I still think John has a point and that when there are a large number of smart electric car chargers on the system we will need a more advanced system than "day ahead pricing everyone pays the same", otherwise you risk all the electric cars jumping on the cheapest half-hour.
Exactly - and that would be true of any system which attempted to control the time of demand by varying prices. With any such system, those (humans or machines) who were 'paying attention' would always jump to the cheapest option whenever prices/times changed, thereby perpetuating periods of high demand (merely 'moving them around').
There are various solutions I can see, for example different suppliers could set their cheapest price at different times. Or suppliers could offer a discounted rate for EV users who agreed to regulate their charging to a supplier-defined profile.
I can also think of 'various solutions', but ones that would achieve much of what we would like (whilst remaining vaguely 'fair') would probably have to be be very complicated/sophisticated, and are probably not currently technologically implementable.
If different suppliers set their cheapest rate at different times, that would certainly help to smooth out the peaks of demand - but that, in itself, would not require 'smart' meters or daily (or even monthly) changes in hour-by-hour prices. Even that approach might be somewhat undermined by the fact that a significant proportion of users probably have similar (correct or incorrect) notions of when they want/need to charge their EVs (or storage heaters, or whatever), so would all tend to migrate to the one supplier whose timings were closest to their perceived 'requirements'.
Ultimately, it's all about trying to spread out demand so that there are no major peaks. In some senses, EV charging probably makes this easier for the industry, since it will considerably increase demand during what traditionally were low-demand times of the day/night. I personally doubt that any system based on playing with hourly prices would ever achieve much 'smoothing' - since, as we have both said, there will always be a strong tendency for users (humans or machines) simply to move the time of peak demand around in response to changes in when is the prevailing 'cheapest time'.
A hypothetical system that presumably would go a long way to 'smoothing' demand would be to forget about having different pricing at different times of day but, instead, having the time at which each charger springs to life being determined randomly each day. One difficulty then would be to find a way of reconciling the 'random' (which could not always be random!) switch-on times with the 'needs' of individual users.
Another possibility is that suggested by Harry - to give 'customised cheap periods' (presumably constantly changing) to each user. However, that would be extremely complicated a and would invoke some of the other difficulties I have mentioned.
It ain't simple!
Kind Regards, John