"Set Square" wrote in message ...
OK - what I was trying to say is that your supplier defines the timing of
the off-peak period...

In fact they do it cleverly these days. Most recent split-rate
installations are radio controlled and the heaters are turned on and
off by the electricity board when they want. They seem to use this for
load balancing. Our storage heaters go on and off at different times
day to day - sometimes they go on for an hour or so during the day at
odd times (3pm, 11am even 7pm at times!). As far as I can tell this
is because adjusting the amount of power generated is difficult and
takes a lot of time - so when demand drops suddenly (or unexpentedly)
they just turn on lots of heaters to soak up the spare. Neat eh?