A day without sun and/or wind is nothing out of the ordinary, so there's no reason for it to make the headlines. But with the introduction of more and more wind- and solar-powered generation units into electricity systems, things are changing. Enough so that the International Energy Agency has devoted several pages of its Electricity 2025 report to this phenomenon.
The threat of dark doldrum
The move away from fossil fuels to produce electricity is accompanied by massive investment in wind and solar farms. In so doing, we're back to being dependent on the laws of nature: day-night alternation, seasonal cycles, shifting air masses and clouds. This loss of control over electricity production is most severe in countries that do not have the decarbonized energy of nuclear power plants. This is the case in Germany, which closed its last nuclear units on April 15, 2023. It's hardly surprising, then, that the German word Dunkelflaute is applied to adverse weather conditions that reduce, or even cancel, electricity generated from renewables. In English, we speak of "dark doldrums" or “dark wind lull".
These episodes can be identified in two ways: on a local scale, by consulting weather data, and on a regional or national scale, by spotting sharp price rises on wholesale electricity markets. On these markets, generating units are ranked in order of increasing operating cost (known as merit order). So, if there is a shortfall in renewable production, the software that regulates the supply-demand balance will automatically call up plants whose production is controllable, but which are ranked lower in the merit order because they are more expensive to operate. These are often natural gas-fired power plants, whose price is known to be strongly affected by political instability in Eastern Europe. There have always been episodes of dark doldrums, but their impact is all the more keenly felt in Europe because they occur in winter, and their frequency and duration are difficult to predict. The IEA report mentions Germany in early November and mid-December 2024 (megawatt-hour price multiplied by 10), and the UK in early January 2025...
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