There are pilot projects looking at shutting-down energy intensive industries for short periods (e.g. industrial refrigeration plants, aluminium smelting) to deal with peaks in demand
Its really not a good idea to cut the power on smelting and high temp processes for a wee while while the nation cooks there dinner. You can do all sorts of damage to the machinery/protective cladding by cooling it down for even 30 mins in an uncontrolled manner. And a controlled manner can take over 2 weeks to make sure the thermal gradients don't cause anything thing to go "bang" never mind the 4 weeks you would need to make sure you don't shag the material properties.
So I suspect that these industrys would have some big generators on standby to cover when they couldn't use the grid. So some big nasty inefficent CO2 belching generators will be getting used anyway.
Tidal has always seemed a great plan to me with some very interesting engineering problems to be over come.