that's not entirely correct..
Heaven forfend that I should defend the science fiction that passes for policy at DECC these days - just look at the 2011 carbon targets document - but they DO have a SLIGHT point in that energy efficiency affects peaks as well as lows. And it MAY be possible to shift some of the peak demand into the low demand phase.,.
For example a simple domestic heat bank of sufficient capacity could be used to power central heating by day. Storage radiators done properly. You would be surprised how much e.g. a concrete underfloor tank of hot water surrounded by insulation can hold. Its actually very cheap, very safe and holds a lot of energy. Its no bloody use as a way of storing ELECTRICITY because the efficiency to turn warm water back to electricity is like 5% or so.
Likewise the vision for electric cars all tucked into their gridslots at night ready for the 20 mile dash they will do if fully charged, is not without some justification. Though watch out for pigshit on your head from porcine aviators.
Shifting demand from day - and especially early evening - to the middle of the night is a very good thing to do wherever possible as it reduces the dispatch demands on the grid, which as you realise add capital cost to the generating plant and the transmission lines themselves - both being sized for peak, rather than average demands.
And reducing demand overall is likewise a good thing, though it wont make electricity any cheaper, you will at least use less of it.
The worst POSSIBLE thing you can do is add intermittent renewable energy to the grid: that means even bigger peak flows from remote places and less AVERAGE operating capacity for the plant you can't get rid of - its still needed when the renewables aren't producing - but is no longer able to amortize its capital costs over a greater amount of electricity produced. Adding wind to e.g. a nuclear grid won't mean you need any less nuclear power stations. It will simply mean you have added the cost of wind and the wires it needs to a grid that already was capable of doing the job on its own, without a single benefit accruing. Yet this is what DECC proposes to do.
Intermittent renewables ONLY have two slight cases to be made for them.
1/. If they are co-operated with gas (thus making you dependent on gas for the majority of the electricity) they MAY overall SLIGHTLY reduce gas consumption. You pay a high price for that though.
2/. If you have the geography and plenty of hydro CAPACITY but you are limited by total rainfall, so you can't run the hydro at full tilt all year, then tacking windmills and solar panels onto a fast acting storage and dispatch system (hydro is the fastest and most efficient way to dispatch power - almost no spin up time, and no thermal cycling involved) will give you full benefit of the extra energy with most of the costly downsides removed. New Zealand is one nation where this may actually work. The United Kingdom is one where it will not. We have nowhere near enough hydro or potential hydro sites for balancing even the paltry amount of wind power we already have.
There is one point that needs stressing again though, and it is this.
IF you bite the nuclear bullet and invest in the training, infrastructure, waste disposal and decommissioning technology to even use a single nuclear power plant at all., you have already made a big investment that you might as well leverage to have a LOT of nuclear power rather than 'just a little' - If low carbon intensity is your aim.
SINCE intermittent renewables only have justification as fuel saving measures for fossil fuel sets,( in the absence of sufficient hydro), there is absolutely NO JUSTIFICATION WHATSOEVER for increasing intermittent renewable capacity beyond the actual fossil capacity you have or you risk throwing wind away when there is too much of it. Worse, you really won't want any expensive intermittent generators on the grid that exceed the difference between nuclear baseload and the MINIMUM grid demand. . Once you have all the fossil generators switched off, any wind beyond that is not achieving any further fuel savings, or emissions reduction at all.
The more nuclear baseload you have, the less justification there is for any intermittent renewables at all. There is no fossil fuel to save or carbon emissions to reduce.
In short a proper nuclear program by any rational analysis is THE END OF (intermittent) RENEWABLE ENERGY altogether. It has a high cost, and no benefit whatsoever.
It is worth understanding those implications, especially when listening to the outpourings of the renewable lobbies when they preach about the evils of nuclear power.