Tesla CEO Elon Musk has teased a new product announcement ahead of the firm’s solar roof unveiling.

The entrepreneur said on Twitter that there will be a new announcement before that October 28 event.

He tweeted: “Tesla product unveiling on the 17th (unexpected by most), followed by Tesla/SolarCity on the 28th.”

So what could the “unexpected” product be?

There is speculation that it will unveil the next generation of autonomous driving hardware, Autopilot 2.0.

That is rumoured to be able to read American stop signs and traffic lights, allowing the electric cars to drive themselves on all roads – not just highways.

Another potential announcement could be Tesla’s energy storage options, the Powerwall – which is designed for home use – and its commercial equivalent the Powerpack.

Full production of those is not expected until the huge Nevada Gigafactory, which will manufacture batteries, is completed in 2017.

It is also possible that the next model of electric car, the Model Y – a compact SUV – will be unveiled.

Musk has grand plans to rival Uber and Lyft with an autonomous taxi fleet.

"We’ve got our next generation technology and we are trying to get up that production line so it’s gonna be heavily concentrated in Q4 and primarily in November and December,” Musk said recently.

"I think it’s going to be really exciting when people see it. That’s why I expect exponential growth from there.

“I think it’s really going to go ballistic."