Electric planes flying on batteries are no longer a midsummer night’s dream, as an Israeli startup named “Eviation” is planning to introduce the first one by 2021 which will carry nine passengers over distances of up to 650 miles (1045 km). The key technological development that makes this possible is the existence of high-density dry batteries such as the ones that Tesla Inc. has been turning to recently. The American automotive and energy company has recently acquired Maxwell Technologies, along with their ultra-capacitor manufacturing unit. Already, Maxwell’s solutions are on the range of 300 Wh/kg, which is about 30% higher than Tesla’s current solutions, but is that enough for aviation applications?
According to Elon Musk, his bulk estimations about the cross-over point is 400 Wh/kg. He believes that in about five years, we will be there, so long-range passenger plans carrying up to 200 passengers could become a reality much sooner than we previously anticipated. Maxwell has already laid out a path of development that foresees a density increase of 15-25% every 2-3 years, so the short-term goals seems feasible. Moreover, Maxwell’s superior technology and production line expertise will enable Tesla to ramp up production by 16 times for the same space, lower the associated costs, and double the battery life.
As some followers of Elon Musk justifiably commented on Twitter, kerosene’s energy density is about 40 times that of the existing lithium-ion batteries, so in their eyes, the transition doesn’t have much prospect. Elon Musk defended his predictions, telling them that the cross-over point isn’t depending solely on the energy density, but also on the weight of the combustion engines against that of electric motors. Moreover, electric motors are much better at converting energy to motion than their conventional counterparts. When flying, these weight and energy conversion rate differences play a massive role in the overall efficiency, so Musk’s claims are not biased statements aimed at helping Tesla’s shares go up.
Everyone agrees that electric propulsion is the future in mobility, both in the automotive and aerospace sector, but there are still mountains to climb before it becomes the de facto standard. It will be especially hard to make an electric airplane for passengers and cargo that can fly over long distances because batteries are very heavy when compared to jet fuel with the same energy density.
Researchers from the University of Illinois think that hybrid-electric powertrain is a viable solution for aircrafts until batteries become dense enough to pack enough electricity in light form factor. The hybrid-electric powertrain that they suggest works similarly to hybrid-electric cars such as the Toyota Prius, where electric motors help the gasoline engine and make it more efficient.
The team consisted of Assistant Professor Phillip Ansell and doctoral candidate Gabrielle Wroblewski made a flying simulation of the Tecnam P2006T airplane, which is a small twin-engine aircraft manufactured in Italy. First, they made a simulation with the planes existing engines and then with a hybrid-electric propulsion system to see if there will be gains fuel consumption, range, and emissions. More precisely, they used the measurements to simulate how different parts of the hybrid-electric powertrain, such as the batteries and level of electrification, will improve the overall impact on efficiency.
This figure shows the a) parallel and b) series drivetrain models. From University of Illinois
This is very important, as just adding batteries may increase the weight of the airplane so much that it becomes less efficient. They also simulated both series and parallel architecture hybrid systems. After all of the simulations were finished, they found that parallel hybrid powertrains can substantially improve the fuel efficiency of aircrafts, especially for short-range flights, where the battery energy can be used to its full potential.
Ansell predicts that with the existing battery technology, this plane can fly around 80 nautical miles and that the electric system can give around 25% of the power. However, his predictions for the future are much brighter – “Fast forward to projections for lighter battery technologies for roughly the year 2030 and the same aircraft could fly two and a half to three times as far. The range increase is nonlinear, so the largest improvements can be seen for the most immediate improvements with battery specific energy density, with gradually diminishing returns for that same proportional increase in specific energy.”
Airbus’s E-Fan 2.0 is the world’s first plane to have fully electric propulsion and represents a major breakthrough in the aviation industry.
Since the cost of fuel drives the prices of flying commercially up, developing a commercial electric passenger plane could result in much cheaper flights.
In fact, Inhabit reports a flight on “E-fan could cost only $16, compared to $55 for a flight in a petrol-powered plane of the same size.”
Airbus’s goal at the moment is to have a prototype electric passenger plane by 2030 but there are many challenges, much more so than developing electric cars.
Chief Technology Officer Jean Botti told Smithsonian.com, “It’s not like a car, where you get 1.2 or 1.5 kilowatts per kilo(gram) and make a car run for an OK distance. The problem we have in aeronautics is gravity; you have to get up to seven to 10 kilowatts per kilo(gram).”
Further of battery technologies within electric planes will be key to the success of a commercial electric plane.