Re: "Tariff Data"
"peak electricity is much more expensive than off-peak "
So, in the UK in 2016, what time of day is peak electricity (in pricing terms)?
Hint: trick question, it's no longer to do with time of day, it's more likely to do with whether the wind's blowing or not.
In short, short term price is to do with demand vs supply. No longer fundamentally related to time of day. Can you afford to delay that wash till the wind is blowing again? Let the freezer warm up till the wind blows again?
Meanwhile, every grid-powered appliance already has a signal which indicates whether demand is tending to exceed supply or not, so there's no need for an expensive smartmeter installation to provide that, especially a smartmeter with a cutoff capability. The mains frequency indicates whether more supply is needed (<50Hz) or whether less supply is needed (>50Hz).
http://www.gridwatch.templar.co.uk/ (where the UK's gridconnected electricity comes from)
http://www.dynamicdemand.co.uk/grid.htm (abandoned years ago but principles still valid)