I am rather interested in this aspect. Recently (1 month ago ) I purchased a BMW Rex with a 60ah range battery (2015 model) . Thanks to our London Mayor's fanaticism to get more money from people. Anyway. This Rex has a limited (upto 70mile) range. I have a high degree of trepidation regarding longer term reliability re engine. Charging on public networks costs from 50p upwards per kwh. Home charging is roughly 30p+ /kwh (I do understand there may be cheaper ways ). As I understand, petrol has theoretically 9kwh energy in 1 litre. Which on a pure cost works out to 17p/kwh (based on £1.50/ltr) . Appreciate petrol engines are not efficient hence possible loss of 50% in conversion (may be even less) ? which perhaps means it may cost 34p /kwh. Taking in to account grid cost of minimum 50p (as far as I have seen ), burning petrol (E5) to charge appears to me cheaper than charging at any grid stations. This also assumes there are chargers available, free to plug in. Not to mention the charging times which can be upwards of 1 hour to just get some charge in (7kw). Grid electricity is also inefficient. There will be transmission losses there too, not to mention generation losses ? Appreciate, electric is one of the most flexible energy sources to store and acquire. Unsure where BMW got there data from re Rex? As I do find the flexibility of a portable generator in the boot useful. Yes, of course, having a larger battery etc may go a way to alleviate problem I may face and does weigh less but the option to have a generator running and adding to the range is useful in the model I currently have. I would of course, love a 120ah or more battery. I do appreciate the lure of pure electric and the elimination of a petrol engine. Currently the cost of electricity on the charging network is too high ( UK ) Have seen charges of upto a minimum 75p /kwh and further a minimum connection charge at times of 30p just to connect? Yuk.
The figures re costings efficiency I obtained from a quick web scan are really a rough guess from the small research done.
I would love to read a better write up from more knowledgable persons here about costings and efficiencies.