There is a brilliant interview with Robert Llewellyn on BBC Radio about this subject, which I commend to anyone interested in the subject.
https://www.bbc.co.uk/programmes/m0000mjy
The simple truth is that electric vehicles are much more efficient.
A few facts:
A typical modern Diesel engine operates at between 30-35% thermal efficiency, ie 30-35% of the energy input (the fuel) is converted to energy output. However transmission losses and power taken for other things in the car mean that only 20% of the energy in the fuel results in power at the wheel. It’s worse for petrol cars.
An electric car will convert approx 60% of electrical power input into power at the wheel on the same basis (allowing for battery losses, transmission losses, and other power uses). By this measure alone, electric cars are 3 x more efficient. Some info is available here:
https://cleantechnica.com/2018/03/10/electric-car-myth-buster-efficiency/
Now, it is often said that because the electricity has to be generated in power stations, it simply exports the emissions elsewhere.
The U.K. electrical power generation mix is about 45% emissions free (if you assume that nuclear is emissions free, and that the French imports are mostly nuclear) - right now it’s around 50%, but then it’s a bit windy tonight, although the sun is in bed so no solar.
Most of the rest is generated by Combined Cycle Gas Turbine power stations, which have an average thermal efficiency of 50-55%. They also have much lower emissions in terms of NOx and particulates. (which are a particular concern from Diesel engines). Of course there are then transmission losses from power station to consumer socket, National Grid estimates these are 7.7%. Let’s call it 10% to be on the safe side.
Taken together, and assuming my maths is right, a standard unit of power delivered to the wheels of a diesel car produces
2.5 to 3 times more emissions than the standard unit of power delivered to the wheels of an electric car. On top of that, the emissions from a diesel are generally more harmful than those from a CCGT power station, and also much more likely to be in a place where people live and work.
Therefore, we can safely say that using electric vehicles is much better in terms of emissions.
There is then the issue of embedded carbon (and other emissions) in the vehicle itself. I won’t go into the detail here, other than to say that the key point is the differnece in embedded carbon between an electric vehicle and a fossil fuelled vehicle. I understand it’s not that much of a difference, but happy to be proved wrong.
Finally there is economics. I have a few friends with EVs, and they will typically spend about 3p a mile on ‘fuel’ on a typical duty cycle. That compares to me spending around 15p/mile on a relatively efficient Golf Diesel, and nearly twice that on a rather less efficient estate car. At 10k miles a year, that’s quite a difference, and there is much less to service / go wrong on an EV, which makes maintenance cheaper too. For people who do a lot of urban driving, it is clearly the best option. Hence why there are now a noticeable number of electric black cabs in London (over 500, and rising daily).
If my next car isn’t electric, the one after will be.