Solar energy isn't currently usable for personal vehicles, and it's going to be a little while still before that changes. Even if we could magically make cars and trucks all battery-EVs tomorrow, most of our power is still generated from fossil fuels, not solar power, and that's not likely to change soon, though it is of course slowly getting better. The more fossil fuels we burn, the more CO2 we put in the atmosphere, and accelerate climate change.

Sure, if we could overnight make all cars and trucks into battery EVs, replace all fossil fuel power plants with solar PV arrays (and wind farms too, since those are basically driven by solar energy too, though indirectly), and come up with some kind of storage technology to handle nighttime, high latitudes, clouds, still air, etc., then the energy aspect wouldn't be such a big deal. (Even better if we can make battery-EV airplanes.) But we're not there yet, and it's not likely we'll be there for quite a while unfortunately.

And even if we did accomplish that, that still doesn't solve the space problem. There just isn't enough room for everyone to have a big suburban house in a nice place with mild weather, and drive a personal vehicle everywhere. But if we tore down our car-based cities and rebuilt some just like Tokyo with that kind of density (and honestly, it really isn't as dense even as Manhattan; there's a lot more tall skyscrapers in NYC), then we actually could, while simultaneously having far, far fewer car-related deaths, and also having a much healthier population.