Dunkelflaute (dark doldrums)

node · earth · north-western Europe

The German term, now used across European power markets, for a period of simultaneously low wind and low solar output across a wide area — typically a winter high-pressure system sitting over north-western Europe with fog or heavy overcast and light winds, lasting from a day to well over a week. It is the specific meteorological event that defines the hard edge of a wind-and-solar system, for three reasons. It is regional, so interconnection with neighbours who are inside the same weather system does not help. It is seasonal, arriving when heating demand is highest and solar resource is lowest. And it is long relative to storage, so a fleet of two-to-four-hour batteries discharges once and is then a spectator. European markets have repeatedly priced these events at extreme levels — German day-ahead prices during the December 2024 episodes rose above nine hundred euros per megawatt-hour in the peak hours, an order of magnitude above the typical clearing price — while gas, coal, hydro, imports and demand response supplied what wind and solar did not. Dunkelflaute is not an argument against wind and solar; it is an argument about what else a wind-and-solar system must keep, and about how that residual capacity is paid for when it runs for a few hundred hours a year.