Nick:
Yes, the utilities have offered cheaper night rates here for many years. It's been common in homes with all-electric heating since the 1960s, and of course, helps the utility make better use of gen. capacity at night.
I don't ever remember seeing storage heaters while I was in America, but they're fairly common here. They "charge" the storage bricks on the night rate so that they radiate heat during the day.
The early systems were usually referred to as "White meter" tariff, because the Electricity Board (as it was then) installed a second meter which was (surprise, surprise) white instead of the regular brown/black. There was also a sealed timeswitch providing switched power to an auxiliary distribution panel to which the heaters were wired.
The "Economy 7" system now in use has a single dual-tariff meter (i.e. two sets of dials) and the changeover switches the whole house to low rate at night. They still provide a separate switched feed so that storage heaters will come on only during low rate.
The mechanical timeswitches have largely been replaced with remote operated "Radio teleswitches" now.
