustion engines built for that purpose, or fuel cells that generate electricity destined for electric motors. It could also be used to create a synthetic form of kerosene which, despite its provenance, would burn and produce greenhouse gases.
Evidently, for this technology to be properly viable environmentally, it would be necessary for the hydrogen used to be considered ‘green’. This is far from true for hydrogen in all its forms. The French government has assigned different forms of hydrogen a colour according to the way in which it’s produced. Black or brown, and thus very polluting, if it’s produced using coal. Grey, and therefore a big greenhouse-gas emitter, if produced using natural gas. Blue if the CO2 released during production is captured. And, finally, green, if the hydrogen is obtained thanks to the electrolysis of water, a relatively simple chemical reaction, carried out using renewable energy.
The latter method, the only one that’s considered truly ‘low carbon’ today, still poses a few questions. “At this stage, the production chains don’t exist. And even if they did exist, they would require enormous quantities of renewable energy, which we don’t have. In a scenario where 40 percent of fleets were powered by green hydrogen in 2050, you’d need the total global production of renewable electricity create this hydrogen”, says Charlène Fleury, coordinator at Rester sur Terre, the French branch of Stay the Ground, a network of 180 groups campaigning for a reduction in air traffic in favour of more eco-friendly forms of transport. She adds: “So there’s a lot to weigh up there. Why would we use our resources for a non-vital sector like aviation rather than for heating homes, public transport or digital technology?”
Worse still, even if hydrogen figures among the best solutions to decarbonise aviation (excluding simply drastically reducing the number of flights), it represents an enormous waste of energy. “Like energy transformation processes, when you use electricity to create hydrogen, you lose around a third of the energy. So it’s sometimes more efficient to use electricity directly. That’s why hydrogen plays a key, but slightly niche role in the energy system. It will probably never be used to the same extent as a fossil fuel”, adds Ines Bouacida.
The point is all the more pertinent because, according to France’s Chamber of Commerce and Industry, in January 2022, 95 percent of hydrogen produced globally is grey, meaning it is derived from fossil fuels. As for its green equivalent, it’s thought it will only make up 20 percent of all hydrogen produced in 2050. It’s thus difficult to imagine this being sufficient to power 46,000 planes that will be likely taking to the skies by that point (double the 23,500 recorded in 2020). Unless, obviously, huge investments are made to develop the ‘green’ means of production.
For Lamis Aljounaidi, director at Paris Infrastructures Advisory and an energy economist, it is largely about politics: “The adoption of green hydrogen depends on the political will of individual states. Although it requires a huge number of production outposts, they aren’t bigger CO2 emitters than those we build permanently for the production of other energies. You’ve got to see it as a long-term investment, a full-on gear shift in the way we think about energy, one which requires taking an ecologically beneficial risk. If this is taken and binding agreements are pushed through, investment and the optimisation of value chains will follow. We’ve already seen a similar effect with the Carbon Border Adjustment Mechanism: the introduction of a regulatory system encourages the industries concerned to accelerate their investments in decarbonisation and increase their R&D into promising solutions.” According to Aljounaidi, this scenario is rather plausible, as the time for hydrogen may well have come. “It’s an energy that has been considered several times over the years but has always lost out in favour of another, first oil, then nuclear energy following the oil shocks of the 1970s. But this time, it seems hydrogen is being considered as a significant part of our response to current energy challenges by world leaders.” For example, France has decided to invest nearly €9 billion to expand the hydrogen industry between now and 2030.
As Lamis Aljounaidi reminds us, from a European perspective, the production of green hydrogen poses another problem. The renewable electricity it requires takes up a lot of space. So it can really be put into place in places where the property doesn’t have much value. In other words, the desert. Viable locations for Europe have been identified in the Morocco/Mauritania region, as well as South Africa and Namibia. It will be just as necessary to put in place transport infrastructure to transport this hydrogen around the world. Perhaps new tankers (themselves powered by hydrogen, perhaps) or pipelines. But once again, building these will be just as polluting as those that transport oil or gas.
However, such a scenario wouldn’t fix all of the problems with aviation. Contrary to popular belief, it’s not just the CO2 emissions we should be worried about. As well as being responsible for 5 percent of greenhouse-gas emissions, they worsen air quality and lead to many premature deaths, according to a study published by MIT (Massachusetts Institute of Technology) in the journal Environmental Research Letters. These are caused by non-CO2 emissions – largely nitrogen oxides and water vapour – which also have a negative impact on the planet. And according to Charlène Fleury, of Rester sur Terre, this wouldn’t necessarily go away if aviation were to pivot to hydrogen fuel.
So in other words, we’ve a long way to go before hydrogen can turn aviation into a sustainable mode of travel. Because on top of the question around its production and the infrastructure linked to it, it would require huge changes to motorisation and aircraft too. As we’ll see next week, this is by no means the simplest of tasks.
