Elon Musk’s latest master plan for Tesla fell flat as the electric car maker shared scant details about next-generation models that will underpin its next phase of growth.

The roughly four-hour presentation was long on calculations of what the sustainable energy transition will require, along with boasts about manufacturing and engineering efficiencies. But Mr Musk and the executives who joined him on stage wrapped Tesla’s investor day without giving a glimpse of cheaper EVs that may still be years away.

“I’d love to really show you what I mean and unveil the next-gen car, but you’re going to have to trust me on that until a later date,” Franz von Holzhausen, Tesla’s design chief, said at the company’s headquarters in Austin, Texas.

“We’ll always be delivering exciting, compelling and desirable vehicles, as we always have.”

Tesla shares fell as much as 8.6 per cent as of 8.40am Thursday in New York, before the start of regular trading. Anticipation of the event contributed to a surge in the stock that added more than $300 billion of market value in two months.

Mr Musk confirmed Tesla will build a new plant in Monterrey, Mexico, in what he said was probably the most significant announcement of the day.

The chief executive said Tesla would make its next-gen vehicle there, and that the company will hold a grand opening and groundbreaking at an unspecified date.

When asked when the car maker will show a prototype and if he could share details about the size, content and performance of the vehicle, Mr Musk responded that Tesla also will hold a “proper sort of product event” at some point, but did not say when.

“We’re gonna go as fast as we can,” said Lars Moravy, Tesla’s vice president of vehicle engineering. “We expect that to be a huge-volume product.”

Takeaways from investor day

Tesla recently broke ground on a lithium-refining plant in Corpus Christi, Texas. Mr Musk reiterated that artificial intelligence stresses him out and called for the creation of a regulatory authority that would ensure the “quite dangerous technology” is operating in the public interest.

The company recently built its four millionth vehicle. After taking 12 years to make its first million, the company manufactured each incremental million units in 18 months, 11 months and seven months. The car maker’s next drive unit will use a permanent magnet motor and no rare earths, according to Colin Campbell, vice president of power-train engineering. The comments sent miner shares tumbling.

Mr Musk opened the event by laying out what Tesla believes will be required to displace fossil fuels, from powering the grid with wind and solar to utilising heat pumps, which he said Tesla might make for homes at some point. Tesla also is planning to offer unlimited overnight home charging in Texas for $30 a month.

“Earth will move to a sustainable energy economy,” Mr Musk said. “And it will happen in your lifetime.”

Investors heard from Tom Zhu, who is on the ascent after overseeing Tesla’s factory in Shanghai become its most productive in the world. Rebecca Tinucci, the head of global charging infrastructure, presented on the “Magic Dock” feature enabling drivers of other EVs to use Tesla’s stations.