In reply to winhill:
> How do we know if that's a good thing or a bad thing?
You need to know the carbon intensity of the electricity and how many km you get per kWh in an EV, then you can calculate the gCO2/km and compare it directly to ICE cars. Last year the CO2 intensity of UK grid electricity was 260g/kWh (
http://electricinsights.co.uk/#/dashboard?period=1-year&start=2016-03-3... My EV uses about 18 kWh/100km including 10% efficiency loss for charging. So that's 0.18 kWh, emitting 47 gCO2, per km. That is a little more than half the CO2 emissions of the lowest CO2 ICE cars. I've been generous to ICE cars here in that I've taken real-world performance of an EV and compared it to manufacturers performance figures for ICE cars.
Furthermore, many (most?) EV users choose to do most of their charging overnight, when the carbon intensity of grid electricity is usually even lower than that.
> It's a very like consumers buying the latest wifi enabled white goods or HVAC devices before they need to replace their existing ones, overall wasting energy, not saving it.The problem is largely that consumption addiction rather than the goods themselves, even more so with cars where you need to be a very high consumer to see the benefits.
There is a common misconception that the embodied energy of goods is more significant than the in-use energy and therefore that replacing inefficient kit with efficient kit is not worth it. That may be the case for very small improvements in efficiency, but it simply isn't true for replacing ICE cars with EVs (or incandescent bulbs with LEDs, or old houses with PassiveHouses, or retrofitting old houses etc etc). Have a look at this great website based on a study from MIT (google 'carboncounter MIT EVs' and you'll find it. UKC wouldn't accept the link for some reason), play around with the axes to explore the relative importance of embodied and in-use energy. First of all, EVs don't look to have any more embodied energy than ICE cars (put 'vehicle emissions' on the Y axis and cost on the X and you'll see the EVs are no higher up than everything else). So if the decision is between buying a new ICE car or buying a new EV, EVs are a clear winner in terms of environmental impact.
If the decision is between keeping an old car or buying a new EV then we have to work out how long it will take to save the CO2 emissions that have been generated by building the new EV. So on that carboncounter site my car looks like ~7.5 tonnes CO2 emitted during manufacture. If my existing ICE car is emitting 150 gCO2/km (this is being quite generous to ICE cars, most old ICE cars will be a lot higher than this), and my EV is emitting 46 gCO2/km (also generous to ICE cars, since I'm mostly charging at night when the CO2 intensity is lower), and I'm driving 19,200km per year (12k miles). So per year in my old ICE car I'm generating 19200km*150g = 2880kgCO2 and in my EV I'm generating 900kg CO2 per year. So I'm saving ~2 tonnes CO2 per year, so it'll pay for it's manufacture, in CO2 terms, in under 4 years. Considerably quicker if doing bigger mileage, charging at night, and the existing ICE car is less efficient than that.