Electricity generated from wind power has massive intermittency due to weather fluctuations. In most countries, the drops in wind power production are compensated by increases in fossil fuel generation; in a few countries, for example Denmark, imports from neighbouring countries are also used to meet demand. Because of the large scale of weather patterns, the wind power production in close neighbouring countries has coherent fluctuations and so any imports must come from a different generation source, usually hydro or again fossil fuel.
The following animations illustrate the fluctuations of wind power and compensation with fossil generation as well as the correlation of wind production between adjacent countries.
This last animation shows just night hours for clarity. During day fossil fuel generation higher to meet increased demand. The following animations show all hours for one day/week.
The plots below give typical examples of the fluctuation in electricity generation data averaged over three days. Measured as a fraction of the total energy consumption in the countries, the swings in Denmark are 10-90%; Germany 5-65%; United Kingdom 5-30% and France 2-16%.