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Is a carbon-free aviation industry really possible?

Aviation: can hydrogen live up to the hype?

On February 2nd, 2021 |
4 min reading time
Johnny Deschamps
Johnny Deschamps
Professor at the Chemistry and Processes Unit (UCP) at ENSTA Paris (IP Paris)
Samuel Saysset
Samuel Saysset
Lead techno advisor at ENGIE Research
Key takeaways
  • Hydrogen seems to be the only fuel that is both “clean” and suitable for the aviation industry of tomorrow.
  • Airbus has announced three concepts for hydrogen planes for 2035 and many start-ups are also working on solutions.
  • The French government has committed to investing more than €7bn in the hydrogen industry by 2030.
  • Before this project can really take off, there are many problems to solve, including hydrogen storage, production and cost.

On 21st Sep­tem­ber last year, Air­bus unveiled three con­cepts for the world’s first zero-emis­sion com­mer­cial air­craft, which could enter ser­vice by 2035 1. While every plane is dif­fer­ent in size, design and range, they all use the same pri­ma­ry pow­er source – hydro­gen. Air­bus, the world’s biggest plane man­u­fac­tur­er in 2019, believes that it “holds excep­tion­al promise as a clean avi­a­tion fuel and is like­ly to be a solu­tion for aero­space and many oth­er indus­tries to meet [their] cli­mate-neu­tral tar­gets.” What’s more, the French gov­ern­ment has com­mit­ted to pour­ing €7bn into this up and com­ing ener­gy source between now and 2030 2.

As it hap­pens, Air­bus is not the only one look­ing into hydro­gen. After all, it is the only fuel source aside from kerosene that seems to be suit­able for com­mer­cial avi­a­tion. While Boe­ing is not con­vinced of its short-term poten­tial, some small­er com­pa­nies have been explor­ing the tech­nol­o­gy. On 24th Sep­tem­ber, start-up ZeroAvia per­formed a tri­al flight with a hydro­gen-fuel-cell-pow­ered, six-seater plane. And Israeli air-taxi devel­op­er Urban Aero­nau­tics has been work­ing with Cal­i­forn­ian start-up HyPoint to cre­ate a ver­sion of their City­Hawk VTOL air­craft that is pow­ered by a hydro­gen fuel cell.

There are two ways that hydro­gen can be used. First, the con­ven­tion­al method is to burn it in an engine. This tech­nol­o­gy is already used by the space indus­try to launch rock­ets. Sec­ond, is to use hydro­gen to pro­duce elec­tric­i­ty via a fuel cell. How­ev­er, this tech­nol­o­gy is still very expen­sive. In any case, both meth­ods still face some tech­no­log­i­cal hurdles.

Storage problems

The main dif­fi­cul­ty comes from fuel stor­age. “Hydro­gen gas is very low in den­si­ty,” John­ny Deschamps, lec­tur­er and researcher in the Chem­istry and Process­es Unit at the ENSTA Paris (IP Paris), and an expert in hydro­gen stor­age, notes. “Even when com­pressed at 350 bars, you still need sub­stan­tial vol­umes – a 210 litre-tank for 5kg of hydro­gen (or a 125-litre tank at 700 bars).”

The sec­ond solu­tion is to store it in liq­uid form, “but it takes a lot of ener­gy to liq­ue­fy hydro­gen, as it requires a tem­per­a­ture of minus 253°C. What’s more, cryo­genic tank insu­la­tion isn’t absolute, so a per­cent­age of the liq­uid hydro­gen will keep evap­o­rat­ing and need to be vent­ed – which is a risky propo­si­tion.” Light, durable mate­ri­als there­fore need to be devel­oped for the tanks.

Fuel tanks also have to be cylin­dri­cal or spher­i­cal. This requires a com­pre­hen­sive review of the shape of the plane, as cur­rent designs store fuel in the wings. With all these lim­i­ta­tions, the idea of using hydro­gen to pow­er a plane for a long-haul flight with sev­er­al hun­dred pas­sen­gers seems unlike­ly at present. Instead, com­pa­nies are look­ing more at air­craft with a few dozen seats for domes­tic flights.

Not all that green

Although hydro­gen engines give off few­er CO2 emis­sions, that doesn’t mean that it is squeaky clean. Burn­ing it at high tem­per­a­tures results in pol­lu­tion in the form of nitro­gen oxides (NOx), and water vapour, which forms con­trails and cir­rus clouds that are also bad for the climate.

Hydro­gen can be pro­duced from water (H2O) using elec­trol­y­sis, or from hydro­car­bons like methane (CH4). Even though elec­trol­y­sis is a clean process, this tech­nol­o­gy can­not yet be rolled out on an indus­tri­al scale. “We can make hydro­gen by elec­trolysing water, espe­cial­ly when the elec­tric­i­ty is being pro­duced in a sta­ble way, such as in a pow­er plant,” Samuel Says­set, lead tech­ni­cal con­sul­tant at Engie, says. “But if we want ‘green’ hydro­gen made with renew­ables, which are an inter­mit­tent pow­er source, we need to devel­op new tech­nolo­gies. Plus, ~95% of hydro­gen is cur­rent­ly made from petrol, gas or coal, which emits CO2.”

At what price?

There is also the all-impor­tant ques­tion of cost, which varies depend­ing on the source. Cur­rent­ly, hydro­gen made from methane costs €1.5–2 per kilo­gram, where­as hydro­gen made by elec­trol­y­sis costs four to ten times more. It is one of the rea­sons for the invest­ment from the French gov­ern­ment: a large propo­si­tion of the €7bn is aimed at find­ing solu­tions to make the price of hydro­gen more reasonable. 

There are also oth­er costs involved – hydro­gen planes would require sig­nif­i­cant invest­ment for fuel pro­duc­tion, trans­port and stor­age infra­struc­ture, new air­craft and mate­ri­als devel­op­ment and, above all, for the heavy tanks. It remains to be seen if a hydro­gen-pow­ered plane would be eco­nom­i­cal­ly viable in the long term.

Nev­er­the­less, the avi­a­tion indus­try seems to be inter­est­ed in hydro­gen, with man­u­fac­tur­ers like Air­bus, and the French gov­ern­ment com­mit­ting to invest in this area. But we still do not know how the many unan­swered ques­tions relat­ing to hydro­gen planes will be resolved. Which engine man­u­fac­tur­ers will be involved? What will be the engines’ fuel con­sump­tion and effi­cien­cy? Will they be pow­ered by inter­nal com­bus­tion or fuel cells? How will the fuel be stored? Hydro­gen has yet to demon­strate that it has a future in aviation.

Pri­vate invest­ment in Hydrogen

Indeed, the finan­cial sec­tor is get­ting behind hydro­gen ener­gy for trans­porta­tion too, receiv­ing sup­port from investors. With over $100 bil­lon assets world­wide invest­ment firm, Ardian, for exam­ple say they are com­mit­ted to sus­tain­able invest­ments in green ener­gy. For them, green hydro­gen is an impor­tant ele­ment of this as it is aligned with Euro­pean Union cli­mate change tar­gets. Amir Shar­i­fi Man­ag­ing Direc­tor at Ardian says this is because, “hydro­gen has sim­i­lar char­ac­ter­is­tics to fos­sil fuels. It can be stored in the form of liq­uid or gas but can also be pro­duced in a green way via elec­trol­y­sis.” Accord­ing to the Hydro­gen Coun­cil, hydro­gen is expect­ed to meet 18% of the world’s ener­gy demand by 2050.


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