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Dynamic demand technology, in which domestic appliances adjust their drain on the national grid so as to smooth out collective spikes and dips, is to get a widespread UK trial next year.

The Guardian, reporting on the new initiative from the Department of Energy and Climate Change, says that three thousand intelligent demand-smoothing fridges will be given away free by the government in a sort of energy-policy beta test.

The idea of "dynamic demand", or "intelligent" appliances is that they contain circuitry which monitors the mains frequency. A fridge normally waits until it has warmed up to a certain amount above set temperature, then runs its pumps until it is a certain amount below.

A smart fridge, though, would also take account of the grid frequency. When the grid was under strain it might not bother cooling all the way down - it might stop as soon as it reached, say, the middle of its normal temperature band. Immersion heaters and air conditioning are other examples where dynamic-demand hardware could be useful.

Dynamic demand doesn't reduce the amount of energy required over time - it merely spreads the demand out so as to make things easier on the grid. This is why the government's 2009 smart-fridges must be given away free; they won't offer any savings for their users.

But the quick-response gas turbine power stations used to iron out sudden gaps between supply and demand are dirtier than most - efficient combined-cycle kit can't be thrashed up and down the output scale the way these plants have to be. Thus the government reckons that dynamic-demand tech could could reduce UK carbon emissions, perhaps by as much as 2 million tonnes annually - a little over 1 per cent of the total. That sounds pretty high - even Friends of the Earth, great boosters of this idea, have previously suggested just half a million tonnes a year (one-third of one per cent).

And the power industry would save money on maintenance for thrashed turbines and backup plant which is left idle much of the time, so they're very much in favour of someone else paying to smooth out consumer demand for them.

Greens such as the FoE people like dynamic-demand too, as it could make life easier for renewable power. The thinking goes that the nation's fridges, aircon, immersion heaters etc could be set to take power when the wind was blowing or the sun shining and the grid was thus overpowered, rather than essentially randomly as they do now.

The idea is examined by Professor J C MacKay of Cambridge University in his book Sustainable Energy - Without the Hot Air, just published in hard copy. He says that's not really true.

Popular soap operas such as Coronation Street and EastEnders typically generate TV pick-ups of 600–800MW … automatically switching off every fridge would nearly cover these daily blips of concerted kettle boiling.

Fluctuations in wind power will be a different matter.

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