In an EV about 90% of the energy used is converted into motion. About 10% goes to heat. [1][3]

In an ICE engine about 30% of the energy becomes motion. About 70% is heat.[2]

In other words electric motors are about 3 times more efficient than ICE.

[1] an interesting side effect of this is that in cold climates you can't just harvest waste heat to heat the cabin (or batteries. ) So you end up using some battery energy if you need heat.

[2] ICE motors vary in effeciency a lot. 20-30% is typical. The Carnot formula comes into play here.

[3] because there is so little heat generated, the cooling systems (EVs still have them) are much smaller. And simpler (for example, no fan, 'cause there's no heat when standing still.)

Transmission losses are orders of magnitude lower than transportation energy costs. You both get dramatically less loss per kilometer, and you have way fewer kilometers to travel. Transmission does get less efficient over longer distances; if you had a 20000km long transmission line it would be less efficient than shipping fossil fuels, but you simply don't need to do that.

You have conversion losses to generate motion but these are again substantially less than the conversion of chemical energy to motion that occurs inside a combustion engine. Powerplants+electric motors will have conversion efficiencies around 30%; internal combustion engines will have conversion efficiencies around 10%.

With the exception of some remote locations or emergency situations with backup generators, you are almost certainly not consuming a fuel that requires refining to generate electricity. If you're burning coal or gas, it's coming from much closer, and it's being transported in bulk to the powerplant. Trucks taking fuels to the local distribution centers and ultimately gas stations are by far the largest transportation energy expense for petrol.

>> The “dirty electricity” angle is less obvious to me.

A power plant typically gets about 60% of energy from a fossil source. A car does about 30%. So even if the electricity comes from say coal, it's still more efficient than buying gas in a car engine.

Of course, these days, it's likely that a substantial portion (up to 100% in some cases) is not "fossil electricity" but rather comes from solar, wind, hydro etc. Ie "clean" electricity.

It's a bit hard to answer the "dirtiest fuel you can find" case specifically, because there are a number of areas where EVs are more efficient. The biggest difference is probably the fact that the internal combustion engine in a car is about 25% efficient, though it depends on the RPM it is running at etc (the reason hybrids can push it up to ~40-ish% depending on how new they are is because the engine is always running at the most efficient RPM when it runs), but the "dirtiest power" specifically would probably be a coal plant which is only about 30% to 40% efficient (9000 to 11000 BTU/kWh in imperial units) due to low temperatures and the inability to run it as a 2-stage, combined-cycle sort of setup (modern combined-cycle gas turbines are ~60% efficient which is one contributing factor to gas-based electricity being cheaper even though gas costs more per GJ, though since the price of natural gas is quite volatile that sometimes changes). Of course the transportation is different depending on which fuel is used for a power plant.

In the worst-case scenario, accounting for the ~90% efficiency of the electric motors... Well, Xunmin et al. (2005) estimates 3–36%, so lifecycle emissions could be reduced by as little as 3% if you power it 100% by coal, which would be less than the what you'd get from a hybrid, but... You're not really going to find a power grid that is powered 100% by coal these days, even in China. Really the biggest advantage of a BEV, and any other electrification, is that if there are future investments in the grid (and there will be since generators don't last forever) you don't have to replace the engine of your car for it to automatically reduce emissions. The efficiency gains are just a cherry on top.

[Xunmin]: https://www.sciencedirect.com/science/article/abs/pii/S17505...

As I understand it, it's a mix of factors.

Charging Lithium, and converting to motive force in motors are both pretty efficient. (Both >90%).

An ICE vehicle has an upper limit on efficiency that is lower than what a modern fossil fuel plant can reach, and the ICE is less likely to sit at peak efficiency all the time. The world record, set this year was 48%. Previously, it was 41%.

Power plants are much more likely to be kept at or near their peak efficiency and have the space for systems like heat recovery (to recapture waste heat) and emissions controls. For a gas turbine plant, I think the record is ~64% sustained.

Grid loss is maybe 5%.

The important driving factor is that generation becomes more efficient when you can use natural gas to turn turbines directly and then capture the waste heat to boil water and turn turbines with steam. This is called combined cycle if you want to google it to learn more.

Another thought exercise, if generating electricity with fossil fuels wasn’t more efficient at scale, why would we bother building a grid in the first place? Every house would just have a gas generator.