Tesla electric jet: Elon Musk says a key technology is ‘3 to 4 years’ away

A key technology that could enable an electric jet may be just three or four years away, Tesla CEO Elon Musk claimed Monday – and Tesla could be set to reveal some more advancements in the space soon.

Responding to a Twitter thread about the potential for an electric jet, Musk stated that the futuristic zero-emissions jet would require a battery pack with a density of 400 watt-hours per kilogram. This battery would also need to be produced in volume, rather than just an experiment in a lab. Musk claimed in his Twitter post that this breakthrough is "probably 3 to 4 years" from reality.

The news comes as Tesla announced plans for its upcoming Battery Day. The event will happen immediately after its annual shareholder meeting on September 22 at 1:30 p.m. Pacific time. Electrek noted Monday that the main event motif bears resemblance to silicon nanowires, an exotic battery technology that could electrify aviation.

In 2008 Musk noted that “an electric plane gets more feasible as battery energy improves,” and four years later he said he had a design in mind for years. Musk even mentioned the idea during his cameo in the 2010 film Iron Man 2. In a 2016 interview, Musk said the jet would take off and land vertically.

So where is it? The main obstacle is battery density, or how much energy each kilogram of battery can hold. That's important for flight, as a plane needs to overcome the force of gravity to lift off in the first place. Musk explained in September 2018 that the energy used for cruise speed is actually quite low, and the plane can depend on gravitational potential energy for the landing phase, so it doesn't need a big bank of reserve energy to return. It's the initial takeoff phase that's tricky, and that's where density is key.

Current electric car batteries are around 250 watt-hours per kilogram, Musk claimed in 2018. Sam Korus, an analyst at ARK Invest, wrote on Twitter that removing 150 kg (330 pounds) from a Tesla Model 3 would add just 15 miles to the car's range between battery charges. For the electric jet, though, increases in battery density could make the vehicle dramatically more useful.

Battery Day could be a step toward that reality. Korus shared a post that showed battery-technology firm Amprius is located near Tesla's facilities in Fremont. Amprius claims to be able to reach past that 400 watt-hours per kilogram mark, with its 100 percent silicon nanowire batteries – the same technology speculated to be the backdrop for Tesla's Battery Day webpage.

For now, Tesla seems more focused on its energy and car businesses than aviation. Musk said in a 2018 interview that the electric jet "isn’t necessary right now" compared to electric cars.

The Inverse analysis – Electrifying ground-based transport is arguably more important than electric jets. The World Resources Institute found that while transport emissions accounted for 24 percent of the world's carbon dioxide emissions in 2016, road-based transport accounted for 72 percent of those emissions.

But if battery technology improves and it becomes feasible to electrify a jet, it could enable humanity to transition to a fully zero-emissions transport system. Thierry Marin-Martinod, aerospace and defense chief technology officer for TE Connectivity, told Inverse in July 2019 that the battery would be the first hurdle, before working out issues with voltage and regulations. Marin-Martinod suggested that the batteries could arrive in the next few years, and the electric airliner could hit the skies in 2040.

It's unclear what Tesla will announce at its battery event, but it could be the first steps on the path to an exciting new future.