“Flying 400 people across the ocean in an electric airplane is something we need to put out of our minds,” claims Joris Melkert, lecturer in aeronautical engineering at the Delft University of Technology (TU Delft, The Netherlands). Together with Paul Peeters, lecturer in sustainable transport and tourism at Breda University of Applied Sciences, Melkert presented an update of their factsheet entitled ‘The future of sustainable aviation‘ to the government in The Hague.
According to Melkert, people tend to assume too readily that if battery technology continues to develop, large-scale electric flights will also become possible. “Battery technology is developing at lightning speed, on average an improvement of about 8 percent per year. But there is a limit to this. The expectation is that the current generation of batteries can be improved by 2, maybe 3, times as much. Then it will stop.”
Not nearly enough for large-scale aviation the scientists contend. For an electric aircraft with a range of 1000 kilometers, the battery must be able to store 7 times more energy per kilogram than is currently the case. For long-haul flights, this is even 15 times more. Melkert: “For the time being, there is no technology that allows for that much more energy storage. But suppose we do succeed in making a battery with this energy density, then what about the safety aspects? Or can this battery provide enough power to abort a landing in an emergency? There’s a lot more to it all than just energy storage.”
So what about emerging battery technology?
And so-called structural batteries? Where the structure of the design – the wing of an aircraft, for example – serves as the battery. This means you don’t have to lug around as much weight in batteries along the way. What does Melkert think of this? “Aircraft structures are already designed to be extremely efficient. I don’t believe that a battery like this can suddenly store a factor of 6 to 7 times more energy. It might make a difference because you won’t need to carry as much weight. But is it enough? We have also been talking about lithium-air for years already, potentially a much lighter technology. However, before you can apply this kind of novel technology in an aircraft, it has to be 100 percent safe. And this kind of battery has to last a long time and be relatively cheap to make, all of which I don’t see happening between now and 2050.”
Read more about structural batteries here.
Peeters also thinks it could easily be another fifteen years or so before the first commercial electric flights take place. “Short-haul flights with at most ten to thirty passengers – in terms of numbers this obviously has nothing to do with what is happening at Schiphol. Nor does this make a difference when it comes to making aviation more sustainable. In order to substantially improve this, we have to abandon the battery route.”
Synthetic kerosene should make aviation cleaner
While aircraft are becoming about 1 to 1.5 percent cleaner each year, this is not nearly enough to be able to fly CO2-neutral by 2050. More needs to be done. Not only should the number of flights be scaled back (on average, aviation grows about 5 percent each year), but also, they argue, the government should invest in the development of e-fuels. “Synthetic kerosene, made with renewable electricity. In this case, the carbon does not come from oil, but CO2 is extracted from the air or sea and blended with green hydrogen. The main advantage of this is that you can fly cleanly without having to modifiy existing aircraft too much,” Peeters explains enthusiastically.
Melkert concurs. Technically speaking, it is in fact quite possible. “We don’t have to break any laws of physics to do this. It’s a matter of choice. If we want to reduce aviation emissions, something has got to change. There is increasing pressure from Brussels and the IPCC report also adds to this. Research programs to develop this industry will run into the billions, but the petrochemical industry is really strong in the Netherlands. We are good at this. Just look at how we have scaled up from coal to oil.”
Fuel cell airplanes
At present, producing e-fuels is still a time-consuming and expensive process, Peeters adds. A factory in Rotterdam has been running for a year to produce 500 liters of synthetic kerosene. “Not even enough to take off,” he notes. Making e-fuels for a flight to Paris takes ten times more wind energy than the same distance with the Thalys trains. Still, Peeters thinks the government should be betting its money on e-fuels. “It will be slow-going at first. Efficiency is around 40 percent right now, but within five years, 60 percent of the green energy that is used can be converted into synthetic kerosene. We will then end up in a kind of S-curve, where the process will also become cheaper yet again.”
Are you curious about how the process of making e-fuels works? Read more about it here.
In addition to e-fuels, the researchers believe that fuel cell airplanes will also play an important role in making air travel cleaner. These planes fly on electricity, drawing power not from a battery but from hydrogen. But Peeters doesn’t see these planes in the air on a large scale “until around 2050 at the earliest.” Developing new airplanes is a long-term investment. These involve trajectories that take about 30 years. “A lot is already happening in this area. I foresee that in about 10 years time, there will be 20 to 30-seaters flying around with fuel cells. But then it will really just be starting, because production lines and ‘old’ planes will also have to be replaced by then, that just takes time.”
Light aviation is just like an incubator
Although both agree that battery electric flights will probably never materialize on a large scale, experiments and research on a smaller scale are useful.
Peeters: “Electric motors have rapidly become five times lighter over the past 10 years. That would never have been possible without experiments on a smaller scale. So, you do need that too.”
Melkert adds: “Light aviation – anything between 6 and 10 passengers – is almost negligible as far as CO2 emissions are concerned, but as an incubator, it is indispensable for the ongoing development of the aviation industry. Aviation is complex, there is a lot to consider. Aerodynamics, efficiency, engines and much more. Many of the improvements made in light aviation are passed on to heavy aviation. That is why research on electric (battery-powered) flight remains interesting, but it will never replace regular flights over the ocean. It is bound to become something like a private jet for extremely wealthy people. That’s why I don’t think any taxpayer’s money should go into this.”