Tesla has launched a feature called "Charge on Solar" that allows owners to fill up their electric vehicles' batteries using only excess solar energy. As TechCrunch notes, the automaker started testing the capability in May, but now it's more widely available to Tesla customers in the US and in Canada. The number of people who can access the feature, however, likely remains pretty limited. To start with, it will only be accessible to those who have newer Teslas — 2021 and later — who also have a Powerwall. That's the company's battery system that stores solar energy harnessed by solar panels.