Anyone who spends a lot of time on planes is used to suffering: if you curl your legs carefully in front of the backrest of the front seat, it becomes quite uncomfortable in the long run. In addition, there is a justified guilty conscience, because flying fuels climate change. Both disadvantages could shrink in the future if an idea from researchers at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) and the Technical University of Munich becomes reality.
“If we rely on solar-powered airships, we can make aviation more climate-friendly pretty quickly,” says Christoph Pflaum, Professor of Computer Science at FAU. Space would also be provided. The Hindenburg, for example, probably the most famous airship of all time, was a kind of floating hotel. Travelers could eat in a dining room and sleep in double rooms.
The Hindenburg, or “LZ 129”, on whose dimensions the researchers from southern Germany based their study, was around 245 meters long and 41.2 meters high and wide: one of the largest aircraft ever built, powered by a diesel engine, and according to Pflaum “a real sensation on the maiden voyage in March 1936”. But a year later, the airship that had taken off from Frankfurt caught fire during a landing in the USA and burned down completely. 36 people died.
The culprit was the hydrogen gas, which provided the buoyancy of the airship in a large textile envelope, but ignited in combination with atmospheric oxygen. In this case, the hydrogen was an emergency solution. Helium is actually the lifting gas of choice, but the USA had banned exports of the non-flammable gas to Germany because of the war.
“Game changer” in aviation
Like the Hindenburg, current airships are usually still powered by fossil fuels. So far, they have mainly been used for research purposes, for example for measurements in the atmosphere. The airship Pflaum is researching is larger than her and is solar powered. It has what it takes to be a “real game changer” as a climate-friendly means of transport in aviation, he emphasizes. Simulations that the team from Nuremberg and Munich recently published in the International Journal of Sustainable Energy should prove this.
The virtual airship is then about the same size as the Hindenburg and covered with flexible thin-film solar cells. At 108 tons, it is around 10 tons lighter than the historical model, which according to the study can be achieved primarily with modern lightweight materials. The weight of the 13,000 square meter solar cells made of copper indium gallium selenide (CIGS), efficiency 17.6 percent, and the lithium-ion battery is already offset. Helium gas and a set of four propeller engines with diameters of a good six and a half meters provide the propulsion. The payload is 60 tons.
During flight, propulsion is provided solely by solar power and a battery. “The battery is needed primarily for night flights and must be charged before take-off,” says Pflaum. With the current electricity mix, this would result in CO2-Emissions that, depending on the load and flight distance, amount to between almost one and a half and five percent of the amount that conventional aircraft currently emit.
In the solar-powered airship, travelers would fly in a more climate-friendly and comfortable way than in an airplane today, but also longer. “According to our calculations, a flight across the Atlantic from New York to London takes about two days and one night. In the opposite direction from London to New York, it takes three days and two nights,” explains the FAU professor. Depending on the wind direction, the cruising speed is between 100 and 200 kilometers per hour. The simulations were based on weather data from 2019.
The German Aerospace Center (DLR) is not currently researching airships. Their size and rather low speed are reasons for this, according to the press office. In addition, the operation is “not necessarily cheap, for example because of the helium filling and the low transport capacity. Nevertheless, an airship for special applications could be an interesting technology that DLR also supports.”
Christoph Pflaum cannot understand DLR’s reasoning. In operation, burning kerosene is significantly more expensive than harvesting free electricity from the sun. “According to our estimates, the energy costs compared to an airplane are not even one percent. It is therefore very unlikely that airships would be more expensive than airplanes,” he believes.
Even if airplanes fly with hydrogen in the future, the direct generation of electricity from solar power would be even more efficient, according to Pflaum. If necessary, expensive helium can be replaced by other gases or gas mixtures with the appropriate safety technology. And in terms of range, the climate-friendly airships would have the edge anyway.
In fact, it may still be a while before airplanes with regenerative propulsion technologies can cross the Atlantic. The website of the DLR concept study for eco-efficient flying states: “The overarching goal is to have the necessary technologies for such an aircraft with at least 70 seats and a range of 2,000 kilometers ready for use by 2040.” The London – New York route is around 5,500 kilometers.
Airship Research International
However, the long-range, solar-powered airship is still just gray theory. The computer scientist Pflaum is therefore following with excitement the development of the “Pathfinder” airships by the Californian company LTA Research, which is supported by Google co-founder Sergey Brin, among others. A drive with electricity from hydrogen fuel cells is planned.
A first version called “Pathfinder I” is about half as long as the Hindenburg and has twelve propellers. It is said to have a top speed of 120 km/h and transport up to 40 tons of cargo. There should already be a successor model. Even the airship enthusiast Pflaum does not know whether, and if so for how long, Pathfinder I and II have been in the air. The company is keeping a low profile, he says. Other companies working on climate-friendly airships include Hybrid Air Vehicles (HAV) in the UK and Flying Whales in France.
How to proceed with the climate-friendly airships will be the subject of an international conference on the subject, to which Christoph Pflaum is inviting at the end of September. Until then, his team wants to refine the simulations. It is still unclear, for example, how exactly it affects the solar power harvest when clouds scatter the sunlight.
What is also still in the stars is the financing of further projects in Germany. “Unlike other research, the development of climate-friendly solar airships has hardly been funded in this country. That’s a real problem,” says the scientist. He hopes that the chances will still be seen and used. So that the airship with solar power does not just remain a study.