Whether from consumers, regulators or climate change experts, the aviation industry faces constant pressure to reduce its carbon emissions, particularly when it comes to the Paris Agreement’s goals of achieving zero-net carbon by 2050. Despite making huge strides over the past decade, aviation is still currently responsible for 3.6% of the EU’s greenhouse gas emissions, according to recent studies.
The pandemic will naturally have an impact on the industry’s CO2 levels over the past year, with airline capacity reportedly down roughly 75% as of early April 2020. While the impact has been and will continue to be, unprecedented, it can also provide a unique opportunity for the industry to reset to a more sustainable model.
The biggest contributor to the industry’s CO2 emissions in aviation is the kerosene fuels used in the industry’s aircraft. So, if the industry strives to tread a more sustainable path, fuel alternatives should be the first place they start. Thankfully, there is already a strong contender, Hydrogen.
Considered as one of the most promising zero-emission technologies for modern aircraft, hydrogen has gained serious traction in recent times as a possible solution for the aviation industry’s carbon emission woes.
Hydrogen is the most abundant element on the planet, only produces water vapour when burned and has an energy-density-per-unit mass that is three times higher than traditional jet fuel. With such attractive benefits, it’s little wonder why it caught the attention of the aviation industry.
The hydrogen-powered aviation report, which was released last year said that hydrogen could feasibly be in use by 2035 to power a commercial passenger aircraft on a flight of up to 3,000 kilometres. The report also added that by 2040 a medium-range flight of up to 7,000 kilometres could also be possible, leaving just long-range flights for traditional aviation.
With plans to launch an entirely hydrogen-fuelled plane by 2035, Airbus is the first major aviation player to have solid plans for the utilisation of hydrogen fuel. In 2020, the aviation giant unveiled three different concepts for a zero-emission, hydrogen-powered commercial aircraft, each of which relies on hydrogen as a primary power source.
Guillaume Faury, CEO of Airbus said, “I strongly believe that the use of hydrogen - both in synthetic fuels and as a primary power source for commercial aircraft - has the potential to significantly reduce aviation's climate impact.”
However, while it might sound like a promising venture for aviation, hydrogen fuel doesn’t come without its fair share of challenges. These will need to be addressed before the industry can even think about pursuing widespread adoption amongst its airlines.
To achieve a successful switch-over to hydrogen fuels, the aviation industry needs to develop a new supply chain. This will not only require finding ways of extracting hydrogen en masse, whilst also make sure its extracted in an eco-friendly way.
Hydrogen can be found in vast quantities in oceans, lakes and the atmosphere, however, it must be separated from oxygen in water in order to be used for industrial purposes. More than 70m tonnes of hydrogen are produced each year with natural gas being the primary source of extraction, otherwise known as “grey hydrogen.” When extracted with fossil fuels, hydrogen production is responsible for around 850m tonnes of CO2 emissions per year.
However, electrolysers powered by electricity which is generated from renewable energy sources such as wind can offer a low-emission alternative. This process produces “green hydrogen” and should be a more preferable supply chain option for the aviation industry to pursue.
According to Glenn Llewellyn, VP of Zero-Emission Aircraft, Airbus is targeting the use of green hydrogen to fuel its future zero-emission aircraft. He believes that the declining costs for renewable energy and the scaling up of hydrogen production could make green hydrogen increasingly cost-competitive with existing options, such as jet fuel and sustainable aviation fuels.
“Cost-competitive green hydrogen and cross-industry partnerships will be mandatory to bring zero-emission flying to reality,” he says.
Storing hydrogen safely on board an aircraft is another particularly big challenge that could even require a total overhaul in the design of the commercial aircraft we know today. Kerosene fuel is typically stored in the wings, where it is also safely circulated to aid in keeping the plane balanced during flight. However, this would not be a possible option for hydrogen fuel, due to its highly flammable nature.
This presents a practical challenge of finding another area within the aircraft where the hydrogen can be stored. Wherever they choose, there will undoubtedly be certain pipelines and systems that are made redundant or require updates to make them more suitable for hydrogen fuel rather than kerosene.
The type of hydrogen used and the extra weight required for fuel storage could also be a hurdle the industry needs to overcome. For liquid hydrogen, the challenge will be making lightweight vacuum-insulated tanks that maintain the fuel below its 20 K boiling point. Gas carries a greater weight penalty as the storage tanks must be built to withstand high pressures of 250–350 bar.
For hydrogen to achieve widespread adoption across the entirety of the aviation industry, it must be available at airports on a worldwide scale. This advancement is still in its infancy. One of the biggest challenges if developing the large-scale transport and infrastructure solutions needed to supply airports with the necessary quantities of hydrogen needed to fuel their aircraft.
In a recent study by the IEA, it was suggested that repurposing existing infrastructure, including the millions of kilometres of pipelines already being used to transport natural gas, could be a cost-effective answer to this problem. This would mean that larger quantities of hydrogen could be transported from pipelines on production sites and smaller quantities could be transported by trucks (which could also be decarbonised).
In some cases, some airports could develop their own hydrogen infrastructure which supports the production of hydrogen on-site, particularly if a renewable energy source could be positioned in close proximity.
As the saying goes, all good things are worth waiting for and hydrogen is no exception. While all signs point to it being a fantastic solution to lowering carbon emissions creating by aircraft, widespread hydrogen adoption is still a long way off. If the industry can work out the kinks and overcome their hydrogen hurdles, it could be an extremely worthwhile endeavour that helps us reach global net-zero carbon targets over the next two decades.