MacKay, and other serious analysts who have considered a future UK grid using a high percentage of renewables (probably wind, given the climate), expect significant national supply variations to occur on a scale of days rather than an hour - which is the longest time that dynamic-demand appliances can put off their needs before food begins to rot.
So dynamic-demand consumer appliances aren't a solution for a renewable grid. They offer only minimal carbon savings in the present power picture. And the idea doesn't offer any direct savings for the consumer. Yet the idea is for consumers to pay for it, probably involuntarily - the plan would be to make the tech compulsory on new appliances at some point.
However, the government is keen to suggest that power companies might pass on their savings on maintenance and spare capacity plant in the form of reduced 'leccy bills.
So, if they did, how much would a normal household save?
Well, the Guardian spoke to Paul Lazarevic, whose company will make the dynamic-demand gear for the upcoming government trial. This is, then, an estimate at the higher end of the scale.
"The national grid forecasts a spend of £544m on balancing the grid for the year 2008-09," he said.
"This is passed on to consumers and works out at about £2 on each bill ... Dynamic demand technology could dramatically reduce this charge."
There were 25 million households in the UK as of 2004, so the most a £544m annual cost could add to monthly bills would be £1.81. But in reality domestic customers use less than half the electricity consumed in the UK. If you take it that industry bears a similar responsibility for grid balancing, and accept Mr Lazarevic's figures on cost, the annual saving to the consumer of completely eliminating the need for grid balancing would be in the order of £10.
Since dynamic demand can't do that (completely eliminate the need for grid balancing), we'd be looking at perhaps a few pounds per year at the moment; the tech could theoretically pay its way in the case of an appliance lasting years, as it wouldn't cost much.
In the wind-heavy grid of the future, unfortunately, we'd be looking at a very serious increase in balancing costs, whether from dirty inefficient turbines or (more expensively yet) from nice clean pumped-storage hydropower. Clever fridges may be able to iron out demand spikes, but not the much bigger ones to be expected from a renewable supply side.
The Guardian piece is here. ®