Well, it's not that you can throw to the bin the energy when those peaks are not happening. Energy production has to be controlled, and thermal plants (such as coal ones), along with hidro-electric plants, are way more flexible than a nuclear reactor. Even in France they use non-nuclear power to adjust production to those peaks. Nuclear power covers just about 75% of electricity generation there.
Anyway, I'm talking about how it IS done currently in MOST countries, like in the States, where only 20% of electricity comes from nuclear power. Any more exceptions apart from France, Finland and two or three other countries?