Elon Musk made a promise this week that he’ll share more details about the Model 3, Tesla’s most affordable car yet, sometime this spring. That will technically be the “part 3” unveiling of the car.

“Today is not the time for that announcement,” Musk said earlier this week, according to Business Insider. “But I mean it’s probably… beginning of spring, or something. Yeah, 3-4 months from now.”

The company started with the initial debut of the Model 3 and then, last month, Tesla revealed part 2 of the plan, when it said that all new cars will have “full self-driving hardware.” While the cars will sport the features to drive on their own, Tesla said they won’t be activated until they’re fully ready for primetime.

Solar-powered Model 3?

We don’t really know what’s in store for part 3. It could be when Tesla unveils the final design of the car, since it hasn’t really done that yet. Business Insider speculates that part 3 of the Model 3 unveil might also include additional details on buyer options for the car. Given Tesla’s recent approval to acquire SolarCity, rumor has it Tesla is acquiring special glass that might be used on the car to provide power. Though, Elon Musk has stated that the best use of solar is probably off of a car, maybe in a more stationary location, like on top of buildings. He added, at the time, that there are too many variables with having solar panels on top of cars, including physical obstructions, time of day, and efficiency. He basically said, it isn’t the best use of your money or the technology.

Might be tough to get enough power, but perhaps it’ll be used for topping off. We’ll find out this spring.