Europe is pushing ahead with the development of hydrogen aircraft. The opportunities and risks of the alternative drive.

Hydrogen is the element with the lowest atomic mass. No conclusions should be drawn about the potential of the element. Not only does it serve the sun as fuel. The substance has the potential to replace fossil fuels in a climate-neutral way.

The German government alone will invest nine billion euros in its hydrogen strategy. In order to become climate neutral by 2050, France and the European Union also pushed ahead with their hydrogen plans. The material should also find a permanent place in aviation. But where are the opportunities and hurdles in aviation for hydrogen?

No emissions, but more space

Hydrogen-powered aircraft with an electric motor do not produce environmentally harmful emissions. Fuel cells convert the element into electricity that drives engines. Instead of climate-damaging exhaust gases, only water and heat are generated. So much for the theory.

Compared to previous fossil fuels, the element also has disadvantages – such as the common jet fuel kerosene. On the one hand, the energy density of hydrogen is significantly lower. With the same amount of energy, the volume of hydrogen is about four times higher than that of kerosene.

Aircraft before fundamental changes

In other words, the size of previous fuel tanks is no longer sufficient. Experts estimate that these should be between three and four times larger. In addition, the liquid hydrogen has to be cooled with additional, complex systems. Larger pressure-resistant tanks and additional systems generate a higher weight – a sensitive factor in aircraft construction, which can not only determine efficiency, but also general ability to fly.

The installation of fuel cells and electric motors also requires that the previous design of aircraft be changed. Airports also have to adapt to this. Not only do aircraft need larger and more complex tanks, but hydrogen depots on the ground are also required.

Not on this earth

The production of hydrogen also poses challenges. Manufacturing is still considered expensive and complicated. Hydrogen is the most common element in the universe. But of all places on our planet it cannot be found in pure form.

However, chemical processes enable the production of pure hydrogen. A common form is the so-called “gray hydrogen”. This is obtained from natural gas, which creates harmful exhaust gases. There are about ten tons of CO2 per ton of the end product. The life cycle assessment of an aircraft would therefore destroy this hydrogen already when refueling.

Gray and green hydrogen

But there is also “green hydrogen”. This is obtained by electricity breaking down water into its individual parts – oxygen and hydrogen. There are no harmful emissions. In order to be able to call green hydrogen green at all, however, the energy for production must also be obtained sustainably.

How this energy can be adequately provided has so far been questioned. One solution is the electricity from wind turbines. Many of them would be needed: For example, in order to produce the hydrogen demand calculated by the Fraunhofer Institute for all of Germany in 2050, an area as large as the Netherlands would have to become a wind farm, reports the radio broadcaster ZDF.

In small steps to the passenger plane

In order for hydrogen aircraft to protect the environment as a whole, it is not just a matter of redesigning aircraft and airports. A nationwide supply of green hydrogen must also be established. That would take many years and cost a lot.

But aviation would only be one of many beneficiaries. The first ships and trains are already running on hydrogen. The element has also been used for a long time in the automotive industry. In the meantime, it is clear that only small aircraft will take over the advance in hydrogen.

First prototypes already in the air

The first aircraft with pure hydrogen propulsion already exist today. The German Aerospace Center DLR and the Slovenian manufacturer Pipistrel developed the HY4. With four seats, the small aircraft with double fuselage is the first hydrogen passenger plane to take off for the first time in 2016. The test pilot can cover up to 1500 kilometers.

The drive technology of the HY4 already provides a view of hydrogen aircraft with up to 40 seats, says the DLR. In the research center, Joseph Kallo has long been involved in the use of fuel cells in aircraft, reports the Neue Zürcher Zeitung. The scientist believes there is a good chance that the first prototypes with a range of up to 80 kilometers could take off within the next ten years.

Technologies available today

The technology for this is already “basically available,” says Kallo. But the technology would still have to be transferred from small aircraft to larger ones. Development and approval should cost a lot. According to the scientist, it will at best take 15 more years for passengers to take a seat on a hydrogen plane.

Initially, these would also be used primarily on short journeys. Because they also fly slower. Ordinary jet-powered passenger aircraft travel at speeds between about 800 and 900 kilometers per hour. With early hydrogen planes, the march speed would be between 550 and 600 kilometers per hour, the scientist says.