Electric cars are an energy-source-agnostic vehicle. Whether their energy comes from coal or nuclear or wind or solar, they are unaffected. Because of this you can gradually swap out pieces of the energy production backbone to renewables, and see a reflective immediate payoff in personal transportation CO2 emissions.

If the vehicle is tightly coupled to burning petrol, that can't happen. Electric cars are merely an exercise in uncoupling energy source and energy use.