@bdbdbd: The thing with wind power (and energy in general) is diversification.
Wind doesn't always blow in the same place... but if you spread wind farms throughout a big area (such as the separate areas in the whole country), the peaks and bottoms should balance out to pretty smooth supply. The same principle can be applied to different energy sources resulting in even smoother supply (for example, combining wind with solar power in countries where that's possible).
Denmark generates around 20% of their electricity from wind power, and during strong winds (such as storms) this can go up to 80% if I recall correctly. That's a pretty big variation, but Denmark is a small country so they can't have such smooth supply I guess. If Denmark has a surplus at certain moments, they sell cheap electricity to Germany and make money while Germany saves money by shutting down some of their power plants.
An idea I've seen a while ago is that with smarter electrical grids spanning several countries (or states in the US), it's probably possible to make an automated system which buys or sells electricity based on current demand, supply and prices set by other regions. Different power stations can be shut down if they're not needed or not as profitable (i.e. efficient) as other power sources. For now these decisions are made manually, which probably isn't so bad either.
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