If you ever watched the 2010 film Iron Man 2 you probably noticed a cameo by Elon Musk. The billionaire entrepreneur is greeted by Tony Stark and then tells him he has an idea for an electric jet.
While this might seem like the stuff of science fiction, Monday Musk took to Twitter to announce that the technology for such a jet is only three to four years away. This announcement has been 10 years in the making.
Back in 2008, Musk first mentioned the idea of an electric jet, explaining how “an electric plane gets more feasible as battery energy improves.” In 2012 and 2015 he said he had a design in mind for the futuristic plane.
So why aren't we currently riding on an electric plane? Because the proper battery density for flight has yet to be achieved. Musk has stated that lithium-ion batteries would need to reach an energy density of 400 Wh/kg for the batteries to outperform kerosene making his electric plane possible.
Today's cells have energy densities of approximately 220 Wh/kg using graphite anodes. This is a long way from the required 400 Wh/kg for an electric plane.
However, researchers are constantly looking to increase that number and it seems they may be close as Musk stated in his Monday Tweet.
400 Wh/kg *with* high cycle life, produced in volume (not just a lab) is not far. Probably 3 to 4 years.— Elon Musk (@elonmusk) August 24, 2020
In September 2018, Musk explained to Inverse that high energy density would be needed only for take-off. After that the plane can rely on gravitational potential energy for the landing phase, so only a small bank of reserve energy is needed to return.
What this means is that half of Musk's plans for an electric plane are probably already feasible. All he needs is the energy reserve to take off. Since he claims that energy density will exist in three to four years, we can't help but be excited about the prospect of an electric plane.