However, electrical solutions are often more efficient, so this can be misleading because a transition means you're getting a large amount "for free" as a result of the improved efficiency.
Instead of moving your car from oil to solar, you're moving the car from oil to electricity, and then electricity is fungible so you don't care that it was made with a solar array - but the efficiency win was from going to electricity.
You have to distinguish between transportation (electricity and oil) and source of energy (only oil).
To have electricity you would need to invest at once in both generation, transport (the grids are not enough), storage and change in use (replace cars with electric ones). Your return will depend as well on the technology developed and none of the above fields is stable yet.
I am a fan of going electric, even if only for more sovereignty, but it is not as simple as "electricity is more efficient".
You have to be especially careful when comparing oil/gasoline vs solar/electric through. Oil has an especially well developed infrastructure for it being drilled, refined, delivered and stored. Electricity on the scale to power all transportation does not, so there are large short-term costs.
In terms of effeciency, you don't replace a billion BTU's of oil with the same amount of electricity, what you want is locomation. Only about 25% of oil's energy ends up spinning the wheels, compared to 85% of energy using an electric powertrain.
In rich countries the electrical grid only needs to roughly double to power all transportation. The US did that in the 01960s, and China did it in the 02010s and probably will have done it again this decade.
This is why I genuinely suggest PV cells mounted into the bodywork of EVs. They'll "only" add 10-20 miles per (good weather) day depending on the specifics, but this is a significant fraction of the (mean) miles driven per day per vehicle, which means the necessary grid upgrades are much smaller.
Almost all those cars still need to be charged, the weather won't always be good, people don't generally choose to leave their cars parked in direct sun if they can help it, etc. — but as a systematic reduction in impact over the entire power grid, it's non-trivial.
The grids is minimally impacted by EV’s. A great deal of charging happens at night when there’s vast excess capacity in generation and transmission. Even if you assume it’s split 24/7 each car only uses roughly 500 watts averaged throughout a year.
More importantly if 100% of new cars went electric it’d still take 25 years to finish so it’s a rounding error to grid operators outside of a trivial number of substations for fast chargers. As crazy as it sounds when you include training LLM’s are using more electricity than every EV combined.
> The grids is minimally impacted by EV’s. A great deal of charging happens at night when there’s vast excess capacity in generation and transmission.
In this context, solar power, charging at night is the exact opposite of a good idea; if anything, you want the power to leave the cars at night to run everything else.
Electricity is already beating oil for lots of low temperature applications (e.g. home heating and cooling) because heat pumps are so much more efficient than burning fuel.
Instead of moving your car from oil to solar, you're moving the car from oil to electricity, and then electricity is fungible so you don't care that it was made with a solar array - but the efficiency win was from going to electricity.