To power your EV's energy needs, it depends on what EV you drive, how far, where and how you drive it. For energy production, it depends on where you are putting the solar panels, angle, azimuth, tilt, shading, and regional weather... There are variables, but with a few tools, you can figure it out. If you want a rule-of-thumb, here's one: Each 1kW of panels will get you about 4 thousand miles of EV driving. Will this be accurate for your home and your Model 3? Nope, it's just a rule of thumb. If you want to get more precise numbers, here's a link that can give you the tools to plug in your car (after it's EPA rated) and your address to get solar energy data for your roof.